TRANSPORT OF DREDGED SEDIMENT PLACED IN THE NEARSHORE 

 ZONE - CURRITUCK SAND -BYPASS STUDY (PHASE I) 



by 



Robert K. Schwartz and Frank R. Musialowski 



I. INTRODUCTION 



1 . Purpose . 



The Corps o£ Engineers is responsible for the dredging maintenance of navi- 

 gation channels through small, shallow coastal inlets. Environmental and eco- 

 nomic factors usually place prohibitive constraints on inland placement of 

 dredged material. Moreover, both inland and deepwater placement of dredged 

 sediment results in a permanent loss of sand to the overall littoral system. 

 Although side-cast dredging has sometimes been fairly effective, the side-casted 

 sand placed adjacent to a dredging site has a relatively high potential for re- 

 entering the entrance channel . 



In 1975, the U.S. Army Engineer District, Wilmington, placed a split-hull 

 barge, the Currituck, in service. The Currituck can transfer sediment exca- 

 vated from coastal inlet entrance channels to a shallow nearshore zone down- 

 drift of a dredged inlet (Fig. 1). When fully loaded, the Currituck can release 

 its load (usually between 190 and 230 cubic meters) at a 2 -meter -minimum water 

 depth. For beach nourishment purposes, this sediment transfer operation is 

 conducted with the view that the placed or dumped materials will be transported 

 by wave-induced currents to the beach and surf zones, thus aiding natural sand 

 bypassing around the inlet and nourishing shores adjacent to the inlet complex. 



The offshore placement of dredged inlet sediment as an approach to beach 

 nourishment is an attractive concept for several reasons. The split-hull barge- 

 type of disposal operation is time-efficient and generally less expensive than 

 alternate means of disposal. The system eliminates the need for double handling 

 or for land-based equipment necessary to place sand on the beach. In addition, 

 sand from the maintained part of the inlet is of excellent quality for beach 

 nourishment due to its source relationship to the littoral zone and due ta high- 

 energy winnowing (sorting) conditions in the inlet itself. Moreover, recent 

 studies indicate that the dredging (sediment -handling) process further improves 

 the textural characteristics of the native sand, making it even more suitable 

 for beach fill (Hobson, 1977a, 1977b). Finally, the size characteristics of in- 

 let sand improve the chances of selective shoreward transport from the offshore 

 zone. This final aspect is discussed further in the following sections. 



The success of the offshore disposal operations is dependent upon sand 

 placed seaward of the surf zone moving shoreward into that zone as a result of 

 wave transport. An experiment was conducted during the summer of 1976 to test 

 that concept, using the Currituck sand transfer system, and to examine the 

 modification and net displacement of sediment placed in shallow water seaward 

 of the surf zone along an open coast. This report discusses the placement, 

 modification, and net transport of the sediment. A summary report on the 

 initial findings was previously published (Schwartz and Musialowski, 1977). 



