Att 1 - Water Distribution Master Plan — Fort Bragg City Council, December 8, 2025 (part 2 of 2)

Texture is given in the standard terms used by the U.S. Department of Agriculture. These terms are defined according to percentages of sand, silt, and clay in the fraction of the soil that is less than 2 millimeters in diameter. "Loam," for example, is soil that is 7 to 27 percent clay, 28 to 50 percent silt, and less than 52 percent sand. If the content of particles coarser than sand is 15 percent or more, an appropriate modifier is added, for example, "gravelly." Classification of the soils is determined according to the Unified soil classification system (ASTM, 2005) and the system adopted by the American Association of State Highway and Transportation Officials (AASHTO, 2004).

The Unified system classifies soils according to properties that affect their use as construction material. Soils are classified according to particle-size distribution of the fraction less than 3 inches in diameter and according to plasticity index, liquid limit, and organic matter content. Sandy and gravelly soils are identified as GW, GP, GM, GC, SW, SP, SM, and SC; silty and clayey soils as ML, CL, OL, MH, CH, and OH; and highly organic soils as PT. Soils exhibiting engineering properties of two groups can have a dual classification, for example, CL-ML.

The AASHTO system classifies soils according to those properties that affect roadway construction and maintenance. In this system, the fraction of a mineral soil that is less than 3 inches in diameter is classified in one of seven groups from A-1 through A-7 on the basis of particle-size distribution, liquid limit, and plasticity index. Soils in group A-1 are coarse grained and low in content of fines (silt and clay). At the other extreme, soils in group A-7 are fine grained. Highly organic soils are classified in group A-8 on the basis of visual inspection.

If laboratory data are available, the A-1, A-2, and A-7 groups are further classified as A-1-a, A-1-b, A-2-4, A-2-5, A-2-6, A-2-7, A-7-5, or A-7-6. As an additional refinement, the suitability of a soil as subgrade material can be indicated by a group index number. Group index numbers range from 0 for the best subgrade material to 20 or higher for the poorest.

Percentage of rock fragments larger than 10 inches in diameter and 3 to 10 inches in diameter are indicated as a percentage of the total soil on a dry-weight basis. The percentages are estimates determined mainly by converting volume percentage in the field to weight percentage. Three values are provided to identify the expected Low (L), Representative Value (R), and High (H).

Percentage (of soil particles) passing designated sieves is the percentage of the soil fraction less than 3 inches in diameter based on an ovendry weight. The sieves, numbers 4, 10, 40, and 200 (USA Standard Series), have openings of

4.76, 2.00, 0.420, and 0.074 millimeters, respectively. Estimates are based on laboratory tests of soils sampled in the survey area and in nearby areas and on estimates made in the field. Three values are provided to identify the expected Low (L), Representative Value (R), and High (H).

Liquid limit and plasticity index (Atterberg limits) indicate the plasticity characteristics of a soil. The estimates are based on test data from the survey area or from nearby areas and on field examination. Three values are provided to identify the expected Low (L), Representative Value (R), and High (H).

References:

American Association of State Highway and Transportation Officials (AASHTO). 2004. Standard specifications for transportation materials and methods of sampling and testing. 24th edition.

Engineering Properties---Mendocino County, Western Part, California Natural Resources
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National Cooperative Soil Survey
5/22/2023

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American Society for Testing and Materials (ASTM). 2005. Standard classification of soils for engineering purposes. ASTM Standard D2487-00.

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Report—Engineering Properties
Absence of an entry indicates that the data were not estimated. The asterisk '*' denotes the representative texture; other possible textures follow the dash. The criteria for determining the hydrologic soil group for individual soil components is found in the National Engineering Handbook, Chapter 7 issued May 2007(http://directives.sc.egov.usda.gov/ OpenNonWebContent.aspx?content=17757.wba). Three values are provided to identify the expected Low (L), Representative Value (R), and High (H).

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Engineering Properties–Mendocino County, Western Part, California Map unit symbol and
soil name
Pct. of
map
unit
Hydrolo
gic
group
Depth USDA texture Classification Pct Fragments Percentage passing sieve number— Liquid limit
Plasticit
y index
Unified AASHTO >10
inches
3-10
inches
4 10 40 200
In L-R-H L-R-H L-R-H L-R-H L-R-H L-R-H L-R-H L-R-H
117—Cabrillo-Heeser
complex, 0 to 5
percent slopes
Cabrillo 50 B 0-26 Sandy loam SM A-4 0- 0- 0 0- 0- 0 100-100 -100
100-100
-100
65-73-
80 35-43-
50 20-25
-30
NP-3 -5
26-35 Sandy clay loam SC A-6 0- 0- 0 0- 0- 0 100-100
-100
100-100
-100
80-85-
90 35-43-
50 30-35
-40
10-15-2
0 35-50 Sandy clay loam,
sandy clay
SC A-6, A-7 0- 0- 0 0- 0- 0 100-100
-100
100-100
-100
80-85-
90 35-43-
50 30-38
-45
10-15-2
0 50-60 Sandy loam, loamy
sand
SM A-2 0- 0- 0 0- 0- 0 100-100
-100
100-100
-100
50-60-
70 10-23-
35 20-25
-30
NP-3 -5
Heeser 30 A 0-34 Sandy loam SM A-2, A-4 0- 0- 0 0- 0- 0 100-100 -100
95-98-1
00 60-70-
80 30-35-
40 20-25
-30
NP-3 -5
34-65 Sandy loam, loamy
sand, sand
SM A-2 0- 0- 0 0- 0- 0 100-100
-100
95-98-1
00 50-65-
80 15-25-
35 — NP
122—Caspar sandy
loam, 2 to 9 percent
slopes
Caspar 80 B 0-16 Sandy loam SM A-4 0- 0- 0 0- 0- 0 100-100 -100
95-98-1
00 60-68-
75 35-43-
50 20-25
-30
NP-3 -5
16-37 Sandy loam, loam,
sandy clay loam
SC-SM,
SC
A-4, A-6 0- 0- 0 0- 0- 0 85-93-1
00 75-88-1
00 50-68-
85 35-43-
50 25-30
-35
5-10-15
37-48 Sandy clay loam,
clay loam, sandy
clay
CL, SC A-6, A-7 0- 0- 0 0- 0- 0 85-93-1
00 75-88-1
00 65-78-
90 35-48-
60 30-38
-45
10-15-2
0 48-62 Sandy loam, loamy
sand
SM A-2 0- 0- 0 0- 0- 0 100-100
-100
100-100
-100
50-60-
70 20-28-
35 20-25
-30
NP-3 -5
Engineering Properties---Mendocino County, Western Part, California Natural Resources
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Engineering Properties–Mendocino County, Western Part, California Map unit symbol and
soil name
Pct. of
map
unit
Hydrolo
gic
group
Depth USDA texture Classification Pct Fragments Percentage passing sieve number— Liquid limit
Plasticit
y index
Unified AASHTO >10
inches
3-10
inches
4 10 40 200
In L-R-H L-R-H L-R-H L-R-H L-R-H L-R-H L-R-H L-R-H
123—CasparQuinliven complex,
30 to 50 percent
slopes
Caspar 50 B 0-16 Sandy loam SM A-4 0- 0- 0 0- 0- 0 100-100 -100
95-98-1
00 60-68-
75 35-43-
50 20-25
-30
NP-3 -5
16-37 Sandy loam, loam,
sandy clay loam
SC-SM,
SC
A-4, A-6 0- 0- 0 0- 0- 0 85-93-1
00 75-88-1
00 50-68-
85 35-43-
50 25-30
-35
5-10-15
37-48 Sandy clay loam,
clay loam, sandy
clay
CL, SC A-6, A-7 0- 0- 0 0- 0- 0 85-93-1
00 75-88-1
00 65-78-
90 35-48-
60 30-38
-45
10-15-2
0 48-62 Sandy loam, loamy
sand
SM A-2 0- 0- 0 0- 0- 0 100-100
-100
100-100
-100
50-60-
70 20-28-
35 20-25
-30
NP-3 -5
Quinliven 35 C 0-4 Sandy loam SM A-2, A-4 0- 0- 0 0- 0- 0 100-100 -100
100-100
-100
60-65-
70 30-38-
45 20-25
-30
NP-3 -5
4-11 Sandy loam, loam CL-ML,
SC-SM,
ML, SM
A-4 0- 0- 0 0- 0- 0 100-100
-100
100-100
-100
65-78-
90 35-48-
60 25-30
-35
5-8 -10
11-18 Loam, sandy clay
loam, clay loam
CL, SC A-6 0- 0- 0 0- 0- 0 100-100
-100
100-100
-100
80-88-
95 45-60-
75 25-33
-40
10-15-2
0 18-51 Clay, sandy clay MH, ML A-7 0- 0- 0 0- 0- 0 100-100 -100
100-100
-100
85-93-1
00 50-73-
95 40-50
-60
10-18-2
5 51-60 Sandy clay loam,
clay loam
CL, SC A-6 0- 0- 0 0- 0- 0 100-100
-100
100-100
-100
80-90-1
00 40-60-
80 30-35
-40
10-15-2
0 60-64 Loamy sand, sandy
loam
SM A-2, A-4 0- 0- 0 0- 0- 0 100-100
-100
100-100
-100
50-63-
75 20-30-
40 20-25
-30
NP-3 -5
Engineering Properties---Mendocino County, Western Part, California Natural Resources
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Engineering Properties–Mendocino County, Western Part, California Map unit symbol and
soil name
Pct. of
map
unit
Hydrolo
gic
group
Depth USDA texture Classification Pct Fragments Percentage passing sieve number— Liquid limit
Plasticit
y index
Unified AASHTO >10
inches
3-10
inches
4 10 40 200
In L-R-H L-R-H L-R-H L-R-H L-R-H L-R-H L-R-H L-R-H
124—CasparQuinliven-Ferncreek
complex, 9 to 30
percent slopes
Caspar 37 B 0-16 Sandy loam SM A-4 0- 0- 0 0- 0- 0 100-100 -100
95-98-1
00 60-68-
75 35-43-
50 20-25
-30
NP-3 -5
16-37 Sandy loam, loam,
sandy clay loam
SC-SM,
SC
A-4, A-6 0- 0- 0 0- 0- 0 85-93-1
00 75-88-1
00 50-68-
85 35-43-
50 25-30
-35
5-10-15
37-48 Sandy clay loam,
clay loam, sandy
clay
CL, SC A-6, A-7 0- 0- 0 0- 0- 0 85-93-1
00 75-88-1
00 65-78-
90 35-48-
60 30-38
-45
10-15-2
0 48-62 Sandy loam, loamy
sand
SM A-2 0- 0- 0 0- 0- 0 100-100
-100
100-100
-100
50-60-
70 20-28-
35 20-25
-30
NP-3 -5
Quinliven 33 C 0-4 Sandy loam SM A-2, A-4 0- 0- 0 0- 0- 0 100-100 -100
100-100
-100
60-65-
70 30-38-
45 20-25
-30
NP-3 -5
4-11 Sandy loam, loam CL-ML,
SC-SM,
ML, SM
A-4 0- 0- 0 0- 0- 0 100-100
-100
100-100
-100
65-78-
90 35-48-
60 25-30
-35
5-8 -10
11-18 Loam, sandy clay
loam, clay loam
CL, SC A-6 0- 0- 0 0- 0- 0 100-100
-100
100-100
-100
80-88-
95 45-60-
75 25-33
-40
10-15-2
0 18-51 Clay, sandy clay MH, ML A-7 0- 0- 0 0- 0- 0 100-100 -100
100-100
-100
85-93-1
00 50-73-
95 40-50
-60
10-18-2
5 51-60 Sandy clay loam,
clay loam
CL, SC A-6 0- 0- 0 0- 0- 0 100-100
-100
100-100
-100
80-90-1
00 40-60-
80 30-35
-40
10-15-2
0 60-64 Loamy sand, sandy
loam
SM A-2, A-4 0- 0- 0 0- 0- 0 100-100
-100
100-100
-100
50-63-
75 20-30-
40 20-25
-30
NP-3 -5
Ferncreek 15 D 0-7 Sandy loam SM A-4 0- 0- 0 0- 0- 0 80-90-1 00 75-88-1
00 65-70-
75 35-43-
50 20-25
-30
NP-3 -5
7-33 Clay, clay loam MH, ML A-7 0- 0- 0 0- 0- 0 80-90-1 00 75-88-1
00 70-80-
90 50-63-
75 40-50
-60
10-18-2
5 Engineering Properties---Mendocino County, Western Part, California Natural Resources
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Engineering Properties–Mendocino County, Western Part, California Map unit symbol and
soil name
Pct. of
map
unit
Hydrolo
gic
group
Depth USDA texture Classification Pct Fragments Percentage passing sieve number— Liquid limit
Plasticit
y index
Unified AASHTO >10
inches
3-10
inches
4 10 40 200
In L-R-H L-R-H L-R-H L-R-H L-R-H L-R-H L-R-H L-R-H
135—Dehaven-Hotel
complex, 50 to 75
percent slopes
Dehaven 45 B 0-17 Gravelly loam GC-GM,
SC-SM,
GM, SM
A-4 0- 0- 0 0- 0- 0 60-70-
80 50-63-
75 45-58-
70 35-43-
50 25-30
-35
5-8 -10
17-34 Very gravelly sandy
clay loam, very
gravelly clay loam
GC A-2 0- 0- 0 0-13- 25 30-45-
60 25-38-
50 25-35-
45 15-25-
35 25-33
-40
10-15-2
0 34-52 Extremely gravelly
sandy clay loam,
extremely gravelly
clay loam
GP-GC,
GC
A-2 0- 0- 0 0-13- 25 25-28-
30 15-20-
25 10-18-
25 5-13- 20 25-33
-40
10-15-2
0 52-56 Unweathered
bedrock
— — — — — — — — — —
Hotel 35 C 0-8 Very gravelly loam GC-GM,
GM
A-2 0- 0- 0 0- 3- 5 40-48-
55 35-43-
50 30-38-
45 25-30-
35 25-30
-35
5-8 -10
8-35 Very gravelly clay
loam, very
gravelly sandy
clay loam,
extremely gravelly
clay loam
GP-GC,
GC
A-2 0- 0- 0 0- 8- 15 20-40-
60 15-35-
55 10-28-
45 5-20- 35 30-35
-40
10-15-2
0 35-39 Unweathered
bedrock
— — — — — — — — — —
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Engineering Properties–Mendocino County, Western Part, California Map unit symbol and
soil name
Pct. of
map
unit
Hydrolo
gic
group
Depth USDA texture Classification Pct Fragments Percentage passing sieve number— Liquid limit
Plasticit
y index
Unified AASHTO >10
inches
3-10
inches
4 10 40 200
In L-R-H L-R-H L-R-H L-R-H L-R-H L-R-H L-R-H L-R-H
136—Dehaven-Hotel
complex, 75 to 99
percent slopes
Dehaven 42 B 0-17 Gravelly loam GC-GM,
SC-SM,
GM, SM
A-4 0- 0- 0 0- 0- 0 60-70-
80 50-63-
75 45-58-
70 35-43-
50 25-30
-35
5-8 -10
17-34 Very gravelly sandy
clay loam, very
gravelly clay loam
GC A-2 0- 0- 0 0-13- 25 30-45-
60 25-38-
50 25-35-
45 15-25-
35 25-33
-40
10-15-2
0 34-52 Extremely gravelly
sandy clay loam,
extremely gravelly
clay loam
GP-GC,
GC
A-2 0- 0- 0 0-13- 25 25-28-
30 15-20-
25 10-18-
25 5-13- 20 25-33
-40
10-15-2
0 52-56 Unweathered
bedrock
— — — — — — — — — —
Hotel 38 C 0-8 Very gravelly loam GC-GM,
GM
A-2 0- 0- 0 0- 3- 5 40-48-
55 35-43-
50 30-38-
45 25-30-
35 25-30
-35
5-8 -10
8-35 Very gravelly clay
loam, very
gravelly sandy
clay loam,
extremely gravelly
clay loam
GP-GC,
GC
A-2 0- 0- 0 0- 8- 15 20-40-
60 15-35-
55 10-28-
45 5-20- 35 30-35
-40
10-15-2
0 35-39 Unweathered
bedrock
— — — — — — — — — —
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Engineering Properties–Mendocino County, Western Part, California Map unit symbol and
soil name
Pct. of
map
unit
Hydrolo
gic
group
Depth USDA texture Classification Pct Fragments Percentage passing sieve number— Liquid limit
Plasticit
y index
Unified AASHTO >10
inches
3-10
inches
4 10 40 200
In L-R-H L-R-H L-R-H L-R-H L-R-H L-R-H L-R-H L-R-H
141—Ferncreek
sandy loam, 2 to 9
percent slopes
Ferncreek 80 D 0-7 Sandy loam SM A-4 0- 0- 0 0- 0- 0 80-90-1 00 75-88-1
00 65-70-
75 35-43-
50 20-25
-30
NP-3 -5
7-33 Clay loam, clay MH, ML A-7 0- 0- 0 0- 0- 0 80-90-1 00 75-88-1
00 70-80-
90 50-63-
75 40-50
-60
10-18-2
5 33-43 Sandy clay loam SC-SM,
SC
A-4, A-6 0- 0- 0 0- 0- 0 80-90-1
00 75-88-1
00 65-73-
80 35-43-
50 25-33
-40
5-10-15
43-61 Sandy clay loam,
sandy loam
SC-SM,
SC
A-4 0- 0- 0 0- 0- 0 100-100
-100
100-100
-100
60-68-
75 35-43-
50 20-25
-30
5-8 -10
148—Gibwell loamy
sand, 2 to 9 percent
slopes
Gibwell 75 C 0-12 Loamy sand SM A-2 0- 0- 0 0- 0- 0 100-100 -100
100-100
-100
50-63-
75 15-23-
30 — NP
12-18 Sandy clay loam,
clay loam
CL, SC A-6 0- 0- 0 0- 0- 0 95-98-1
00 90-95-1
00 80-88-
95 40-55-
70 30-35
-40
10-13-1
5 18-26 Sandy clay, clay MH, ML A-7 0- 0- 0 0- 0- 0 95-98-1 00 90-95-1
00 85-90-
95 50-65-
80 40-50
-60
10-18-2
5 26-42 Sandy clay loam SC A-6 0- 0- 0 0- 0- 0 95-98-1
00 90-95-1
00 75-83-
90 35-43-
50 30-35
-40
10-13-1
5 42-65 Sandy loam, loamy
sand, sand
SM A-2 0- 0- 0 0- 0- 0 100-100
-100
100-100
-100
50-63-
75 10-20-
30 — NP
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Engineering Properties–Mendocino County, Western Part, California Map unit symbol and
soil name
Pct. of
map
unit
Hydrolo
gic
group
Depth USDA texture Classification Pct Fragments Percentage passing sieve number— Liquid limit
Plasticit
y index
Unified AASHTO >10
inches
3-10
inches
4 10 40 200
In L-R-H L-R-H L-R-H L-R-H L-R-H L-R-H L-R-H L-R-H
149—Gibwell loamy
sand, 9 to 15
percent slopes
Gibwell 75 C 0-12 Loamy sand SM A-2 0- 0- 0 0- 0- 0 100-100 -100
100-100
-100
50-63-
75 15-23-
30 — NP
12-18 Clay loam, sandy
clay loam
CL, SC A-6 0- 0- 0 0- 0- 0 95-98-1
00 90-95-1
00 80-88-
95 40-55-
70 30-35
-40
10-13-1
5 18-26 Sandy clay, clay MH, ML A-7 0- 0- 0 0- 0- 0 95-98-1 00 90-95-1
00 85-90-
95 50-65-
80 40-50
-60
10-18-2
5 26-42 Sandy clay loam SC A-6 0- 0- 0 0- 0- 0 95-98-1
00 90-95-1
00 75-83-
90 35-43-
50 30-35
-40
10-13-1
5 42-65 Sandy loam, loamy
sand, sand
SM A-2 0- 0- 0 0- 0- 0 100-100
-100
100-100
-100
50-63-
75 10-20-
30 — NP
157—Harecreek
sandy loam, 2 to 9
percent slopes
Harecreek 85 A 0-2 Slightly
decomposed plant
material
PT A-8 0- 0- 0 0- 0- 0 — — — — — —
2-10 Sandy loam SM A-2-4, A-4 0- 0- 0 0- 0- 0 95-97-1
00 85-91-1
00 62-70-
81 30-35-
43 20-25
-30
—
10-18 Sandy loam SM A-4 0- 0- 0 0- 0- 0 95-97-1
00 85-91-1
00 62-70-
81 30-36-
43 20-25
-30
—
18-45 Sandy loam, sandy
clay loam
SC-SM,
SC, SM
A-2-4, A-4 0- 0- 0 0- 0- 0 95-97-1
00 85-92-1
00 68-79-
88 34-42-
48 25-30
-35
5-8 -10
45-65 Sand, loamy sand,
sandy loam
— — 0- 0- 0 0- 0- 0 95-97-1
00 86-92-1
00 66-74-
84 9-13- 19 — —
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Engineering Properties–Mendocino County, Western Part, California Map unit symbol and
soil name
Pct. of
map
unit
Hydrolo
gic
group
Depth USDA texture Classification Pct Fragments Percentage passing sieve number— Liquid limit
Plasticit
y index
Unified AASHTO >10
inches
3-10
inches
4 10 40 200
In L-R-H L-R-H L-R-H L-R-H L-R-H L-R-H L-R-H L-R-H
173—IrmulcoTramway complex,
30 to 50 percent
slopes
Irmulco 70 B 0-1 Slightly
decomposed plant
material
PT A-8 0- 0- 0 0- 0- 0 — — — — — —
1-7 Loam SC-SM,
CL, ML
A-4 0- 0- 0 0- 0- 0 90-95-1
00 76-86-1
00 65-80-
96 45-57-
72 25-30
-35
5-8 -10
7-42 Loam, clay loam,
gravelly loam
SC-SM,
CL, SC
A-2-4,
A-4, A-6
0- 0- 0 0- 0- 0 76-86-1
00 49-69-1
00 43-64-
98 31-49-
78 25-33
-40
5-10-15
42-62 Clay loam, gravelly
clay loam
CH, SC A-2-4,
A-6,
A-7-6
0- 0- 0 0- 0- 0 76-86-1
00 48-68-1
00 41-63-1
00 30-49-
81 30-40
-50
10-18-2
5 62-72 Bedrock — — — — — — — — — —
Tramway 16 C 0-2 Slightly
decomposed plant
material
PT A-8 0- 0- 0 0- 0- 0 — — — — — —
2-9 Loam SC-SM,
CL, ML
A-4 0- 0- 0 0- 0- 0 91-95-1
00 77-87-1
00 66-77-
91 47-56-
66 25-30
-35
5-8 -10
9-14 Loam CL-ML,
CL
A-4, A-6 0- 0- 0 0- 0- 0 91-95-1
00 78-87-1
00 67-78-
93 50-59-
71 25-33
-40
5-10-15
14-30 Clay loam, gravelly
clay loam
CL, SC A-2-4,
A-6,
A-7-6
0- 0- 0 0- 0- 0 76-85-1
00 48-68-1
00 40-62-
98 31-48-
78 30-38
-45
10-15-2
0 30-43 Bedrock — — — — — — — — — —
Engineering Properties---Mendocino County, Western Part, California Natural Resources
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5/22/2023

