The folly of unimpaired flows for water quality management

Nov 28, 2018 at 2:00pm

California Water Blog

Unimpaired streamflow has long been the benchmark against which current stream flows are evaluated for environmental purposes. The underlying assumption is that if there is water in a stream, the stream must be healthy. In California’s Shasta River watershed, a tributary to the Klamath River, unimpaired flows have been the basis of recent Instream Flow Needs studies. Recently, another study uses unimpaired flows for a larger regulatory effort to address California’s Water Action Plan. 

The approach in the draft Shasta River study plan follows a familiar pattern: first, develop a flow model to better understand current water supply, water demand, and instream flow patterns. Then, remove all human activity (e.g., diversions, pumping, storage) to estimate unimpaired flows. Ultimately, use the model to evaluate water management scenarios that address ecosystem objectives – in California, these ecosystem objectives frequently focus on anadromous fish such as salmon.

Here are four questionable assumptions outlined in the article that form the basis of many unimpaired flow strategies:

-Today’s unimpaired flows would support anadromy and native fish.

-Water temperature and water quality problems are changed by instream flow management.

-Watershed-scale models provide detailed insights for managing localized water temperature and water quality.

-“Best available data” will be enough to develop effective, watershed-wide regulatory management.

Click here for the full article to read more about these management strategies.