ABSTRACT

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Many waterways in California’s Central Valley have water quality impairments resulting from urban and agricultural impacts, and the Lower Calaveras River (LCR) is no exception. The goal of this study is to identify the sources of these impairments to the watershed through measurement of water quality parameters at multiple locations along the LCR during both the wet and dry seasons. The LCR begins at the outlet for New Hogan Dam (NHD) near Valley Springs and flows west to Bellota where it is divided into the Old Calaveras River and Mormon Slough. The LCR provides drinking and irrigation water to the City of Stockton and surrounding communities as well as majority of Calaveras County. The LCR is also a habitat for steelhead salmon and rainbow trout.

Samples were collected during a number of longitudinal surveys – two during extended dry periods and the remaining immediately following major precipitation events during water years 2006 and 2007. Field measurements of temperature, conductivity, pH, and turbidity were collected at 8 monitoring sites. In addition, samples were collected for fecal coliform (FC), total coliform (TC), and standard geochemical analysis at the University of the Pacific. 

Results indicate there is a positive correlation between turbidity and bacteria levels. In addition, nitrate concentrations positively correlate to FC in the tributaries to the LCR. These correlations suggest bacteria may originate from the same source as the turbidity and/or nitrate. Cosgrove creek, a tributary leading into the LCR immediately downstream of NHD, exhibits the highest levels of bacteria. In addition, two smaller un-named tributaries also contributed significant levels of bacteria to the LCR. Livestock around the upper reaches of Cosgrove and urban runoff around the lower reach of Cosgrove Creek are possible sources of bacteria entering Cosgrove. Leaky septic tanks and agriculture runoff are possible sources for bacteria entering the smaller tributaries.