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4. ENVIRONMENTAL ANALYSIS 4.8 HYDROLOGY AND WATER QUALITY — TABLE 4.8-1 _ HYDROLOGIC CHARACTERISTICS OF ADJACENT AND CONTRIBUTING WATERSHEDS TO THE PROJECT SITE Mean Annual Mean Annual Mean Runoff Yield Basin Area Precipitation Runoff (acre-feet per (square-miles) (inches) (acre-feet) square mile) Basmsa — Lone Tree Creek 19.6 11 630 32.2 Hospital Creek 32.2 12 1,300 40.4 — Ingram Creek 12.9 10 320 24.8 a Source: Nady,P.and L.L.Larragueta 1983. Estimated Average Annual Stream flow into the Central Valley of — California. U.S.Geological Survey Hydrological Investigations Atlas HA-657. received by the watersheds,there are no perennial streams near the project site. 2 Project site topography slopes gradually toward the northeast at less than 1 percent with elevations that range from over 200 feet above msl in the southwest comer to 155 feet above msl along the northeastern border.3 The natural topography and modifications to the topography for State Water Project aqueducts and other water conveyance facilities influence existing surface drainage. Surface water features near the proposed project site are presented in Figure 4.8-1. The Delta-Mendota Canal and the California Aqueduct are located adjacent to the site and 2,200 feet west of the project site, respectively. These man-made conveyance facilities have substantially altered the natural drainage because only select streams cross over the aqueduct. These cross-over structures and — their discharge points control the location and maximum discharge to channels on the down slope side of the aqueducts. Water is present throughout the year in these water conveyance facilities. Hospital Creek is an intermittent stream4 that drains a 32-square mile basin in the Diablo Range, located south-southwest of the project site. The creek borders the southern boundary of the project site and traverses its southwest corner after crossing over the Delta-Mendota Canal in a box culvert. Hospital Creek continues eastward in a straightened and modified channel both upstream and downstream of the project site. Perennial streams are streams that have flow at all times of the year. — 3 The slope represents the change in elevation(rise)across a measured distance(run)and is expressed in units of feet per feet or as a%slope which is the rise/run as a percentage. 4 An intermittent stream flows for extended periods but not all year,typically flowing throughout the wet season,due to relatively greater subsurface flows and larger contributing areas than an ephemeral stream(but less than a perennial stream). RMC Pacific Vernalis Quazry Mining and Reclamation Project 4.8-2 ESA/203015 Administmdi a Draft EIR Match 2004