penetrate this reflector contain a wide variety of materials, often of dis- 

 tinctly different character than the shoal material. 



39. Where they occur, linear shoals provide the most favorable pros- 

 pects for fill material because of their dominantly sand-size composition, 

 large volume, general uniformity, and accessibility. An added advantage is 

 their distinctive morphology that can usually be recognized on large to medium 

 scale contoured bathymetric charts; thus, they can be targeted efficiently for 

 more intensive geophysical and coring operations than areas of lesser 

 potential . 



40. Linear shoals, especially when located on the shoreface or inner 

 continental shelf where their crests are at a relatively shallow depth, may 

 significantly alter waves passing over them. Any borrow source operation that 

 results in changing the shoal bathymetry can produce undesirable effects on 

 nearby shore areas by increasing or focusing wave energy impinging on the 

 shore. This disadvantage can be avoided or minimized by study of the possible 

 modification in wave characteristics, if any, that may occur by comparing wave 

 transformation for previous post-dredging shoal morphology. 



41. The main ecological effects of dredging on linear shoals are direct 

 mortality of sessile benthonic organisms, and creation of silt plumes in the 

 water column that may affect the biological conditions in peripheral areas. 



Arcuate Shoals 



42. Swift et al . (1972) defined two general classes of arcuate shoals: 

 cape-associated (Figure 4) and estuary-associated (Figure 5) . Cape-associated 

 shoals occur off cuspate forelands where there is a convergence of littoral 

 drift. Estuary- associated shoals occur near the mouths of large estuaries and 

 sounds where littoral drift is intercepted by tidal currents flowing into and 

 out of the entrance. Remnants of arcuate shoals have been recognized extend- 

 ing from the existing capes and estuaries to well out on the continental 

 shelf. These shoal fields, termed shoal retreat massifs (Swift 1975), were 

 formed and abandoned as the parent capes and estuaries retreated across the 

 shelf during the Holocene transgression. 



43. In many parts of active shoal areas, especially arcuate shoals, 

 direct data collection is restricted by shallow crest depths and shoal mobil- 

 ity, which create hazardous navigation conditions. Detached linear shoals and 



19 



