Truly a Watershed Event: California’s Water Board Proposes Base Flows for the San Joaquin River Tributaries

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On September 15, 2016, the State Water Board released its draft of a proposed update to the Water Quality Control Plan for the San Francisco Bay/Sacramento-San Joaquin Delta Estuary, often referred to as the Bay Delta Water Quality Plan. The update to the Bay Delta Water Quality Plan is being undertaken pursuant to requirements under the federal Clean Water Act and California’s Porter-Cologne Water Quality Act. To ensure adequate water conditions for fisheries (such as salmon, steelhead trout and smelt) that are present in and migrate through the Bay Delta, the September 15, 2016 draft of the Bay Delta Water Quality Plan update recommended that a range of between 30 and 50 percent (with a starting point of 40 percent) of the “unimpaired flows” of the Stanislaus, Tuolumne and Merced Rivers be left instream until their confluence with the San Joaquin River. According the State Water Board, “Unimpaired flow is the rate and volume of water that would be produced by the rain and snow accumulating in a watershed absent any diversion, storage or use of water. An unimpaired flow approach generally mimics the natural variability of California’s river flows that support native fish like salmon and steelhead and for which they have evolved.”

Although current data suggests that average base flow for the Stanislaus River is already about 40 percent of unimpaired flow, the average flows for the Tuolumne River and Merced River are currently 21 percent and 26 percent, respectively, of unimpaired flow. The State Water Board’s proposed base flows for the Tuolumne River and Merced River, if implemented, would therefore result in a measurable increase in water left instream in these San Joaquin River tributaries and presumably a corresponding decrease in the amount of water available for diversion from these waterways.


Found in the online journal, California Water Law Journal, published by the University of the Pacific, McGeorge School of Law, 2016.