SWG Data 

 ' Prolher ond Sorensen -5-- 



Square root of the difference between 

 ttie gulf and boy woter levels (ft)'2 



Figure 65. 



Relationship between average velocity 

 and head difference, Rollover Pass. 



concluded that the actual average velocities are closer to the 3. 1 feet per 

 second predicted using the 1965 relationship than to the 0.66 calculated by 

 Prather and Sorensen (1972). 



e. Inlet Stability. 



(1) Observed . Rollover Pass, when first built, was in an extremely 

 unstable erosion condition. However, with the artificial stabilization of the 

 banks by sheet pile and the cross-channel weir, velocities were reduced and 

 further erosion was halted. Figure 66 shows the variation in cross-sectional 

 area at four locations since 1957. The minimum cross-sectional area, always 

 located at station 500S (see Fig. 66), has been constant since 1963; however, 

 Prather and Sorensen (1972) showed that between 1968 and 1971 the deepest part 

 of the channel south of the weir moved from the east to the west side. In 

 addition, a deep scour hole just south of the weir in 1968 shoaled extensively 

 by 1971, reducing the maximum depths from 28 feet to only about 12 feet 

 (Fig. 67). This shoaling, combined with a possible increase in the inlet 

 length due to deposition in Rollover Bay, may be the cause of the decreased 

 efficiency of the pass (i.e. , lower bay ranges and longer lags) which occurred 

 between 1965 and 1971. 



(2) Theoretical . O'Brien and Dean's (1972) stability method was used 

 to predict the response of Rollover Pass to sedimentation. The most difficult 



74 



