142
R.H. Charlier and Chr. P. De Meyer
The model can now be conveniently handled into two stages. In the first, the
beach above MSL is assumed sufficiently wide that any seawall behind it has no
significant effect on the alongshore sediment transport. This situation is shown
diagrammatically in Fig. 33. and can be represented by the equation :
BH
Y -> Yw + -(96)
tan/?
where yw is the distance of the sea wall from the baseline.
Considering sediment motion across two lines fix apart and perpendicular to the
base line (y = 0), for a small time interval (St, we obtain for the change in beach
volume in that strip :
b'V = &(Q - (Q + ~ c'Txll
(97)