DRAFT EIR Calaveras County Draft General Plan June 2018 4.8 HYDROLOGY AND WATER QUALITY 4.8.1 INTRODUCTION The Hydrology and Water Quality chapter of the EIR describes existing drainage patterns and water resources for the project area and the region, and evaluates potential impacts of the project with respect to drainage and water quality concerns. The hydrology and water quality impact analysis is primarily based on information from the Calaveras County Local Agency Groundwater Protection Program, the Mokelumne/Amador/Calaveras Integrated Regional Water Management Plan Update,1 and the Calaveras County Water District’s 2015 Urban Water Management Plan Update. 2 Water supply (including groundwater supply), wastewater systems, and storm drainage are addressed in Chapter 4.12, Public Services and Utilities, of this EIR. 4.8.2 EXISTING ENVIRONMENTAL SETTING The following setting information provides an overview of the existing precipitation, surface water, groundwater, and flooding conditions in Calaveras County. Precipitation The topography in Calaveras County varies greatly, from near sea level in the Central Valley (western portion of the County) to elevations around 8,100 feet in the mountainous Sierra Nevada (eastern portion of the County). Due to the pronounced difference in elevation from west to east, levels of precipitation vary widely throughout the County. Average annual precipitation is 20 inches in the western region and 60 inches in the northeastern region. Precipitation increases with altitude, and includes both snow and rain. Snow accounts for much of the precipitation in the higher elevations (up to 300 inches per year), while snowfall is rare in the lower-elevation foothills. The rainy season generally lasts from October 1 to May 1. Surface Water Calaveras County contains three major rivers – Mokelumne, Calaveras, and Stanislaus. The rivers carry runoff from the western slopes of the Sierra Nevada westward across Calaveras County, and into the Central Valley. All three rivers are dammed at one or more locations. The lower stretches of the rivers provide irrigation water for valley agriculture and are used for municipal water supply within the County and the surrounding areas. Figure 4.8-1 shows the location of the Mokelumne, Calaveras, and Stanislaus rivers and their associated watersheds. 1 Upper Mokelumne River Watershed Authority. Mokelumne/Amador/Calaveras Integrated Regional Water Quality Management Plan Update. January 2013 2 Calaveras County Water District. 2015 Urban Water Management Plan Update. June 2016. Chapter 4.8 – Hydrology and Water Quality 4.8 - 1 DRAFT EIR Calaveras County Draft General Plan June 2018 Figure 4.8-1 Watersheds of Major Rivers within Calaveras County Source: Calaveras County Water District, 2003. Chapter 4.8 – Hydrology and Water Quality 4.8 - 2 DRAFT EIR Calaveras County Draft General Plan June 2018 Watersheds within Calaveras County include the following: • Upper and Lower Mokelumne; • Upper and Lower Calaveras; • Upper and Lower Stanislaus; and • Lower San Joaquin River. The watersheds listed above represent all or part of a surface water drainage basin or distinct hydrologic features. Boundaries of the watersheds are not coterminous with the boundaries of the County. The watersheds primarily consist of a major river system (the Mokelumne, Calaveras, Stanislaus, or San Joaquin), together with the tributaries of the river systems. Each of the aforementioned river systems are discussed below in further detail. Mokelumne River The Mokelumne River runs in three forks (North, Middle, and South) from the Sierra Nevada Mountains in Alpine County. Snowmelt serves as the primary source of water for the Mokelumne River. An area of approximately 660 square miles is drained by the Mokelumne River, which flows southwest, with the forks all joining near Lodi, then turns northwest to end in the Sacramento River delta lands, and finally empties into the San Joaquin River approximately 20 miles north of Stockton. The Mokelumne River forms the County’s northern boundary with neighboring Amador County, and was considered the division between the southern and northern mining districts during the Gold Rush. The river passes through several reservoirs in the County, including Salt Springs Reservoir, Pardee Reservoir, and Camanche Reservoir.3 Calaveras River The Calaveras River originates in the Sierra Nevada Mountains, extends west-southwest approximately 60 miles toward and through the Stockton metropolitan area, and terminates at the San Joaquin River, outside of Calaveras County. Within the County, the Calaveras River runs in two forks (North and South). The river is fed almost entirely by rainfall and encompasses approximately 550 square miles. In the Upper Calaveras watershed, above New Hogan Dam and within the County, the primary tributaries are Esperanza, Jesus Maria, Calaveritas, San Antonio, and San Domingo Creeks. Below New Hogan Dam, in the Lower Calaveras watershed, the main tributaries conveying runoff in the County are the Cosgrove, Indian, and South Gulch Creeks. Stanislaus River The Stanislaus