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CL, GC,
SC
A-6, A-7 0- 0- 0 0- 0- 0 65-83-1
00 60-80-1
00 55-75-
95 40-60-
80 30-38
-45
10-15-2
0 28-32 Weathered bedrock — — — — — — — — — —
Engineering Properties---Mendocino County, Western Part, California Natural Resources
Conservation Service
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5/22/2023

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Engineering Properties–Mendocino County, Western Part, California Map unit symbol and
soil name
Pct. of
map
unit
Hydrolo
gic
group
Depth USDA texture Classification Pct Fragments Percentage passing sieve number— Liquid limit
Plasticit
y index
Unified AASHTO >10
inches
3-10
inches
4 10 40 200
In L-R-H L-R-H L-R-H L-R-H L-R-H L-R-H L-R-H L-R-H
196—QuinlivenFerncreek complex,
2 to 15 percent
slopes
Quinliven 60 C 0-5 Slightly
decomposed plant
material
PT A-8 0- 0- 0 0- 0- 0 — — — — — —
5-9 Sandy loam SM A-4 0- 0- 0 0- 0- 0 100-100
-100
100-100
-100
72-77-
83 34-40-
46 20-25
-30
—
9-16 Loam, sandy loam SC-SM,
ML, SC
A-2-4, A-4 0- 0- 0 0- 0- 0 100-100
-100
100-100
-100
69-77-
85 32-40-
50 25-30
-35
5-8 -10
16-23 Loam, sandy clay
loam, clay loam
CL A-6 0- 0- 0 0- 0- 0 100-100
-100
100-100
-100
83-91-
96 59-69-
76 25-33
-40
10-15-2
0 23-56 Clay, sandy clay MH, ML A-7-5 0- 0- 0 0- 0- 0 100-100 -100
100-100
-100
84-92-1
00 67-80-
89 40-50
-60
10-18-2
5 56-65 Sandy clay loam,
clay loam
CL, SC A-6 0- 0- 0 0- 0- 0 100-100
-100
100-100
-100
79-87-
95 42-51-
60 30-35
-40
10-15-2
0 65-75 Loamy sand, sandy
loam
SM A-2-4 0- 0- 0 0- 0- 0 100-100
-100
100-100
-100
75-82-
89 18-22-
33 20-25
-30
—
Ferncreek 25 C 0-2 Slightly
decomposed plant
material
PT A-8 0- 0- 0 0- 0- 0 — — — — — —
2-9 Sandy loam SM A-2-4, A-4 0- 0- 0 0- 0- 0 85-91-1
00 67-80-1
00 49-61-
84 24-31-
48 20-25
-30
—
9-35 Clay loam, clay MH, SM A-7-5 0- 0- 0 0- 0- 0 85-90-1 00 65-78-1
00 57-75-1
00 44-61-
91 40-50
-60
10-18-2
5 35-45 Sandy clay loam SC-SM,
CL, SC
A-2-4,
A-4, A-6
0- 0- 0 0- 0- 0 85-90-1
00 66-79-1
00 54-69-
92 30-39-
54 25-33
-40
5-10-15
45-63 Sandy loam, sandy
clay loam
SC-SM,
SC
A-2-4, A-4 0- 0- 0 0- 0- 0 100-100
-100
100-100
-100
71-77-
84 34-40-
48 20-25
-30
5-8 -10
Engineering Properties---Mendocino County, Western Part, California Natural Resources
Conservation Service
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Engineering Properties–Mendocino County, Western Part, California Map unit symbol and
soil name
Pct. of
map
unit
Hydrolo
gic
group
Depth USDA texture Classification Pct Fragments Percentage passing sieve number— Liquid limit
Plasticit
y index
Unified AASHTO >10
inches
3-10
inches
4 10 40 200
In L-R-H L-R-H L-R-H L-R-H L-R-H L-R-H L-R-H L-R-H
199—ShinglemillGibney complex, 2
to 9 percent slopes
Shinglemill 45 C/D 0-2 Slightly
decomposed plant
material
PT A-8 0- 0- 0 0- 0- 0 — — — — — —
2-10 Loam ML, SM A-4 0- 0- 0 0- 0- 0 84-88-
95 68-78-
95 55-69-
89 38-49-
65 25-30
-35
—
10-17 Sandy clay loam,
loam
CL, SC A-6 0- 0- 0 0- 0- 0 85-90-1
00 66-79-1
00 56-71-
91 42-54-
69 30-35
-40
10-13-1
5 17-27 Clay, clay loam MH, ML A-7-5 0- 0- 0 0- 0- 0 85-90-1 00 65-78-1
00 60-74-1
00 51-62-1
00 40-53
-65
10-18-2
5 27-65 Sandy clay, clay MH, SM A-2-7,
A-7-5
0- 0- 0 0- 0- 0 85-90-1
00 65-78-1
00 48-66-
91 30-44-
63 45-55
-65
15-20-2
5 Gibney 35 C 0-9 Loam SC-SM,
ML, SC
A-4 0- 0- 0 0- 0- 0 83-90-1
00 62-78-1
00 51-68-
91 36-48-
66 25-30
-35
5-8 -10
9-29 Sandy clay loam,
clay loam
CL, SC A-2-4, A-6 0- 0- 0 0- 0- 0 84-90-1
00 63-79-1
00 51-68-
92 31-42-
59 30-35
-40
10-15-2
0 29-55 Clay MH, SM A-7-5 0- 0- 0 0- 0- 0 83-90-1
00 62-78-1
00 51-72-1
00 44-63-
91 40-50
-60
10-18-2
5 55-63 Sandy clay loam,
sandy clay
CH, SC A-2-4,
A-6,
A-7-6
0- 0- 0 0- 0- 0 84-90-1
00 63-79-1
00 49-69-
98 30-45-
67 30-40
-50
10-18-2
5 Engineering Properties---Mendocino County, Western Part, California Natural Resources
Conservation Service
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Engineering Properties–Mendocino County, Western Part, California Map unit symbol and
soil name
Pct. of
map
unit
Hydrolo
gic
group
Depth USDA texture Classification Pct Fragments Percentage passing sieve number— Liquid limit
Plasticit
y index
Unified AASHTO >10
inches
3-10
inches
4 10 40 200
In L-R-H L-R-H L-R-H L-R-H L-R-H L-R-H L-R-H L-R-H
212—TregoningCleone complex, 0
to 5 percent slopes
Tregoning 60 B/D 0-2 Slightly
decomposed plant
material
PT A-8 0- 0- 0 0- 0- 0 — — — — — —
2-11 Sandy loam SM A-4 0- 0- 0 0- 0- 0 100-100
-100
100-100
-100
72-77-
81 33-39-
45 20-25
-30
—
11-25 Loamy sand, sandy
loam
SM A-4 0- 0- 0 0- 0- 0 100-100
-100
100-100
-100
70-76-
82 30-38-
46 20-25
-30
—
25-64 Sand — — 0- 0- 0 0- 0- 0 100-100
-100
100-100
-100
78-80-
83 11-14-
16 — —
Cleone 20 B 0-3 Loamy sand — — 0- 0- 0 0- 0- 0 100-100
-100
100-100
-100
76-80-
85 19-23-
28 — —
3-7 Sandy loam SM A-2-4, A-4 0- 0- 0 0- 0- 0 87-92-1
00 70-83-1
00 52-63-
79 25-31-
41 20-25
-30
—
7-13 Gravelly sandy
loam, gravelly
loamy sand
SC-SM,
SC
A-2-4, A-4 0- 0- 0 0- 0- 0 76-81-
86 57-70-
86 41-54-
70 19-27-
37 20-25
-30
—
13-40 Sandy loam, loamy
sand
SC-SM,
SC
A-2-4, A-4 0- 0- 0 0- 0- 0 95-97-1
00 86-92-1
00 61-70-
82 29-35-
44 20-25
-30
—
40-62 Loamy sand, sand — — 0- 0- 0 0- 0- 0 100-100
-100
100-100
-100
77-80-
84 19-23-
26 — —
Engineering Properties---Mendocino County, Western Part, California Natural Resources
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Engineering Properties–Mendocino County, Western Part, California Map unit symbol and
soil name
Pct. of
map
unit
Hydrolo
gic
group
Depth USDA texture Classification Pct Fragments Percentage passing sieve number— Liquid limit
Plasticit
y index
Unified AASHTO >10
inches
3-10
inches
4 10 40 200
In L-R-H L-R-H L-R-H L-R-H L-R-H L-R-H L-R-H L-R-H
213—TregoningCleone complex, 5
to 15 percent slopes
Tregoning 55 B/D 0-2 Slightly
decomposed plant
material
PT A-8 0- 0- 0 0- 0- 0 — — — — — —
2-11 Sandy loam SM A-4 0- 0- 0 0- 0- 0 100-100
-100
100-100
-100
72-77-
81 33-39-
45 20-25
-30
—
11-25 Loamy sand, sandy
loam
SM A-4 0- 0- 0 0- 0- 0 100-100
-100
100-100
-100
70-76-
82 30-38-
46 20-25
-30
—
25-64 Sand — — 0- 0- 0 0- 0- 0 100-100
-100
100-100
-100
78-80-
83 11-14-
16 — —
Cleone 25 B 0-3 Loamy sand — — 0- 0- 0 0- 0- 0 100-100
-100
100-100
-100
76-80-
85 19-23-
28 — —
3-7 Sandy loam SM A-2-4, A-4 0- 0- 0 0- 0- 0 87-92-1
00 70-83-1
00 52-63-
79 25-31-
41 20-25
-30
—
7-13 Gravelly sandy
loam, gravelly
loamy sand
SC-SM,
SC
A-2-4, A-4 0- 0- 0 0- 0- 0 76-81-
86 57-70-
86 41-54-
70 19-27-
37 20-25
-30
—
13-40 Loamy sand, sandy
loam
SC-SM,
SC
A-2-4, A-4 0- 0- 0 0- 0- 0 95-97-1
00 86-92-1
00 61-70-
82 29-35-
44 20-25
-30
—
40-62 Loamy sand, sand — — 0- 0- 0 0- 0- 0 100-100
-100
100-100
-100
77-80-
84 19-23-
26 — —
221—Vandamme
loam, 9 to 30
percent slopes
Vandamme 85 C 0-9 Loam CL-ML,
ML
A-4 0- 0- 0 0- 0- 0 95-98-1
00 85-90-
95 70-78-
85 55-63-
70 25-30
-35
5-8 -10
9-42 Clay, clay loam CH, MH A-7 0- 0- 0 0- 0- 0 95-98-1 00 85-90-
95 80-85-
90 75-80-
85 50-55
-60
20-25-3
0 42-46 Bedrock — — — — — — — — — —
Engineering Properties---Mendocino County, Western Part, California Natural Resources
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CL, GC,
SC
A-6, A-7 0- 0- 0 0- 0- 0 65-83-1
00 60-80-1
00 55-75-
95 40-60-
80 30-38
-45
10-15-2
0 28-32 Weathered bedrock — — — — — — — — — —
Data Source Information
Soil Survey Area: Mendocino County, Western Part, California Survey Area Data: Version 18, Sep 7, 2022
Engineering Properties---Mendocino County, Western Part, California Natural Resources
Conservation Service
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Water Distribution System Master Plan
City of Fort Bragg
Appendix C. Climate Risk And Vulnerability

Climate Risk and
Vulnerability Assessment
Fort Bragg Distribution System Master
Plan
City of Fort Bragg
May 27, 2025
Fort Bragg Distribution System Master Plan
Climate Risk and Vulnerability Assessment
May 27, 2025 | i
Table of Contents

1.0 Introduction ........................................................................................................................ 1

2.0 Climate Analysis ................................................................................................................. 2

2.1 Overview ......................................................................................................................... 2

2.2 Historic Climate Trends .................................................................................................. 2

