facilitate rapid advance of the fill and close the remaining portion of the breach, a narrow mound
of sand was bulldozed across the breach at slack tide to prevent water flow through it (Figure 9).
Once the flow of water was stopped, additional material was added to the narrow mound to fill
the remaining design template without the losses caused by the tidal current. The final closure
began at high tide and was completed at low tide, thus allowing several hours for the berm to be
widened the berm before wave runup began to erode the berm at higher water levels. No
material was stockpiled in advance, but a 2,300 cy yd/hour dredge production rate provided a
sufficient source of sand to build a small dike across the remaining breach. It was observed that
the final closure would have been facilitated by stockpiling sand on the bank opposite the dredge
pipe outlet. The stockpile would have allowed sand to be pushed from both sides of the breach.
Figure 9. A view of the first attempt to complete the closure looking to the west from
the eastern bank of the breach (Wutkowski 2004).
Surveys of the breach area indicated that approximately 440,000 cu yd was placed in the breach
area, with sand loss of only approximately 8 percent. Sand losses were low compared to beach
nourishment projects, which typically range from 10 to 20 percent. The low loss is attributed to
the medium-coarse sand that resisted dispersing forces of the waves and current during
placement. The rebuilding of NC12 was completed on 18 November 2003.
MECHANICAL BREACHING: Breaches can have positive consequences and, therefore,
creation of controlled breaches is common. Breaches may lower the water level in coastal
ponds, lagoons, and bays, thereby reducing the risk of flooding to adjacent property; decrease or
increase water salinity in the pond, lagoon, or bay; improve water quality by promoting water
exchange; or facilitate the migration of marine organisms. Therefore, it can be desirable to
mechanically breach a coastal barrier, if its size and longevity of are limited (controlled). The
following case studies document several experiences with mechanical breaching.
Rollover Pass, Texas. Rollover Pass is an inlet created by mechanical breaching that is located
on Bolivar Peninsula, 22 miles northeast of Galveston, Texas. Bolivar Peninsula is a low barrier
16
Previous Page
