By DR. ROB LUSARDI
CalTrout/UC Davis Wild &
Coldwater Fish Research Lead
WHAT THE SCIENCE SAYS
Defining protective stream flow requirements (environmental flows) for native trout and salmon is often a source of contention in California. This is particularly amplified in agricultural landscapes where the demand for water is increasing and precipitation patterns are changing. To complicate matters, California’s Mediterranean climate is highly variable, providing the vast majority of water during winter with little precipitation during the summer growing season. This supply-demand mismatch means that water for fish and agriculture is often at a premium during California’s long, dry summers.
Quantifying environmental flows for salmon and trout in California has traditionally focused on regulated rivers where hydropower and water storage dams require flow release prescriptions, but is complicated in unregulated watersheds where water availability and streamflow requirements vary by region, watershed, and species. Additionally, there are numerous “competing” methods to quantify ecologically protective streamflows. One thing most biologists agree on is that environmental flows should reflect the natural variability of a river’s hydrograph (e.g., the size and frequency of a flow event, the timing and duration of those events, and the rate of change of those events). Less clear, however, is 1) exactly how much water can be diverted without negatively affecting stream ecology and 2) which attributes of a river’s hydrograph are necessary to capture when designing environmental flows for regulated rivers.
Two recent published papers in the latest edition of Freshwater Biology address these questions and others.
In this column we highlight important scientific publications,
by CalTrout staff and others, that expand upon our understanding
of the management or science regarding trout, steelhead and salmon in California.
Instream Flows
and DARREN MIERAU
CalTrout North Coast Director