Seawall 



188. A seawall, or, in general, any shore-parallel nonerodible barrier 

 such as a rocky cliff, imposes a constraint on the position of the shoreline 

 because the shoreline cannot move landward of the wall. Hanson and Kraus 

 (1985, 1986b) developed a procedure for calculating the position of the 

 shoreline constrained by a seawall. The procedure is consistent with shore- 

 line response modeling theory and has the following three properties: 



a. The shoreline in front of a seawall cannot recede landward of 

 the wall . 



b. Sand volume is conserved. 



c. The direction of longshore sand transport at the wall is the 

 same as that of the potential local transport. 



GENESIS first calculates longshore sand transport rates along the beach based 

 on the assumption that the calculated amount of sand is available for trans- 

 port (the potential transport rate). At grid cells where the seawall con- 

 straint is violated, the shoreline position and the transport rate are 

 adjusted. These quantities in neighboring cells are also adjusted, as 

 necessary, to preserve sand volume and the direction of transport. The 

 calculation procedure is complex, and the reader is referred to Hanson and 

 Kraus (1986b) for full details. Flanking of the seawall is not possible since 

 it would lead to a double-valued shoreline position at the same grid cell. 



Beach Fill 



189. Beach fill is a traditional and increasingly popular method of 

 shore protection and flood control, and nourished beaches also have value for 

 recreational, commercial, and environmental purposes. Fill is commonly placed 

 together with the building of coastal structures such as groin fields and 

 detached breakwaters. GENESIS is capable of representing the behavior of 

 fills under the following assumptions: 



a. The fill has the same median grain size as the native sand. 



b. The profile of the fill represented in the model has the 

 equilibrium shape corresponding to its grain size. 



c. The berm height of the nourished beach is the same as the 

 natural beach. 



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