2.2.1 Flooding (Coastal, Storm Surge, and Riverine) ....................................................... 3

2.2.2 Precipitation ............................................................................................................. 4

2.2.3 Coastal Bluff Erosion (Coastal) & Landslides .......................................................... 8

2.2.4 Temperature / Extreme Heat ................................................................................. 10

2.2.5 Wildfire .................................................................................................................. 11

2.2.6 Drought .................................................................................................................. 11

2.3 Projected/Possible Climate Scenarios .......................................................................... 12

2.3.1 Flooding (Sea Level Rise, Storm Surge and Riverine) .......................................... 12

2.3.2 Precipitation ........................................................................................................... 15

2.3.3 Coastal Bluff Erosion (Coastal) and Landslides .................................................... 18

2.3.4 Temperature / Extreme Heat ................................................................................. 19

2.3.5 Wildfire .................................................................................................................. 21

2.3.6 Groundwater ......................................................................................................... 22

2.3.7 Drought .................................................................................................................. 22

2.4 Conclusion/Key Findings .............................................................................................. 22

3.0 Climate Change Impact Assessment ............................................................................... 24

3.1 Approach ...................................................................................................................... 24

3.2 Interdependency CRVA ................................................................................................ 26

3.2.1 Transportation ....................................................................................................... 30

3.2.2 Energy and Electrical ............................................................................................ 30

3.2.3 Water Infrastructure ............................................................................................... 31

3.2.4 Telecommunications ............................................................................................. 31

3.2.5 Critical Infrastructure ............................................................................................. 31

3.2.6 Impacted Communities .......................................................................................... 32

3.2.7 Natural Systems .................................................................................................... 32

3.2.8 Key Findings .......................................................................................................... 32 Fort Bragg Distribution System Master Plan
Climate Risk and Vulnerability Assessment
May 27, 2025 | ii

3.3 Water Distribution System CRVA ................................................................................. 33

3.3.1 Water System Climate Risk and Vulnerability Assessment ................................... 33

3.3.2 Assumptions .......................................................................................................... 34

3.3.3 Key findings ........................................................................................................... 38

4.0 Recommendations ........................................................................................................... 39

4.1 Regional Recommendations ........................................................................................ 39

4.2 Water Distribution System Recommendations ............................................................. 39

4.3 Next Steps / Further Studies ........................................................................................ 39

5.0 References ....................................................................................................................... 40 List of Tables
Table 1 – Prioritization of Regional Infrastructures ..................................................................... 32 Table 2 – Assets Prioritization .................................................................................................... 38 List of Figures
Figure 1 – Project Area, City of Fort Bragg Water System ........................................................... 1 Figure 2 – FEMA 100-Year Event Flood Risk ............................................................................... 4 Figure 3 – Observed Annual Maximum 1 Day Precipitation at Fort Bragg 5 N Station (1950- 2023) ............................................................................................................................................. 5 Figure 4 – Observed Total Annual Precipitation at Fort Bragg 5 N Station (1950-2023) .............. 6 Figure 5 – Observed Number of Days Where Rainfall Exceed 1 Inch (blue), 2 Inches (green), 3 Inches (orange), 4 Inches (red), with Trendlines Plotted in Each Respective Color ..................... 6 Figure 6 – Geologic Hazards, Fort Bragg ..................................................................................... 8 Figure 7 – Relative Slope Instability in the Fort Bragg Area (After CGS Map 58, 2011) .............. 9 Figure 8 – Observed Annual Mean Maximum Temperature at Fort Bragg 5 N station (1950- 2023) ........................................................................................................................................... 10 Figure 9 – Observed Annual Mean Minimum Temperature at Fort Bragg 5 N station (1950-2023) .................................................................................................................................................... 11 Figure 10 – Flooding Risk Projected: Highest Water Levels Mapped in the Regional Water Level Viewer, Equal to 10 Feet SLR over the MHHW Elevation .......................................................... 14 Fort Bragg Distribution System Master Plan
Climate Risk and Vulnerability Assessment
May 27, 2025 | iii
Figure 11 – Projected Total Annual Precipitation for Fort Bragg Based on Climate Scenario RCP

4.5. .............................................................................................................................................. 15 Figure 12 – Projected Total Annual Precipitation for Fort Bragg Based on Climate Scenario RCP

8.5. .............................................................................................................................................. 16 Figure 13 – Projected Number of Days with Greater Than 1 Inch of Precipitation for Fort Bragg Based on Climate Scenario RCP 4.5 .......................................................................................... 17 Figure 14 – Projected Number of Days with Greater than 1 Inch of Precipitation for Fort Bragg Based on Climate Scenario RCP 8.5 .......................................................................................... 17 Figure 15 – Existing Coastal Erosion Risk .................................................................................. 18 Figure 16 – Projected Annual Mean Maximum Temperatures Expected in Fort Bragg for the Years 2020-2100 Based on the RCP 4.5 Climate Scenario ....................................................... 19 Figure 17 – Projected Annual Mean Maximum Temperatures Expected in Fort Bragg for the Years 2020-2100 Based on the RCP 8.5 Climate Scenario ....................................................... 20 Figure 18 – Projected Annual Mean Maximum Temperatures Expected in Fort Bragg for the Years 2020-2100 Based on the RCP 4.5 Climate Scenario ..................................................... 20 Figure 19 – Projected Annual Mean Minimum Temperatures Expected in Fort Bragg for the Years 2020-2100 Based on the RCP 8.5 Climate Scenario ..................................................... 21 Figure 20 – Illustration of Steps for Developing a Climate Risk and Vulnerability Assessment (CRVA) ........................................................................................................................................ 24 Figure 21 – Vulnerability Matrix .................................................................................................. 25 Figure 22 – Risk Matrix ............................................................................................................... 25 Figure 23 – Critical Assets .......................................................................................................... 27 Figure 24 – Regional Asset Map and Flooding Risk ................................................................... 28 Figure 25 –Regional Asset Map of Existing Landslide and Coastal Erosion Risk ...................... 29 Figure 26 – Regional Asset Map of Existing Wildfire Risk .......................................................... 30 Figure 27 – Water Distribution Assets Map ................................................................................ 34 Figure 28 – Water Distribution Assets Map and Flooding Risk ................................................... 35 Figure 29 – Water Distribution Assets Map and Erosion and Landslide Risk ............................. 36 Figure 30 – Water Distribution Assets Map and Fire Risk .......................................................... 37 Fort Bragg Distribution System Master Plan
Climate Risk and Vulnerability Assessment
May 27, 2025 | iv
Executive Summary
This Climate Risk and Vulnerability Assessment (CRVA) report addresses and quantifies risk associated with the impacts of climate change on the Fort Bragg Water System (Water System).

This step-by-step analysis utilizes historic climate trends to set the baseline for understanding projected future climate trends so that the Water System site risk/vulnerabilities can be correlated to those that are anticipated due to climate change. Once the observed climate trends and projections were collected, the findings were used to identify the building and regional infrastructure vulnerability to projected climate changes as part of this CRVA.

The Water System challenges adapting to more extreme climate events are:
 Increased air temperatures will produce added demand and stress on the Water System and exacerbate the threat of wildfire in the region.
 Increased air temperatures, coupled with an increase in year-over-year variability in precipitation, will make for years in which water management will become increasingly difficult to balance between years of flood and years of drought.  Sea Level Rise (SLR) and extreme rain events with subsequent periods of drought are most likely to increase the risk of landslides and erosion.  Wildfire remains a concern for the urban area impacting infrastructure.

The key regional infrastructure elements supporting the Water System that are most at risk are:
 Transportation: Bridges are most at risk of being impacted by Sea Level Rise and Storm Surge or flooding. While the City does not own or maintain any bridges, the two main bridges in town are on Highway 1 and are 85'+ above sea level, making them unlikely to flood. However, they still might be impacted by erosion. It is recommended that the City develop a more comprehensive understanding of the risks associated with sea level rise and work in partnership with Caltrans to assess and implement resilient measures that will not obstruct access to critical water infrastructure.  Energy Systems: Transmission lines exposed to wildfire could impact operations of water pump(s) for the water distribution system.
 Water: Water treatment plant is at the edge of wildfire susceptibility.  Critical Infrastructure: The Fort Bragg Fire Station #2 is vulnerable to wildfires, which could hinder its ability to effectively respond and protect water system assets.

Assets of the water distribution systems to be enhanced by resiliency strategies are:
 Pump Station: Pump station inundated by 100-year, and base water surface in 2070.  Mains: Landslides along creek banks.
 Storage Tanks: Vulnerable to wildfire.
 Water Treatment Plant: The climate assessment was limited to a high-level preliminary review of the area within the study boundaries and did not consider risks to individual assets or infrastructure inside the treatment plant. It is recommended that a detailed climate vulnerability assessment be conducted for the water treatment facility itself.

Resiliency and Climate Risks
Fort Bragg Water System
May 27, 2025 | 1

1.0 Introduction
This CRVA overview provides information for the development of a Climate Action Plan that will identify and better prepare the Fort Bragg Water System for climate change-related hazards.

For this report, resiliency is defined as the ability to anticipate, prepare for, and adapt to changing conditions and withstand, respond to, and recover rapidly from disruptions. The stepby-step analysis utilizes historic climate trends to set the baseline for understanding projected future climate trends for the Water System (Figure 1) and supporting infrastructure. It is based on best available information providing for a framework that can be updated with new information when available.

Figure 1 – Project Area, City of Fort Bragg Water System (Source: HDR GIS based on Fort Bragg database)
Fort Bragg Distribution System Master Plan
Climate Risk and Vulnerability Assessment
May 27, 2025 | 2

2.0 Climate Analysis

2.1 Overview
The project is in the City of Fort Bragg, California. The city is located on the north central coast of California that is strongly influenced by its proximity to the cool waters of the eastern Pacific.

It has a population of 6,970 (est. 2021) and an official elevation of 85 feet above sea level. This study analyzed environmental hazards/threats as they exist in the present day and provides guidance on how those hazards/threats to the City’s water system are expected to change in the future. The key hazards are listed below:
 Flooding (SLR, Storm Surge, and Riverine).
 Precipitation.
 Landslides / Slope Instability / Erosion.
 Temperature / Extreme Heat.
 Wildfire.
 Groundwater.
 Drought.

Time horizons selected for the project matched the state-adopted timeframe and the life expectancy of the Water System being designed for a 50-year standard. For this study, climate scenarios have been developed for:
 Baseline/ existing conditions (historic record).
 Mid-term: 2050.
 Long-term: 2070.

Projected climate scenarios utilized in this study came from the Coupled Model Intercomparison Project 5 output with GDDP (NASA) downscaling for the Representative Concentration Pathway (RCP) climate emissions scenarios 4.5 and 8.5. RCP 4.5 is a scenario where emissions continue to increase at their current rate until the year 2050, when they begin to decrease through the year 2070, at which point they begin to decline through the remainder of the 21st century. RCP 8.5 is an emissions scenario that sees emissions increase unabated through the end of the 21st century.

2.2 Historic Climate Trends
An analysis of climatic trends provides perspective on the climate projections and evolution of anticipated future climate threats that is discussed in Section 2.3.

Fort Bragg Distribution System Master Plan
Climate Risk and Vulnerability Assessment
May 27, 2025 | 3

2.2.1 Flooding (Coastal, Storm Surge, and Riverine)
Fort Bragg’s juxtaposition along the California coast at the mouth of the west-east oriented Noyo River makes it susceptible to a combination of ocean swell, storm surge, wind waves, and astronomical tides, as well as a tsunami originating anywhere within the “Ring of Fire” surrounding the adjacent Pacific Ocean. As can be seen in Figure 2, FEMA base flood elevations (BFEs) along the coast (Zone VE) range from 29 to 36 feet along the bluffs, 19 feet at the beach immediately north of the Noyo River mouth, and 40 feet at the mouth of the Noyo River and adjacent bluff within the bay. These values represent 100-year recurrence interval water levels at current sea level conditions, including wave setup and runup. Wave setup and runup are dependent on the slopes of the terrain, both below the stillwater level and above it along beaches and bluffs. The variability in mapped water levels is based on the differing conditions at individual transects in the FIS study, which are indicated on the map as dashed lines numbered 25 through 31 within the City.

Elevated tides and higher wave heights can occur coincidentally with high river flows on the Noyo River. The FEMA floodplain modeling and Zone designations along the Noyo River are based on mean higher-high water at current climactic conditions and do not include elevated tides or future climate changes. Therefore, when riverine flows are combined with high tides, the water levels along the Noyo River, particularly closer to the mouth of the river, may be higher than indicated by the BFEs.

An analysis of year-over-year coastal water surface elevations shows that the highest annual water surface elevations in the region are the result of thermal expansion of the Pacific Ocean during years of significant El Niño conditions (i.e. 1992, 1997-1998, 2015, and 2023).

Outside the scope of this analysis but worth noting is the threat of a tsunami, although rare, is ever-present in the region of the north-central California coast. Any one of the hundreds of earthquake faults surrounding the Pacific Rim can produce a tsunami that could reach the City of Fort Bragg. The California State Department of Conservation maintains a website devoted to the transfer of knowledge and information regarding Mendocino County Tsunami Hazard Areas.1 This website provides real-time information about what to do before, during, and after a tsunami event.
1 https://www.conservation.ca.gov/cgs/tsunami/maps/mendocino Fort Bragg Distribution System Master Plan
Climate Risk and Vulnerability Assessment
May 27, 2025 | 4
Figure 2 – FEMA 100-Year Event Flood Risk
(Source: FIRM map at https://hazardsfema.maps.arcgis.com/apps/webappviewer/index.html?id=8b0adb51996444d4879338b5529aa9cd)

2.2.2 Precipitation
Historic climate trends are critical to setting a relationship between observed changes in the climate and projected changes in the future climate. They represent the “here and now” of climate hazards and how those hazards have changed over time in the observed record. This section investigates current and future extrapolated climate trends, so that those extrapolations can be compared with future climate scenarios for the following environmental parameters.

The National Center for Environmental Information (NCEI) was the primary source of data for historical observations, which were developed from the Fort Bragg 5 N (Station ID:

USC00043161) meteorological reporting station located 5 miles north of Fort Bragg (Figure 3).

The reporting station is used for a period of record (POR) from 1950 to present day for temperature and precipitation data.

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Figure 3 – Observed Annual Maximum 1 Day Precipitation at Fort Bragg 5 N Station (1950-2023) (Source: NCEI)
The observed maximum single day precipitation in Figure 3 shows a flat trend (neither decreasing nor increasing) from 1950 to present day. However, this trendline does not highlight the increasingly variable nature of single-day precipitation events. Precipitation events across the region and in Fort Bragg are increasing in relative intensity and variability. In other words, while a similar amount of rain may fall each year, that rain will likely be concentrated into heavy rainfall events interspersed with more intense dry periods.

This seasonal variability is also reflected in the Observed Total Annual Precipitation shown in Figure 4. While the trendline of total annual precipitation is also relatively flat, the intensity has increased dramatically in recent years. For example, in Figure 4, it is observed that since the early 1980s, there have been 15 years where the difference in precipitation from one year to the next is greater than 15 inches. Another way of measuring the increasing variability is through the standard deviation of the precipitation, or in other words, how much does the rainfall varies from year to year. In Fort Bragg, the standard deviation of the total annual precipitation from 1950-1986 was 7.68 inches. From 1987-2023 it increased to 11.83 inches. Therefore, it is shown that statistically speaking, the amount of precipitation that falls annually in Fort Bragg is becoming more variable from year to year.

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Figure 4 – Observed Total Annual Precipitation at Fort Bragg 5 N Station (1950-2023) (Source: NCEI)
Figure 5 – Observed Number of Days Where Rainfall Exceed 1 Inch (blue), 2 Inches (green), 3 Inches (orange), 4 Inches (red), with Trendlines Plotted in Each Respective Color (Source: NCEI)
0 5
10 15
20 25
1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015 2020 Number of Days per Year
Year
Number of Days Per Year with Rainfall > Threshold
(1950‐2023) Fort Bragg, CA
1 inch 2 inch 3 inch 4 inch
Linear (1 inch) Linear (2 inch) Linear (3 inch) Linear (4 inch) Fort Bragg Distribution System Master Plan
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The number of days that experience extreme rainfall events can be associated with increasing variability and relative intensity of rainfall in the region. Figure 5 highlights the number of days each year with 1-4 inches of rainfall on a single day. The associated trendlines are especially helpful in understanding the rate of increase in the heaviest rainfall events with a slight decline in moderate rainfall. While the blue trendline (1-inch rainfall days) remains relatively flat, the green (2-inch) and orange (3-inch) trendlines decrease slightly, which gives rise to the extreme red (4-inch) trendline visible in the bottom right of the figure. This demonstrates that there has already been an increase in the extreme rainfall events in the past 20 years where we see fewer 2- and 3-inch rainfall events per year and instead see occasional 4-inch or greater rainfall days, which have historically over-stressed City water management and breached riverine flood barriers.

It is important to note that as the historic record shows an increase in storms producing greater than 4 inches of daily precipitation, the increased flows because of these storms in Virgin Creek, Pudding Creek, and the Noyo River will increase the likelihood of coincidental coastal flooding.

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2.2.3 Coastal Bluff Erosion (Coastal) & Landslides
Bluff erosion is influenced by sea level rise in addition to the mechanisms that impact landslides inland and need to be evaluated concurrently. Figure 6 below documents geologic hazards with risk of erosion and landslides.

