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.