62. Proglacial deposits are formed beyond the glacial front by 

 sediment -laden meltwater streams issuing from the glacier. These streams are 

 usually braided in an intricate pattern and the channels frequently migrate 

 laterally so that the interfluve areas are not stable, and erosion and deposi- 

 tion occur throughout the area. Proglacial deposits are intricately bedded, 

 usually coarse-grained, and form topographically subdued outwash plains that 

 may be very extensive. Many outwash plains contain material that is suitable 

 for beach fill but, because of their complex bedding, the sediment character- 

 istics are usually not uniform and thus may require more detailed sampling to 

 determine their suitability for a given beach fill project. 



63. An example of glacial drift material that is potentially usable as 

 fill is found in the area north of Erie, PA, described in CERC MR 82-9 

 (Williams and Meisburger 1982). Here, a large submerged ridge of glacial till 

 and stratified drift (believed to be a moraine formed near the end of the last 

 glaciation) was drowned by the filling of Lake Erie. As the lake filled, the 

 moraine was subject to waves and littoral processes that washed and sorted the 

 till material forming beach and dune deposits of relatively clean sand and 

 gravel. Many other examples of erosion and selective sorting of till sedi- 

 ments which formed paleo-coastal features can also be found in marine areas. 



Inter-Reef Deposits 



64. A type of sediment deposit that occurs in the continental United 

 States south of Boca Raton, FL was discussed in CERC TM-29 (Duane and 

 Meisburger 1969). Low, reef-like, shore-parallel ridges have formed inter- 

 reef troughs in this area that have partially filled with predominantly bio- 

 genic sand and gravel-size sediment. Although not ideally suited for beach 

 fill, this material was the only unconsolidated sediment available in the area 

 within feasible dredging depths and large quantities were used for beach fill 

 on adjacent beaches. 



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