| Drop and Grade Control Structures
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and Grade Control Structures
Reducing the velocity of flowing water is one approach to arresting
the degradation of stream channels. The volume of water is difficult
to change but modifying the effective slope of the channel can be
accomplished by creating small soil-cement drop (hydraulic-control)
structures that raise the normal water surface elevation across
a reach of the channel.
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| Stepped soil-cement erosion control structure
on La Barranca Arroyo at Rio Rancho, New Mexico |
The velocity of the water is decreased in the reach upstream of
the drop structure and also the potential for erosion is decreased.
If desired, the velocity could be decreased to cause deposition
of sediments upstream of the structure. Hydraulic-control structures
often are used to reestablish previously degraded channels.
The water is allowed to spill over the erosion resistant soil cement
drop structure and back into the natural channel. Often there will
be a series of drop structures when the channel gradient is fairly
steep. The design of these structures requires an understanding
of the impact on the channel upstream and downstream to prevent
excessive scour, degradation and sediment deposition. The channel
hydraulic conditions must be determined to make sure design water
depths and velocities are not exceeded.
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| Water flowing over a series of drop structures
at Marcy Gulch, CO |
In the Highlands Development, south of Denver, 15 soil-cement drop
structures were used along Marcy Gulch. The material for the soil-cement
came from the overbank deposits and was mixed with cement on site
in a portable pugmill plant. The structures were designed and constructed
to look natural and blend in with the park setting. A similar series
of drop structures were constructed at Shop Creek in Aurora, Colorado.
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| Series of drop structures along Shop Creek
in Aurora, CO |
Close-up of Shop Creek drop structure |
Soil-cement grade-control (bed-control) structures are also used
to prevent degradation of stream channels. The crest of a grade-control
structure is generally constructed at or near the existing channel
bed with a cross section that resembles the upstream channel dimensions.
The purpose of the grade-control structure is to maintain the existing
bed of the upstream channel and to force the degradation zone to
occur at the erosion resistant soil-cement structure.
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| Soil-cement bank protection and grade-control
structures for Unnamed Wash at Laughlin, Nevada |
At the Unnamed Wash in Laughlin, NV,eleven soil cement bed control
structures were completed in 1994. The project also included soil-cement
bank protection to provide erosion control for a 1.7 mile long stretch
on the wash.
The geotechnical stability of drop and grade control structures
is evaluated in a similar manner to that of bank protection. Generally
hydrostatic uplift, bearing capacity, piping potential, and sliding
stability must be evaluated.
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More on Soil Cement:
Overview
Embankment Slope Protection
Bank Protection/Levees
Drop and Grade Control Structures
Liners
FAQs
Southern California Case Study
Moss Creek Dam Case Study
Rueter-Hess
Dam and Reservoir Case Study
RCC/Soil Cement Contractor Directory
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