Using Hydraulic Modeling to Determine Viable Emergency Water Supply Options for the City Of San Francisco s Largest Reservoir and Pressure Zone

Transcription

1 Using Hydraulic Modeling to Determine Viable Emergency Water Supply Options for the City Of San Francisco s Largest Reservoir and Pressure Zone October 28, 2015 Presented by: Brian Barry, SFPUC Karen Chu, SRT Consultants

2 Objective To find alternative conveyances to supply the City of SF s largest reservoir when major transmission mains are out of service 2

3 Agenda SFPUC Water System Overview Peninsula Pipelines Seismic Upgrade Project (PPSU) Hydraulic Modeling Process Workaround Options Option A: Alemany Pump Station Supply Option B: San Andreas No. 2 Pipeline Supply Conclusions 3

4 SFPUC Water System Overview Gravity fed system supplies water to 2.6 million people 167 miles of transmission mains from the Hetch Hetchy Reservoir to SF $4.8 billion Water System Improvement Program (WSIP) 4

5 City of SF System Overview 5 transmission mains feeding from the Peninsula 23 pressure zones 1,250 miles of distribution pipe 17 reservoirs and tanks, combined storage of 416 MG (4-5 day supply) Sunset pressure zone is largest (denoted in blue) 5

6 Water System Overview (cont d) Average Day Demand: 63 MGD in the City of San Francisco (October 2015) Terminal Reservoirs: Sunset, University Mound, and Merced Manor 6

7 PPSU Project Peninsula Pipelines Seismic Upgrade Project Last phase of Water Supply Improvement Program (completion in 2017) Stern Grove section of SAPL2 will be out of service California Seismic Safety Commission requested operational workaround so that Sunset Reservoir has backup supply 7

8 PPSU Project (cont d) Normal Operations 8

9 PPSU Project (cont d) During Construction SAPL2 out of Service Main feed through SSPL 9

10 Sunset Reservoir Source: baycrossings.com Constructed in 1938 (North Basin) and 1960 (South Basin) Seismic upgrade in 2009 (North Basin only) Spill Elevation: 385 feet Several options to supply Sunset Reservoir Largest City reservoir at 178 MG (40% of the City s storage) 10

11 Lake Merced Pump Station Built in 1929, fully replaced in 1953, seismically upgraded in 2013 Largest SF pump station (7 pumps, 23 MGD each) Elevation: 15 feet Primary function: Feed source for Sunset and Sutro Reservoirs Backup function: Able to feed raw water from Lake Merced in an emergency Low zone vs. High zone 11

12 Alemany Pump Station Originally built in 1949, seismic upgrade in 2009 Elevation: 130 feet Primary function: Pump water to McLaren Tanks from University Mound Reservoir Backup function: Pump water to Sunset Reservoir from University Mound Reservoir 12

13 Hydraulic Modeling Process 1. Conceptualize possible workaround options with operations group 2. Set model boundary conditions Verify valving and facilities controls, etc. Operations to field verify functionality of assets 3. Utilize model to confirm test options Tools Used: Hydraulic Modeling: Synergi v. 4.6 GIS: ArcMap v

14 Workaround Options 1. Option A: Alemany Pump Station Feed 2. Option B: SAPL2 at County Line Feed 14

15 Option A: Alemany Pump Station Assumptions: Out of service: 1. Lake Merced Pump Station 2. SAPL2 at County Line 3. SAPL2 at Stern Grove Alemany Pump Station is primary feed to Sunset Reservoir 15

16 Normal Conveyance Sunset Zone Transmission Mains General Flow Path 16

17 Option A Conveyance Sunset Reservoir Supply Trace General Flow Path. 17

18 Option A: Alemany Pump Station Model Results: 26 Sunset Reservoir Ten Day Level Modeling Level (ft) One Alemany Pump Two Alemany Pumps Time (days) Sunset Reservoir Critical Level (10 feet below spill) 18