Figure 6 – Geologic Hazards, Fort Bragg
(Source: Department of Conservation Division of Mines& Geology. 1983) Fort Bragg Distribution System Master Plan
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Figure 7 – Relative Slope Instability in the Fort Bragg Area (After CGS Map 58, 2011) Figure 7 above shows the rankings from “Susceptibility to Deep-Seated Landslides” from beige to red. This is not identified landslides, but an evaluation of the risk of land sliding. Based on this map of the system, the sections near the creeks and rivers appear vulnerable. Most of the area is flat and shows low potential for land sliding. Findings from this high-level analysis will need to be compared and coordinated with the soil/Geotech evaluations part of the risk assessment.

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2.2.4 Temperature / Extreme Heat
A similar scenario is seen with the observed temperature in Fort Bragg as has been shown with observed precipitation. The trendline is flat in the observed annual mean maximum temperature for the period from 1950-2023 (Figure 8). However, the variability of the annual mean maximum temperature is plainly seen in the last 30 years. In this case, the standard deviation of the annual mean maximum temperature nearly doubles in variability from the first half of the dataset to the most recent half. From 1950-1986 the standard deviation of temperature was 0.97 °F.

From 1987-2023 it increased to 1.63 °F. Therefore, it is shown that statistically speaking, the average hottest days in Fort Bragg each year are becoming more variable.

Figure 8 – Observed Annual Mean Maximum Temperature at Fort Bragg 5 N station (1950-2023) (Source: NCEI)
Interestingly, the observed annual mean minimum temperature (Figure 9) shows a decreasing trend, meaning that on average the coldest days are getting colder in Fort Bragg. In terms of statistical variability, there is a small increase in variability in the second half of the annual mean minimum temperature data, which is consistent with the rest of the temperature and precipitation data and supports the overall trend towards more variable weather patterns depicted in the climate section.

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Figure 9 – Observed Annual Mean Minimum Temperature at Fort Bragg 5 N station (1950-2023) (Source: NCEI)

2.2.5 Wildfire
The California Air Resources Board (CARB) has unequivocally stated that, “Climate change, primarily caused by the burning of fossil fuels, is increasing the frequency and severity of wildfires not only in California but also all over the world. Since 1950, the area burned by California wildfires each year has been increasing, as spring and summer temperatures have warmed, and spring snowmelt has occurred earlier (CARB, 2023).” As seen in the graph of annual precipitation and annual maximum temperatures (Figure 4 and Figure 8), the most recent drought in California (2020-2022) was accompanied by increased air temperatures as well. This combination of lack of precipitation, increased temperatures, and even increasing wind events has resulted in a dramatic increase in the frequency and intensity of wildfire in all of California.

2.2.6 Drought
As previously mentioned in Section 2.1.2, precipitation has historically been highly variable within California. This was particularly true in the last six years, where the water year 2016-2017 produced well above normal precipitation in northern California, while 2020-2022 were years of significantly below normal precipitation. The water year 2022-2023, in turn, produced record snowfall in the Sierras and well-above normal precipitation elsewhere in the state. That yearover-year variability will continue to challenge water managers in the future and will require continued conservation efforts during times of drought.

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2.3 Projected/Possible Climate Scenarios
Climate change projections are manifestations of output from global climate models that use future climate scenarios (climate forcing) to quantify future changes in atmospheric parameters.

Changes in air temperatures and precipitation, which may result in consequential changes in other hazards such as flooding, ice storms, lightning, and tornadoes, are assessed using climate scenarios.

The emission of Greenhouse Gases (GHG) from human activity is expected to be largely responsible for the magnitude of climate change through the end of this century. To capture an understanding of different climate change outcomes, this study utilized two future emissions (climate) scenarios or Representative Concentration Pathways (RCP) to provide a perspective on future change. RCP 4.5 represents a future wherein GHG emissions continue to increase until the year 2050 and then begin to decrease through the year 2100. In this scenario it takes until the year 2070 before that decrease becomes impactful to the projections. RCP 8.5 represents a future where emissions continue to accelerate through the year 2100. RCP 4.5 is considered the middle-of-the-road case, while RCP 8.5 represents the highest level of future emissions.

The climate projection data utilized in this study comes from the U.S. Climate Resilience Toolkit Climate Explorer (CRTCE, 2023). This resource is supported by data from NOAA's National Centers for Environmental Information (NCEI) and shows results generated by global climate models for the Coupled Model Intercomparison Project Phase 5 (CMIP5). While this is not the most current CMIP (CMIP6), the projected data still gives an accurate idea of the expected climate trends. For any major discrepancies between the projected data shown here and the projections shown by the State of California can be attributed to the use of CMIP5 by the CRTCE. It is expected that integrating CMIP6 data into these projections would produce more intense trends.

2.3.1 Flooding (Sea Level Rise, Storm Surge and Riverine) Sea level rise is accelerating along the California coast and will continue to rise substantially during the 21st century, threatening coastal communities, natural resources, cultural sites, and infrastructure. State of California Sea Level Rise Guidance: 2024 Science and Policy Update (“2024 State Guidance”) was published by the California Ocean Protection Council (OPC) to provide recommendations for evaluating proposed projects against future sea level rise scenarios. The 2024 State Guidance includes relative sea level rise projections for a series of NOAA tide gauges along the California Coast. The closest tide gauge to the project location is the Arena Cove, CA gauge, located 45 miles south of Fort Bragg, which indicates 1.2 ft to 2.8 ft of sea level rise by 2070 and between 2.9 ft and 6.4 ft by 2100 under the Intermediate and high sea level rise projection scenarios, respectively. Though the exact amount of sea level rise for a specific location in a certain year is unclear, we know that water levels are rising, and communities need to be prepared. Coastal wave events and king tides, in combination with current and rising sea levels, will increase flood impacts on land, which will exacerbate the impact on coastal assets. Rising sea levels may also raise groundwater tables, causing Fort Bragg Distribution System Master Plan
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increased flooding and leading to impacts that will further damage buried and low-lying infrastructure2.

Sea level rise projections were selected based on the 2024 State Guidance. For planning purposes, and in alignment with California Coastal Commission guidance3, the high sea level rise projection scenario was selected to determine conservative SLR projections at the Project location (OPC 2024). Sea level rise values corresponding to the nearest NOAA tide gauge to the Project location, Arena Cove, CA, were used. The high sea level rise projections for lateand end of century at Fort Bragg are as follows:
 2070: 2.8 feet.
 2100: 6.4 feet.

To appropriately assess the resiliency of a region or select assets, we typically evaluate sea level rise added to the 100-year water surface elevation, also characterized as the Base Flood Elevation (BFE) in FEMA mapping. For this preliminary planning-level assessment, we assume that the future 100-year water level is equal to the BFE plus the sea level rise quantity. This is because more detailed bathymetric data than what is currently available is required to develop these calculations for future conditions and map them. This is a high-level estimate, and as projects are identified and moved into the design phase, detailed site-specific calculations should be performed to account for the impacts of sea level rise on wave setup and runup in more detail.

Using these high-level assumptions, for example, at Noyo Bay, the coastal BFE is 19 feet NAVD 88 (see FIRM). By adding sea level rise projections, we could assume the future BFE with sea level rise would be approximately 22.8 feet NAVD 88 by 2050 (19+2.8) and 25.4 feet NAVD 88 by 2100 (19+6.4). This estimation procedure would be limited to coastal Zone VE BFEs. The analysis for the FEMA fluvial zones reflects different considerations, and a more detailed hydraulic study would be needed to properly reflect both coastal impacts from sea level rise and concurrent riverine flows. Such studies are recommended for individual projects as needed for the scale and impact of those projects.

Along the bluff face, we also reviewed the BFEs plus sea level rise as an approximation of the future total water levels including wave effects. Based on this preliminary analysis, the total water elevations in areas along the bluff would not reach the top of the bluff. Waves may overtop the bluff in future sea level conditions. This overtopping could be unsafe for pedestrians and cars, but the infrastructure evaluated for this study is not in these locations, so a more detailed evaluation is beyond the scope of this study.
2https://climateresilience.ca.gov/overview/impacts.html#:~:text=The%20daily%20maximum%20average%20temperat ure,worsen%20drastically%20throughout%20the%20state.
3 https://www.coastal.ca.gov/climate/slr/vulnerabilityadaptation/infrastructure/#:~:text=The%20goal%20of%20the%20Commission's,managers%2C%20and%20other%20 stakeholders%20with
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Sea level rise mapping data was pulled from the NOAA Sea Level Rise Viewer (NOAA 2022).

The sea level rise values are projected over mean higher-high water (MHHW) elevations, representing sea level rise under daily conditions. This mapping of sea level rise over MHHW is shown below (Figure 10) for reference, because it is the best available mapping currently for the location, although it does not correspond directly to the future BFE scenarios described above.

Sea level rise is anticipated to impact the interactions between the Noyo River and the Pacific Ocean. It is anticipated that sea level rise will cause coastal backwaters to propagate up through the Noyo River which may impact portions of the Fort Bragg’s water distribution system that interact with this river including intakes or outfalls. Beyond the Noyo River, sea level rise is not anticipated to have a significant impact on the water distribution system infrastructure.

Determining water levels in detail is beyond the scope of this planning-level study. More detailed hydraulic modeling of the combined riverine and coastal conditions is recommended when developing projects, particularly at the Noyo River. More detailed hydraulic modeling would be required to assess the relative contributions to riverine water levels from sea level rise and riverine flows.

Figure 10 – Flooding Risk Projected: Highest Water Levels Mapped in the Regional Water Level Viewer, Equal to 10 Feet SLR over the MHHW Elevation
(HDR based on NOAA Sea Level Rise Viewer (NOAA 2022). FEMA historic flooding risk) Fort Bragg Distribution System Master Plan
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The coincidental occurrence of heavy rains, high stream flows, SLR, storm surge, and high astronomical tides are expected to increase the threat of coastal inundation in the future.

Rainfall runoff occurring simultaneously with high tides will result in inundation areas greater than what is shown. As sea levels rise, this situation is expected to be exacerbated during times of storm, king tide, or both.

2.3.2 Precipitation
California is known for its highly variable precipitation and has the highest variability of year-toyear precipitation in the contiguous United States. California’s variable precipitation is also characterized by multi-year wet or dry periods. As a result, future average precipitation is difficult to predict (Figure 11 and Figure 12) but may likely not change substantially when measured by annual precipitation. However, there is high confidence in projections that even if precipitation remains stable or increases, drought severity and the number of dry years will increase, even as more extreme precipitation events may occur. Warming air temperatures will increase moisture loss from soil, which will lead to drier seasonal conditions even if precipitation increases. The snowpack in California’s mountains is a key source of surface and groundwater in the state, and rising temperatures will cause a decline in snowpack by more than a third by 2050 and more than half by 2100, even if precipitation levels remain stable4.

Figure 11 – Projected Total Annual Precipitation for Fort Bragg Based on Climate Scenario RCP

4.5. 4https://climateresilience.ca.gov/overview/impacts.html#:~:text=The%20daily%20maximum%20average% 20temperature,worsen%20drastically%20throughout%20the%20state Fort Bragg Distribution System Master Plan
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Figure 12 – Projected Total Annual Precipitation for Fort Bragg Based on Climate Scenario RCP

8.5. Figure 11 shows the projected change in total annual precipitation for Fort Bragg based on climate scenario RCP 4.5. Projected precipitation under this scenario is reflective of the nature of the RCP 4.5 scenario wherein precipitation intensities show some increase through the midcentury but then level off as emissions begin to decrease during the latter portion of the century.

Interestingly, Figure 12 also reflects this despite RCP 8.5 having an increase in GHG emissions.

The relatively flat profile of both the RCP 4.5 and 8.5 projected total precipitation curves indicates that while precipitation intensity will increase, the total amount of rainfall is projected to remain the same. In other words, a similar amount of rain each year will be segregated out into fewer more powerful storms. This combination is a recipe for flooding events.

In Figure 13 and Figure 14, the projected number of days that will see 1 inch or more of rainfall is shown for RCP 4.5 and 8.5, respectively. This set of projections shows that in either cast (4.5 or 8.5) there is expected to be an increase in the number of days each year where Fort Bragg receives 1 inch or more of rain. While a single inch of rain in a day is not always cause for concern, this highlights the general trend of increasing variability where the amount of rain that falls per year is expected to be stable, but the events in which it falls are expected to be less frequent and more intense, producing periods of drought between heavier rainfall events.

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Figure 13 – Projected Number of Days with Greater Than 1 Inch of Precipitation for Fort Bragg Based on Climate Scenario RCP 4.5
Figure 14 – Projected Number of Days with Greater than 1 Inch of Precipitation for Fort Bragg Based on Climate Scenario RCP 8.5
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2.3.3 Coastal Bluff Erosion (Coastal) and Landslides
The noted increase in year-over-year precipitation variability is likely to result in bank destabilization and increase in slope instability during the water years with greater precipitation.

It is a double-edged sword of drought years killing off vegetation that might otherwise stabilize a hillside followed by years of heavy precipitation that cause the soils to destabilize and produce landslide. This would be further exacerbated by drought years that produce significant wildfire in the watersheds above the city of Fort Bragg.

Bluff erosion is influenced by SLR in addition to the mechanisms that impact landslides inland.

Cliff retreat data was pulled from the Coastal Storm Modeling System Coastal Cliff Retreat dataset (Barnard et al 2022). The data assumes a “let it go” cliff retreat scenario where the model allows cliffs to recede regardless of existing cliff armoring. The boundary drawn (see Figure 15) represents the projected uncertainty band for future cliff top edge. Like the sea level rise water level evaluation, the closest available ranges in that dataset to the projections were used to represent late- and end of century conditions.

Figure 15 – Existing Coastal Erosion Risk
(Source: Coastal Storm Modelling System (CoSMoS), US geological Survey (USGS), 2022) Fort Bragg Distribution System Master Plan
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2.3.4 Temperature / Extreme Heat
Annual temperature increases experienced over most of California have already exceeded 1°F, with some areas exceeding 2°F. The daily maximum average temperature, an indicator of extreme temperature shifts, is expected to rise 4.4°F–5.8°F by mid-century and 5.6°F–8.8°F by late century. Heat-Health Events (HHEs), which better predict risks to populations vulnerable to heat, will worsen drastically throughout the state. By midcentury, the Central Valley is projected to experience average HHEs that are two weeks longer, and HHEs could occur four to ten times more often in the Northern Sierra region5.

The projected annual mean maximum temperatures shown below in Figure 16 through Figure 19) are showing similar trends. As discussed previously, the trends here are produced with CMIP5 informed climate models. In the case of both RCP 4.5 and RCP 8.5 the mean maximum temperature is expected to increase annually.

Figure 16 – Projected Annual Mean Maximum Temperatures Expected in Fort Bragg for the Years 2020-2100 Based on the RCP 4.5 Climate Scenario
5https://climateresilience.ca.gov/overview/impacts.html#:~:text=The%20daily%20maximum%20average% 20temperature,worsen%20drastically%20throughout%20the%20state.) Fort Bragg Distribution System Master Plan
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Figure 17 – Projected Annual Mean Maximum Temperatures Expected in Fort Bragg for the Years 2020-2100 Based on the RCP 8.5 Climate Scenario
Figure 18 – Projected Annual Mean Maximum Temperatures Expected in Fort Bragg for the Years 2020-2100 Based on the RCP 4.5 Climate Scenario
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Figure 19 – Projected Annual Mean Minimum Temperatures Expected in Fort Bragg for the Years 2020-2100 Based on the RCP 8.5 Climate Scenario
The annual mean minimum temperature for Fort Bragg, based on data from the POR 1950- 2023, shows a slight decreasing trend, which is reflected here in the projected annual mean minimum temperatures (Figure 18 and Figure 19 above) until just before the year 2030 in RCP

4.5 and until 2023 in RCP 8.5. Then an annual increase in the mean minimum temperature is expected.

2.3.5 Wildfire
Wildfires are concentrating in upper watersheds, further compounding crises like drought. The year 2020 was the largest wildfire season recorded in California’s modern history, with nearly 10,000 fires that burned over four million acres in total. However, fewer than 40 fires accounted for most of the area burned, pointing to the accelerating severity and frequency of extreme fires.

In 2021, California experienced 4 of the 20 largest wildfires in the state’s history, with 8,000 wildfires burning over 2.5 million acres. The 2021 fire season also marks the first time that fire crossed the granite crest of the Sierra, California’s largest natural fuel break. A model developed for California’s Fourth Climate Change Assessment projected up to a 77 percent increase in average area burned and a 50 percent increase in the frequency of fires exceeding 25,000 acres by 21006.
6https://climateresilience.ca.gov/overview/impacts.html#:~:text=The%20daily%20maximum%20average%20temperat ure,worsen%20drastically%20throughout%20the%20state.)
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Fortunately, Fort Bragg was spared from the recent Mendocino Complex Fire but that does not mean that the threat of wildfire to the region is not being exacerbated by climate change. As noted earlier in this document, the increased year-over-year variability in precipitation and air temperatures is expected to continue to increase the threat of wildfires. The greatest threat will come in years that are hot and dry following a year, much like water year 2022-2023, that has significantly above normal rainfall contributing to brush and ground cover growth. Peak months for the likelihood of wildfires in the region are from August through September during periods of strong offshore winds or during times when thunderstorms can produce dry lightning in the region.

The threat of wildfire is expected to increase. This will require resilient actions on the part of local, regional, and state agencies because the City is dependent on surface water for it’s drinking water supply. The intense heat related to wildfires drastically changes the runoff characteristics of a watershed and increases the threat of sedimentation and severe water quality issues. Wildfire heat will also negatively impacs pipe integrity and poses a threat to the City’s raw water pipeline infrastructure.

