Dean and Walton (1973) have presented a methodology for the calculation of 

 beach material volume (sand, shell, etc.) in the ebb-tidal delta complex. 

 This methodology, shown in Figure 4-84, is somewhat subjective because it 

 relies on the ability to interpret the "no inlet" bathymetry. It involves 

 calculating the volume difference between the present and "no inlet" 

 bathymetries. 



Walton and Adams (1976) found that the volume of sand comprising the ebb- 

 tidal delta is a function of both the tidal prism of the inlet and the level 

 of vBve activity on the ebb-tidal delta. They have presented equations for 

 the volume of sand stored in the ebb-tidal delta as a function of tidal prism 

 for highly exposed (Pacific), moderately exposed (Atlantic and western gulf), 

 and mildly explosed (eastern gulf) coasts in terms of average wave activity. 



These relationships are, in metric (a) and English (b) units, 

 V = 1.975 X 10~^ pl*23 Pacific coast 



(4-7 la) 



V = 8.7 X lO"^ P^'^^ 



Pacific coast 



(4-71b) 



V = 2.384 X 10~^ P^*^'^ 



Atlantic & western gulf coast 



(4-72a) 



V = 10.5 X 



10-5 pi. 23 



Atlantic & western gulf coast 



(4-72b) 



V = 3.133 X lO"''* P^*^"^ 



Eastern gulf coast 



(4-73a) 



— S 1 9"^ 

 V = 13.8 X 10 P 



Eastern gulf coast 



(4-73b) 



where V is the volume of sand (or beach-type material) stored in ebb-tidal 

 delta complex in cubic meters (cubic feet) and P is the tidal prism in cubic 

 meters (cubic feet) . 



This type of analysis assumes that the inlet has been relatively stable in 

 position. A similar approach to the sand storage in inner flood-tidal deltas 

 has not been developed, owing partially to the complexity of the inner inlet 

 physiographical system. 



It is well known that flood-tidal deltas have a capacity to trap enormous 

 quantities of sand due to the lack of wave action penetration into the lagoon 

 on ebb tide and consequent reduced entrainment of sediments into the ebb flow. 



Dean and Walton (1973) have shown that a relatively stable inlet will trap 

 sand in its interior shoals until the system becomes filled to capacity (i.e., 

 achieves an equilibrium shoaling volume). The history of the filling of one 

 such inlet, presented in Figure 4-85, shows that shoaling over a continuous 

 period of 70± years has occurred at a reduced rate with time. 



In the event the channel frictional characteristics are changed such that 

 the inlet becomes hydraulically unstable, it will close completely (a 



4-174 



