5.3 Tuolumne River System and Downstream Water Bodies 5.3 Tuolumne 5.3 River 5. WSIP Water Supply and System Operations – Setting and Impacts 5.3 Tuolumne River System and Downstream Water Bodies Section 5.3 Subsections 5.3.1 Stream Flow and Reservoir Water Levels 5.3.2 Geomorphology 5.3.3 Surface Water Quality 5.3.4 Surface Water Supplies 5.3.5 Groundwater 5.3.6 Fisheries 5.3.7 Terrestrial Biological Resources 5.3.8 Recreational and Visual Resources 5.3.9 Energy Resources (References included under each section) 5.3.1 Stream Flow and Reservoir Water Levels The following setting section describes the streams and reservoirs in the Tuolumne River watershed and downstream that could be affected by the WSIP. The impact section (Section 5.3.1.2) provides a description of the changes in stream flow and reservoir water levels that would result from implementation of the WSIP. 5.3.1.1 Setting The Tuolumne River flows from the crest of the Sierra Nevada westward to its confluence with the San Joaquin River. The San Joaquin River flows north to the Sacramento–San Joaquin Delta. Water from the Delta discharges to the San Francisco Bay Estuary and the Pacific Ocean. Surface water bodies in the Tuolumne River system that could be affected by the proposed program include the Tuolumne River, Cherry Creek, Eleanor Creek, and a quarter-mile reach of Moccasin Creek. Several reservoirs could be affected by the WSIP, including Hetch Hetchy Reservoir, Lake Lloyd, Lake Eleanor, and Don Pedro Reservoir. Because the Tuolumne River drains to the San Joaquin River and the Sacramento–San Joaquin Delta, these water bodies could also be affected by the WSIP. The proposed program could affect flow in the streams and water levels and water quality in the reservoirs. Tuolumne River General Description The Tuolumne River rises in Yosemite National Park and flows approximately 130 miles to its confluence with the San Joaquin River about 10 miles west of the city of Modesto. Its headwaters are streams that descend the slopes of Mount Lyell and Mount Dana in the Sierra Nevada and join SF Planning Department Case No. 2005.0159E 5.3.1-1 PEIR on SFPUC Water System Improvement Program / 203287 5. WSIP Water Supply and System Operations – Setting and Impacts 5.3 Tuolumne River System and Downstream Water Bodies to form the river itself at Tuolumne Meadows. The Tuolumne River drains an area of 1,958 square miles. Its watershed is shown in Figure 5.3.1-1. From Tuolumne Meadows (at an elevation of 8,600 feet above sea level), the river descends rapidly through a deep canyon in wilderness areas of Yosemite National Park to Hetch Hetchy Reservoir (at an elevation of about 3,500 feet). Six miles below O’Shaughnessy Dam, which impounds Hetch Hetchy Reservoir, the Tuolumne River leaves Yosemite National Park and enters the Stanislaus National Forest. Except for a short reach at Early Intake Reservoir, the river flows unimpeded through a deep canyon for approximately 40 miles, from O’Shaughnessy Dam to the upstream end of Don Pedro Reservoir. Don Pedro Reservoir is at an elevation of about 500 feet. Several tributaries, including Cherry Creek, Jawbone Creek, the Clavey River, the North Fork of the Tuolumne River, and Turnback Creek, join the river from the north between Hetch Hetchy and Don Pedro Reservoirs. The South Fork of the Tuolumne joins the river from the south. Moccasin Creek and Woods Creek drain directly into Don Pedro Reservoir. Below Don Pedro Reservoir, the Tuolumne River flows 2.3 miles to La Grange Dam, where water is diverted into two irrigation canals. Below La Grange Dam, the Tuolumne River descends through the Sierra Nevada foothills to the floor of the San Joaquin Valley and on to its confluence with the San Joaquin River, which is at an elevation of about 60 feet above sea level. This reach of the river flows through land used primarily for irrigated agriculture. A major tributary, Dry Creek, joins the river from the north in the city of Modesto. Runoff in the Tuolumne River basin is produced by rainfall and snowmelt. Rainfall runoff occurs primarily in the Sierra foothills and the valley floor between December and March. Runoff from the upper basin is produced by snowmelt and occurs primarily between April and July. Annual runoff in the Tuolumne River basin is highly variable. Average annual “unimpaired” runoff1 at Don Pedro Reservoir is estimated to be about 1.85 million