Please use this identifier to cite or link to this item: https://hdl.handle.net/11681/2874
Title: Transport of dredged sediment placed in the nearshore zone--Currituck sand-bypass study (phase I)
Authors: Schwartz, Robert K.
Musialowski, Frank R.
Keywords: Sediment transport--North Carolina
Beaches--North Carolina
Publisher: U. S. Army Corps of Engineers, Coastal Engineering Research Center
Series/Report no.: Technical paper (Coastal Engineering Research Center (U.S.)) ; no. 80-1.
Abstract: New dredge-disposal techniques may serve the dual role of aiding sand bypassing across coastal inlets, and beach nourishment, provided the dredged sediments placed seaward of the surf zone move shoreward into that zone. During the summer of 1976, 26,750 cubic meters of relatively coarse sediment was dredged from New River Inlet , North Carolina, moved downcoast by a split-hull barge, and placed in a 215-meter coastal reach between the 2- and 4-meter depth contours. Bathymetric changes on the disposal piles and in the adjacent beach and nearshore area were studied for a 13-week period (August to November 1976) to determine the modification of the surrounding beach and nearshore profile, and the net transport of the disposal sediment. The sediment piles initially created a local shoal zone with minimum depths of 0.6 meter. Disposal sediment was coarser (Mn = 0.49 millimeter) than the native sand at the disposal site (bln = 0.14 millimeter) and coarser than the composite mean grain size of the entire profile (Mn = 0.21 millimeter). Shoaling and breaking waves caused rapid erosion of the pile tops and a gradual coalescing of the piles to form a disposal bar located seaward (= 90 meters) of a naturally occurring surf zone bar. As the disposal bar relief was reduced, the disposal bar-associated breaker zone was restricted to low tide times or period of high wave conditions. The disposal bar eventually migrated landward, in some cases at a rate between 2.5 and 4.5 meters per day, although movement appeared sporadic and to coincide most directly with periods of increased wave activity. With development of the disposal bar, the inner surf zone bar was displaced landward. Sediment, some similar in appearance to disposal sediment, filled the inshore surf zone trough located landward of the surf zone bar. The trough downdrift from the disposal site also became choked with this type of material, evidencing longshore transport. In some cases, accretion occurred along the lower end of the seaward flank of the disposal bar, possibly as a result of slope adjustment and onshore sediment transport. Final surveys showed accretion at the base of the foreshore, complete filling of the surf zone trough, a platform or new trough at the initial surf zone bar position, disappearance of the surf zone bar, and generally a more seaward surf zone boundary. Profiles adjacent to the disposal area showed slight accretion seaward of the surf zone. The predominant transport direction of disposal sediment was shoreward into the surf zone (in the direction of the coarsest native sand) and then in the direction of the longshore current. During storms, the disposal bar served as a storm bar with major transport occurring in a shore-parallel direction along the bar axis. The increased width of the platform-disposal bar complex may provide additional benefits by increasing the amount of wave energy dissipation in the surf zone and hence, lessening erosion of the beach.
Description: Technical Paper
URI: http://hdl.handle.net/11681/2874
Appears in Collections:Technical Paper

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