2.3.6 Groundwater
The same conditions that are the result of an increase in year-over-year variability for drought and heavy precipitation (Section 2.1.7) will impact groundwater availability in the region. As identified in other locations in the West (Jensen, M.N., 2016), groundwater supplies may be further stressed by increasing evapotranspiration because of increasing air temperatures.

Increasing sea levels will increase groundwater elevations. The rate at which groundwater will rise depends on the types of soils present at the site and quantifying that rate is beyond the scope of this study. However, it is worth mentioning that most of Fort Bragg is at high elevation and consequently this is probably not a near-term concern.

2.3.7 Drought
As shown in the prior sections, historic year-over-year precipitation variability between years of flood and drought is expected to be exacerbated by climate change in the region. Increasing air temperatures combined with years of below normal precipitation will produce a multiplying effect on water usage through increasing demand, evaporation, evapotranspiration, and, of course, the increased risk of wildfire during drought years.

2.4 Conclusion/Key Findings
The historic climate trends provide a baseline for understanding projected future climate trends.

The Water System site risk/vulnerabilities have been correlated to those that are anticipated to change at future time scales due to climate change. The Water System challenges adapting to more extreme climate events are:
 SLR and extreme rain events with subsequent periods of drought are most likely to increase the risk of landslides and erosion.

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 Increases in air temperatures, which will produce added demand and stress on the Water System and exacerbate the threat of wildfire in the region.

Acknowledging that the area will be under water stress, the resilience and effectiveness of the water distribution system is consequently becoming more critical. There are often inefficiencies in water distribution and water losses that should not be exacerbated because of increased stress caused by climate impacts (chronic changes in operating conditions as well as acute extreme events) on the distribution infrastructure. The increases in air temperatures coupled with an increase in year-over-year variability in precipitation, will make for years in which water management will become increasingly difficult to balance between years of flood and drought.

The observed climate trends and climate projections will allow for identification of Water Distribution asset vulnerability to projected changes in climate as part of this CRVA.

Although not addressed in this scope, we recommend addressing the following topics at a later stage and/or when new information becomes available:
 A more robust understanding of flooding risk caused by extreme events. Particularly, flooding extends associated with future 100-year storms superimposed on SLR elevations.
 Monitoring impact of high temperature for longer periods of time for the level of operations of the water distribution systems.
 Impact of groundwater changes.
 Impact of sea level rise on groundwater levels and saltwater intrusion into freshwater resources, especially the Noyo River.

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3.0 Climate Change Impact Assessment

3.1 Approach
The Climate Risk and Vulnerability Assessment (CRVA) approach is based on the Schematic Basis of Design. The proposed approach for conducting the CRVA is aligned with best practices adapted to match the Fort Bragg unique conditions. Preliminary findings need to be reviewed and adjusted to reflect the client’s preference in assessing risk and identifying priorities.

The CRVA is conducted by first assessing possible exposure to identified climate risks, followed by conducting a vulnerability assessment based on the sensitivity of assets or functions and their adaptive capacity to identified climate threats. The third and final step is to conduct a risk assessment based on the consequences of an asset or function failing and the probability of identified climate threats. The steps used for the CRVA (Figure 20) informs the prioritization of asset functions or systems that should be resilient and the development of an implementation plan.

Figure 20 – Illustration of Steps for Developing a Climate Risk and Vulnerability Assessment (CRVA)
(Source: HDR)
Vulnerability is a function of exposure, sensitivity, and adaptive capacity.  Exposure determines which assets are exposed to climate risks using the best available information. For the purposes of this study, exposure is considered for the primary climate parameters as identified within the scope and resources of climate analysis in Section 2.
 Sensitivity is the degree to which an asset can be affected by a hazard. For this initial assessment, it is assumed that all assets exposed to a hazard are sensitive to it.  Adaptive Capacity is assessed based on whether assets had technological or operational protections in place and system-wide redundancy to help mitigate or cope with the impacts of exposure.

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For this high-level assessment, vulnerability (Figure 21) has been assessed by exposure defining sensitivity.

Figure 21 – Vulnerability Matrix
(Source: HDR, Adapted from ICLEI)
Risk is a function of consequences (of an asset failing) and the likelihood/probability it will occur (e.g., observed or projected) as illustrated in Figure 22. Likelihood was scored as either “High” or “Highest” (as informed by the exposure to the identified climate scenarios) while consequence of failure could be scored as “Low,” “Medium,” or “High” per anticipating possible consequences.

Figure 22 – Risk Matrix
(Source: HDR, Adapted from ICLEI)
Prioritization is the last step in the risk and vulnerability assessment. Prioritization takes in all the information gathered related to vulnerability and risk and allows for a final assessment of infrastructure or assets that may or may not be a priority for focus. The prioritization of critical assets and infrastructure can then lead to better guidelines for climate-related issues and can Fort Bragg Distribution System Master Plan
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focus an action plan on assets that are a higher priority, and, therefore, introduce changes to help assets become more resilient.

3.2 Interdependency CRVA
The purpose of the interdependencies CRVA is to identify regional infrastructure, critical for supporting the Water Distribution System operations (Figure 23). It is also intended to highlight vulnerable communities with greater risk in the event of water system failure.

Risks and vulnerabilities were assessed for the following interdependent asset categories:
 Transportation systems: These assets are critical for accessing the Water System to properly repair, maintain, and operate.
 Energy and electrical systems: Energy assets must provide safe and sufficient power delivery to support pump station operations and any leak detection or monitoring.  Interconnected water infrastructure: Reliable and safe potable water supply is inextricably linked to water intake and treatment facilities.  Telecommunication/IT: Some Water System assets or procedures may require telecommunication connectivity.
 Critical facilities: Emergency and protection services play an outsized role in stabilizing and restoring community capacities. As such, these critical facilities should be identified and prioritized.
 Serviced communities: End-user demographics have varying degrees of adaptive capacity. Low-Income and Disadvantaged Communities within the service area should be specifically identified.
 Natural systems: The furthest upstream assets are the water resources supplying fresh water to the Water Treatment Plant. Attention should be given to protect and preserve the quantity and quality of these resources. Additionally, natural land cover and urban tree canopies offer myriad ecological benefits, including flood mitigation.

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Figure 23 – Critical Assets
(Source: HDR GIS Fort Bragg)
The boundaries for the interdependency CRVA include the area being serviced by the water distribution system of Fort Bragg and extend to the next larger scale of interdependent systems.

Figure 24 illustrates the relationship between identified interdependent assets and flooding/SLR.

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Figure 24 – Regional Asset Map and Flooding Risk
(Source: HDR GIS based on Fort Bragg database; FEMA 2022)

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Figure 25 illustrates the relationship between identified interdependent assets and coastal erosion and landslides.

Figure 25 –Regional Asset Map of Existing Landslide and Coastal Erosion Risk (After CGS Map 58, 2011)

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Figure 26 illustrates the relationship between identified interdependent assets and wildfires.

Figure 26 – Regional Asset Map of Existing Wildfire Risk (Source: HDR GIS based on Fort Bragg database; CA Department of Forestry 2022)

3.2.1 Transportation
The Noyo River Bridge is the single means for automobiles to cross the Noyo Basin and River.

Erosion, landslides, and other acute or chronic conditions could result in premature bridge failure. Bridge closure can prevent access to Water System assets for repairs or maintenance.

The assets most at risk are those south of Noyo River; resources, staff, and equipment are primarily located on the north side.

3.2.2 Energy and Electrical
Fort Bragg has a single substation transmitting electrical power to all community assets, including the pump station located along S Harbor Drive. Additionally, the on-site sodium hypochlorite generation (OSHG) used for primary disinfection at the Water Treatment Plant requires reliable and continuous electricity. The substation is not at risk, as informed by our current available information. Transmission lines carrying electricity to the substation are at risk of wildfires, as they are predominately wood and traverse through forested corridors. Damaged transmission lines could result in a loss of power for all Water Systems. Distribution lines were Fort Bragg Distribution System Master Plan
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not assessed within this scope. However, it is worth noting there is an increased risk of power outages from the substation to the pump station and treatment facility. Per the climate projection assessment, Fort Bragg is likely to experience an increase in maximum daily temperatures.

Future extreme heat events could overburden the weakest link in the energy infrastructure, resulting in power outages.

3.2.3 Water Infrastructure
For the purposes of this study, interdependent water infrastructure includes:
 Intake structures off Madsen Lane, Simpson Lane, and Summers Lane: SLR is projected to increase up to 5 feet by 2070. This will likely be accompanied by an increase in saline concentration at the three intake structures, which could result in premature deterioration of intake equipment and materials.
 Summers Lane Reservoir: This asset is not at risk, as informed by our current available information.
 Pump station at Madsen Lane intake: This asset is not at risk, as informed by our current available information.
 Centralized Water Treatment Plant near Monsen Way and Cedar St:
o This asset was identified as being at risk of wildfire. Dense woodlands extend close to the plant, but there are a few blocks between the Storage Tanks and the dense forest with only a few buildings and urban trees. Fire risk for this facility should be further investigated. The plant’s primary treatment method is OSHG. More saline water entering the treatment facility as a product of rising sea levels could prematurely deteriorate equipment.
o In 2021, an emergency desalination-reverse osmosis treatment system was installed to treat brackish water from the Noyo River. While this temporary treatment process has been effective, more detailed study needs to be performed to consider the impact of brackish water on raw water sources of the Water Treatment Plant.

3.2.4 Telecommunications
No telecommunication assets were identified in connection with the current Water System infrastructure. This will need to be assessed if remote system management is ever implemented.

3.2.5 Critical Infrastructure
For this study, critical infrastructure includes support emergency infrastructure and schools:
 Fire station: There are three fire stations. The two facilities north of Noyo River are not at risk, as informed by our current available information. The facility south of Noyo River (Fort Bragg Fire Station 2) is at risk of wildfire. Because the facility is at the furthest limits Fort Bragg Distribution System Master Plan
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of the Water System the water pressure may be low. Additionally, the water main does not appear to be looped, thus reducing capacity for fire protection.  Hospital: There is one hospital serving Fort Bragg. This facility is not at risk, as informed by our current available information.
 Schools: There are six schools served by the Water System – five north of Noyo River, and one south. These facilities are not at risk, as informed by our current available information.

3.2.6 Impacted Communities
The CalEnviroScreen has been used as a placeholder to address socio economic vulnerability for Fort Bragg. It is a is a screening tool used to identify communities disproportionately burdened by multiple sources of pollution and with population characteristics that make them more sensitive to pollution. It indicates the entirety of Fort Bragg is in the >50-60 range, which represents higher vulnerability compared to the much lower 0-10 CalEnviroScreen Score for the surrounding area. Within Fort Bragg, populations east of Main Street and South of Oak St. have a moderately Higher Social Vulnerability Index. Given the available information, we are not able to meaningfully identify EJ Communities to be prioritized.

3.2.7 Natural Systems
Currently, Fort Bragg’s Water System is fed by three water sources, all of which utilize surface water: Waterfall Gulch (tributary to Hare Creek), the Noyo River, and the Summers Lane Reservoir. As the sea level rises, these surface waters are expected to become more saline. As noted in Section 2.2.5, drought and flooding conditions are likely to become even more variable.

The Noyo River may continue to experience severe drought conditions like that of 2021.

3.2.8 Key Findings
Table 1 highlights which key infrastructure elements are most at risk of being impacted by climate change events and consequently place the water system operations at risk.

Table 1 – Prioritization of Regional Infrastructures
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3.3 Water Distribution System CRVA
Most of the Water System is located along the coastal zone and bordered north and south by two rivers. Exposure has been assessed using the existing climate risks and projected climate scenarios developed in Section 2.

3.3.1 Water System Climate Risk and Vulnerability Assessment The Risk and Vulnerability Assessment is conducted by assets within the geographic boundaries shown on Figure 27. This approach allows for an understanding of risk per water system asset group providing targeted information on how best to develop a range of resiliency strategies by mitigating exposure, decreasing sensitivity, or enhancing adaptive capacity.

Assets reviewed in the CRVA include:
 Water Mains: Water distribution mains in the distribution system include gravity-fed lines and a pressure zone fed from the Willow Street Pump Station.  Water Pump Stations: There is one pump station located on Willow St. between Lincoln St. and Minnesota Ave.
 Storage Tanks: There are four storage tanks within the service area. Three are located at the Water Plant on the east side of Fort Bragg, where the elevation is highest. The last storage tank is located south of Noyo River, at Fort Bragg Fire Station 2.

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Figure 27 – Water Distribution Assets Map
(Source: HDR GIS based on Fort Bragg database)

3.3.2 Assumptions
The following assets associated with the water distribution system were not assessed within this RVA:
 Valves.
 Hydrants.
 Metered Laterals.
 Other Appurtenances.

While these assets may still be vulnerable to identified climate hazards, it is assumed the risk associated with these assets is less than that of the assets included in the CRVA.

Figure 28 illustrates the relationship between Water System assets and flooding/SRL.

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Figure 28 – Water Distribution Assets Map and Flooding Risk (Source: HDR GIS based on Fort Bragg database; NOAA 2023; FEMA 2022)

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Figure 29 below illustrates the relationship between Water System assets and coastal erosion.

Figure 29 – Water Distribution Assets Map and Erosion and Landslide Risk (Source: HDR GIS based of Fort Bragg database; CA Department of Conservation 2011; CoSMoS 2022)

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Figure 30 illustrates the relationship between Water System assets and wildfires.

Figure 30 – Water Distribution Assets Map and Fire Risk (Source: HDR GIS based on Fort Bragg database; CA Department of Forestry 2022)  Water Mains – Water mains crossing the Noyo River are vulnerable to bank and channel erosion. The water system does loop, so if one main is taken offline, the other can still provide water south of Noyo River. Several mains, particularly along the Noyo River and Pudding Creek banks, are vulnerable to landslides. Landslides are likely to damage pipes resulting in the need for repairs and disinfection of the water distribution system. Mains within steeper slopes near SR 20 are also susceptible to landslides.  Water Pump Stations: This facility is not at risk, as informed by current available information.
 Storage Tanks: The storage tank located at Fort Bragg Fire Station 2 is at risk of wildfire as it is located well within the Severe Fire Hazard Zone. The three storage facilities located at the Water Treatment Plant were also identified as being at risk of wildfire, but at a lower likelihood. Dense woodlands extend close to the plant, but there are a few neighborhood blocks between the Storage Tanks and the dense forest which contain a few buildings and urban trees. Storage tank material and coatings, as well as Fort Bragg Distribution System Master Plan
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proximity to and height of adjacent fuel, should be further investigated for all storage tanks.

3.3.3 Key findings
The Water System assets most at risk (Table 2) are the water mains across and adjacent to the Noyo River as well as the Pump Station within the Noyo Harbor District.

Table 2 – Assets Prioritization

Lower (Low & Medium) Higher
Water Mains crossing Noyo River Storage Tank near Ft. Bragg Fire Station 2 Water Mains adajacent to Noyo River
Storage Tank near Water Treatment Plant
Vulnerability
Higher
Lower
Risk
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4.0 Recommendations
This report considers phased adaptation as recommended in the California Sea Level Rise Guidance for Critical Infrastructure7.

4.1 Regional Recommendations
 Transportation: Bridges are at risk of flooding. It is recommended to have a better understanding of risk by developing further the climate risk for SLR and work in partnership with Caltrans and the community to assess implementable resiliency measures.  Energy Systems: Transmission lines exposed to wildfire and could impact operations of water pump(s) for the water distribution system.
 Water: The Water Treatment Plant is at the edge of wildfire susceptibility.  Critical Infrastructure: Fire Station #2 is vulnerable to wildfire, and this could impact response in protecting the Water System assets.

4.2 Water Distribution System Recommendations
 Pump Station: No identified risks within existing location. To be reassessed if location is changed.
 Mains: Landslides along creek banks.
 Storage Tanks: Vulnerable to wildfire

4.3 Next Steps / Further Studies
 Evaluation of land subsidence, particularly as it relates to decreasing soil moisture as a product of droughts.
 Wildfire assessment for Water Treatment Plant and Fire Station #2.  Forecast salinity study at intake points at the Noyo River, Waterfall Gulch, and Newman Gulch.

While the scope of this project is focused on the Water Distribution System, we would like to highlight that the project is part of an interconnected and interdependent system of infrastructure, economics, community, ecology, and hydrology that must perform and adapt to sustainably serve Fort Bragg. Some systems are more critical than others and some systems have adaptive capacity in the sense that they, and the residents they serve, could be relocated. 7 https://documents.coastal.ca.gov/assets/slr/SLR%20Guidance_Critical%20Infrastructure_12.6.2021.pdf Fort Bragg Distribution System Master Plan
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5.0 References
California Air Resources Board (CARB), 2023. Wildfires and Climate Change. Website:
https://ww2.arb.ca.gov/wildfires-climate-change
Jensen, M.N., 2016. How Climate Change Will Affect Western Groundwater. University of Arizona. Website: https://news.arizona.edu/story/how-climate-change-will-affectwesterngroundwater#:~:text=Groundwater%20already%20is%20being%20withdrawn,th ose%20aquifers%2C%20the%20researchers%20report.

IPCC, 2022: Climate Change 2022: Impacts, Adaptation, and Vulnerability. Contribution of Working Group II to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [H.-O. Pörtner, D.C. Roberts, M. Tignor, E.S. Poloczanska, K.

Mintenbeck, A. Alegría, M. Craig, S. Langsdorf, S. Löschke, V. Möller, A. Okem, B.

Rama (eds.)]. Cambridge Univ
University Press. Cambridge University Press, Cambridge, UK and New York, NY, USA, 3056 pp., doi:10.1017/9781009325844.

