Salmonid Restoration Federation
31 March - 3 April, 2020
Santa Cruz, California

Assessing Ecological Risks from Streamflow Diversions in Coastal California Streams

31 March 2020
9:00am - 5:00pm
Workshop Coordinators:
Bill Trush, Co-Director HSU River Institute 
Valerie Zimmer, State Water Resources Control Board
Katrina Nystrom, HSU Graduate Student, Dept. Envt’l Science and Management
By restricting streamflow diversions to a relatively small percentage
change in ambient riffle crest thalweg (RCT) depth in unregulated
streams, the natural magnitude, duration, frequency, and timing of
streamflow (Q) remain protected. Workshop participants will be shown
how to quantitatively link basic stream hydraulics and stream ecosystem
processes, then apply these linkages to practically and quantitatively
evaluate ecological risks from cumulative streamflow diversions. The
morning session will review field techniques for measuring riffle crests,
show how basic stream channel hydraulics can be estimated from RCT-
Q rating curves, and then calibrate an RCT-Q rating curve from the
realtime USGS gaging website. Real spatial and real temporal variability
will then be folded-into this hydraulic RCT framework to explain how
stream ecosystem complexity can be quantified at a top-down scale
necessary for regionalizing diversion strategies/policies. The afternoon
session will synthesize the morning’s RCT-Q rating curve background,
then demonstrate its usefulness as a simple tool for prescribing instream
diversions. Depending on participant preference, a step-by-step risk
analysis of adult steelhead spawning in the Big Sur River OR steelhead
pre-smolt outmigration in the Arroyo Seco River will occupy the
workshop’s mid-afternoon (preferably bring laptops, but at least a hand
calculator). In late-afternoon (approximately 3:30), additional ecological
processes of concern to workshop participants will be opened-up for
discussion. And last, the final half-hour will be reserved for discussing
the future of top-down versus bottom-up strategies for instream flow
diversion policies in California.