IV. Retreating Shorelines
229
At Kings Bay, Georgia (U.S.A.), 688,00 m 3 (900,000 cu. yd.) were to be
excavated from the bay channel section to a depth of 15 m (51 fl). The work has
been performed by cutter dredgers and all of the material pumped through
pipelines to replenish local beaches. Still at Kings Bay, the excavation of 4.3
million m 3 (5.6 million cu. yd.) from the entrance channel section of the project
was performed by hopper dredgers and bucket dredgers. The material was then
hauled to an open water disposal area located in the Atlantic Ocean.
At Mobile Harbor, cutter dredgers excavated maintenance material, pumping
through relatively short pipelines to open-water disposal areas located in the bay
near the channel. The bay channel improvement work was done by bucket
dredgers and dredged material transported by hopper barges over an average oneway distance of 40 km (25 miles) to an open-water disposal area in the Gulf of
Mexico. Hopper dredgers excavated the Bar channel and transported material
about 6.2 km (4 miles) to an open-water disposal area in the Gulf. All the
material deriving from the improvement work was used to construct a stable
underwater berm.
For the Kill van Kull project in New York, bucket dredgers loaded with hopper
barges, transported the dredgings to an open water site in the Atlantic Ocean.
(Murden, W.R., 1987, The Station of Dredging in the USA, now and in the near
future : 47 AItg. Coast. Eng. Res. Bd (May 19), 21-24).
As 95 percent of the material, excavated each year in the U.S.A. is not polluted,
underwater berms provides a unique and beneficial alternative to the traditional
disposal of dredged material.
Of the two viable approaches to the construction of underwater berms, the feeder
beach concept involves the placement of beach quality sand in relatively shallow
water, with the expectation that the material will move downdrift, but remain in
the nearshore coastal region, or area between the surf zone and the 9 m (30 r)
isobath. A stable berm involves placement of dredged material in deeper waters,
less subject to waves and currents. The justified expectation is that the material
will remain in place. In contrast to the feeder berm, a wide variety of dredged
material (silts and fine-grained sand) can be used in the construction of stable
berms.
The objective of the feeder placement concept is to add sand, which will result in
a less steep underwater slope and contribute to a reduction in the erosion effects
on the shoreline. Dredging costs can be reduced, nearshore disposal sites being
generally closer to the dredging sites than designated offshore disposal sites.
229
At Kings Bay, Georgia (U.S.A.), 688,00 m 3 (900,000 cu. yd.) were to be
excavated from the bay channel section to a depth of 15 m (51 fl). The work has
been performed by cutter dredgers and all of the material pumped through
pipelines to replenish local beaches. Still at Kings Bay, the excavation of 4.3
million m 3 (5.6 million cu. yd.) from the entrance channel section of the project
was performed by hopper dredgers and bucket dredgers. The material was then
hauled to an open water disposal area located in the Atlantic Ocean.
At Mobile Harbor, cutter dredgers excavated maintenance material, pumping
through relatively short pipelines to open-water disposal areas located in the bay
near the channel. The bay channel improvement work was done by bucket
dredgers and dredged material transported by hopper barges over an average oneway distance of 40 km (25 miles) to an open-water disposal area in the Gulf of
Mexico. Hopper dredgers excavated the Bar channel and transported material
about 6.2 km (4 miles) to an open-water disposal area in the Gulf. All the
material deriving from the improvement work was used to construct a stable
underwater berm.
For the Kill van Kull project in New York, bucket dredgers loaded with hopper
barges, transported the dredgings to an open water site in the Atlantic Ocean.
(Murden, W.R., 1987, The Station of Dredging in the USA, now and in the near
future : 47 AItg. Coast. Eng. Res. Bd (May 19), 21-24).
As 95 percent of the material, excavated each year in the U.S.A. is not polluted,
underwater berms provides a unique and beneficial alternative to the traditional
disposal of dredged material.
Of the two viable approaches to the construction of underwater berms, the feeder
beach concept involves the placement of beach quality sand in relatively shallow
water, with the expectation that the material will move downdrift, but remain in
the nearshore coastal region, or area between the surf zone and the 9 m (30 r)
isobath. A stable berm involves placement of dredged material in deeper waters,
less subject to waves and currents. The justified expectation is that the material
will remain in place. In contrast to the feeder berm, a wide variety of dredged
material (silts and fine-grained sand) can be used in the construction of stable
berms.
The objective of the feeder placement concept is to add sand, which will result in
a less steep underwater slope and contribute to a reduction in the erosion effects
on the shoreline. Dredging costs can be reduced, nearshore disposal sites being
generally closer to the dredging sites than designated offshore disposal sites.