Cal-Adapt database. (as of 09-2023). https://cal-adapt.org/about/ CalEnviroScreen, 4.0 Tool (September 2023) Maps & Data - CalEnviroScreen - OEHHA - CA.gov
Critical Infrastructure at Risk: Sea Level Rise Planning Guidance for California’s Coastal Zone.

California Coastal Commission.
(2021)https://www.coastal.ca.gov/climate/slr/vulnerability-adaptation/infrastructure/ California Adopts Level Rise Guidance. California Ocean Protection Council (OPC). (2018). https://www.opc.ca.gov/webmaster/ftp/pdf/agenda_items/20180314/Item3_ExhibitA_OPC_SLR_Guidance-rd3.pdf U.S. Climate Resilience Toolkit Climate Explorer (CRTCE), 2023. Observed and Future Climate Projections for Fort Bragg, CA. Website: Fort Bragg | Climate Resilience Toolkit Climate Explorer. National Environmental Modeling and Analysis Center (NEMAC), University of North Carolina Asheville.

National Centers for Environmental Information (NCEI), 2023. Daily Observational Data, Fort Bragg 5 N, CA US. Website: NCEI Daily Observations. NCEI GIS Team, Asheville, NC.

Water Distribution System Master Plan
City of Fort Bragg
Appendix D. Software Selection Technical
Memorandum
Hydraulic Model Software
Selection Technical
Memorandum
Ft. Bragg Distribution System Master Plan
City of Fort Bragg
July 26, 2023
Hydraulic Model Software Selection Technical Memorandum Ft. Bragg Distribution System Master Plan
July 26, 2023 | i
Table of Contents

1.0 Introduction.................................................................................................................................1

1.1 Methodology ...........................................................................................................................1

2.0 Discussion of Alternatives ..........................................................................................................2

3.0 Summary of Analysis..................................................................................................................2

4.0 Recommendation .......................................................................................................................4 List of Tables
Table 1 - Water Modeling Software .......................................................................................................2 Table 2 - Water Hydraulic Model Evaluation Matrix ..............................................................................5 Hydraulic Model Software Selection Technical Memorandum Ft. Bragg Distribution System Master Plan
July 26, 2023 | 1

1.0 Introduction
HDR is in the process of developing a Water System Master Plan for the City of Fort Bragg (City), which includes the development of a water system hydraulic model.

The City currently uses WaterCAD/WaterGEMS (developed by Bentley) as their water system modeling software. The model was developed by and is maintained by KASL Engineering. The City does not currently own a WaterCAD software license. It should be noted that WaterGEMS is a superset of WaterCAD and contains all of the features of WaterCAD in addition to other modeling features and the ability to run in the ESRI GIS environment. For the purposes of this Technical Memorandum (TM), WaterGEMS will be used to indicate either software platform.

HDR conducted a review of the City’s existing WaterGEMS model and has the following observations:
• The model does not match the City’s existing GIS or CAD data • The model only contains steady state scenarios, limiting the ability to perform operational analysis and water quality simulations.
• The Water Treatment Plant is modeled as a “boundary node” reservoir, meaning it will provide an infinite amount of supply to the distribution system. This was common modeling practice historically, however, advancements in modeling algorithms and run times allow us to model treatment plants with storage tanks and pump stations similar to how these facilities actually operate in the field.

HDR is in the process of developing a GIS database of the water system through conversion of the City’s existing CAD water system map. The new GIS database will include ESRI’s new Utility Network and will have full network functionality. In addition, the new GIS database will contain the most up to date and spatially accurate data set. It will be more efficient to develop a new model based on the updated GIS data than to try to update the existing model. For this reason, HDR is recommending a new model build as part of the master plan project. As this will be a new model build, as opposed to a model update, this presents the City with an opportunity to evaluate commercially available water modeling software for use on this project.

The purpose of this TM will be to develop evaluation criteria and provide a recommended modeling software for the project and the City’s use in the future.

1.1 Methodology
HDR has formulated evaluation criteria for determining hydraulic modeling software suitability. Our criteria focuses on functionality that best satisfies the needs of the City for the Water System Master Plan, as well as future analysis and studies. This recommendation will be based on the following:
• Ease of use (i.e. user-friendly)
• Technical accuracy
• Primary use of the model
Hydraulic Model Software Selection Technical Memorandum Ft. Bragg Distribution System Master Plan
July 26, 2023 | 2
• Cost of the software
• Ease of future modeling updates
• GIS compatibility
• Results/report generation
• Availability and quality of technical support

2.0 Discussion of Alternatives
The water hydraulic modeling software programs being considered as part of this evaluation are listed in Table 1.

Today’s commercially available water modeling applications come in two varieties; those that use the Kentucky Pipe (KYPIPE) algorithm; and those that use the EPANET algorithm. Each algorithm is widely used and universally accepted as accurate in the water modeling industry. The two leading commercially available software manufacturers, Bentley (formerly Haestad Methods and Autodesk (formerly Innovyze) both use the EPANET algorithm. The advantage of the EPANET algorithm is its highly advanced water quality simulation capabilities. Recognizing the difficulty to use, update and modify models through KYPIPE combined with its complex interface with GIS data, eliminated KYPIPE from consideration and therefore is not included as an alternative listed in Table 1.

Table 1 – Water Modeling Software
Model Distributed By
EPANET U.S. Environmental Protection Agency
InfoWater Autodesk/Innovyze
InfoWater Pro Autodesk/Innovyze
WaterGEMS Bentley/Haestad Methods
Each of the software listed in Table 1 was evaluated based upon the criteria discussed above, with the leading consideration for the City being compatibility with the GIS database. A spreadsheet outlining the details of each software application is attached as Table 2. The evaluation includes pricing and software annual maintenance based on a 5,000 link version. Bentley prices their software according to the number of links required. They sell 250, 1,000, 2,000, 5,000, 10,000 and unlimited link versions at varying price points. Our preliminary estimates indicate that a 5,000 link version will be adequate to model City’s water distribution system, as the City’s GIS database contains approximately 3,000 links.

3.0 Summary of Analysis
Each of the software applications listed in Table 1 was evaluated in the comparison matrix presented in Table 3 (attached). The comparison matrix defined the following criterion and weighting factors:

Hydraulic Model Software Selection Technical Memorandum Ft. Bragg Distribution System Master Plan
July 26, 2023 | 3
• Ease of Use (15%)
• Technical Accuracy (5%)
• Cost (15%)
• Ease of Updates (20%)
• GIS Compatibility (30%)
• Results and Report Generation (15%)
Since all of the models being considered use the same hydraulic engine, the weighting factor of the Technical Accuracy criteria has been reduced to 5%, as all models are assumed to be equally accurate.

This leaves either the Bentley product or the Autodesk family of products. The City currently maintains their water system mapping in AutoCAD format, however, HDR is converting the CAD files to a GIS database as part of the Master Plan project. GIS integration for not only the model build, but for future update and maintenance is a key factor when recommending a software platform for the City.

This narrows the selection down to either WaterGEMS or InfoWater /InfoWater Pro. Info Water runs within the ESRI ArcGIS Desktop environment, while InfoWater Pro runs in the ESRI ArcGIS Pro environment. It is important to note that ESRI plans to retire AcGIS Desktop in March 2026.

InfoWater and InfoWater Pro use the same modeling database and contain the same features. For the purposes of this evaluation, only InfoWater Pro is being considered.

A few years ago, the biggest distinguisher between WaterCAD and InfoWater was that WaterCAD used the KYPIPE algorithm, which at the time did not support water quality analysis, and InfoWater used the EPANET algorithm. Today, both software applications use the EPANET algorithm, and both solve water quality hydraulic simulations. The models will yield similar hydraulic results, so the choice between models comes down to price, technical support and features.

A 5,000-pipe version of WaterCAD with AutoCAD support costs $8,785 for a 12-month subscription.

InfoWater Pro is only available in an unlimited link version and is $13,425 annually and the pricing can be locked in for a period of 3 years at a time.

We have worked extensively with both WaterGEMS and InfoWater Pro and based upon our experience, when using heavy GIS integration, the InfoWater Pro platform is superior, as the modeling database uses an open architecture database that can be accessed outside of the software platform. The WaterGEMS platform uses a proprietary database that presents challenges when trying to perform advanced data manipulation and GIS integration. Additionally, the WaterGEMS software typically is one version behind in ArcGIS Pro compatibility (currently, they only support ArcGIS Pro 2.9), while InfoWater Pro is typically compatible with the current ArcGIS Pro version (they currently support the latest ArcGIS Pro 3.1 release).

EPANET is listed as an option in Table 1 and presents a low cost alternative to the City for running simple hydraulic analyses. There are limited features in EPANET that make scenario management difficult, but as mentioned previously, all EPANET models will yield similar results.

Hydraulic Model Software Selection Technical Memorandum Ft. Bragg Distribution System Master Plan
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4.0 Recommendation
Based on the results of our criteria evaluation and our extensive experience with water modeling software, we are recommending InfoWater Pro as the modeling software for the Master Plan.

EPANET files can be provided to the City for “in-house” hydraulic analysis in the future. The final scoring matrix is shown in Table 2.

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Table 2- Water Hydraulic Model Evaluation Matrix
Software Evaluation Criteria
Weighting Factor
Total
Score
Ease of Use
15%
Technical
Accuracy
10%
Cost
15%
Ease of
Updates
20%
GIS
Compatibility
30%
Results and
Report
Generation 10%
EPANET 4 5 5 1 1 1 2.3
InfoWater1 5 5 2 5 5 5 4.6
InfoWater Pro 5 5 2 5 5 5 4.6
WaterGEMS 4 5 3 2 3 5 3.4
1InfoWater is not preferred due to discontinuation of ArcGIS Desktop in March 2026 Water Distribution System Master Plan
City of Fort Bragg
Appendix E. Risk Assessment Factors

Risk Assessment Technical
Memorandum
Fort Bragg – Water Distribution Master Plan
May 23, 2025

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Risk Assessment Technical Memorandum

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Contents
1 Introduction ............................................................................................................................ 4

1.1 Purpose and Objectives ................................................................................................. 4

1.2 Organization ................................................................................................................... 5

1.3 System Description ......................................................................................................... 5 2 Risk Assessment Framework ................................................................................................ 5

2.1 Risk Factors .................................................................................................................... 6

2.2 LOF Factors and Weights ............................................................................................... 6

2.3 COF Factors ................................................................................................................... 7

2.4 Data Preparation ............................................................................................................ 9

2.4.1 Consequence of Failure .......................................................................................... 9

2.4.2 Likelihood of Failure ................................................................................................ 9 3 Summary of Findings and Recommendations ..................................................................... 11 4 Applying the Risk Model ...................................................................................................... 16 Appendix A – Risk Factor Scoring Tables .................................................................................. 17 List of Tables
Table 1. Total Risk – LOF and COF Weighting ................................................................. 6 Table 2. Likelihood of Failure Factors, Data Sources, and Weights ................................. 6 Table 3. Consequence of Failure Factors Data Sources and Weights ............................. 8 List of Figures
Figure 1 – System Map ..................................................................................................... 5 Figure 2 Water Distribution Risk Formula ...................................................................... 11 Figure 3 - Cumulative Length Compared to Total Risk ................................................... 12 Figure 4 - Total Risk ........................................................................................................ 13 Figure 5. Likelihood of Failure ......................................................................................... 14 Figure 6. Consequence of Failure ................................................................................... 15 Risk Assessment Technical Memorandum

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1 Introduction

1.1 Purpose and Objectives
Risk analysis is an asset management technique used to help prioritize decision-making for maintaining infrastructure. From an asset management perspective, the goal of a utility is to provide the level of service that its customers and stakeholders expect at the ‘lowest cost of asset ownership’. ‘Cost of asset ownership’ includes not only those costs that impact the utility’s direct expenditures, but also external social and economic costs to the community such as traffic disruption or environmental impacts etc. so the ‘lowest cost of asset ownership’ may be better described as the appropriate investment in infrastructure that provides the expected level of services for the ‘smallest impact on the community’.

There are many types of risks to consider when assessing the possible failures of a water distribution system to provide the expected levels of service. Risk management drives decisions regarding expansions, improvements, and new facilities such as risk of not meeting growth in demand, risk of failing to comply with regulatory guidelines as well as risks related to maintaining and replacing aging infrastructure. Many of these risks were assessed in other sections of the Master Plan. Ultimately risk and the perception of risk drive all asset decision making, including decisions regarding preventive maintenance, repair, and replacement of assets to avoid the risk of unexpected failure.

So how do we compare these risks to one another? A successful utility will define a practical framework. Risk is evaluated in asset management by developing a numerical risk score for each asset. The risk score provides a numerical ranking that is calculated by evaluating a set of risk factors for all assets. The risk score is a relative value, meaning that it compares the assets to each by assigning numerical scores for each of the factors. The risk score is not an objective score, meaning that there is no specific value that determines how quickly an asset is going to fail. The risk model generates a risk score for every asset and is composed of two main components:
• Consequence of Failure (CoF) – factors that describe the impact to the District and community if the asset fails
• Likelihood of Failure (LoF) – factors that determine the condition of the asset and how soon the asset may fail
Some assets that have a high consequence of failure are termed “critical” assets. These are assets that will have a significant impact on the level of service if they fail. A utility may focus on these assets and be willing to invest more to monitor the condition of these assets or to maintain contingency plans and proactively replace these assets to reduce their likelihood of failure. On the other hand, many assets may be less critical and will not have a signifianct impact on the level of service if they fail. These assets may be fixed or replaced as time allows. The City may consider simply monitoring or using some of these assets until failure.

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This Technical Memorandum (TM) documents the methodology and analysis used for calculating risk scores for each of the City’s water distribution mains. It describes likelihood of failure and consequence of failure factors and weights, and summarizes data sources, assumptions, dependencies, and risk assessment outcomes.

1.2 Organization
This report is organized into the following sections:
 Section 1: Introduction
 Section 2: Project Background
 Section 3: Risk Assessment Framework
 Section 4: Summary of Findings and Recommendations

1.3 System Description
City of Fort Bragg (City) owns and operates a
water distribution system including 41 miles of
distribution pipes that provide potable water to
7,000 residents through 3,000 service
connections (2,700 residential and 300
commercial/industrial). Although the City owns
and maintains both water tanks and mains, this
risk assessment pertains only to water mains.

Prior to starting work on this assessment, the
City identified a few key concerns:
 Aging Infrastructure: Water Mains
may be approaching the end of their
expected useful lives.
 Seismic Risk: Fort Bragg is in a
seismically active area with higher
probabilities of water infrastructure
failure near the Pudding Creek and
Noyo River bridges.
 Shallow Pipes: Shallow pipes may be
prone to damage from heavy use on the surface above.
 Mains on Private Property: Water mains crossing private can be difficult to access and maintain.
2 Risk Assessment Framework
A risk model was developed for the treated water pipelines in the distribution system.

Because there is only one pump station and very few other major assets in the system, only pipelines were included. The model calculates a LoF score, CoF Score and a Total Risk Score for each pipe. The CoF and LoF scores for a water main are first multiplied Figure 1 – System Map
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May 23, 2025 | 6
by a relative group weight, then added together to calculate the main’s Total Risk Score.

The LoF score is often weighed higher than CoF to bias high risk mains towards those with a high likelihood of failure. This is because rehabilitation actions typically change the LoF calculation much more than the CoF calculation and therefore the weighting makes it easier to identify assets that will benefit the most from rehabilitation and to measure the overall risk reduction results.

The relative weights of Likelihood of Failure and Consequence of Failure are defined in Table 1 below.

Table 1. Total Risk – LOF and COF Weighting

2.1 Risk Factors
To develop the risk model, potential risk factors were identified based on the City’s level of service objectives and common water distribution failure factors. This initial list, along with factor weightings, was refined through two virtual workshops on August 15th 2023 and September 20th 2023.

Each of the risk factors was assigned a weighting factor to reflect the relative importance compared to the other factors. Development of the weightings for each factor was completed using a pair-wise comparison analysis. This analysis compared each pair of criteria within each of the categories and assigned points based on a 1 to 3 scale. When considering each pair of factors the considered to be more important will receive a higher score (e.g. a 3). The less important factor will receive a 1. If the factors are considered equal they will both receive a score of 2. The points received for each factor were then summed and the percent of the grand total of points was calculated for each.

The total weighting will equal 100 percent each for the LoF and CoF factors.

2.2 LOF Factors and Weights
Six criteria were established to evaluate likelihood of failure. These are listed along with their descriptions, and relevant data sources in Table 2 below.

Table 2. Likelihood of Failure Factors, Data Sources, and Weights No. Factor Data Data Source(s) Weight
(%)
1 Remaining
Service Life
Pipe Material Fort Bragg UN 22
Approximate Install
Date
1986 Water System Master
Plan
City of Fort Bragg Water
System Comprehensive
Engineering Study Dec 1974
Factor Weighting Factor (%)
Likelihood of Failure 60
Consequence of Failure 40
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No. Factor Data Data Source(s) Weight
(%)
2 Taps per 10ft Number of Taps Fort Bragg UN 13
Pipe Length Fort Bragg UN
3 Seismic
Risk
River Crossings Fort Bragg UN/ ESRI Maps/
City Information
10 High Risk
Landslide
Susceptibility
California Geological Survey
– Susceptibility to DeepSeated Landslides (May
2011)
4 Pipe Depth Known Shallow
Pipe
Operations Staff
Experience
13 5 Break History Break History 2023_05_18_Main
Breaks Google Earth.xls
25 6 Groundwater
Fluctuations
Known
Groundwater
Fluctuation
Operations Staff
Experience
17  Remaining Service Life - Pipes that are approaching or are past their estimated service life, may be more likely to fail and will receive an elevated LoF score. It should be noted that approximate remaining useful life is not always a reliable indicator of pipe condition. Pipes may fail much sooner or later than their estimated useful life based on other conditions.
 Taps per 10 ft – Pipes with greater numbers of lateral connections have more potential failure points and will be assigned a higher LoF score.  Seismic Risk – Some pipes like bridge crossings or pipes in known landslide zones are more likely to be impacted by seismic activity will receive a higher LoF Score.
 Pipe Depth – Shallow pipes are more susceptible to damage from surface use and will receive an elevated LoF score.
 Break History – Pipes with a known break history may indicate poor overall condition will receive an elevated LoF score.
 Groundwater Fluctuations – Pipes in locations with known groundwater fluctuation may experience more stress from ground movement and will receive an elevated LoF score.

