108 



^ = ii = -|^+SS + B (7.17) 



at at ax 



in which the first term on the right hand side is the local convergence of 

 cross -shore bottom sediment transport, the second term, SS, represents 

 deposition of suspended sediment and the last term is the local biogenic 

 production. The required magnitudes of each of these in order to 

 compensate for a eustatic sea level rise of 1.2 mm/yr alone is presented 

 below. 



Convergence of Cross -shore Sediment Transport - Considering a shelf 

 width of 40 km 



q^ = 40,000 m(0.0012 m/yr) = 48 m^/yr (7.17a) 



Suspended Sediment Deposition 



SS = 0.0012 m/yr (7.17b) 



Biogenic Production 



b = 0.0012 m^/m2/yr (7.17c) 



At present, knowledge is extremely poor concerning the rates of the three 

 components addressed above. However, until improved quantification is 

 available, all should be regarded as potentially substantial contributors 

 to the shoreface sediment budget. 



7.3.2 Dynamical Considerations 



It is clear that there are net shoreward directed hydrodynamic forces 

 acting on a sediment particle; otherwise an upward sloping beach could not 

 be in equilibrium against the forces of gravity. The near-bottom flow 

 field due to a storm system is complex and consists of net forces and 



