Water Supply Assessment for the
Santa Rosa General Plan 2050
City Council Meeting
July 25, 2023
Colin Close
Senior Water Resources Planner
Santa Rosa Water
2 Overview
• SB 610 – Water Supply Assessments (WSA)
• Santa Rosa General Plan 2050
• WSA for General Plan
• Water Demand & Supply Analysis
• Sufficiency Determination
• Recommendation
2 3
Water Supply Assessment (WSA)
Senate Bill 610 (2001)
• Required for certain projects subject to CEQA
(California Environmental Quality Act).
• Assess sufficiency of water supply to meet
demands of project plus existing and planned
future water uses over the next 20 years.
• Prepared by water supplier upon request of
land use authority.
• Governing body has 90-days to provide adopted
WSA. Water supplier can request one 30-day
extension.
4 Santa Rosa General Plan 2050
• Prepared by Planning & Economic
Development (land use agency).
• Long-term vision and framework for
zoning and land use decisions
• Future growth projections
Population
Housing
Economic development
Services
Connectivity
Infrastructure
5 Santa Rosa General Plan 2050
• Requires CEQA review (California
Environmental Quality Act).
• Fits the definition of a “project” under
California Water Code (CWC) 10912(a)(7).
• Is subject to SB 610.
6 Water Supply Assessment
for General Plan 2050
• Introduction
• Applicability
• Future & existing supplies
• Demand analysis
• Dry year analysis
• Sufficiency determination
7 Water Demand & Supply Analysis
• Considers new development anticipated by 2050,
compared to baseline (2019).
• Projects water demand for new development.
• Calculates total water demand by 2050.
• Assesses existing (2019) and projected (2050) water
supply:
• Normal water year
• Single dry year
• Multi-dry year
• Assumes anticipated new development will occur
within 20-year horizon of WSA (by 2043).
• Compares supply and demand.
8 Demand Projection Methodology
• Residential Equivalency Factors (REFs) are used to assess demands using a standard methodology across various land use classifications Example: 1,000 square feet of retail development equal to 1 REF • 1 REF = Average water use of one single-family home per year (65,345 gallons) Source: 2010-2019 average single-family home usage (2020 UWMP , Appendix E Water Demand Analysis)
Number of
REFs
65,345 gallons
per REFx Total
Demand=
9 Baseline vs Growth in Development
Land Use Category (Units) Baseline (2019) Growth Increment Buildout (2050) Residential Detached (dwelling units) 46,435 11,810 58,245 Residential Attached (dwelling units) 29,418 12,280 41,698 Retail (square feet [sf]) 10,434,662 945,000 11,379,662 Office (sf) 6,704,000 2,100,000 8,804,000
Industrial (sf) 11,429,000 1,500,000 12,929,000
Public/Institutional (sf) 3,793,000 727,000 4,520,000
Park/Public Landscape (sf) 81,363,600 3,092,760 84,288,600 Hotels (rooms) 2,086 69 2,155
Education (students) 53,131 4,797 57,928
Source: Planning & Economic Development, based on data from Sonoma County Transportation Authority’s Vehicle Miles Traveled Model 10 Converting Growth to Residential Equivalency Factors Land Use Category
Net Project
Area
(square feet)
Net Project
Rooms/Students
Net
Residential
Units
REF Conversion
Factor REFs
Residential Detached - - 11,810 1 REF/unit 11,810
Residential Attached - - 12,280 0.7 REF/unit 8,575
Retail 945,000 - - 1 REF/1,000 SF 945
Office 2,100,000 - - 1 REF/500 SF 4,200
Industrial 1,500,000 - - 1 REF/1,300 SF 1,154
Public/Institutional 727,000 - - 1 REF/500 SF 1,454
Park/Public Landscape 3,092,760 - - 1 REF/2,819 SF 1,097 Hotel - 69 - 0.75 REF/Room 52
Education - 4,797 - 0.11 REF/Student 536
Total 8,364,760 N/A 24,090 N/A 29,823
11 Projected water demand for new development by 2050
+
29,823 REFs 65,345
gallons/REFx 1.949 Billion
Gallons= or 5,981 acre
feet
5,981 acre
feet
504 acre feet
(non-revenue water and
misc. water sales)
= 6,484 acre
feet *
* Sum of values before rounding.
Plus non-revenue water use (e.g., firefighting) and misc. sales (e.g., construction). 12 Projected total demand
for General Plan 2050
Category Water Demand
(AFY)
Existing Water Demand (2019) 17,832
Net Demand Increase by 2050 6,484
Total 24,316
13 Projected Normal Year Water Supplies
Water Supply
Sources
2020
actual 2025 2030 2035 2040 2045
Sonoma Water 18,024 29,100 29,100 29,100 29,100 29,100
City produced
groundwater 1,253 2,300 2,300 2,300 2,300 2,300
Recycled water 110 140 140 140 140 140
Total 19,387 31,540 31,540 31,540 31,540 31,540
Source: City of Santa Rosa, 2020 Urban Water Management Plan, June 2021 14 Water Supply vs Demand (AFY) - Normal Year
(WSA assumes growth occurs by 2043)
Normal
Year 2028 2033 2038 2043
Supply * 31,540 31,540 31,540 31,540
Demand 20,032 21,369 22,796 24,316
Difference 11,508 10,171 8,744 7,224
Shortage 0% 0% 0% 0%
* Interpolated linearly from Urban Water Management Plan to align with WSA 5-year projections 15 Water Supply vs Demand (AFY) - Single Dry Year
(WSA assumes growth occurs by 2043)
Single Dry
Year 2028 2033 2038 2043
Supply* 21,447 20,818 20,962 21,405
Demand 20,032 21,369 22,796 24,316
Difference 1,415 -552 -1,834 -2,911
Shortage 0% 3% 8% 12%
* Interpolated linearly from Urban Water Management Plan to align with WSA 5-year projections 16 Water Supply vs Demand (AFY) – Multiple Dry Years
(WSA assumes growth occurs by 2043)
5th Dry Year 2028 2033 2038 2043
Supply * 23,514 24,424 25,058 25,790
Demand 20,032 21,369 22,796 24,316
Difference 3,481 3,055 2,263 1,474
Shortage 0% 0% 0% 0%
* Interpolated linearly from Urban Water Management Plan to align with WSA 5-year projections 17 Sufficiency Determination
The WSA finds that Santa Rosa has adequate existing
and projected water supplies to meet existing and
planned development, including new development in
the proposed Santa Rosa General Plan 2050, with the
implementation of demand management measures in
dry years as needed.
NOTE: WSA will be included in the EIR for General Plan. 17 18
Recommendation
It is recommended by Santa Rosa Water that the Council, by resolution, approve the Water Supply Assessment for the Santa Rosa General Plan 2050.
19 Questions?