T 1 1 — I — I — i—r-r 



Locus of A( critical 



-i — \ — I — r~r 



1,000 



J I I I L 



B Locotion of Ac ond Vmox for Dotes Shown 

 -L-LJ 1 I I I I I I 



5,000 10,000 



Minimum Cross-Sectional Area, Aj (ft 



50,000 



100,000 



Figure 38. ^j^^-^ versus A^ stability curves, San Luis Pass, Texas. 



(increase) in velocity. Note that the actual values of A and V indi- 

 cate that San Luis Pass is slightly below the critical area for the calculated 

 length of 4,325 feet. 



Another measure of the stability of San Luis Pass is to use Jarrett's 

 (1976) relationship between equilibrium cross-sectional area, A and 

 diurnal tidal prism, P, for unjettied gulf coast inlets: 



^ce = 3.5 X 10 '^ P O.i 



(8) 



For the average tidal prism of 1.6 x 10^ cubic feet, an equilibrium area of 

 27,490 square feet is found, which is only slightly greater than the present 

 value of 25,790 square feet. 



f. Summary . Throughout its history, San Luis Pass has been a downdrift 

 offset inlet in the classic pattern described by Hayes, Goldsmith, and Hobbs 

 (1970) and Galvin (1971), and has remained in the same location at the south- 

 west end of West Bay, typifying the stable Texas Inlet (Price, 1951). Between 

 1853 and 1933, annual sediment volume changes within the inlet system were 

 relatively minor, with a net erosion of the ebb tidal delta associated with a 

 counterclockwise rotation of the delta and thalweg. The eroded material may 

 have moved downcoast or into the bay where deposition occurred on the flood 

 tidal delta. The minimum cross-sectional area has doubled since 1853; un- 

 fortunately, there are not enough data to determine the possible causes. 

 Hurricane Carla apparently caused a major change in ebb tidal delta configura- 

 tion in about 1961, but since then both the cross-sectional area and the inlet 

 width have remained relatively constant. Long-term changes on the adjacent 

 beaches indicate a relatively stable updrift area with minor erosion downdrift 

 of the pass, probably due to sediment trapping by the pass (Fig. 39). Theo- 

 retical stability predictions agree well with the actual stability, indicating 

 that San Luis Pass has been in- an unstable scouring mode, but is predicted to 



48 