acre-feet for the period from 1918 to 1991. The maximum estimated value is 3.84 million acre-feet in 1969, and the minimum is 0.39 million acre-feet in 1977 (Beck, 1992). Stream Flow and Water System Operations Flow in the Tuolumne River remained unaffected by humans until the 1860s, when water from the lower reaches of the river began to be diverted for agricultural irrigation. In 1871, a private company constructed Wheaton Dam near the site of present-day La Grange Dam. Wheaton Dam was used to divert water into irrigation canals. In 1887, the newly formed Turlock Irrigation District (TID) and Modesto Irrigation District (MID) constructed a new diversion dam, La Grange Dam, to replace Wheaton Dam (TID/MID, 2005). 1 Unimpaired flow at a point on a river is the flow that would have occurred if there were no upstream water diversions or storage reservoirs. For the Tuolumne River, it is roughly equivalent to “natural flow”; that is, the flow that would have occurred prior to Euro-American settlement. SF Planning Department Case No. 2005.0159E 5.3.1-2 PEIR on SFPUC Water System Improvement Program / 203287 Tuolumne River Watershed Boundary ek re C y rr e h C rk o F t s e k e W e r C ry r YOSEMITE NATIONAL PARK r e e h v C i R y e Cherry v la k C Reservoir e re C (Lake Lloyd) r o r an e le iv k E k R e e e e r e n Lake Eleanor r C m C r u e l C k o n r O‘Shaughnessy c o u o a T Holm b n b a Dam k w n e r r l Powerhouse a u o E J uolu T F Hetch T m n e N k Hetchy POWER TUNNEL e R Lumsden re i C Reservoir ve ry r r Campground e r Ward's Ferry Tu h CANYON POWER TUNNEL olumn CHERRY ve W e R C i o Bridge iv R ne o e lum Ri d r Tuo ver ana For s ne le D k C uolum dd re T Mi e Moccasin Regulating k Tuolumne Reservoir L y Meadows e Kirkwood l l Moccasin F Powerhouse o r Powerhouse k and Early akdale S ou MOUNTAIN TUNNEL t Intake Bypass Portal L h FOO NE F THILL TUNNEL FOO TUN M or THILL o k T c uo c lumne River a Priest Moccasin s Don Pedro in Regulating Reservoir C r e Reservoir e k La Grange Dam 0 5 Miles MARIPOSA CO SFPUC Water System Improvement Program . 203287 SOURCE: ESA+Orion, 2006; USGS 1970 Figure 5.3.1-1a Tuolumne River Watershed, Headwaters to Don Pedro Reservoir 5.3.1-3 Tuolumne River Watershed Boundary Delta New Melones Lake STOCKTON Ward's FerryTuolum Tulloch ne R W Bridge iv Reservoir o o d s C re e k Moccasin Reservoir Oakdale Portal MOUNTAIN TUNNEL THILLFOO TUNNEL S a MoccasinPriest n v islaus Ri er J an Don Pedro Regulating MOSSDALE o St a MANTECA Reservoir q Reservoir u i n R i v e r D 3 . 1, 2 AN S NOS PELINE N PI SAN JOAQUI Modesto Reservoir La Grange Dam l VERNALIS na Ca odesto Main Tesla Dr Canal M y C Mode ain ree sto M l Portal k a MODESTO n MARIPOSM a A C RIP in a OS L Turlock Main Canal M NE k C TUN r c A C A O E o CO AST RANG T ive url uo R T O lumne Turlock Lake 0 5 Miles SFPUC Water System Improvement Program . 203287 SOURCE: ESA+Orion, 2006; USGS 1970 Figure 5.3.1-1b Tuolumne River Watershed, Don Pedro Reservoir to San Joaquin River 5.3.1-4 5. WSIP Water Supply and System Operations – Setting and Impacts 5.3.1 Stream Flow and Reservoir Water Levels Early in the 20th century, development of the Tuolumne River accelerated. In 1918, the City and County of San Francisco (CCSF) completed Lake Eleanor, a reservoir on Eleanor Creek. Eleanor Creek is a tributary of Cherry Creek, which is itself a tributary of the Tuolumne River. Hetch Hetchy Reservoir and the original Don Pedro Reservoir, on the main stem of the river, were completed in 1923 (Hetch Hetchy by the CCSF and Don Pedro Reservoir by TID and MID). Hetch Hetchy Reservoir was expanded in 1938. In 1955, the CCSF completed Lake Lloyd on Cherry Creek. In 1971, TID and MID completed the new Don Pedro Reservoir, a much larger reservoir two miles downstream of the site of the original Don Pedro Reservoir (SFPUC, 2005). Hetch Hetchy Reservoir, Lake Eleanor, and Lake Lloyd are owned by the CCSF and operated by the SFPUC, and Don Pedro Reservoir is owned and operated by TID and MID. The CCSF paid a portion of the construction costs of Don Pedro Reservoir and in return has indirect access to, and control of, a portion of the storage capacity of the reservoir by means of a water banking arrangement with the districts.2 Figure 5.3.1-2 is a diagrammatic representation of the natural features of the Tuolumne River showing the water and hydropower facilities that affect flow in the river.