5.5 SF5.5 Peninsula 5.5 San Francisco Peninsula Streams and Reservoirs 5. WSIP Water Supply and System Operations – Setting and Impacts 5.5 San Francisco Peninsula Streams and Reservoirs Section 5.5 Subsections 5.5.1 Stream Flow and Reservoir Water Levels 5.5.2 Geomorphology 5.5.3 Surface Water Quality 5.5.4 Groundwater 5.5.5 Fisheries 5.5.6 Terrestrial Biological Resources 5.5.7 Recreational and Visual Resources (References included under each section) 5.5.1 Stream Flow and Reservoir Water Levels The following setting section describes the streams and reservoirs on the San Francisco Peninsula that could be affected by the WSIP. The impact section (Section 5.5.1.2) provides a description of the changes in stream flow and reservoir water levels that would result from implementation of the WSIP. 5.5.1.1 Setting The SFPUC operates four water supply reservoirs on the San Francisco Peninsula: Pilarcitos, Upper and Lower Crystal Springs, and San Andreas Reservoirs. The Spring Valley Water Company built the reservoirs between 1864 and 1890. The four reservoirs and two streams (San Mateo Creek and Pilarcitos Creek) on the Peninsula could be affected by the WSIP. San Mateo Creek, and its tributary San Andreas Creek, flow southward in the rift valley formed by the San Andreas fault and then turn east, flowing to San Francisco Bay. Pilarcitos Creek also flows southward, but it turns to the west and flows to the Pacific Ocean. Figure 5.5.1-1 shows the boundaries of the drainage areas of the four Peninsula reservoirs, and Figure 5.5.1-2 shows the SFPUC regional facilities associated with these reservoirs. The SFPUC’s water supply facilities on the San Francisco Peninsula lie within two watersheds, the San Mateo Creek and Pilarcitos Creek watersheds, which are referred to collectively as the Peninsula watershed. San Mateo Creek General Description San Mateo Creek, and its major tributary San Andreas Creek, rises in the Coast Range mountains west of the city of Millbrae. San Mateo and San Andreas Creeks are fed by rainfall, which varies with altitude and is in the range of 25 to 40 inches annually. Almost all of the rainfall occurs between October and April. SF Planning Department Case No. 2005.0159E 5.5.1-1 PEIR on SFPUC Water System Improvement Program / 203287 San Harry W. Tracy Andreas Water Treatment Plant Reservoir SAN ANDREAS RESERVOIR S a n SUB-BASIN M a t LOWER e o Pilarcitos C r CRYSTALSPRINGS C Reservoir r o RESERVOIR e Lower t PILARCITOS a SUB-BASIN M P Crystal ila n RESERVOIR a rc Springs ito S SUB-BASIN s Reservoir C r r s C to ci Upper lar Pi UPPER Crystal CRYSTAL SPRINGS Springs RESERVOIR Reservoir SUB-BASIN 0 5 Miles SFPUC Water System Improvement Program . 203287 SOURCE: ESA + Orion; USGS 1978 Figure 5.5.1-1 Peninsula Watersheds and Drainages 5.5.1-2 Harry W. Tracy Water Treatment Plant San Andreas Reservoir San Andreas Davis Dam Tunnel S Crystal Sprin a n San Andreas Creek M a t e o S Mud p C gs/San Andreas Pipeline r ri e Dam #1 n e g k V a lle ek y re C C re o e e k at Creek M Pilarcitos Tunnel No.2 an S Pilarcitos Crystal Springs Pump Station Reservoir Pilarcitos Tunnel No.2 Tunnel No.1 San Mateo Pilarcitos Dam Mud P i Dam #2 la rc Stone Dam ito s Tunnel No. 1 C re e k Lower Crystal Lower Springs Dam Stone Crystal Dam Springs Reservoir Upper Crystal Springs Dam Upper Pulgas Pump Crystal Springs Station Reservoir Pulgas Balancing Reservoir ek re Pulgas C s Tunnel o it rc Pulgas Portal la Pi and Valve Lot Pulgas Water Temple 0 2 Pulgas Dechloramination Miles Facility SOURCE: ESA + Orion; USGS 1978 Bay Division Pipelines SFPUC Water System Improvement Program . 203287 No. 1 & 2 No. 3 & 4 Figure 5.5.1-2 Peninsula Watershed Facilites and Flow Locations Analyzed 5.5.1-3 THIS PAGE INTENTIONALLY LEFT BLANK 5. WSIP Water Supply and System Operations – Setting and Impacts 5.5.1 Stream Flow and Reservoir Water Levels The upper reaches of San Mateo Creek and all reaches of San Andreas Creek are in undeveloped land, most of which is owned by the City and County of San Francisco (CCSF). The lower reaches of San Mateo Creek below Lower Crystal Springs Dam flow through a densely developed urban area to San Francisco Bay, about 1.6 miles north of the Hayward–San Mateo Bridge. The main tributary of San Mateo Creek downstream of Lower Crystal Springs Dam is Polhemus Creek. Stream Flow and Water System Operations Flow in San Mateo and San Andreas Creeks was first affected by water system operations in 1870 when San Andreas Dam was built in the upper reaches of San Andreas Creek. The dam impounds San Andreas