Integrated Restoration and Adaptive Management of the Las Vegas Wash - Restorative Redevelopment of Devastated Ecocultural Landscapes - page 108

twenty feet and lateral migration of the channel, which together can mobilize and
send well over a hundred thousand tons of sediment downstream into Lake Mead.
The Las Vegas valley agencies have collectively accomplished a good deal in
order to try to get water quality under control by implementing best management
practices (Scharnhorst 2004). The perchlorate contamination resulting from chemi-
cal pollution stretching back half a century is being dealt with through installation
of an interception system in the groundwater and subsequent treatment of the plume.
The Nevada Division of Environmental Protection estimates that within the next ten
years, all the gravel and sands of the Wash will have been flushed free of perchlorate
to background concentrations.
So the major problem, therefore, remains the severe erosion in the Wash. For
example, from the air it is possible to observe the massive sediment plumes enter-
ing Lake Mead which deposit from one to three hundred thousand tons of material
a year.
RESTORATION EFFORTS
The restoration of the Las Vegas Wash provides an exemplary lesson about the value
of taking early action (Scharnhorst 2004). Following the flood of 1975, experts esti-
mated that four erosion control structures would be needed at a cost of about $200,000.
By 1986, only five years later but subsequent to another very bad flood, estimates
suggested the need for eleven erosion control structures (mostly aesthetically attrac-
tive, natural-looking installations) at a cost of $15 million. The erosion continued to
worsen such that by 1991, fifteen structures were suggested to be required at a cost
of $30 million. Today, the most current estimates are for $125 million to be spent to
construct twenty-two difficult-to-build and highly engineered structures to be put in
place to stabilize the Wash. The lesson here, of course, is that anytime one can obtain
the financing, the resources, and the collaboration necessary to do something early
on in terms of restoration—it doesn't matter if it is controlling invasive species, ero-
sion, or whatever else is the issue—do it immediately (Scharnhorst 2004).
Las Vegas residents and environmental managers finally came to realize that if
efforts were not made to immediately stabilize the Wash, there soon would be noth-
ing left to save. Hydraulic and hydrologic modeling was used to map the fluvial
and geomorphological processes in the Wash in order to understand sediment ero-
sion and transport and thus aid in the design and construction of the stabilization
measures. Stabilization is usually a three-pronged approach (Scharnhorst 2004): (1)
downward channel bed degradation has to be stopped, (2) lateral channel migration
must be halted, and (3) revegetation has to be recognized as being a major part of
the solution.
Twenty-two erosion control structures are planned to create a stable elevation gra-
dient of twenty feet per mile. The current grade of the Wash is between thirty-eight
and eighty feet per mile, indicating the challenge involved with stabilizing and flat-
tening out the grade so that erosion is halted. By 2004, eight weirs have been com-
pleted, four are in planning and design, and an additional ten are planned to be built
over the next decade. Four miles of bank stabilization have now been completed, and