Hydrology Report
for
TR 38921
Located in the City of Riverside
County of Riverside
APN: 136-220-016
Prepared For:
W Warmington
RESIDENTIAL
3090 Pullman Street
Costa Mesa, CA 92626
Prepared by:
adkan
ENGINEERS
6879 Airport Drive
Riverside, CA 92504
Tel (951) 688-0241
Fax (951) 688-0599
Job No. 10574
February 26, 2024
adkan
CIVIL ENGINEERING • SURVEYING • PLANNING
ENGINEERS 6879 AIRPORT DRIVE, RIVERSIDE, CA 92504
Tel: 951.688.0241 • Fax: 951.688.0599
www.adkan.com
Table of Contents
1. Purpose.... 1
2. Project Description
A. Vicinity Map.. 1
3. Pre-Development Hydrology. 1
4. Post-Development Hydrology ..1
5. Method of Analysis.. 2
6. Conclusion .. 2
Pre-Development Unit Hydrograph .. ...3
Post-Development Unit Hydrograph
Riverside County Plates .............. .....5
adkan
CIVIL ENGINEERING • SURVEYING • PLANNING
ENGINEERS
1. Purpose
The purpose of this study is to substantiate the hydrology design of Tract 38921 for the purposes of Entitlement Approval. Adkan Engineers has prepared this study to ensure that adequate size and proper operation of drainage facilities are incorporated into the Post-Development project site.
2. Project Description
Tract 38921 is located in the City of Riverside at the northeast corner of Victoria Avenue and La Sierra Avenue.
The planned development will consist of 49 single family residential lots and 2 open space lots on 7.9+/- acres.
The site will treat the 2 year 24 hour storm event through the use of an infiltration basin with an additional gravel layer beneath it. Since site flows are tributary to the Arizona Channel, all other storm events (5, 10 & 100 year) are not required to be analyzed.
A. Vicinity Map
THOMAS BROS. MAP PG 744 GRID G-3
ARIZONA AVE
MIDDLEBOROUGH GROVELAND
VICTORIA AVE KATJAY ST
SITES
SIERRA CLEVELAND ST
VICINITY MAP
N.T.S.
SEC. 24 T.3S. R.6W
3. Pre-Development Hydrology
The site is currently a functioning orange grove and there are no existing storm drain facilities on site. Onsite runoff sheet flows to the south west corner of Millsweet Place and Victoria Ave to an existing drop inlet structure that feeds site flows to City SD tributary to the Arizona Channel.
4. Post-Development Hydrology
Onsite flows are being directed towards the north east corner via a series of gutters throughout the project site.
Surface flows in these proposed gutters will be captured via drop inlets and conveyed via an onsite storm drain 1 adkan
CIVIL ENGINEERING • SURVEYING • PLANNING
ENGINEERS
system to an infiltration basin located in the north east corner of the site. The infiltration basin will have an additional gravel layer beneath to mitigate the 2 year 24 hour storm flows.
Basin Storage Volume Calculations
Infiltration Basin Bottom Area (sf) 3674
Basin Top Arca (sf) 4899
Depth of Basin (ft) 2.5
Open Basin Volume Provided (cf) 10716
Rock Storage depth (ft) 4.6
Rock Storage Volume (40% void) (cf) 6755
Total Flood Volume Stored 17472
Ex. 2-yr 24-hr Storm Volume (cf) 8233
Prop. 2-yr 24-hr Storm Volume (cf) 26528
Allowable 2-yr 21-hr Storm Volume
(mitigated to 110% of existing) (cf) 9056
Prop. 2-yr 24-hr Storm Volume (cf) 26528
Total Flood Volume Stored 17472
Remaining Storm Volume 9056
5. Method of Analysis
The site hydrology was based upon Riverside County Flood Control and Water Conversation District Hydrology Manual, from which pertinent soil and rainfall information was obtained.
Storm flows were determined by the "RATIONAL METHOD HYDROLOGY COMPUTER PROGRAM", Riverside County Flood Control & Water Conservation District 1978 Hydrology Manual, produced by Bondamin Engineering.
The site was also analyzed by the "SYNTHETIC UNIT HYDROLOGY METHOD COMPUTER PROGRAM", Riverside County Flood Control & Water Conservation District 1978 Hydrology Manual, produced by Bondamin Engineering.