19 Option A: Alemany Pump Station Results: Sunset System Pressure at 8:00am (Maximum Demand) Pressure Summary Baseline 1 Pump 2 Pumps Average Sunset Pressure (psi) Average Absolute Pressure Change from Baseline (psi) Maximum Pressure Increase from Baseline (psi) Nodes with Δp > 20 psi(vs. Baseline)

20 Option A: Alemany Pump Station Maximum Demand at 8:00am, 1 Pump Change in Pressure: < 10 psi psi > 20 psi Sunset Reservoir Alemany Pump Station 20

21 Option A: Alemany Pump Station Maximum Demand at 8:00am, 2 Pumps Change in Pressure: < 10 psi psi > 20 psi Sunset Reservoir Alemany Pump Station 21

22 Option A: Alemany Pump Station Results: Sunset System Pressure at 4:00am (Minimum Demand) Pressure Summary Base Line 1 Pump 2 Pumps Average Sunset Pressure (psi) Average Absolute Pressure Change from Base Line (psi) Maximum Pressure Increase from Base Line (psi) Nodes with Δp > 20 psi(vs. Base Line)

23 Option A: Alemany Pump Station Minimum Demand at 4:00am, 1 Pump Change in Pressure: < 10 psi psi > 20 psi Sunset Reservoir Alemany Pump Station 23

24 Option A: Alemany Pump Station Minimum Demand at 4:00am, 2 Pumps Change in Pressure: < 10 psi psi > 20 psi Sunset Reservoir Alemany Pump Station 24

25 Workaround Options 1. Option A: Alemany Pump Station Feed 2. Option B: SAPL2 at County Line Feed 25

26 Option B: SAPL2 at County Line Assumptions: Out of service: 1. Lake Merced Pump Station 2. SAPL3 Supply 3. SAPL2 at Stern Grove 54 SAPL2 at county line as primary feed 26

27 Normal Conveyance Sunset Zone Transmission Mains General Flow Path 27

28 Option B Conveyance Sunset Reservoir Outlets Sunset Reservoir Inlets General Flow Path 28

29 Option B: SAPL2 at County Line Model Results: Minimum Flow Rate Required (MGD) Velocity (ft/s) Time to drop to critical level* (days) *Sunset Reservoir critical level = 10 feet below spill level 29

30 Option B: SAPL2 at County Line Model Results: 30

31 Option B: SAPL2 at County Line Model Results: Sunset Reservoir Levels and Fill Trends (+) Fill (-) Drain 82 MGD through SAPL2 31

32 Conclusions Benefits and risks for the two alternatives: Primary Source Benefits Risks Alemany Pump Station Function of APS is to serve as a backup source to fill SSR. Using 1 pump at APS yields ~10 days of supply at SSR before reaching critical level. No existing back-up facility for APS. Field monitor system pressure increases with 2 pumps in operation. System reliability running APS constantly for an extended duration is unknown. Reverse flows may cause water quality issues. 32

33 Conclusions Benefits and risks for the two alternatives: Primary Source Benefits Risks SAPL2 at County Line - Supply to the Sunset zone through SAPL2 is gravity-fed via Harry Tracy Water Treatment Plant (HTWTP). - Baden Pump Station is a back-up to HTWTP. - SAPL3 supply can also be used as a back-up feed if SAPL2 is offline. - Relatively high flows through SAPL2 at county line (e.g. 82 MGD for a 7- day supply). - Risk of wider pressure fluctuations in the Sunset system. - Reverse flows may cause water quality issues. 33

34 Conclusions and Next Steps The investigation determined that utilizing Alemany Pump Station is most effective: Relatively new facility Single pump operation is preferred and can minimize system pressure increases SAPL2 can be utilized as a backup supply source Next Steps: Investigate high pressure areas (surge analysis) Investigate low pressure areas Address water quality concerns Full-scale testing 34

35 Questions? Thank you for listening! Contact Information Brian Barry San Francisco Public Utilities Commission Karen Chu SRT Consultants 35