Anchorage, average yearly precipitation is equiva-
Table 11. Retention basin model results
lent to 38.7 cm of water. Table 11 shows the results
summary.
of the model for dredging a 0.8-ha site over an
eight-day period. As is indicated, the amount of
water that will pass through the basin into the EOD
System characteristic
Pad
Weir
pad is about one quarter what would normally
pass through the pad through natural precipita-
Cumulative totals in cubic meters
969
17,684
tion. This model, as well as the results of the tests
Equivalence in cm of water/year
12
218.5
done on the physical characteristics of the EOD
pad and retention basin materials, indicated that
the basin as designed would satisfy the require-
area with the peaty silt as a liner is achievable. Fig-
ments of the RPMs as well as be feasible for the
ure 20b shows that as long as the water content is
pilot dredge program. The RPMs thus approved
in the range of about 3860%, the peaty silt will
the use of the EOD pad for the dredge spoils re-
provide the desired protection against infiltration.
tention basin.
At water contents below 38% the hydraulic con-
ductivity of the peaty silt increases significantly,
much as would be expected.
SITE PREPARATION
Prior to deployment of the dredge, much site
Model calculation
preparation and construction work needed to be
A model was then constructed and data from
carried out. Among the major projects were con-
the preceding tests input to determine feasibility
struction of the retention basin and its associated
of the design (Appendix B). One important factor
structures, the drop inlet structure and inflow
in the determination of the adequacy of the de-
pads; a road from the EOD pad to Clunie Creek,
sign is the additional water that will be percolating
where the dredge was to be deployed into the
through the pad because of the retention basin. In
Figure 21. Retention basin berms.
24
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