6. Conclusion
The hydrologic calculations provided herein substantiate the design of the Post-Development project and indicate the following:
• The Post-Development facilities demonstrate the ability to limit flow discharge from the project site to no greater than 110% of the pre-development 2-year peak flow.
Since site flows are tributary to the Arizona Channel, no other storm events need to be mitigated/analyzed.
Therefore, it is our conclusion this project does not negatively impact the local community or watershed goals. 2 adkan
CIVIL ENGINEERING • SURVEYING • PLANNING
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Section 1
Pre-Development Unit Hydrograph
THE COMMUNITY OF WINCHESTER, COUNTY OF RIVERSDE, STATE OF CALIFCRNIA THOMAS BROS. MAP PG 744 GRID G-3 PRE DËVELOPMEN UNIT HYDROGRAPH
HONTY HAP
SEC. 24 T.3S R.GW
GE GROVE
asker
Unit Hydrograph A n a lys is
Copyright (C) CIVILCADD/CIVILDESIGN, - 2008, Version 8.1 Study date 02/22/24 File: EX2YR242.out
+++ -+++++
Riverside County Synthetic Unit Hydrology Method
RCFC & WCD Manual date - April 1978
Program License Serial Number 5006
English (in-1b) Input Unit
inalish Rainfall Data (Inches) Input values Usel
English Units used in output format
Drainage Area 7.00(AC.) Sq. Mi.
Drainage Area for Depth-Area Areal Adju$96. 00(Ft.) 7.00(AC.) 0.011 Sq. Mi.
Length along longest watercourse =
Length along longest watercourse measured to centroid = 300.00(Ft.) Length along longest watercourse 0.113 Mi
Length along longest watercourse measured to centroid = 0.057 Mi.
Difference in elevation 26.00(Ft.)
slope along watercourse 230.3356 Ft./Mi.
Average Manning's 'N' = 0.030
Lag time = 0.038 Hr.
Lag time = 2.26 Min.
25% of lag time = 0.56 Min.
40% of lag time 0.90 Min.
Unit time = 5.00 Min.
Duration of storm F124 Hour (S).00 (CFS)
User Entered Base Flow =
2 YEAR Area rainfall data:
Rainfall (In) [2] weighting[1*21
.00 1.80
100 YEAR Area rainfall data:
Area (Ac. 1:00 Rainfall(In) [2] weighting[1*2]
.00 6.00 42.00
STORM EVENT (YEAR)
Area Averaged 2-Year Rainfall 1.800(In)
Area Averaged 100-Year Rainfall = 6.000(In)
Point rain (area averaged) 1.800(In)
Areal adjustment factor = 100.0°1. 800 (In)
Adjusted average point rain =
Sub-Area Data:
Area(Ac.) Runoff Index Impervious %
7.000 72.00 0.100
Total Area Entered = 7.00(AC.)
Infil. Rate Imperviou: (In/Hr)
(In/Hr) A 48531 Rate area
Sum (F) =
Anima some loss rate (In 3n024 0.489
Minimum
(for 24 hour storm duration)
loss rate (decimal) = 0.820
Unit Hyd raph
VALLEY 5-Curve
Unit Hydrograph Data
Unit time period Time % of lag Distribution unit Cds)graph (hrs) Graph %
EX2YR24HR Page 1 of 9
0.083 221.634 46.905 3.30%
0.167 443.269 41.886 .95!
