Restoration / Barrier
Initial feasibility studies determined
that, to restore the stream and valley to stable, historic conditions,
the work would involve complete reconstruction of the stream
channel and associated valley floodplain, requiring redistribution
of 100,000 cubic yards of overburden materials. The first step
in the design process was to characterize the hydrology of the
stream. A bankfull discharge of 46 cubic feet per second was used as the design
discharge to model channel crosssection templates. Hydrology
was estimated using various US Geological Survey regional regression equations,
hydraulics based on existing undisturbed channel geometry sections,
and computation of a weighted average based on a two-year return
interval flow for a similar and adjacent basin with discharge
records.
Channel geometry was designed to
convey bankfull flow and was based on empirical relationships
for width:depth for mountain streams. Channel geometry was further
refined to reflect a variety of natural crosssections representative
of step-pools and pool-riffle-run sequences, to create channel
variability and fish habitat. Channel planform was designed
with a sinuosity between 1.1 and 1.2, to be consistent with geomorphic
conditions up- and downstream of the project area. Channel slope
varied from 1.7 to 1.9 percent, to accommodate variability in
sinuosity through a reconstructed constant floodplain slope
of 2.1 percent (figure
1).
Channel and floodplain design incorporated bed and bank stability
measures to protect against channel incision and bank erosion,
while still allowing for the natural evolution of the stream
channel and its bedforms. Bank stability was accomplished using
bioengineering methods; which included a rock toe, fabric-reinforced
contoured stream banks, and native vegetation for long-term
stability. Bed stability was achieved by installing stream bed
gravels sized to withstand tractive forces and calculated scour
depths of flows exceeding bankfull. Additional bed stability
components included designs for valley-wide grade control structures,
at 400-foot intervals to protect against channel incision in
the event of unexpected or premature channel migration.
 |
|
 |
|
 |
| Beginning of restoration – valley bottom reconstruction. In this project it was ... |
|
After grade and slope features were constructed, a biodegradable soil stabilizat... |
|
Immediately following final construction when water was returned to the channel.... |
A barrier to upstream fish movement was also constructed at
stream kilometer 10.6 in the fall of 1995. This barrier was constructed
using treated wood and consisted of a 1.5-meter drop onto a treated
wood apron, designed to prevent the formation of a scour
pool at the base of the barrier that could be used as a jump
pool. In addition, the channel was widened immediately below
the barrier to prevent water from backing up against the barrier
at peak streamflows.
White's Creek fish barrier prior to installation. The barrier, built in 1995, wa... |
Click on
a photo for a larger view and more information. |
Fish barrier, immediately after installation. The barrier consists of a 1.5 m dr... |
Brook Trout Removal
Electrofishing was used to remove
brook trout and estimate populations of brook and westslope cutthroat trout
using depletion estimators. Each year from 1993 to 1995, multiple
electrofishing passes were made in various sections of the
stream. Electrofishing estimates and associated brook trout
removal efforts continued annually from 1996 through 2000.
Click here to read the full manuscript as published in
Intermountain Journal of Sciences 2002, 8(3): 193-214.
|
