Currents in 1965 and July 1976 were measured only in the center of 

 the inlet throat; therefore, a relationship between total discharge through 

 the inlet and average centerline velocity was needed to determine the 

 tidal prisms. The June 1976 centerline measurements showed that Q^ = 19,050 

 V^, where Qy is the instantaneous discharge through the entire pass, and V^ 

 is the average speed at the centerline of the gorge. This relationship was 

 used to calculate the July discharges (Fig. 35). However, no centerline 

 measurements were made in 1962, so a predicted centerline speed was calculated 

 using the observed 1976 relationship V^ = 1.05 V . Using equation (5) and the 

 appropriate flow areas, discharges for 1965 conditions were calculated 

 (Fig. 36). Tidal prisms were obtained by integrating the area beneath the 

 discharge curves of Figures 35 and 36 (see Table 4). 



In 1969 no discharges were measured and tidal prisms were obtained by 

 multiplying the bay tidal range by the bay area affected by that range. The 

 mean tidal prisms for July and August 1969 in each bay (Table 5) indicate that 

 West Bay accepts most of the flow passing through San Luis Pass. 



Table 5. Mean tidal prisms in San Luis Pass, July and August 1969. 



Location 



Tidal prism 

 (ft3 X 10"^) 



Total flow 



through pass 



(pet) 



Bay area 



(ft2 X 109) 



Bay tidal 

 range 

 (ft) 



West Bay (Alligator Point) 



Chocolate Bayou 



Christmas and Bastrop Bays 



1.76 

 0.16 

 0.31 



79 



7 

 14 



1.93 



0.167 



0.318 



0.91 

 0.94 

 0.98 



Total 



2.23 



100 



2.42 



0.92 



For comparison purposes, prisms based on bay tidal ranges were also com- 

 puted for discharge measurement periods (Table 4) . Relationships between the 

 ranges measured at the three locations in 1969 were used to arrive at the 

 following equation for San Luis Pass tidal prism, P: 



West Bay prism Chocolate Bayou prism Christmas and Bastrop Bays prism 



P = \,b Rwb 

 where 



(^ '^.b)(Acb) 



+ 



0.91 ^b^V+b^ 



(6) 



^^b 



\rb 

 ^Cb 



\+b 



tidal range at Alligator Point in West Bay 



area of West Bay (to Carancahua Reef only), 1.06 x 10^ square 

 feet 



area of Chocolate Bayou, 0.17 x 10^ square feet 



area of Christmas and Bastrop Bays, 0.32 x lO'^ square feet 



ind 



= (1.06 R^b + 0-176 R^b + 0-3« %h^ X 10^ 



= 1.58 X 10- 



\b 



Using both discharge and range-area tidal prisms, the average San Luis Pass 

 prism computed from discharge measurements is 1.65 x 10^ cubic feet; the 



44 