0.250 664.903 7.981 0.563
0.333 886.537 3.228 0.228
Sum 100.000 Sum= 7.055
rate subtracted from the Stol tain to produce the makem erectale lain vale The following loss rate calculations reflect use Unit Time Pattern Storm Rain Loss rate(In./Hr) Effective (Hr.) Percent (In/Hr) Max LOW (In/Hr)
0.08 0.07 0.014 0.867) 0.012 0.003
0.17 0.07 0.014 0.863) 0.012 0.003
0.25 0.07 0.014 0.860) 0.012 0.003
. 33 0.10 0.022 0. .857) 0.018 0.004
.42 1.10 022 853) 0.018 0.004
0.50 10 850) 01 0.004
∞0 ∞
58 10 847) 0.004
. 67 , 843) 0.004
0000
75 . 840) 0.004
10 0 . 83 0.837) 0.005
11 0.92 13 0.834) 4 0.005
12 1.00 0 13 029 0.830) 0.005
13 1.08 0.10 022 0.827) 8 0.004
10 .022 . 004
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0. 0.014 cod 888
0. 0.014
275 22 92 07 014 0. ,250 0.003
276 23.00 014 0.003
277 23.08 014 0.003
278 23.17 014 0.003
279 23.25 014 248 0.003
280 23 . 33 014 247 .003
281 23.42 014 24 003
282 23 :. 50 014 246) 003
283 23.58 014 0.246) 003
284 23.67 0.014 0.245)
285 23.75 0.014 0.245) 1.003
286 23.83 07 0.014 0.245) 0.003
287 23.92 0.07 0.014 0.245) 0.003
288 24.00 0.07 0.014 0.245) 0.003
(Loss Rate Not Used)
Sum 100.0 Sum = 3.9
Flood volume = Effective rainfall 0.32 (In)
times area 7.0(Ac.)/[(In)/(Ft.)] = 0.2 (AC.Ft)
Total soil loss 1.48(In)
Total soil loss 0.861(AC.Ft)
Total rainfall 1.80(In)
Flood volume = 8232.7 Cubic Feet
Total soil loss = 37504.6 Cubic Feet
Peak flow rate of this hydrograph = 0.311(CFS)
24 HOUR STORM
Run f f Hydrog rap h
Hydrograph in Minute intervals ((CFS))
Time(h+m) Volume AC.Ft Q(CFS) 2.5 5.0 7.5 10.0
0+ 5 0.0001 0.01
0+10 0.0002 0.02 Q
0+15 0.0003 0.02
0+20 0.0004 0. 02
0+25 0.0006 .03
0+30 ). 0008 03
0+35 ). 0010
0+40 ). 0012
0+45 .0014
0+50 0016
0+55 1. 0018
1+ 0.0021 . 04
1+ 5 0.0023 1.03
1+10 . 0025 1.03
1+15 .0027 03
1+20 0029 . 03
1+25 0.0031 03
1+30 0.0033 .03
1+35 0.0035 0.03
1+40 0.0037 0.03
1+45 0.0038 0.03 Q
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24+10 0. 1890
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EX2YR24HR Page 9 of 9
adkan
CIVIL ENGINEERING • SURVEYING • PLANNING
ENGINEERS
Section 2
Post-Development Unit Hydrograph
N THE COMMUNITY OF WINCHESTER, COUNTY OF RIVERSCE, STATE OF CALIFORNIA THOMAS BROS. MAP PG 744 GRID G-3
POST DEVELOPMENT UNIT HYDROGRAPH
aME....
HONITY HAP
SEC. 24 T.3S R.GW
N THE COMMUNITY OF WINCHESTER, COUNTY OF RIVERSCE, STATE OF CALIFORNIA THOMAS BROS. MAP PG 744 GRID G-3
POST DEVELOPMENT UNIT HYDROGRAPH
aME....
HONITY HAP
SEC. 24 T.3S R.GW
0.083 288.833 5.504 3.916
0.167 577.666 37.752 2.663
0.250 866.500 6.744 0.476
Sum 100.000 Sum= 7.055
The following loss rate calculations reflect use
to frede estefanimentece Rate
rate subtracted from the Storm Rain
Unit Time Pattern Storm Rain Loss rate (In./Hr) Effective (Hr.) Percent (In/Hr) Max LOw
0.08 0.014 0.006 (In/HD.008
0.07 0.468)
HAMi 0.17 0.07 0.014 0.466) 0.006 0.008
0.25 0.07 0.014 0.464) 0.006 0.008
. 33 0. 10 0.022 0.463) 0.009 0.013
0.42 0.10 461) 0.009 0.013
. 50 1.10 459) 0.009 013
0.58 10 457) 0.009 0.013
0.67 0.455) 0.009
75 0. 454) 0. 009 0.013
10 0.83 0.452) 012
11 0 . 92 13 0.450) 0.012 .017
12 1.00 13 0.448) 012
13 1.08 10 0.447) 0.009 .013
14 1.17 0.10 0.445) 0.009 ).013
10 .022 0.443) 0.013
0. 0.013
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0.07 0.014 0.006 008
