Instream flows when flows are intermittent

Conventional criteria for determining suitable instream flows in a managed river such as the Santa Maria River, a river that despite being dry six or more months every year supports federally endangered southern California steelhead, do not address the dynamic channel morphology and critical importance of headwater flows that characterize intermittent mainstem rivers. Dr. Derek Booth (Senior Geologist) along with Stillwater co-authors Dr. Yantao Cui (Senior Hydraulic Engineer), Zooey Diggory (Senior Ecologist), and Dirk Pedersen (Senior Fisheries Biologist), recently published “Determining appropriate instream flows for anadromous fish passage on an intermittent mainstem river, coastal southern California, USA” in the June issue of the international journal Ecohydrology. Their paper summarizes Stillwater’s work in the Santa Maria basin of evaluating human-induced changes in the frequency, duration, and timing of fish passage in dryland rivers. Utilizing a hydrologic analysis of pre-dam flows, coupled with established criteria for successful steelhead migration, the study produced a generalized set of operational goals to support anadromous fish populations in such river systems.