Reservoir. Upper Crystal Springs Dam was built just upstream of the confluence of San Andreas Creek and San Mateo Creek in 1877 and formed Upper Crystal Springs Reservoir. In 1890, Lower Crystal Springs Dam was built on San Mateo Creek downstream of Upper Crystal Springs Reservoir, forming Lower Crystal Springs Reservoir. In 1924, culverts were built through Upper Crystal Springs Dam to hydraulically link Upper and Lower Crystal Springs Reservoirs. The current maximum capacities of San Andreas and Crystal Springs Reservoirs are 19,000 and 56,800 acre-feet, respectively. (The California Department of Water Resources, Division of Safety of Dams, currently restricts Crystal Springs Reservoir storage). Figures 5.5.1-3 and 5.5.1-4 show historical water surface elevations in San Andreas and Crystal Springs Reservoirs between 1998 and 2006. San Andreas and Crystal Springs Reservoirs serve as terminal reservoirs for the SFPUC water system. They not only capture local runoff but also store water conveyed from the Tuolumne River, the Alameda Creek watershed, and Pilarcitos Creek; consequently, the reservoirs are larger than would be necessary if their sole purpose were to capture runoff from local watersheds. The reservoirs on San Andreas and San Mateo Creeks eliminate flow in the creeks immediately below the dams, except for occasional spills or releases from the reservoirs and seepage through the dams. The creeks gain flow in a downstream direction as a result of tributary flow from surface and groundwater sources. No measurements of flow in either creek are available. Although flood reduction was not one of the original purposes of the CCSF’s reservoirs in the San Mateo Creek watershed, Crystal Springs Reservoir reduces peak flow in the creek most of the time. Space for floodwaters is provided in the reservoir when major storms are expected. Once the space allocated for flood storage is filled, uncontrolled flow over the spillway at Lower Crystal Springs Dam can occur, or controlled releases can be made from outlets equipped with valves. Before the valves are opened, the SFPUC considers potential downstream effects. The dam is operated so that peak flows do not increase above the peak flows that would have existed had the reservoirs not been constructed. Pilarcitos Creek/Pilarcitos Reservoir General Description Pilarcitos Creek rises on the eastern flanks of Montara Mountain in the Coast Ranges. The creek flows southward through the mountains before turning westward and discharging to the Pacific Ocean at Half Moon Bay, as shown in Figure 5.5.1-5. Rainfall in the Pilarcitos Creek watershed SF Planning Department Case No. 2005.0159E 5.5.1-5 PEIR on SFPUC Water System Improvement Program / 203287 5.5.1-6 SOURCE: SFPUC, HH/LSM (see Appendix H) SOURCE: SFPUC, HH/LSM(see Elevation (FT, Datum Unknown) 425 430 435 440 445 450 455 Jul-98 Oct-98 Jan-99 Apr-99 Jul-99 Oct-99 San AndreasReservoirSpillwayElevation=452feet Jan-00 Apr-00 Jul-00 Oct-00 Jan-01 Apr-01 Jul-01 Oct-01 Jan-02 Apr-02 Jul-02 Oct-02 San Andreas Reservoir,HistoricalWater Levels,1998to2006 Jan-03 Apr-03 Jul-03 Oct-03 Jan-04 Apr-04 SFPUC Water SystemImprovement Program SFPUC Water Jul-04 Oct-04 Jan-05 Apr-05 Jul-05 Oct-05 Jan-06 Figure 5.5.1-3 Apr-06 . 203287 5.5.1-7 SOURCE: SFPUC, HH/LSM (see Appendix H) SOURCE: SFPUC, HH/LSM(see Elevation (FT, Datum Unknown) 250 255 260 265 270 275 280 285 290 300 Jul-98 Oct-98 Jan-99 Apr-99 Crystal SpringsReservoirSpillwayElevation=295feet (DSOD restrictionimposedin1983) DSOD Restriction=284feet,msl Crystal SpringsReservoirMaxPoolElevation, Jul-99 Oct-99 Jan-00 Apr-00 Jul-00 Oct-00 Jan-01 Apr-01 Jul-01 Oct-01 Jan-02 Apr-02 Jul-02 Crystal Springs Reservoir,Historical WaterLevels,1998to2006 Oct-02 Jan-03 Apr-03 Jul-03 Oct-03 Jan-04 SFPUC Water SystemImprovement Program SFPUC Water Apr-04 Jul-04 Oct-04 Jan-05 Apr-05 Jul-05 Oct-05 Figure 5.5.1-4 Jan-06 Apr-06 . 203287 Pilarcitos Dam Stone Dam 0 8000 Feet SFPUC Water System Improvement Program . 203287 SOURCE: Todd Engineers Figure 5.5.1-5 Pilarcitos Creek Watershed 5.5.1-8 5. WSIP Water Supply and System Operations – Setting and Impacts 5.5.1 Stream Flow and Reservoir Water Levels is variable, ranging from 26 inches annually at the coast to 42 inches near Pilarcitos Reservoir. The approximately 27-square-mile Pilarcitos Creek watershed consists primarily of relatively rugged uplands, characterized by shrubs and grasslands. The CCSF owns substantial portions of the upper watershed, and the Peninsula Open Space Trust protects large areas of the lower watershed above Arroyo Leon.