during those times would contribute to a faster movement of material through the area to the 

 west. 



Sand sources 



Four areas can be considered as sources of sand for use in a bypass system. The choice of a 

 particular source may to some extent dictate the method of bypassing. The pros and cons of each 

 of the four locations are discussed below. 



a. The updrift fillet contains a substantial volume of sand both subaerially and subaqueously 

 that could be used for bypassing. By comparing the shoreline positions and nearshore 

 slopes of the 1933 (pre-inlet) and 1995 hydrographic surveys, at least 4.1 million m 3 



(5.4 million yd 3 ) of material can be identified in the first 1 km of updrift fillet. The design 

 bypass quantity of 100,000 m 3 /year (13 1,000 yd 3 /year) is only 2.4 percent of the total 

 volume in the fillet, so bypassing from this source should have minimal impact on the 

 fillet. For design, the 1 00,000-m 3 (131 ,000-yd 3 ) annual volume (or part thereof if 

 combined with other sources) could be bypassed from the fillet using either a fixed or 

 semifixed plant on the subaerial portion of the fillet or a floating or semifixed plant on the 

 subaqueous portion of the fillet. In the case of a fixed or semifixed plant (subaerial or 

 subaqueous), a submerged pipeline could transport the material to the downdrift beach. 

 Concerns associated with using the updrift fillet as a sand source may include: (1) danger 

 of undermining the east jetty if too much material is removed from near the toe; 

 (2) opposition by property owners to removing sand from the first 1 km of beach (even 

 though this is County property) for fear that their fronting beaches will erode more rapidly 

 to replace the removed material. The small percentage of material required and the rate of 

 resupply from the east makes this concern not scientifically warranted; and (3) beach 

 bathing safety related to equipment on the beach and any holes/craters formed. 



b. Use of the ebb shoal as a source of sand for bypassing can be controversial. However, 

 HQUSACE (1991) states that if the bypassing amount is a small percentage of the total 

 ebb shoal volume, removal of this material should cause no problems. Removal of large 

 percentages of material is believed to have significant impacts on the local coastal 

 processes, but these impacts have not yet been adequately documented at inlets (Cialone 

 and Stauble 1998). The 1996 SHOALS survey indicates that the ebb shoal contains 

 approximately 6.4 million m 3 (8.4 million yd 3 ) of sand. The design bypass rate of 

 100,000 m 3 /year (131,000 yd 3 /year) would only account for about 1.6 percent of the total 

 ebb shoal volume. Strategic dredging to "skim" off small volumes of material (i.e., from 

 the seaward slope) over large areas should minimize ebb shoal and downdrift impacts 

 (paragraph (1) below), especially if the ebb shoal is nearing equilibrium. The advantage of 

 this location for a sand source is that material naturally bypassing the inlet comes from the 

 ebb shoal. A bypass system that takes from the ebb shoal thus works in the same manner 

 as nature. Using the ebb shoal as a sand source for bypassing will require a floating plant 



Chapter 4 Design Criteria 45 