0.07 0.014 0.006 108
276 23.00 07 014 0. 135) 0.006
277 23.08 014 0.134) 0.006
278 23. 17 014 0. 134) 0.006
279 23.25 014 0.134) 0. 006
280 23.33 014 133) 0.006
281 23.42 014 133)
282 23.50 014 133) 0.006
283 23 . 58 014 0.133) 006
284 23.67 0.014 0.133) 006
285 23 75 0.014 0.132) 006 008
286 23 . 83 07 0.014 0.132) 006
287 23 92 0.07 0.014 0.132) 0.006
288 24.00 0.07 0.014 0.132) 0.006
(Loss Rate Not Used
Sum 100.0 Sum = 12.5
Flood volume = Effective rainfall 1.04(In)
times area 7.0(Ac.)/[(In)/(Ft.)] 0.6 (Ac. Ft)
Total soil loss = 0.76(In)
Total soil loss 0.441(AC.Ft)
Total rainfall 1.80(In)
Flood volume 26527.7 Cubic Feet
Total S011 loss = 19209.7 Cubic Feet
Peak flow rate of this hydrograph = 1.002 (CFS)
24 HOUR S TO R M
R U f f Hydr rap h
Hydrograph in Minute intervals ((CFS))
Time(h+m) Volume Ac.Ft Q(CFS) 2.5 5.0 7.5 10.0
0+ 5 0.0002 0.03
0+10 0.0006 0.05
0+15 0.0010 0.06
0+20 0.0015 0.08
0+25 0.0021 0. 09
0+30 0.0027 .09
0+35 0033 09
0+40 1.0040
0+45 0046
0+50 .0053
0+55
1+ 1. 0069
1+ 0.0076
1+10 ). 0082
1+15 1.0088 09
1+20 0094
1+25 . 0100 09
1+30 0106
1+35 0113
1+40 0.0119 0.
1+45 0.0125 0.09
1+50 0.0132 0.10
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24+ 5 0.6090
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adkan
CIVIL ENGINEERING • SURVEYING • PLANNING
ENGINEERS
Section 3
Riverside County Plates
5 ›AB
SITE
(LAKE MATHEWS) в' BC' BC' C D BC B AB
LEGEND HYDROLOGIC SOILS GROUP MAP
SOILS GROUP BOUNDARY
FOR
SOILS GROUP DESIGNATION
RCFC & WCD B RIVERSIDE -WEST
HyDroLoGY MANUAL
FEET 5000
PLATE C-1.15
RUNOFF INDEX NUMBERS OF HYDROLOGIC SOIL-COVER COMPLEXES FOR PERVIOUS AREAS-AMC II Cover Type (3) Quality of Soil Group
Cover (2) A D
NATURAL COVERS -
Barren 78 86 91 93
(Rockland, eroded and graded land)
Chaparrel, Broadleaf POor 153 70 80 85
(Manzonita, ceanothus and scrub oak) Fair 140 63 75 81
Good 31 $ 57' 71 78
Chaparrel, Narrowleaf POOL 171 182 188 91
(Chamise and redshank) Fair 55 72 81 86
Grass, Annual or Perennial POOF 67 78 86 89
Fair 50 69 79 84
Good 38 161 74 80
Meadows or Cienegas POOr 63 77 85
(Areas with seasonally high water table, Fair 51 70 80
principal vegetation is sod forming grass) Good 30 58 72 Open Brush POor 162 76 84 88
(Soft wood shrubs - buckwheat, sage, etc.) Fair 146 66 77 83 Good 41 63 75 81
woodland POOL 145 66 77 83
(Coniferous or broadleaf trees predominate. Fair 36 60 73 79 Canopy density is at least 50 percent) Good 28 55 70 77 Woodland, Grass PoOr 57 73 82 86
(Coniferous or broadleaf trees with canopy Fair 144 165 77 82 density from 20 to 50 percent) Good 33 58 72 79
URBAN COVERS -
Residential or Commercial Landscaping Good 32 56 75
(Lawn, shrubs, etc.)
Turf Poor 58 74 83 187
(Irrigated and mowed grass) Fair 44 165 177 82
Good 33 |58 72 179
AGRICULTURAL COVERS -
Fallow 76 185 90 192
(Land plowed but not tilled or seeded)
RCFC & WCD RUNOFF INDEX NUMBERS
FOR
HYDROLOGY MANUAL
PERVIOUS AREA
PLATE D-5.5 (1 of 2)
RUNOFF INDEX NUMBERS OF HYDROLOGIC SOIL-COVER COMPLEXES FOR PERVIOUS AREAS -AMC II Quality of Soil Group
Cover Type (3) Cover (2) A B
AGRICULTURAL COVERS (cont.) -
Legumes, Close Seeded POOr 166 177 85 89
(Alfalfa, sweetclover, timothy, etc.) Good 158 172 81 85 Orchards, Deciduous See Note . 4
(Apples, apricots, pears, walnuts, etc.)
