equilibrium dissipation is independent of both wave characteristics and water 
depth to the accuracy of available data (Moore 1982). 
136. The relationship between cross-shore sediment transport rate and 
offshore bathymetric change is described by the one-dimensional continuity 
equation, written in the following form: 
dx aie (10) 
dt dh 
in which the distance x toa known contour line is written as a function of 
the change, or gradient, in the sediment transport rate. For example, if 
more sediment enters the system than exits, sediment accumulates on the bottom 
and the distance from a fixed point on the beach to the same contour line 
increases. 
Implementation and Assumptions 
137. Equation 10 is numerically solved by an implicit scheme at each 
time step for the time-dependent surge level to yield a total volume of 
sediment eroded or deposited in the area bounded approximately by the water 
line and the breaker line. Recession of the dune and berm is related to the 
total volume deposited offshore through the assumption that this deposited 
volume originated from the dune and berm complex. If onshore transport is 
indicated, the offshore volume of erosion is assumed to accrete uniformly on 
the berm face. Accretion to the dune face is not allowed. 
138. Only cross-shore sediment transport is considered in this one- 
dimensional approach. This points out an important assumption that alongshore 
sediment transport is negligible with respect to the cross-shore component 
during a storm. This is often not a valid assumption, but two-dimensional 
considerations were beyond the scope of model development. Longshore varia- 
tions will be introduced through empirical considerations. 
139. The input data necessary for simulating the impact of a storm 
event are as follows: 
a. The dune area is specified according to a height, distance to 
edge of the dune face (from some arbitrary reference point 
landward of the feature), and slope of the dune face. 
In 
The berm zone is specified according to a width (if a horizon- 
tal transition between the dune face and berm face exists; 
otherwise, zero), height, and berm face slope. 
A shape parameter, A, (Equation 6) is defined to provide a 
best fit to the active portion of the offshore profile. 
10 
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