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The
Issues
Over the past 30 years, erosion has destabilized the Wash channel and caused
increased sedimentation in Lake Mead. The Comprehensive Adaptive Management
Plan developed by the Las Vegas Wash Coordination Committee (LVWCC) identifies stabilizing the Wash
as one of three key initial steps needed for long-term management of the Las Vegas Wash.
As a result, the LVWCC has developed the Las Vegas Wash Capital
Improvements Plan , which will help to stabilize the channel over
the years.

Demonstration Weir
One way to deal with erosion is by placing erosion control structures (which are also known as grade control structures or weirs) throughout the Wash. In total, 22 structures are planned for the Wash. As of January 2008, eleven weirs are in place, and construction will soon be completed on the twelfth. As we succeed in stabilizing sections of the channel, we develop additional riparian and wetland habitat. The erosion control structures help slow the water, creating a pond behind the structures in which wetland plants can establish. Weir construction activities also clear acres of invasive plants such as tamarisk from the banks of the Wash. These cleared areas are then revegetated with native wetland, riparian, and upland species.

Downstream of Rainbow Gardens Weir
Achieving
Equilibrium
Addressing conditions such as: increasing and variable daily flows, highly
erodable soils, water quality concerns, the need to protect wildlife
habitat, and other environmental concerns present formidable challenges
to controlling erosion in the Wash. However, efforts are currently
under way to promote channel stabilization by decreasing channel
bed downcutting, reducing stream bank erosion, armoring the channel
with vegetation, balancing sediment transport and enhancing the ecosystem.
TABLE
1
GENERAL LAS VEGAS WASH DESIGN GOALS
Present
Conditions |
Stable
Conditions |
- Variable,
changing flows
- 0.20
to 0.80 % channel slope
-
20 active headcuts
-
Flood velocities at 10 to 20 feet per second
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Little channel or bed protection
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Highly variable sediment carrying capacity
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- Predictable
base flow ranges
- 0.05% to 0.3% channel
slopes
- Stable channel without headcutting erosion
- Flood velocities
below 10 feet per second
-
Stable channel sideslopes
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The sediment amount entering the system is equal to the amount of sediment leaving the system
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