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California Water Science Center - Santa Ana Basin, National Water Quality Assessment Program

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Santa Ana Basin

National Water-Quality Assessment Study Units In 1991 the U.S. Geological Survey initiated the National Water-Quality Assessment (NAWQA) Program to assess the status and trends in the quality of freshwater streams and aquifers, and to provide a sound understanding of the natural and human factors that affect the quality of these resources.  As part of the program, investigations will be conducted in 59 areas-- called "study units"-- throughout the Nation to provide a framework for national and regional water-quality assessment.  Together, these areas account for 60 to 70 percent of the Nation's water use and population served by public water supplies, and cover about one-half of the land area of the Nation.

Santa Ana River BasinAs part of the NAWQA program, the U.S.G.S. is evaluating water quality in the Santa Ana Basin. The Santa Ana River is the largest stream system in southern California and the study unit covers an area of about 2,700 square miles in parts of Orange, San Bernardino, Riverside, and Los Angeles Counties. The study unit is home to more than 4 million people who not only rely on water resources that originate within the basin, but also on water imported from northern California and the Colorado River.

Prado wetlands

Prado Wetlands
(Photograph by Scott Hamlin, U.S. Geological Survey)

In general, the quality of surface and ground water in the Santa Ana Basin becomes progressively poorer as water moves along hydraulic flow-paths. The highest quality water is typically associated with tributaries flowing from surrounding mountains and ground water recharged by these streams. Water quality is altered by a number of factors including consumptive use, importation of water high in dissolved solids, run-off from urban and agricultural areas, and the recycling of water within the basin.

Santa Ana River

Santa Ana River
(Photograph by Orange County Water District)

Beginning in 1998, and continuing for a period of three years, the Santa Ana NAWQA project intensively investigated the quality of water resources in the study unit. The largest and most important component of the intensive-study phase was an "Occurrence and Distribution Assessment". The goal of this assessment was to characterize, in a nationally consistent manner, the broad-scale geographic and seasonal variations of water-quality related to major contaminant sources and background conditions.


If you have questions and comments related to the Santa Ana Basin NAWQA, contact:
Robert Kent, Project Chief (rhkent@usgs.gov)
or write:
Robert Kent, NAWQA Project Chief
U.S. Geological Survey
Water Science Center
4165 Spruance Rd., Suite 200
San Diego, California 92101-0812

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Page Last Modified: Tuesday, 15-Jan-2013 10:48:11 EST