Sandy Hook. Evident in the regional perspective of longshore sand transport is a 

 tendency of increasing northbound transport with distance to the north because of 

 increasing wave sheltering by Long Island. These estimates of the average net 

 longshore sediment transport and longshore transport gradient can serve as a 

 means of calibrating the longshore sand transport mode! in GENESIS. 



Calibration to shoreline. Inhial calibration of GENESIS began with com- 

 parisons of shoreline change between October 1996 and April 1997. (During this 

 period, the Long Branch directional wave gauge was inoperative, but this period 

 is the only one available in which no shoreline disturbances related to placement 

 of beach fill are evident.) Gated boundary' conditions were established at each 

 lateral boundary to represent the prefill conditions south of the hot-spot region. 

 Calibration to shoreline change resulted in a A'/ = 0.8 and A': = 0.4. The resulting 

 annual net longshore sand transport rates at the lateral boundaries are 

 1 ,3 1 0.000 cu yd/year ( 1 ,000,000 cu m/year) to the north at the northern boundary 

 and 209.000 cu yd/year (160,000 cu m/year) to the north at the southern 

 boundary, which are considered excessively high (compare Caldwell 1966). 



The transport rate at the north boundary and the transport gradient across the 

 modeled domain are not rational in light of previous estimates of the average- 

 annual transport rate. The overestimation of the calibrated longshore transport 

 rate is probably caused by contamination through cross-shore adjustment of the 

 beach fill by interseasonal differences in the short record. The beach profiles of 

 the initial calibration shoreline (October 1996) were likely in a near-summer 

 condition and steeper than equilibrium because of the December 1995 emergency 

 beach fill. This beach profile would be expected to adjust offshore during the 

 erosive wave conditions of winter, resulting in shoreline recession that can only 

 be accounted for by longshore transport rate in the shoreline change model. 

 Compensating for the cross-shore profile adjustment with the shoreline change 

 model results in the relatively large value of A/ and, consequently, large long- 

 shore transport rates. Because of the irrational results obtained with the cali- 

 bration to available shoreline positions, calibration to an accepted sediment 

 budget was initiated. 



Calibration to sediment budget. In addition to the complications asso- 

 ciated with the available shoreline data, lateral boundarj' conditions representing 

 the prefill condition south of the hot spot are inappropriate for evaluating the 

 functioning of the beach fill after completion of Section I (Figure 1). The gated 

 boundary condition specified in the initial calibration functions to allow a 

 relatively constant flux of sand into the model domain. As fill material placed to 

 the south of the hot spot erodes under exposure to the regional gradient in the 

 transport rate, the supply of sand available for transport north into the model 

 domain is expected to decrease. With this in mind, a moving boundary condition 

 was applied to the south boundary to represent the eroding condition of the beach 

 fill. The initial shoreline position was established to coincide with the shoreline 

 position of the construction template adjusted to the equilibrium beach-profile 

 shape. The rate of shoreline movement at the south boundary was specified such 

 that the shoreline would be eroded to the prefill condition at the end of the beach- 

 fill design life (6 years). Shoreline movement to the prefill condition was 

 selected because movement to the prefill condition is a conservative approach of 



Chapter 3 Functional Design 



21 



