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5
Beneficial Use Analysis
The dredged material from the flexible-discharge dustpan dredge demon-
stration was used beneficially for wetlands restoration. It was pumped upstream,
over the dike, adjacent pasture, and existing marshland, and placed in an area
designated by MVN (Figure 2). The right-of-way across the dike, adjacent
pasture, and existing marshland consisted of a 100-ft-wide corridor (Photo 15).
As the placed dredged material built up above the surface of the water in the
marsh area, additional shore line was added to extend the placement further into
the marsh (see Photo 14). Two hydraulic backhoes (swamp buggies) mounted on
swamp tracks were used to move the pipe and build temporary dikes to direct
discharge flow (see Photo 15). Other than the temporary dikes, no other con-
tainment structures were used in the placement process.
Photographs of the BD and AD placement site are shown in Photos 29 and
30, respectively. BD and AD placement site surveys were conducted by the
contractor's survey crew and inspected by MVN, using airboats, mobile DGPS
for horizontal positioning, and spirit leveling for vertical control. The results
from these surveys are plotted on Figures 11 and 12 (BD and AD surveys,
respectively). The difference plot between the BD and AD surveys is shown in
Figure 13. The dredged material deposit's footprint covers an area of approxi-
mately 20 acres. From the surveys, the contractor calculated a deposition volume
of 177,700 cu yd. Assuming a 20 percent loss in fines in runoff, this volume was
adjusted up to a gross volume of 222,000 cu yd. Contract specifications required
that no dredged material exceed a vertical placement height of +3.5 ft MLG, but
Figure 12 (referenced to the MLG datum) indicates elevations that exceed
+3.5 ft. This resulted from the impact of an inspection conducted 13 June of the
placement area, when USACE and OAS personnel discovered several least tern
and American avocet nests containing eggs (Photo 31). The nests had been
constructed some distance from the active placement point and were not being
disturbed, but MVN decided to terminate the grading operations, along with the
dredging operations, at 2100 hr on 13 June to preclude any damage to the nests.
This rapid colonization by the least terns and American avocets, as well as other
species, is an aspect that should be considered for future dredging projects of a
similar nature.
39
Chapter 5
Beneficial Use Analysis

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