Final Report Abstract

A practical ecological management strategy recognizes that the annual snowmelt hydrograph and winter floods are dominant components of the natural hydrograph that sustain native river ecosystems. The purpose of this Project was to develop general guidelines for releasing pulse flows in steep boulder-bedrock Sierra Nevada rivers that should help recover and sustain regulated Sierra Nevada river ecosystems. This was accomplished by linking geomorphic thresholds for the channelbed to variable flood peaks and field-mapping fish, amphibian, benthic macroinvertebrate, and woody riparian vegetation habitat throughout the WY2005 snowmelt hydrograph for the mainstem Clavey River, a 157 mi2 watershed on the western slope of the Sierra Nevada and tributary to the Tuolumne River. Recommended pulse flow guidelines for hydropower projects located in the snow/rainfall transition zone of large Sierra Nevada river watersheds are: (1) maintain the magnitude and frequency of unregulated 3-yr to 15-yr winter flood peaks, (2) Divert the rising limb, peak, and fast recession limb of the unregulated annual snowmelt hydrograph using a fixed percentage of the unregulated streamflow without significantly impairing the reference condition that emphasizes woody riparian initiation and early-establishment, as well as sensitive life stages of selected fish, amphibians, and benthic macroinvertebrates. Preliminary analyses suggest maximum fixed daily diversion rates of 25% to 35%, and (3) do not divert past the annual snowmelt hydrograph recession node, the streamflow transition from the fast snowmelt recession limb to the slow snowmelt recession limb. These guidelines provide a way to prioritize existing dam operations that might have the infrastructure to promote recovery of native Sierra Nevada river ecosystems. Small capacity reservoirs capable of passing winter flood peaks up to the 15-yr flood would have high priority. While there are many demands on any given operation, the goal of recovering native river ecosystems should be done in places with the best chance of success. A next step is to apply the pulse flow guidelines to several existing and hypothetical dam operations to evaluate impacts on hydropower generation and dependable water supply.

Bill Trush, Scott McBain, and Jennifer Vick at Cottonwood Bar on the Clavey River	Amphibian habitat model site on Cherry Creek
Amphibian habitat model site on the Clavey River	Sediment deposition and spawning habitat model site on the Clavey River

Seed release observation willow on the Clavey River

Photo credit: McBain and Trush, Inc.
(Please request permission from bill@mcbaintrush.com for use of pictures)