As mentioned previously, ebb discharges predominate between the gulf ward 

 jetty ends at range 1. Thus, about 24 percent of the flood prism enters the 

 inlet through the small-boat passes and perhaps the jetty stones. On ebb 

 flow, the channel through the barrier island and the jetties confine the flow, 

 and all the ebb prism passes through range 1. This ebb flow predominance 

 promotes self-maintenance of the jetty channel, keeping shoaling rates below 

 what they would be if the flow were balanced. 



Flood and ebb flows at range 2 were evenly balanced, since river discharge 

 was far below normal during the measurement period. Nonetheless, its effect 

 on flow distribution in the pass can be determined by comparing the discharges 

 through each vertical section of this range. Table 13 shows that ebb flows 

 predominate in the usually fresher upper layer, while floodflows predominate 

 in the denser bottom layer. Temperature, salinity, and current data taken ii 

 1974-75 more clearly illustrate this condition (Ward and Johnston, 1977). 



At range 4 (Port Arthur canal entrance) , peculiar circulation patterns 

 develop. Note that on 19, 20, and 21 July 1962, while certain ebb flows were 

 occurring at all other ranges, floodflow was passing through this range. As a 

 result, flood discharges predominated by about 1.7:1. This also is evident in 

 Figure 77 which shows that water flowed into the canal while it flowed out of 

 the lake and pass. 



At range 3 (Sabine Lake entrance), ebb flows predominate for two reasons: 

 First, freshwater from Sabine and Neches Rivers exits here. Second, floodflow 

 predominance through the Port Arthur Canal must also leave Sabine Lake (i.e., 

 there is a net clockwise circulation through the canal and lake). 



During the simultaneous measurements at all four locations (19 to 21 

 July), the accuracy of the discharge calculations was checked by summing the 

 values from ranges 3 and 4 and comparing them to those of range 2. For the 

 six tidal phases in which the flow directions were always in agreement 

 (footnote 2 values in Table 12) the average difference was only 7 percent and 

 in all but one case the sum of the two channels exceeded the pass discharge. 

 This small error adds confidence to the estimate of the effective cross- 

 sectional area of range 2 determined earlier in this report. 



An attempt was made to verify the tidal discharges by calculating the 

 tidal prism as the product of bay area and bay tidal range. However, the only 

 bay tide data were from the Port Arthur SWG gage, and these data were not 

 compatible with discharges through Sabine Pass, since the canal receives water 

 (i.e., floods) during parts of ebb flow in the pass. 



Rathbun and Goodwin's (1976) data reported in Ward and Johnston (1977) are 

 plotted in Figures 78 to 81. Note the same pattern exhibited in the 1962 

 data: floodflow into Port Arthur canal, ebb flows from Sabine Lake. The two 

 measurement periods (1974 and 1975) were during diurnal tides; the 1962 dis- 

 charges were semidiurnal. Therefore, the more recent average tidal cycle 

 discharges are about twice those of 1962 (Table 14). 



d. Theoretical Stability Analysis . O'Brien and Dean's (1972) stability 

 method was again used to predict the response of this jettied entrance to 

 sedimentation. The 1973 tide data indicated that the Sabine Lake tidal range 

 was about 0.41 the jetty range which, from Figure 37, yields a K value 



86 



