WWRC 89-07
Sediment Transport Relations and Channel Maintenance Implications for Big Sandstone Creek
Executive Summary
Study Objectives
The objective of this study has been to investigate sediment
transport and storage processes in the Big Sandstone Creek drainage in
the vicinity of proposed water diversion structures and relate these
findings to the need for channel maintenance flow releases.
Study Approach
In July 1986, three reaches were selected for study in the Big
Sandstone Creek drainage. Two reaches were located at proposed diversion
points on the North and South Forks, while a third was downstream
below the confluence of these tributaries. Multiple transects were
established at each reach to investigate bedload and suspended load
transport and sediment storage characteristics through the 1987 and 1988
spring runoff seasons. Based upon dimensionless flow duration analysis
and the developed sediment transport relations, mean annual sediment
budgets were determined for each reach. Also, simulated hydrographs and
sediment budgets were developed for the lowermost study reach by applying
a development scenario to the measured 1987 and 1988 natural hydrographs.
Study Findings
Under the natural flow regime, sediment storage in the Big
Sandstone reaches is quite stable. High, short duration flows import
more finer material (less than 2.0 mm) into the reaches than is
exported, while lower, more frequent discharges tend to export this
excess, thus maintaining a relative balance. Dominant discharges are
less than 10 times the average annual flow and are less than bankfull.
Analysis of natural and simulated post-development average annual
sediment budgets indicates that channel aggradation and encroachment
should not occur in upper Big Sandstone Creek as a result of water
development. This conclusion is supported by the findings of Wesche et
al (1988), who found that the dimensions of steep, rough mountain stream
channels could be maintained despite significant flow depletion in the
forest snowpack zone. The key to maintaining such channels does not
appear to be the release of relatively large channel maintenance flow
regimes, but rather an effective erosion control program during and
after construction.
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