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4.3 Hydrology and Water Quality 4.3 HYDROLOGY AND WATER QUALITY 4.3.1 INTRODUCTION TO HYDROLOGY AND WATER QUALITY This section describes water resources at Pacific Gas and Electric Company’s hydroelectric facilities and associated Watershed Lands in Northern and Central California, and addresses how utilization and management of the water resources for power production affects the physical environment and other beneficial uses. The section provides an overview of discretionary and non- discretionary factors affecting water use and management, including applicable regulatory constraints. The section then addresses the following for each asset: the location of the drainage basin, the flow of water through the different facilities, a general discussion of water quality, physical characteristics of Pacific Gas and Electric Company’s water conveyance systems and capacities, maximum powerhouse capacities, and considerations, including specific regulatory constraints, that affect the management of water for power production and other purposes. Pacific Gas and Electric Company’s hydroelectric facilities were built, for the most part, in the early and mid part of the 20th Century. The existing facilities and their operations are integrated into the water supply system for the State and can affect water quality in the surrounding watershed. 4.3.1.1 Water Use Water is used at Pacific Gas and Electric Company’s hydroelectric facilities primarily for the nonconsumptive purpose of generating electric power. Other uses include minor consumption at powerhouses and recreational facilities (e.g., for drinking water, sanitation, or maintenance activities), provision of recreational opportunities, sale or delivery to other parties, and fish and wildlife preservation and enhancement. Other users of the waterway may use water (and, in some cases, Pacific Gas and Electric Company facilities such as reservoirs) for these same uses, and may also use the water for irrigation and public water supply. Pacific Gas and Electric Company does not pump groundwater for power generation purposes, although groundwater may in some cases naturally contribute to surface flows on a river system. Pacific Gas and Electric Company’s uses of the Watershed Lands have less potential to affect water resources than the hydroelectric facilities. The majority of the Watershed Lands are undeveloped. With the exception of some canals and flumes that may cross certain parcels, these Watershed Lands do not contain any generation facilities or support activities that result in significant consumptive or non-consumptive uses of water (PG&E Co., 1999). Uses of Pacific Gas and Electric Company’s Watershed Lands include grazing, recreational activities, housing, and timber harvesting. These land uses do not divert or use water in volumes great enough to result in major effects on water resources. Grazing activities are typically seasonal and occur on areas that are supported by natural rainfall. The licensees have the option to request service from a local water district to meet their needs (i.e. irrigation, drinking, sanitary facilities, general usage, etc.) but this is more the exception than the norm. Occupants of recreational home November 2000 4.3-1 Hydrodivestiture Draft EIR 4.3 Hydrology and Water Quality sites authorized by Pacific Gas and Electric Company utilize either wells or natural springs located on the property. Even where Pacific Gas and Electric Company maintains water rights for water in streams or other tributaries crossing the Watershed Lands, Pacific Gas and Electric Company does not typically authorize the licensor/lessor to draft or divert water from those sources except under very specific circumstances. Where specific permissions have been granted for use of water from the site or through Pacific Gas and Electric Company’s water rights, they are discussed in the following sections. There are no significant uses of water resources associated with timber management, although these activities have the potential to affect watercourses through erosion, debris, and heavy equipment use. Such effects of timber management on water resources are addressed through the THP process. Use of on-site water for the watering of roadways at select locations could be required as a condition of a THP when water is available. 4.3.1.2 Sources of Water Resources Impacts at Hydroelectric Facilities Use and management of water resources at a typical hydroelectric facility can affect both the natural environment in the vicinity of the facilities and other beneficial users of water resources. Use of water resources at hydroelectric facilities has the potential to affect the natural environment and other uses through the diversion and impoundment of water and the manipulation of water flow fluctuations through controlled releases and uncontrolled spills. Impacts on the Natural Environment Pacific Gas and Electric Company’s hydroelectric facilities divert water from the natural stream channel and utilize conveyance systems to pass the water through powerhouses, eventually returning it to the natural stream. Diversion can impact water resources by reducing the flow levels in the natural stream, which can affect the use of the water resource by fish and wildlife. In addition, diversion intake structures can potentially impact fish by causing impingement of fish on screens and trash racks and entrainment of fish in powerhouse conveyances. Impacts from water diversion activities on biological resources are discussed in Sections 4.4 and 4.5. Water impoundment’s artificially alter natural stream conditions and change a river environment to a lake environment. Reservoirs can capture bedload sediments, resulting in armoring and/or scour in downstream reaches. Dams can also reduce downstream nutrients and substrate migration, cause reductions in dissolved oxygen for fish, block pathways for migrating fish and pose hazards for wildlife resources. Management of reservoir sediment (sluicing, flushing, dredging, etc.) and temporary operations associated with repair activities can also affect water quality downstream of Pacific Gas and Electric Company facilities. Operation of storage reservoirs, including controlled releases and uncontrolled spills, can lead to thermal stratification, supersaturation, and changes in dissolved oxygen levels, all of which Hydrodivestiture Draft EIR 4.3-2 November 2000 4.3 Hydrology and Water Quality adversely impact fisheries resources. Impoundment may also lead to increased water temperatures due to thermal heating. These effects of impoundment on biological resources are discussed in detail in Section 4.4. In addition to impacts on biological resources, regular release of impounded water can decrease vegetation along the shoreline, leading to an increase in erosion. Erosion can contribute to sedimentation problems. Impacts on Other Beneficial Uses Pacific Gas and Electric Company’s utilization and management of water resources at its hydroelectric facilities have the potential to affect other beneficial uses of these resources. Although Pacific Gas and Electric Company’s water rights are largely nonconsumptive, the infrastructure related to impoundment, diversion, and power generation may affect other water users. Hydroelectric facilities may function as an integral component of the water supply and distribution system for domestic water supplies and irrigation in some areas. In such cases, Pacific Gas and Electric Company typically has agreements with the affected water users regarding the volume, timing, and location of diversions. In addition, hydroelectric facilities create and impact water-related recreational opportunities. Reservoirs and other facilities can affect recognized beneficial uses such as boating, fishing, and swimming. Hydroelectric diversion and conveyance systems can also have potentially adverse impacts on certain recreational activities such as river rafting by altering natural stream flows, creating physical obstacles such as dams, and creating lake habitat from the river environment. For further discussion of recreational uses, please see Section 4.6. 4.3.1.3 Water Management Water management refers to operational decisions to store, release, and spill available water, and all factors relating to the timing or quantity of water stored, released and spilled. In addition to maximizing revenue, water management must consider other uses such as recreation, habitat enhancement, irrigation and other domestic uses, and the need to handle emergency situations such as floods, are also taken into account in an overall water management strategy. Note that many of these issues are not typically addressed by FERC regulatory requirements and as such are largely voluntary considerations on the part of the operator. A key consideration in water management strategies is hydrological and operational links among specific facilities. Hydrological linkage exists where facilities are located on an interrelated system of watercourses, such that actions at upstream facilities can directly impact operations and water management at downstream facilities, and must be taken into account for safety purposes and economically efficient operations. In some cases, Pacific Gas and Electric Company’s facilities are hydrologically linked with facilities owned by others, which can create the need for coordination or communication between the separately owned facilities. November 2000 4.3-3 Hydrodivestiture Draft EIR 4.3 Hydrology and Water Quality Some facilities are not

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