The average floodflow discharge rate is 2.57 cubic feet per second- 

 foot and, from the area under the curve, the flow volume per foot of weir 

 crest during floodtide is 25,800 cubic feet per foot. For ebb flow, the 

 average discharge rate is 2.83 cubic feet per second-foot and the volume 

 is only 15,800 cubic feet per foot. The results for (b) above (weir 

 crest 1.5 feet below MTL) are given in Table 3 and shown graphically in 

 Figure 16. The average discharge rate is 4.50 cubic feet per second-foot 

 during floodtide and 4.52 cubic feet per second-foot during ebbtide. The 

 corresponding volumes per foot of weir length are 65,200 cubic feet per 

 second-foot and 25,200 cubic feet per foot on flood and ebb tides, 

 respectively. 



Table 3. 



Weir discharge calculations for 

 weir crest 1.5 feet below MTL. 



Time, t/T 

 (fraction of 

 tidal cycle) 



h (ocean) 1 

 (ft) 



h (channel) 2 

 (ft) 



q 



(ft 3 /s-ft) 



0.15 



















0.20 





0.70 





0.45 



1.48 



0.25 





1.50 





1.20 



3.59 



0.30 



V 



2.20 



V 



1.90 



5.54 



0.35 





2.95 





2.70 



6.90 



0.40 





3.50 





3.30 



7.39 



0.45 





3.85 





. 3.80 



4.12 



0.50 





4.00 





4.10 



-6.19 



0.55 



h 2 



3.95 



h l 



4.05 



-6.11 



-0.60 





3.60 





3.60 







Obtained from tidal curve for oceanside of weir 

 in Figure 11. 



2 0btained from tidal curve for channel side of 

 weir in Figure 11. 



When the weir-crest elevation is 1.5 feet below MTL there is a larger 



difference between the inflow and outflow volumes; i.e., 65,200 - 25,200 



= 40,000 cubic feet per second-foot as compared with 25,800 - 15,800 

 = 10,000 cubic feet per second-foot when the weir crest is at MTL. 



Changes in the weir elevation, jetty geometry, and inlet hydraulic 

 characteristics will cause changes in the tidal curves on the inlet side 

 of the weir. Since the tidal curves in Figure 11 were obtained in a 

 model test with a weir elevation at MTL, they will not exactly pertain 

 to the condition when the weir is 1.5 feet below MTL. Therefore, the 

 solution to this part of the problem is only an approximation. The 

 problem is determining a priori the tidal curves and phase lag that will 

 be obtained for the jetty geometry and weir elevation of a given inlet. 

 At present, the only way to establish the hydraulic characteristics of an 

 inlet-weir system is to conduct a hydraulic model study. At the same 

 time as the inlet tidal curves are derived from the model, the fraction 

 of the tidal prism entering the inlet across the weir can also be 

 determined. 



The volume of water carried over the weir by wave overtopping can be 

 estimated from methods presented in Section 7.22 of the SPM (U.S. Army, 



31 