Orchards, Evergreen POOr 157 73
(Citrus, avocados, etc.) Fair 144 165
Good 33 58
Pasture, Dryland Poor 167 78
(Annual grasses) Fair 50 169
Good 161
Pasture, Irrigated POOr 58 74
(Legumes and perennial grass) Fair 144 165
Good 133
Row Crops POOI 72 81 88
(Field crops - tomatoes, sugar beets, etc.) Good 167 178 85 Small Grain Poor 65 76 84 88
(Wheat, oats, barley, etc.) Good 163 75 83 187
Vineyard See Note 4
1 Notes:
1. All runoff index (RI) numbers are for Antecedent Moisture Condition (AMC) II.
2. Quality of cover definitions:
Poor-Heavily grazed or regularly burned areas. Less than 50 per- cent of the ground surface is protected by plant cover or brush and tree canopy.
Fair-Moderate cover with 50 percent to 75 percent of the ground sur- face protected.
Good-Heavy or dense cover with more than 75 percent of the ground surface protected.
3. See Plate C-2 for a detailed description of cover types.
1. Use runoff index numbers based on ground cover type. See discussior under "Cover Type Descriptions" on Plate C-2.
5. Reference Bibliography item 17.
RCFC & WCD RUNOFF INDEX NUMBERS
HYDROLOGY MANUAL FOR
PERVIOUS AREA
PLATE D-5.5 (2 of 2)
ACTUAL IMPERVIOUS COVER
Recommended value
Land Use (1) Range-Percent For Average
Conditions-Percent (21
Natural or Agriculture 0 - 10 LO
Single Family Residential: (3)
40,000 S. F. (1 Acre) Lots 10 - 25 20
20,000 S. F. (4 Acre) Lots 30 - 45 40
7,200 - 10,000 S. F. Lots 45 - 55 50
Multiple Family Residential:
Condominiums 45 - 70 165
Apartments 65 - 90 80
Mobile Home Park 60 - 85 75
Commercial, Downtown 80-100 90
Business or Industrial
Notes:
1. Land use should be based on ultimate development of the watershed.
Long range master plans for the County and incorporated cities should be reviewed to insure reasonable land use assumptions.
2. Recommended values are based on average conditions which may not vary greatly even on comparable sized lots due to differences in dwelling size, improvements, etc. Landscape practices should also be considered as it is common in some areas to use ornamental grav- els underlain by impervious plastic materials in place of lawns and shrubs. A field investigation of a study area should always be made, and a review of aerial photos, where available may assist in estimat- ing the percentage of impervious cover in developed areas.
3. For typical horse ranch subdivisions increase impervious area 5 per- cent over the values recommended in the table above.
RCFC & WCD IMPERVIOUS COVER
FOR
HYDROLOGY MANUAL
DEVELOPED AREAS
PLATE D-5.6
SITE
SITE
під, 197
ROFE WCD
WATER CONSERVATION DISTRCT
PRECIPITATION
SITE
SITE
ROFCESEWCD
RIVERSIDE COUNTY FLOW CONTROL
WATER CONSERVATION BUSTAICT
100-YEAR — i-HOUR
PRECIPITATION
FLATE 9.4.0
SITE
5 SITE
NCO
HE TONY
WATER CONSENVATION
SLOPE
INTENSITY DURATION
CURVE
SITE
SITE
ROFA WCO
WATER CONSSWATION TAY
2-YEAR... 3-HOUR
PRECIPITATION
44725
SITE
SITE
RAREA WCD
WATER CONSERVATKIN BISYMET
Ю0-YEAR « 3-HOUR
PRECIPITATION
SITE
SITE
ROEIC SIWCD
SHE:
ANERUDE COUNTY SLODO CONTRO
WATER CONTERVATION METRICE
PRECIPITATION
PLATE E.4
SITE
SITE
CAINTY FLOOD CONTROL
WATER CONSERYATION BESTHICT
PRECIPITATION
2227
SITE
SITE
REFC A WED
MUSATE COIN PUCE
WATER BENSERVATION AMONEY
2-YEAR - 24-HOUR
PRECIPITATION
SITE
ROP AWCO
RIVERSIDE COUNTT FLOOD CONTROL
WATER CONSERVATION METRICT
100-YEAR. 24-HOUR
PRECIPITATION