Figure 3. Dredging layout.
held in the basin until the larger solids (> 0.1 mm
through to the pump, lodging in the pump eye.
diam.) settle out, whereupon the supernatant is
Analysis of pump behavior and assessment of the
decanted over a weir and back into the Flats via an
dredging environment led to a solution. This is a
outflow pipe. The sediment retention basin was
cutter and grate system with auxiliary tines on
constructed on the Explosive Ordnance Disposal
the auger, which excludes items with a dimen-
(EOD) pad with compacted native and imported
sion larger than 13 mm (Fig. 4). Vegetation is
sheared by the cutter as it passes the top of the
gravel. Special precautions had to be taken to en-
grates. This system allowed almost continuous
sure that water from the spoils pumped by the
dredge would not percolate through the pad and
dredging in the very difficult conditions encoun-
mobilize contaminants that may lie beneath it.
tered at the Flats.
Working with the Corps of Engineers Alaska Dis-
Spoils are pumped from the dredge to shore
through 20-cm-diam. 76-m flexible rubber hose
trict, a 0.8-ha retention basin structure capable of
containing 1.2 ha-m of spoils was designed and
sections. On shore, the hose transitions to 25-cm-
diam. 12.2-m polyethylene pipe sections for the
built. Extensive testing of the pad and the basin
were conducted both at CRREL and on site to
335-m trip to a retention basin. The spoils are then
Figure 4. Cutter and grate system for dredge intake.
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