front major foredune systems in different geographical locations. For 

 example, fine sand beaches front a massive foredune system on Mustang 

 Island, Texas, and coarse sand beaches front dunes on the Cape Cod spits, 



Godfrey (1972) discusses the effect of a foredune system on the 

 long term stability of the barrier islands of the Cape Hatteras and Cape 

 Lookout National Seashores, North Carolina. Important implicit asstimp- 

 tions of the discussion are that no new supply or inadequate new supplies 

 of sand are available to the barrier island system, and that rising sea 

 level is, in effect, creating a sand deficit by drowning some of the 

 available island volume. The point of the geomorphic discussion is that 

 under such conditions the islands must migrate landward to survive. A 

 process called "oceanic overwash" (the washing of sand from low foredunes 

 or from the beach over the island crest onto the deflation plain by over- 

 topping waves) is described as an important process in the landward migra- 

 tion of the islands. Since a foredune system blocks overtopping and pre- 

 vents oceanic overwash, foredunes are viewed as a threat to barrier island 

 stability. 



Granted the implicit assumptions and a geologic time frame, the 

 geomorphic concept presented has convincing logic and probably has merit. 

 However, the assumptions are not valid on all barrier islands or at all 

 locations in most barrier islands or at all locations in most barrier 

 island systems. Too, most coastal engineering projects are based on 

 a useful life of 100 years or less. In such a short period, geologic 

 processes, such as sea-level rise, have a minor effect in comparison with 

 the rapid changes caused by wind and waves. Therefore, the island crest 

 elevation and foredune system will maintain their elevation relative to 

 the mean water level on stable or accreting shores over the life of most 

 projects. On eroding shores, the foredunes will eventually be eroded 

 and overwash will result in shoreward migration of the island profile; 

 sand burial and wave and water damage will occur behind the original 

 duneline. Therefore, planning for and evaluation of the probable suc- 

 cess of a foredune system must consider the general level of the area of 

 the deflation plain to be protected, the rate of sea level rise, and the 

 rate of beach recession. 



4.7 SEDIMENT BUDGET 

 4.71 INTRODUCTION 



4.711 Sediment Budget . A sediment budget is based on sediment removal, 

 transportation and deposition, and the resulting excesses or deficiencies 

 of material quantities. Usually, the sediment quantities are listed 

 according to the sources, sinks, and processes causing the additions and 

 subtractions. In this chapter, the sediment is usually sand, and the 

 processes are either littoral processes or the changes made by man. 



The purpose of a sediment budget is to assist the coastal engineer 

 by: identifying relevant processes; estimating volume rates required for 

 design purposes; singling out significant processes for special attention; 

 and, on occasion, through balancing sand gains against losses, checking 

 the accuracy and completeness of the design budget. 



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