0.1 



0.2 



0.3 0.4 0.5 0.6 0.7 



Time ( froction of tidal cycle ),t/T 



0.8 



0.9 



Figure 16. Discharge over weir as a function of time during a tidal cycle 

 (weir 1.5 feet below MTL). 



Corps of Engineers, Coastal Engineering Research Center, 1977). This 

 involves determining the time variation of freeboard during a tidal cycle 

 and the variation of water depth along the weir section, and then from 

 these variations computing the overtopping rate. Since the weir section 

 will not normally be perpendicular to the direction of wave approach, the 

 overtopping volume computed should be reduced appropriately. In the 

 absence of specific criteria on which to base an overtopping rate reduc- 

 tion, a reduction factor equal to the square of the cosine of the angle 

 between the weir and incoming wave ray is suggested. Therefore, 



q' = q cos' 



(9) 



where q' is the reduced overtopping rate, q the overtopping rate if 

 the waves were approaching perpendicular to the weir, and a the angle 

 between the incident wave ray and the axis of the weir. 



*************** EXAMPLE PROBLEM 2*************** 



GIVEN ; The beach profile along the vertical sheet-pile section of a jetty 

 is as shown in Figure 17. The wave height at the end of the weir is 3.0 

 feet and the wave period is 7.0 seconds. The tidal curves are as given 

 in Figure 11. The weir crest is at MTL and the waves approach the weir 

 at a 45° angle. 



32 



