ERDC/CHL CETN IV-22
December 1999
offshore borrow site. To improve navigability, the channel can be relocated (perhaps updrift of
the ebb shoal).
Construct a deposition basin
Sediments that would otherwise be deposited in navigation channels can be intercepted and
temporarily stored through construction of a deposition basin (Seabergh 1983, Bruun 1966). The
recommended site for a deposition basin is in a region where the wave and current climate is
mild and sand can accumulate at some distance from the channel. Removal of the trapped
sediment can be accomplished with minimal interruption to navigation, and sediments will be
less likely to be transported outside the basin by more energetic waves and currents. Deposition
basins can be constructed interior to (e.g., to the lee of a weir jetty) or exterior to (e.g., to the lee
of an updrift weir groin) the inlet.
A dual jetty system was constructed at Murrell's Inlet, South Carolina in 1977, with a 400-m
weir section constructed at 0.7-m above mean low water (mlw) on the shoreward portion of the
north jetty (Douglass 1987). The weir section was designed to allow southerly moving sand to
pass over and into a deposition basin (dredged to 6 m mlw) located within the shelter of the
jetty, but outside the navigation channel (dredged to 3 m mlw) (Figure 3). A pre-construction
hydraulic model investigation recommended that a third structure, a deflector dike, be included
to prevent the main channel from migrating into the deposition basin (Perry, Seabergh, and Lane
1978). This structure was not constructed.
Figure 3. Murrell's Inlet, South Carolina showing weir jetty,
deposition basin, and spit formation encroaching channel
(photograph dated 7 April 1982)
Results of a 9-year monitoring program indicated that sediment tended to transport over and
through the weir jetty, as designed. However, sediment then bypassed the deposition basin,
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