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San Joaquin NAWQA
Number: Location: Cooperating Agencies: Project Chief: Period of Project:
96779bi8 Earth,United States, San Joaquin River Basin Kratzer, Charles R. 1991 - Present

Statement of Problem:

The San Joaquin-Tulare Basins study unit covers approximately 31,200 square miles in central California. The study unit includes the western slope of the Sierra Nevada to the east, the San Joaquin Valley, and the eastern slope of the Coast Ranges to the west. The study unit can be separated into the San Joaquin Basin to the north and the hydrologically closed Tulare Basin to the south. The San Joaquin River receives water from tributaries draining the Sierra Nevada and Coast Ranges, and except for streams discharging directly to the Sacramento San Joaquin Delta, is the only surfacewater outlet from the study unit. The Sierra Nevada is predominantly forested land, and the Coast Ranges and the foothills of the Sierra Nevada are rangeland. Most of the valley floor is used for agriculture.


The water quality in the study area is highly influenced by the agricultural land uses. Since the beginning of Cycle I changes in the intensity of agricultural input have occurred in the study area. Total water use increased 33% from 30.2 to 40.1 million ac-ft per year, from 1990 to 1995. While most of this can be accounted for by hydroelectric power production, total offstream water use increased 5% from 16.1 to 16.9 million ac-ft per year. Over the last decade (1991 to 1999), pesticide use in the study area increased 43% from roughly 79.4 to 114.1 million pounds active ingredient. This number may also reflect better reporting as well as increased use. From 1987 to 1996, the number of dairy cattle in the San Joaquin Valley has increased 46% from 582,000 to 850,000.

While the study unit is still an important agricultural area, urban land use has become more important as the cities grow to accommodate the rise in population. In the last decade, the population of the study unit has increased 20%, from 2.9 to 3.5 million. Most of this growth is concentrated on the valley floor.


The objectives of the NAWQA program are: to describe the quality of the Nation's water (STATUS), to assess longterm changes in water quality (TRENDS), and to provide an understanding of the factors that govern water quality (UNDERSTANDING). These objectives have not changed as NAWQA moves into Cycle II, but the emphasis on the three components has. In Cycle I the main emphasis was on STATUS. In Cycle II the emphasis has shifted to TRENDS and UNDERSTANDING.

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