47 



rise. Let S = sea level rise, a^y = HW tidal amplitude in the bay relative 

 to mean bay level and B = bay superelevation. Let Aajjy and AB represent 

 changes in a^y and B, respectively. Then, initially, the HW level with 

 respect to the initial mean sea level will be aj^y + B. After sea level 

 rise, it will be S + a^y + Aa^y + B + AB. Note that in the example 

 considered, AB is a negative quantity. Relevant quantities in the present 

 case are: S = 1.3 m, ajjy = 0.28 m, Aa^y = 0.38 m, AB = 0.27 m and AB = 

 -0.16 m. Thus the initial HW level relative to initial sea level was 

 0.55 m, which rose to 2.07 m subsequent to sea level rise. 



The significance of the above result is self-evident; sea level rise 

 could, in addition, increase the tidal range so that, in spite of a 

 decrease in bay superelevation, high water level rise within the bay would 

 become greater than that corresponding to sea level rise alone. It must be 

 pointed out that certain mitigating factors including bottom friction in 

 the bay, ignored in the above example, could lead to a less drastic effect 

 of sea level rise on the bay tide range. Therefore this illustration 

 should be considered to represent an extreme case in terms of quantitative 

 effects. 



A noteworthy conclusion based on the result of Fig. 4.3 is that the 

 secular rate of water level rise would be lower in the bay than in the sea, 

 on account of the decrease of bay superelevation. Hicks (1984) selected 19 

 pairs of gages, one inside the bay and the other at the closest location 

 outside the entrance, for which long-term data were available. For each 

 pair, the difference (outside minus inside) in the secular rate of change 

 of mean water level (mm/yr) was calculated. In 12 cases, this difference 

 was positive, which means a greater water level rise outside than inside 

 the bay. With the exceptions of the Long Branch (NJ)/New York (NY) and 

 Springmaid Pier/Charleston (SC) pairs, where the differences were large 

 (13.1 and 13.6 mm/yr, respectively), the mean of the remaining 10 pairs was 

 2.6 mm/yr. If bay superelevation changes were the sole effect involved 

 (which is not by any means certain, since the gage data were probably 

 contaminated by any nxomber of physical phenomena), this 2.6 mm/yr change 

 would be indicative of the rate of decrease of superelevation. 



Mann (1987) showed that the changes in bay response are greater in 

 shallow inlets than in deep ones. He also found that considering, for 



