California Water Science Center
Sacramento River Basin NAWQA: Environmental Setting
The Sacramento River Basin NAWQA study unit (figure 1) consists of the following physiographic provinces: the Sacramento Valley, the Coast Ranges, the Klamath Mountains, the Cascade Range, the Sierra Nevada, the Modoc Plateau, and the delta of the Sacramento River (figure 2).
The surface water network is shown in figure 1. The northern-most area (Modoc Plateau) is a high desert plateau and is characterized by cold snowy winters with only moderate rainfall, and hot, dry summers. The average annual precipitation is 12 inches. The other mountainous parts in the north and east have cold, wet winters with major amounts of snow providing considerable runoff for the summer water supply. Snow melt is the major source of freshwater for the rivers of the study unit. These higher mountainous areas may receive rainfall during any month of the year. Summers are usually mild. Precipitation totals from 21 to 41 inches. The Sacramento Valley, the south-central part of the region, has mild winters with less precipitation. Precipitation usually takes place from October through May and virtually no precipitation occurs from June to September. The average annual precipitation in the city of Sacramento is 18 inches. Of the 7 physiographic provinces (figure2), the Sacramento Valley will be given the most attention because it is there that the greatest amount of water use, and potential impacts on water use occur. Although the other physiographic provinces are relatively sparsely populated, and the land- uses are less intense, there exists some potential to impact downstream water quality. This is particularly the case for the Coast Ranges, and the Sierra Nevada, two potential sources of mercury and other trace elements to the adjacent lowlands, and the Klamath mountains, a major source of trace elements to the upper Sacramento River (below Shasta Reservoir).
The GIRAS land use map and graphical representation of Anderson land-use categories are shown in figures 3 and 4, respectively.
The land-uses of the Sacramento Valley are dominated by agriculture and rice is one of the most important crops. Orchards, principally walnut, almond, prune, and peach, tend to be located along river channels in order to take advantage of well-drained soils. Rice is one of the principal crops because of the relatively impermeable soils of the valley as demonstrated by the STATSGO soils map (figure 5).
Figure 5 Statsgo Soils Map
Rice can also be grown because of the availability of irrigation water supplied by the Sacramento River. The total population of the study unit is 2,208,900. The largest city in the study unit, with a population over one million, is Sacramento, and is located near the southern-most part of the study unit, just at the confluence of the Sacramento and American Rivers.
All major rivers of the study unit (Sacramento, Feather, American, Yuba) are impounded just above the margin of the Sacramento Valley. The reservoirs are managed to collect snowmelt and to provide flood protection. The capacity of Shasta Dam is 4,552,000 acre feet. The upper Sacramento River, McCloud River and Pit River supply water to that reservoir. Lake Oroville, on the Feather River, has a capacity of 3,537,600 acre feet. Folsom dam, on the American River, has a capacity of 974,500 acre feet. New Bullards Bar Reservoir, on the Yuba River, has a capacity of 966,100 acre feet. The amount of snowmelt runoff to these reservoirs on a yearly, or multi-year cycle, dominates the discussions of water allocation for the study unit and for export to other locations of California. The average annual runoff from the basin is 22,389,700 acre feet. The average annual precipitation for the study unit is 36 inches, most of which occurs as rain or snow during the months of November through March. Water is released from the reservoirs from spring through summer to provide irrigation water to the Sacramento and San Joaquin Valley agricultural communities, and to provide drinking water to Central Valley residents and residents of southern California, and to protect water quality of the delta of the Sacramento and San Joaquin Rivers. Water quality entering the reservoirs is of high quality, so the focus of the study will be on downstream impacts. The reservoirs blocked the routes of migratory fish such as salmon and steelhead trout. Therefore, the remaining populations and impacts on those populations are in stretches of river below the reservoirs.
The surface water activities for the Sacramento River Basin NAWQA will include assessments of the Sacramento River and its major tributaries, as well as an assessment of the major agricultural impacts to the river, and runoff from an urban source. Agriculture, mining, and urban inputs are the three major land uses affecting the Sacramento River. Industrial sources of contaminants to the river are considered minor. The Sacramento River, below Lake Shasta, is considered the major water resource under investigation and the design of the study is centered about that stretch of river. The majority of water uses and potential impacts from water use from the greatest population centers (both within the study unit and out of the study unit) is for the Sacramento River. The goals of the NAWQA program will be completed by basic and intensive fixed site samplings, by the completion of synoptic surveys on pesticides, volatile organic chemicals, and metal inputs to the river, and by the completion of various ground water sampling activities involving pesticides and volatile organic chemicals. The biological assessment will focus on the rivers of the Sacramento Valley. In addition to the above, the Sacramento River Basin NAWQA will participate in special studies related to the volatile organic chemical national synthesis, including a detailed assessment of air-transported pesticides and other chemicals and an assessment of surface and ground water quality within an urban area (greater Sacramento metropolitan area).