River drains a narrow basin of approximately 980 square miles above the foothills on the western slope of the San Joaquin River, forming the southern boundary of the County. Elevations along the river range from 15 feet above sea level at the river mouth to 10,000 feet at the crest of the drainage area. The three tributary forks (North, Middle, and South) of the Stanislaus 3 RMC. Mokelumne/Amador/Calaveras Integrated Regional Water Management Plan: Public Draft. December 14, 2006. Chapter 4.8 – Hydrology and Water Quality 4.8 - 3 DRAFT EIR Calaveras County Draft General Plan June 2018 join above New Melones Lake, approximately three miles north of Parrots Ferry. The North Fork is located within Calaveras County while the Middle and South Forks are in Tuolumne County. San Joaquin River The San Joaquin River starts in the Sierra Nevada and flows southwest to the San Joaquin Valley. As noted above, the San Joaquin River receives flows from the Mokelumne, Calaveras, and Stanislaus Rivers. Some of the primary tributaries to the San Joaquin River include Bear Creek, Calaveras River, Mormon Slough, Mosher Slough, Stockton Diverting Canal, and the French Camp Slough. Lakes and Reservoirs Naturally-occurring lakes of notable size do not exist in the County; however, some smaller mountain lakes are found within the Sierra Nevada. Several reservoirs are located within the County and are described in detail below. Pardee Reservoir Pardee Reservoir is owned and operated by the East Bay Municipal Utility District (EBMUD), was completed in 1929, receives water from the Mokelumne River, and provides municipal and industrial water, flood control, and hydroelectric power. The reservoir straddles the Mokelumne River above Camanche Reservoir, with a capacity of 198,000 acre-feet (af). Water in the Pardee Reservoir is an important source of domestic drinking water. As such, the water is subject to strict water quality standards and is not used as intensively for recreational uses as other reservoirs within the County. Camanche Reservoir Camanche Reservoir is owned and operated by the EBMUD, is located downstream of Pardee Reservoir within the Mokelumne River watershed, and was completed in 1963 with additional recreational and power uses added in 1983. Capacity of the reservoir is 417,000 af. Camanche Reservoir is a source of municipal and industrial water supplies, and provides flood control. New Hogan Reservoir New Hogan Reservoir is owned and managed by the U.S. Army Corps of Engineers (USACE), was completed in 1964 for purposes of flood control and water supply, and receives water from the Calaveras River. The reservoir is located 28 miles northeast of Stockton along the Calaveras River. Storage capacity of the reservoir is 317,000 af, which supplies irrigation water to the Stockton East Water District and the Calaveras County Water District. Tulloch Reservoir The Tulloch Reservoir was developed as part of the Tri-Dam Project in the 1950s by the Oakdale and South San Joaquin Irrigation Districts and continues to be managed by them for use as Chapter 4.8 – Hydrology and Water Quality 4.8 - 4 DRAFT EIR Calaveras County Draft General Plan June 2018 irrigation and domestic water supply. Tulloch Reservoir is located in Copperopolis on the lower Stanislaus River below New Melones Reservoir. Capacity of the reservoir is approximately 67,000 af. New Melones Reservoir New Melones Reservoir was completed in 1978 and is owned and operated by the U.S. Bureau of Reclamation. With a capacity for 2,420,000 af, New Melones Reservoir is one of California’s largest reservoirs, located behind the 625-foot New Melones Dam on the Stanislaus River. Irrigation water, flood control, and hydroelectric power are provided by New Melones. Salt Springs Reservoir Salt Springs Reservoir was completed in 1931 and is owned and operated by the Pacific Gas and Electric Company (PG&E) for hydroelectric power purposes. The reservoir is located at a high elevation within the Stanislaus National Forest along the North Fork of the Mokelumne River on the Calaveras/Amador County border. Salt Springs has a capacity of approximately 140,000 af. Spicer Reservoir Spicer Reservoir is owned by the Calaveras County Water District and operated by the Northern California Power Agency for power generation. The reservoir is located at a high-elevation on the Stanislaus River system, eight miles southwest of State Route (SR) 4. In addition to the reservoirs described above, a number of smaller older reservoirs built for irrigation and flood control purposes are found throughout the County. Such reservoirs include Hunter Reservoir, Salt Springs Valley Reservoir, Tiger Creek Reservoir, Calaveras Reservoir, Emery Reservoir, Schaads Reservoir, Old McCormick Reservoir, Copperopolis Reservoir, and the Goodwin Diversion Dam. In addition, several reservoirs were created as part of mine reclamation, such as Mine Run Reservoir near Camanche Reservoir.4 Major Streams and Diversion Canals Below is a list of 23 major streams and diversion canals. Lesser perennial and seasonal creeks are not included in the list.