The overtopping rate as a function of time through a tidal cycle is shown 

 in Figure 18. A cutoff for the curve was arbitrarily assumed at Q = 600 cubic 

 feet per second. The area under the curve is approximately equal to the 

 volume of water carried over the weir by waves during the tidal cycle. Obvi- 

 ously, if the wave conditions changed during the tidal cycle or if other tidal 

 conditions prevailed, the overtopping volume would be different. The effect 

 of a change in weir length on the total volume of overtopping can also be 

 investigated. 



600 - 



S 400 - 



o 300 - 



- 200 - 



100 - 



0.2 0.3 0.4 0.5 0.6 0.7 0.8 

 Time ( fraction of tidal cycle), t/T 



Figure 18. Time variation of overtopping rate. 



V. WAVE CONDITIONS IN DEPOSITION BASIN 



An important factor in establishing the weir-crest elevation is the level 

 of wave action that can be tolerated in the deposition basin. The allowable 

 level of wave action is dictated by the operating characteristics of the 

 dredge used to perform the bypassing and by the amount of protection required 

 by vessels navigating the channel. 



The level of wave action in the deposition basin for a given weir-crest 

 elevation can be estimated from available wave transmission formulas. Assum- 

 ing no wave energy enters between the jetties and no wave energy passes 

 through the weir section, transmission is by overtopping only; Goda's equation 

 (Goda, Takeda, and Moriya, 1967; Goda, 1969; Seelig, 1976) can then be used, 

 given by 



H t 



-£■ = 0.5 



1 - sin 



2a V H. / 



(ID 



where 

 H 



t 



H i 

 h 



d„ 



transmitted wave height 



incident wave height 



height of structure crest above the bottom 



water depth at the structure 



35 