Appendix A lists the score tables for each factor.

2.3 COF Factors
Six criteria were selected to evaluate the consequences of failure, including the following. These are listed along with their descriptions, and relevant data sources in Table 3 below.

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Table 3. Consequence of Failure Factors Data Sources and Weights No. Factor Data Data Source(s) Weight
(%)
1 Critical
Customers
Critical
Customers
Fort Bragg UN/ ESRI Maps/ City
Information
25%
2 Hydraulic
Risk Score
Hydraulic
Risk Score
Fort Bragg Hydraulic Model 22%
3 Damage
from Break
Pipe Material Fort Bragg UN 17%
4 Land Use
and Zoning
Zoning Fort Bragg UN 17%
5 Repair
Difficulty
Pipes within
Easements
Fort Bragg UN/ City Information 12%
6 Geotechnical
Risk
Flood Zone Special Flood Hazard Area FEMA.gov 8%
Fire Risk Cal Fire Severity Zones (April 1, 2024)
 Critical Customers - Pipes that supply water to essential services like hospitals, emergency services, and schools may face operational disruptions from pipe failure and will receive a higher CoF score.
 Hydraulic Risk Score - Pipes that convey more flow or provide flow to densely populated areas will receive a higher CoF score. These pipes can lead to significant water loss in the event of a failure and may have broader impact compared to other pipes. To calculate the hydraulic risk score, the model was used to isolate or remove each pipe from the system to measure these hydraulic impacts. One pipe was removed at a time to determine in impact on the system and the availability of water to customers.
 Break Damage - In the event of a break: PE, PVC, AC, and DIP pipes are known to break more catastrophically and may cause more damage to surrounding ground and infrastructure than other material types. These pipes will receive a higher CoF score.  Land Use & Zoning - While Critical Customers identify specific entities requiring uninterrupted water supply, Land Use and Zoning focuses on geographic areas designated for specific types of development where the impact of water pipe failure can impact a broad range of activities and functions. Commercial and Industrial zones, for example, depend on water for operations and may suffer financial losses from a loss of service. Land Use zones that may face more of an impact from water main failure will receive a higher CoF score.  Repair Difficulty - Water mains crossing private properties are more difficult to repair and maintain and should be prioritized for preventive maintenance or prioritized for relocation. These pipes will receive a higher CoF score.
 Geotechnical Risk - Pipes within a FEMA Special Flood Hazard Area may pose higher impact to nearby infrastructure and will receive a higher CoF score. Pipes within a moderate to very high fire risk zone should be prioritized to be able to function adequately in the event of a wild fire and will receive an elevated risk score.

Appendix A lists the score tables for each risk factor.

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2.4 Data Preparation
To accurately score the criteria listed above, some data processing was required. Data preparation processes are detailed below.

2.4.1 Consequence of Failure
 Break Damage – No data processing was required.
 Critical Customers – In discussion with the City, HDR identified parcels associated with essential services and vulnerable customers.  Land Use & Zoning – Water mains that intersected land use and zoning parcels were assigned factor scores as defined in Appendix A. If a main line intersected with multiple zones, the higher score was assigned.
 Hydraulic Risk Score – The hydraulic risk score was calculated in the Fort Bragg Hydraulic Model to assess the hydraulic impact of pipe failure and used four parameters – percentage of total system demand not supplied, number of critical customers without supply, percentage of critical customers demand not supplied and number of connected low pressure junctions. To evaluate pipe criticality, model inputs included a selection set of all pipes in the system excluding the pipes representing pump station connections. Including these specific pipes would skew the criticality results, so their exclusion ensures a realistic comparison of criticality among the remaining system pipes.  Geotechnical Risk – Water Mains intersecting with either FEMA Flood Boundary Zones or Cal Fire Hazard Moderate or higher Severity Zones were assigned an elevated risk score.
 Repair Difficulty – HDR developed an intersect layer of water mains crossing through privately owned parcels. This layer was further refined both internally and in collaboration with the City with the goal of identifying only those mains located within parcels in a way that impedes the City’s ability to access them.

2.4.2 Likelihood of Failure
 Remaining Service Life – The installation date is unknown for much of the water system. In lieu of this information, HDR digitized system maps from the 1974 Comprehensive Engineering Study and the 1986 Water System Master Plan to estimate the ages of the mains. Pipes found on the 1974 map were assigned an approximate installation year of 1974. Mains found on the 1986 map, which were not already shown on the 1974 map, were assigned an approximate installation year of 1986 Mains installed between 1986 and the current utility network were assigned an approximate Installation Year of 2005 (the median year between then and today). These estimated installation years were used to calculate the remaining service life as a percentage, by subtracting the approximate age from the estimated useful service life of the main based on its material type. Pipes were then assigned scores according to their percentage of remaining service life.
 Taps per 10 ft – A ‘Junction Count’ was included as a water main attribute in the Fort Bragg Utility Network. This junction count represented the number of taps along a main and was normalized to taps per 10 feet based on the pipe length Risk Assessment Technical Memorandum

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recorded in the Utility Network. A normal distribution of the resulting taps per 10 feet was analyzed to determine how to score the tap counts in relation to each other.
 Seismic Risk – First, the California Department of Conservation’s CGS Seismic Hazards Fault Traces map was reviewed to identify mains near active faults.

Since there are no faults in close proximity to the City, it was determined that water mains crossing rivers or intersecting with areas with a landslide susceptibility rating of seven or above (on a scale from 0 to 10, low to high) would be assigned an elevated risk score.
 Pipe Depth – City staff identified known shallow mains.  Break History –City records were used to identify pipes with a known break history. Mains with a history of breaks were assigned elevated risk scores.  Groundwater Fluctuations - City staff identified mains within areas of known groundwater fluctuation.

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3 Summary of Findings and Recommendations
A total of 1,818 active water main segments, approximately 41 miles, were assessed using the risk framework. A risk score was calculated for each pipe based on the formula in Figure 2 and the process described above. The risk scores can potentially range from 0 to 5, with 5 indicating the highest relative risk. In this assessment, risk scores ranged from 0 to 2.7. As discussed earlier, due to limited data on pipe age and condition, these scores represent relative, not absolute, risk. They can help prioritize segments for repair or replacement based on condition or hydraulic needs and can also guide system renewal or further condition assessment. The uses of this risk model are discussed in the next section.

Figure 2 Water Distribution Risk Formula
Based on this analysis, the following conclusions are provided:
• The system has very low relative risk scores. The highest risk score calculated is 2.7 out of 5. Approximately 92 percent of the system has a risk score of 2 or below. • The system has relatively low LoF scores. The highest calculated score is 3.4 out of

5. Approximately 95% of the system has a risk score of 2 or below • Biggest drivers of LoF are pipe age, high water table, landslide area and river crossing. Break history also contributes to the top 10 highest risk pipes. Factors affecting LoF are the most likely areas to drive the overall risk down through replacement or renewal of infrastructure. CoF factors will likely remain the same even if an existing pipe is replaced with a new one.
• CoF scores have a big impact on some of the highest risk pipes. CoF scores range from 0.2 to 3.9 out of 5. In the top one mile of the highest risk pipe in the system, about half a mile has a CoF score above 3. This indicates that these pipes will likely be critical even if they are rehabilitated or replaced.

Figure 3 compares the risk scores with the cumulative pipe length for the distribution system.

The figure supports the conclusion that there is low relative risk in the system based on the Risk Assessment Technical Memorandum

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parameters and formulas used in this analysis. The figure shows that there are approximately 3 miles of pipe that have a risk of 2 or higher, and that only 11 miles have a risk of 1.5 or higher.

Figure 3 - Cumulative Length Compared to Total Risk
Figure 4 ‐ Total Risk shows the distribution of total risk scores across the water system. High‐risk segments are concentrated near the high school, the infrastructure surrounding or crossing the Noyo River, and the Georgia Pacific (GP) Mill build‐out site. Medium‐risk areas are primarily located near Mendocino Coast Hospital and along or near Cedar and Oak Streets.

Figure 5. Likelihood of Failure shows the estimated likelihood of failure across the system.

Elevated scores are observed near the Noyo River, the GP Mill site, and in scattered areas throughout the system. These higher likelihood areas are largely driven by break history, zones of known landslide risk, groundwater fluctuations, or locations where pipe depth is shallow.

Figure 6. Consequence of Failure shows the consequence of failure for each pipe segment. The highest consequence areas include those near the high school, Mendocino Coast Hospital, and Mendocino College Coast campus, reflecting the more critical nature of infrastructure in these locations compared to the rest of the system based on the defined risk framework.

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Figure 4 - Total Risk
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Figure 5. Likelihood of Failure
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Figure 6. Consequence of Failure
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4 Applying the Risk Model
The risk model provides a numerical value that quantitates the risk factors analyzed for the City.

It provides a risk score for each of the pipes relative to the other pipes in the system. Because the risk model incorporates factors that the City believes are major risks to the water distribution infrastructure, it can be used as a guide to reduce risk of service failure in the system. The factors used for LoF and CoF represent indirect evidence of the condition and criticality of each of the pipes, however none of the factors used provide direct evidence of pipeline condition. Therefore, the risk model should be used to prioritize assessment and rehabilitation work, however it should not be relied upon as direct evidence that a rehabilitation action is needed. Additional assessment will be needed to determine the true condition and expected useful life of any given asset.

Examples of how the risk model can be used are:

Prioritizing existing capital projects – When two or more projects are proposed (e.g. valve installation, pipeline expansion or enlargement) the risk model can be used to break a tie when other considerations are equal. If all other considerations are equal and one or more project must be delayed, the pipe segment with the lowest risk score can be differed because the risks are comparatively lower.

Prioritizing condition assessment – One of the programs initiated during this master plan is the testing of asbestos cement pipeline walls to determine the residual calcium remaining. This is a good indicator of pipeline condition. The risk model can be used to determine where to sample next. This enables the District to focus on the higher risk pipes and mitigate any issues that will have a high consequence of failure.

Prioritizing maintenance – Frequently maintenance staff must choose between multiple demands on their time. Using the risk model to determine what maintenance activities should be done first enables the City to make risk‐based maintenance decisions.

The risk model can also be continually improved as the City collects more data, learns more about the system and implements system changes. Periodically the model should be evaluated against additional information to determine if it should be updated. If there are additional pipeline breaks, it would be useful to look at the risk model to see if the risk results are consistent with the conditions that caused the break. If additional asbestos testing is completed, it can be compared with the model results. As new infrastructure is added or replaced, the model can be updated to accurately reflect current conditions.

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Appendix A – Risk Factor Scoring Tables
Consequence of Failure
 Maximum COF score: 5
 Minimum COF score: 0
Break Damage
 Weighting: 17%
 Max score: 3
 Minimum score: 1
Value Grade
PVC 3
DIP 2

AC, SP, PE, COP, CAS,
or Unknown
1 Critical Customers
 Weighting: 25%
 Max score: 5
 Minimum score: 0
Value Grade
Hospitals & Clinics 5
Schools 4
Pomo Tribal Land,
Community Resilience
Centers, Senior Living
3 Law Enforcement, Fire
Stations, Grocery Stores
2 Public Facilities 1
Other 0

Land Use & Zoning
 Weighting: 17%
 Max score: 5
 Minimum score: 0
Value Grade
Harbor District, Highway
Visitor Commercial, Central
Business District
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Value Grade
Heavy Industrial, Public
Facilities and Services
4 General Commercial, Light
Industrial, Neighborhood
Commercial, Office
Commercial
3 Very High/High Density
Residential
2 Other Residential, Timber
Resources Industrial
1 Open Space, Parks and
Recreation
0 Hydraulic Risk Score
 Weighting: 22%
 Max score: 5
 Minimum score: 0
Value Grade
20 5
10 3
7 2
5 1
0 0
No Data 0
Geotechnical – Fire & Flooding
 Weighting: 8%
 Max score: 5
 Minimum score: 0
Value Grade
Flood Risk 5
Fire Risk 4
None 0

Repair Difficulty
 Weighting: 12%
 Max score: 5
 Minimum score: 0
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Value Grade
Located within Private
Property
5 Other 0
Likelihood of Failure
 Weighting: 60%
 Max score: 5
 Minimum score: 0
Remaining Service Life
 Weighting: 22%
 Max score: 5
 Minimum score: 0
Value Grade
< ‐100% 5
10 to ‐100% 4
40 to 10% 3
90 to 40% 2
90 to 100% 1
Taps per 10 ft
 Weighting: 13%
 Max score: 5
 Minimum score: 0
Value Grade
3 5
2 4
1 3
0 to 1 2
0 0
Seismic Risk
 Weighting: 10%
 Max score: 5
 Minimum score: 0
Value Grade
River Crossings 5
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Value Grade
High Risk Landslide
Zone
4 Other 0
Pipe Depth
 Weighting: 13%
 Max score: 5
 Minimum score: 0
Value Grade
Shallow Pipe 5
Not Shallow/Unknown 0
Break History
 Weighting: 25%
 Max score: 5
 Minimum score: 0
Value Grade
2 or more 5
1 4
None 0

Groundwater Fluctuations

Value Grade
Known Groundwater
Fluctuation
5 No Known Groundwater
Fluctuation
0 Water Distribution System Master Plan
City of Fort Bragg
Appendix F. 10-Year Capital Plan and Preliminary
Engineering Reports
Ten-Year Capital Improvement Plan
Priority
Ranking
CIP
ID Project Name Project Description Total Pipe Footage (FT) Time
Frame
(years)
Risk
Score Category Escalated Project Costa
1 PS-1 Pump Station Upsize Upsize Willow Street Pump Station capacity to 2,000 GPM. - < 5 -
Capacity or
Fire Flow
Deficiency
$8,141,000
2 V-1 Oak Street Valves
Addition of two 10-inch isolation valves
and one 18-inch isolation valve to
water main on Oak Street.
930 < 5 1.746 Operational
Improvements $93,000
3 P-1
Cedar Street Water Line
Replacement
Replacement of Cedar Street water
main. Increase 53 FT of 6-inch pipe
diameter to 16-inch. Increase 4,195 FT
of 8-inch pipe diameter to 16-inch.
4,248 < 5 1.646
Capacity or
Fire Flow
Deficiency
$3,357,000
4 T-1 Tank 1 Upgrade Replacement of Tank 1 at WTP. - < 5 0.988 Asset Renewal $8,955,000
5 P-2
North Fort Bragg Water Main
Extension
North Fort Bragg Water Main Extension.

Place new 2,144 FT of 10-inch main. 2,144 < 5 0.98
Capacity or
Fire Flow
Deficiency
$1,384,000
6 PL-1
System Renewal- Pipe
Replacement
Provision for additional projects to
meet 1% annual system renewal goal,
based on condition.
5,000 < 5 -
Asset
Renewal $2,830,000
7 O-1 Opportunistic Pipe Sampling Collect and test condition of 3-5 AC pipe samples per year. - < 5 - Other $69,000
8 O-2 CIP Update Update capital project list every 5
years
- < 5 - Other $110,000
9 O-3 CMMS Needs Analysis Evaluate Computer Maintenance Management Software (CMMS) Needs. - < 5 - Other $39,000 Next 5 Year Sub-Total $24,978,000
10 P-7
East Laurel Street Water Main
Replacement
Increase 6-inch pipe diameter to 8-
inch. 539 5 to 10 2.194
Capacity or
Fire Flow
Deficiency
$354,000
11 P-3 Noyo Center Water Line
Noyo Center Water Line Replacement.

Upsize 1,500 FT of existing 4-inch main
to 12-inch. Place new 2,500 FT of 12-
inch main.
4,018 5 to 10 2.018
Capacity or
Fire Flow
Deficiency
$2,985,000
12 P-6
North Main Street Water Main
Replacement
Increase 32 FT of 6-inch pipe diameter
to 8-inch.

Increase 867 FT of 6-inch pipe
diameter to 10-inch.

Increase 220 FT of 6-inch pipe
diameter to 12-inch.

Increase 3,665 FT of 10-inch pipe
diameter to 12-inch.

