WWRC 88-19
Stream Channel Response to Flow Depletion
Summary and Conclusions
Channel width, depth, width to depth ratio, cross-sectional area
and conveyance capacity were measured above and below diversion structures
on 20 mountain stream reaches in Wyoming and Colorado. Diversion
structures ranged in age from 12 to 106 years and reduced streamflow up
to 90 percent. Statistical analysis indicated no significant differences
in channel dimensions above and below diversions on steep (slope
> 4.0 percent) and moderate (slope 1.5 to 4.0 percent) gradient
channels. Low gradient (slope < 1.5 percent) channels responded to
streamflow depletion by significantly reducing their depth, area and
capacity.
Based upon these findings, additional comparisons were made on low
gradient reaches of foothill and basin streams. Results were similar.
Channel width, depth, area and capacity were significantly reduced below
diversion structures. Using regression analysis, equations were
developed expressing these channel properties as a function of discharge.
Our results indicate that moderate to high gradient mountain
stream channels located in the forest snowpack zone may be maintained
with reduced streamflow regimes. Channel maintenance flow studies
should focus on low gradient stream reaches where encroachment and
aggradation are more likely to occur. The regression equations presented
can be used to estimate the physical response of this channel
type to flow depletion.
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