Increase 645 FT of 8-inch pipe
diameter to 10-inch.
5,429 5 to 10 2.014
Capacity or
Fire Flow
Deficiency
$4,016,000
Ten-Year Capital Improvement Plan
13 P-13 East Alder Street Water Main
Replacement
Increase 6-inch pipe diameter to 8-
inch. 717 5 to 10 1.784
Capacity or
Fire Flow
Deficiency
$470,000
14 P-10 Chief Celeri Dr Water Main
Replacement
Increase 6-inch pipe diameter to 10-
inch. 1,362 5 to 10 1.622
Capacity or
Fire Flow
Deficiency
$951,000
15 P-4
Noyo Point Road Water Main
Replacement
Increase 6-inch pipe diameter to 10-
inch. 651 5 to 10 1.416
Capacity or
Fire Flow
Deficiency
$455,000
16 P-8 Maple Street Water Main Loop Install new 8-inch pipe. 313 5 to 10 1.34 Capacity or
Fire Flow
Deficiency
$206,000
17 P-5
East Elm Street Water Main
Loop Install New 12-inch Pipe. 194 5 to 10 1.33
Capacity or
Fire Flow
Deficiency
$145,000
18 P-9
East Chestnut Street Water
Main Replacement
Increase 6-inch pipe diameter to 10-
inch. 472 5 to 10 1.182
Capacity or
Fire Flow
Deficiency
$330,000
19 P-11 Spruce Street Water Main
Replacement
Increase 6-inch pipe diameter to 8-
inch. 1,330 5 to 10 1.156
Capacity or
Fire Flow
Deficiency
$873,000
20 PL-2
System Renewal- Pipe
Replacement
Provision for additional projects to
meet 1% annual system renewal goal,
based on condition.
5,000 5 to 10 -
Asset
Renewal $3,280,000
21 O-4 Opportunistic Pipe Sampling Collect and test condition of 3-5 AC pipe samples per year. - 5 to 10 - Other $80,000
22 O-5
CMMS Acquisition &
Implementation
Acquire and implement new CMMS.

Only if recommended in O-3 CMMS
Needs Assessment.
- 5 to 10 - Other $191,000
23 O-6 CIP Update Update capital project list every 5
years
- 5 to 10 - Other $127,000
5-10 Year Sub-Total $14,463,000
Total $39,441,000
aProject Costs Escalated For Inflation

Improvement Name: Pump Station Upsize
Project ID: PS-1
CIP Year: 2030
Description: Increase the capacity of the existing Willow Street Pump Station to meet fire flow requirements of the
East Fort Bragg Booster Zone. The pump station is
currently undersized to provide the required 2,000
gpm fire flow.

Purpose: The main purpose of this project is to provide adequate fire flow to the East Fort Bragg Pressure
Zone to meet the current fire flow requirement of
2,000 gpm. The existing fire pumps are sized to
provide 1,000 gpm.

Hydraulic Model Results During fire flow conditions, pressures drop below 20 psi at hydrants requiring 2,000 gpm fire flow.

Alternatives Analysis There are limited alternatives to improving pressure in a “closed”, boosted pressure zone. However, there is
always a “no project” alternative that can be
considered. The “no project” alternative for PS-1
results in not providing the fire flow requirement
during a fire flow demand scenario.

Project Trigger: The primary driver for PS-1 is mitigating an existing fire flow deficiency at the Willow Street Pump Station.

Expected Environmental
Compliance:

This project may qualify as categorically exempt as
the increased size is required to meet existing system
requirements. However, the increased size may
trigger an Initial Study (IS). If the IS identifies no
significant impact, the project may adopt a Negative
Declaration and proceed with implementation. If the
IS identifies significant impacts, but the impacts can
be reduced to a less than significant level through
mitigation then the project may adopt a Mitigated
Negative Declaration (MND) and proceed. Projects
with significant impacts that cannot be mitigated to
less than significant levels must be evaluated in an
Environmental Impact Report (EIR).

OPCC (2025 dollars): $7,450,000
Funding Opportunities: Funding would need to be evaluated further. WIFIA funding may be an option, as this project is
potentially over the $5 million project minimum.

Projects can be combined to reach the minimum
project size. Fort Bragg qualifies as a small and rural community based on the USDA’s eligibility criteria of
providing loans to populations of 10,000 or less and
USDA loans may be available at a lower than market
interest rate. A cost-benefit analysis should be used
to evaluate if a USDA loan would be worth applying for
when compared to water revenue bonds. To qualify,
Fort Bragg must propose projects that expand
services to very small, rural parts of the town. Eligible activities include legal and engineering fees,
acquisitions, start-up operations and maintenance,
interest incurred during construction, and the
purchase of facilities to expand service. Other
potential funding sources include EDA Public Works
and EPA SRF.

Improvement Name: Oak Street Valves
Project ID: V-1
CIP Year: 2030
Description: Addition of 3 isolation valves on water mains in Oak Street per recommended valve spacing of 100 feet
per inch diameter of pipe. 2 valves on each parallel
10” main at the intersection of Oak Street and
Livingston Street and 1 valve on the existing 18” main
at Oak Street and Oak Terrace Court. The depth of the
existing water mains are unknown at this time.

According to the City’s existing utility maps, there is an existing 6” gravity sewer main in Oak Street,
approximately 5’ in depth. Additional utility conflicts will need to be identified during pre-design.

Purpose: Reduces risk if pipeline isolation is required for repairs or to isolate a main break.

Hydraulic Model Results While there is some additional minor loss through a valve, the addition of isolation valves does not
significantly impact the model results.

Alternatives Analysis Valve replacement has a very limited set of alternatives. The exact location of the valves could be moved slightly to avoid conflicts, if those are detected in pre-design. there is always a “no project”
alternative that can be considered. The “no project”
alternative for V-1 results in higher than desired
amount of pipeline that must be isolated in the event
of a main break or needed repair on the water mains
within Oak Street.

Project Trigger: Existing pipeline risk mitigation.

Expected Environmental
Compliance:

Class 1 Exemption for Existing Utilities. Class 1
consists of the operation, repair, maintenance,
permitting, leasing, licensing, or minor alteration of
existing public or private structures, facilities,
mechanical equipment, or topographical features,
involving negligible or no expansion of use beyond
that existing at the time of the lead agency's
determination. The key consideration is whether the
project involves negligible or no expansion of an
existing use.

OPC (2025 dollars): $85,000 (2-10” valves and 1-18” valve) Funding Opportunities: Funding would need to be evaluated further. WIFIA funding may be an option, however, there is a $5
million project minimum. But projects can be
combined to reach the minimum project size. Fort
Bragg qualifies as a small and rural community based
on the USDA’s eligibility criteria of providing loans to populations of 10,000 or less and USDA loans may be
available at a lower than market interest rate. A costbenefit analysis should be used to evaluate if a USDA loan would be worth applying for when compared to
water revenue bonds. To qualify, Fort Bragg must
propose projects that expand services to very small,
rural parts of the town. Eligible activities include legal and engineering fees, acquisitions, start-up.

Improvement Name: Cedar Street Water Line Replacement
Project ID: P-1
CIP Year: 2030
Description: Replace approximately 4,200 LF of existing 6-8” main in Cedar Street to a 16” C900 pipe. The project area
extends from the terminus of the existing 16” main
from the Water Treatment Plant (approximately at the
intersection of a private road between Dennison Lane
and Mall Lane, westerly to Morrow Street. The depth
of the existing water mains are unknown at this time.

According to the City’s existing utility maps, there is an existing 6” gravity sewer main in Cedar Street,
approximately 6’ in depth. Additional utility conflicts will need to be identified during pre-design.

Purpose: The main purpose of this project is to extend the recently constructed 16” main from the City’s Water
Treatment Plant in Cedar Street westerly to Morrow
Street. This project will also improve fire flow
availability and serve future peak demands to the
western portion of the water service area (specifically growth in the GP Mill site area).

Hydraulic Model Results During fire flow conditions, velocities in the existing 6” main exceed 13 feet per second. This is reduced to
less than 5 feet per second with the system
improvement.

Alternatives Analysis Pipeline replacement projects have a limited alternative alignment and associated alternatives
analysis; however, there is always a “no project”
alternative that can be considered. The “no project”
alternative for P-1 results in higher than desired
velocities during fire flow conditions and increases
the risk of main breaks on ageing Asbestos Cement
Pipe.

Project Trigger: There are multiple project triggers for P-1. The primary driver is the age and condition of the existing 6/8” main, which is Asbestos Cement Pipe and is an
older main. The secondary driver is to improve flow to
support growth projected by the City’s current LCP
Amendment 1-24, which includes growth in the GP
Mill Site.

Expected Environmental
Compliance:

This project may qualify as categorically exempt.

However, the increased size to support future growth
may trigger an Initial Study (IS). If the IS identifies no significant impact, the project may adopt a Negative
Declaration and proceed with implementation. If the
IS identifies significant impacts, but the impacts can
be reduced to a less than significant level through
mitigation then the project may adopt a Mitigated
Negative Declaration (MND) and proceed. Projects
with significant impacts that cannot be mitigated to
less than significant levels must be evaluated in an
Environmental Impact Report (EIR).

OPCC (2025 dollars): $3,072,000
Funding Opportunities: Funding would need to be evaluated further. WIFIA funding may be an option, however, there is a $5
million project minimum. But projects can be
combined to reach the minimum project size. Fort
Bragg qualifies as a small and rural community based
on the USDA’s eligibility criteria of providing loans to populations of 10,000 or less and USDA loans may be
available at a lower than market interest rate. A costbenefit analysis should be used to evaluate if a USDA loan would be worth applying for when compared to
water revenue bonds. To qualify, Fort Bragg must
propose projects that expand services to very small,
rural parts of the town. Eligible activities include legal and engineering fees, acquisitions, start-up
operations and maintenance, interest incurred during
construction, and the purchase of facilities to expand
service.

Improvement Name: Tank 1 Replacement
Project ID: T-1
CIP Year: 2030
Description: Replace existing Tank 1 at the Water Treatment Plant.

Purpose: The main purpose of this project is the replacement of an existing ageing tank at the Water Treatment
Plant.

Project Trigger: Existing repairs are necessary, and the existing tank is in poor condition.

Hydraulic Model Results Replacement of existing infrastructure does not impact hydraulic modeling results.

Alternatives Analysis Replacement of existing infrastructure on an existing site has a limited number of alternatives. However,
there is always a “no project” alternative that can be
considered. The “no project” alternative for T-1
results in higher increased risk of asset failure, which can often result in higher project costs to mitigate
emergency scenarios.

Expected Environmental
Compliance:

Class 2 Exemption for Replacement or
Reconstruction. Class 2 consists of replacement or
reconstruction of existing structures and facilities
where the new structure will be located on the same
site as the structure replaced and will have
substantially the same purpose and capacity as the
structure replaced.

OPC (2025 dollars): $8,195,000
Funding Opportunities: Funding would need to be evaluated further. WIFIA funding may be an option, as this project is
potentially over the $5 million project minimum.

Improvement Name: North Fort Bragg Water Main Extension Project ID: P-2
CIP Year: 2030
Description: Construction of a new 10” C900 water main to the northern extents of the City’s water service area. The
project area extends from an existing 8” C900 water
main at the intersection of North Main Street and
Airport Road, northerly to the northern extents of the
City’s water service area (approximately 2,144 LF).

The depth of the existing water mains are unknown at
this time. According to the City’s existing utility maps, there are no additional water, sewer or storm drain
utilities along this alignment. Additional utility
conflicts will need to be identified during pre-design.

Purpose: Provide water service and fire flow to the area north of Airport Road in North Main Street.

Hydraulic Model Results The proposed pipeline has been sized to maintain a velocity of less than 5 feet per second during peak
demands and less than 10 feet per second during fire
flow demands.

Alternatives Analysis Pipeline construction projects have a limited alternative alignment and associated alternatives
analysis; however, there is always a “no project”
alternative that can be considered. The “no project”
alternative for P-2 results in the City not being able to provide water service to parcels north of Airport Road
and within their existing water service area.

Project Trigger: The main purpose of this project is to provide water service to the parcels north of Airport Road that are
within the City’s existing water service area.

Expected Environmental
Compliance:

Initial Study (IS). If the IS identifies no significant impact, the project may adopt a Negative Declaration
and proceed with implementation. If the IS identifies
significant impacts, but the impacts can be reduced
to a less than significant level through mitigation then the project may adopt a Mitigated Negative
Declaration (MND) and proceed. Projects with
significant impacts that cannot be mitigated to less
than significant levels must be evaluated in an
Environmental Impact Report (EIR).

OPC (2025 dollars): $ 1,266,000
Funding Opportunities: Funding would need to be evaluated further. WIFIA funding may be an option, however, there is a $5-
million project minimum. But projects can be
combined to reach the minimum project size. Fort
Bragg qualifies as a small and rural community based
on the USDA’s eligibility criteria of providing loans to populations of 10,000 or less and USDA loans may be
available at a lower than market interest rate. A costbenefit analysis should be used to evaluate if a USDA loan would be worth applying for when compared to
water revenue bonds. To qualify, Fort Bragg must
propose projects that expand services to very small,
rural parts of the town. Eligible activities include legal and engineering fees, acquisitions, start-up
operations and maintenance, interest incurred during
construction, and the purchase of facilities to expand
service.

Water Distribution System Master Plan
City of Fort Bragg
Appendix G. AC Pipe Condition Assessment
hdrinc.com
1 AC Pipe Condition Assessment Methods
AC Condition Assessment Methods
The predominant drivers for AC pipe deterioration in the US are cement leaching and salt cracking. Salt cracking occurs when salts migrate into the pipe wall through capillary and evaporation processes and then expand when hydrated.

Stain Test Method
The first step of free lime conversion to calcium carbonate can be measured by spraying phenolphthalein stain (i.e. stain test) on a freshly exposed cross-section of the pipe wall. The portion of the pipe wall that is stained is un-carbonated whereas the portion of the pipe wall that is unstained is carbonated. Figure 2 shows a pipe that has been recently tested where the left side is the inner portion of the pipe wall, and the right side is the outer portion of the pipe wall.

Figure 2. Stain Test Results
Carbonation starts at both the inner and outer wall surfaces. Over time, it progresses towards the center of the pipe, which is typically un-carbonated. In AC and other non-reinforced concrete applications, carbonation itself does not weaken the pipe. In fact, studies in non-reinforced concrete actually show a minor strengthening effect after carbonation. However, in AC pipes, carbonation is a precursor to corrosion.

EDS Testing Method
In step two of the AC pipe corrosion process, if the environment allows for calcium carbonate to be dissolved and carried away from the calcium-silicate-hydrate and other cement products in the concrete matrix, strength is lost and the pipe becomes more susceptible to failure.

The extent of this degradation process can be measured by assessing the remaining calcium (Ca) content using the Energy Dispersive X-Ray Spectroscopy (EDS) test. Figure 3 shows the EDS test results for the same sample shown in Figure 2. In this test, calcium content is measured at multiple points along the thickness of the pipe. At installation, calcium content is relatively uniform across the pipe wall hdrinc.com
2 thickness. As the AC pipe wall corrodes from the inner and outer wall surfaces, the calcium content will be significantly lower than the calcium content at the center of the pipe wall.

The remaining calcium content at each wall location is reported as a percentage and calculated as the calcium content at that location divided by the maximum calcium content measured at all locations along the wall. Where the remaining calcium content is high, the pipe is healthy and strong and less likely to break. Where the remaining calcium content is relatively low, the pipe is not healthy and is more likely to break. Typically, active corrosion occurs over a relatively narrow portion of the pipe wall.

Figure 3. EDS Test Results
While the physical wall thickness does not change over time, the effective wall thickness decreases over time as calcium carbonate leaches from the pipe wall. This thinning of the effective wall will continue until the effective wall thickness can no longer resist the stresses on the pipe (e.g. internal pressure, external loads, bending due to ground movement) resulting in a break. Since larger pipes require thicker walls to resist a particular load, the percentage of the thickness remaining is used to determine the condition of a pipe. Therefore, the percent of the design thickness remaining is calculated as:

TR = (CaAve * TMeasured ) / (CaMax * TDesign)
Where:

TR = Percent of the original class 200 design thickness remaining CaAve = Average calcium content across the sample thickness CaMax = Maximum calcium content across the sample thickness TDesign = The design wall thickness for class 200 pipe
TMeasured = The measured wall thickness
hdrinc.com
3 Measured pipe wall thicknesses should be collected and used in the future since the thickness of a particular pipe of the same diameter can vary significantly. For the purposes of this assessment, it was assumed that the measured wall thickness equals the design wall thickness.

EDS and Stain Testing Results Comparison
Figure 4 orients both tests for a single sample to each other to correlate the results. On the inner pipe wall, the fresh water conveyed by the pipe is an ideal medium to dissolve and carry away calcium carbonate (Step 2 of the corrosion process). As a result, shortly after each layer carbonates (Step 1), the pipe corrodes (Step 2). This means that Stain and EDS tests typically correlate very well with each other on the inner pipe wall. However, on the outer pipe wall, there is not a consistent medium to dissolve and carry away the calcium carbonate. Therefore, carbonation can often penetrate deep into the pipe, but the pipe may not corrode nor lose strength. To confirm and correlate actual corrosion, it is recommended that EDS data be used to determine the severity of corrosion.

Figure 4. EDS versus Stain Test Correlation
hdrinc.com
4 Comparing data from different utilities can be useful in understanding how this can be used in the future.

However, this approach does have limitations as risk tolerances, operating conditions, and data quality vary significantly from utility to utility. As a utility builds on their own data set and it becomes larger, the relationship between pipe condition, pipe stress, and breaks will become clearer within any utility's unique operating environment.

Extrapolating EDS Testing Results
While condition assessment data collected using EDS data accurately measures the condition at a certain point along a pipe, it is not yet clear how far that condition can be extrapolated along a pipe. In theory, the condition of AC pipe can vary significantly by project because of differences in installation practices and manufacturing quality. Differences in condition within a project should be less variable but will exist due to manufacturing flaws or isolated damage during construction. Therefore, these tests provide moderate confidence in extrapolating the condition to the project, and low confidence in extrapolating the condition beyond the project.

Fort Bragg City CouncilDecember 8, 2025

Fort Bragg City Council
December 8, 2025