82 



Because jetties usually have long life spans, they may require lengthening 

 and raising of the crest of the structure. The possible increase in tidal 

 prism and current magnitudes could increase scour and undermine jetties. 

 The jetties at Indian River Inlet, Delaware are currently threatened by 

 scour induced by an increase in tidal prism. 



A typical example of the shoreline response to jetties is the inlet at 

 Ocean City, Maryland shown in Fig. 6.11. A hurricane cut the inlet in 

 August, 1933 and jetties were constructed shortly thereafter. By 1976 the 

 updrift shoreline had advanced 245 m while the downdrift had retreated 

 335 m. The shoreward end of the south jetty has had to be rebuilt and 

 extended several times. It is doubtful that in the 50 years since 

 "stabilization," the shorelines have regained a state of dynamic 

 equilibrium, so the effects of 50 years of sea level rise cannot be deduced 

 accurately. 



Beach n ourishment - is the mechanical placemer^o^san^on a beach to 

 advance the shoreline. It is a "soft" protective and remedial measure that 

 leaves a beach in a more natural state than hard structures, and preserves 

 its recreational value. Beach fills cannot "modify" shoreline response to 

 sea level rise because the natural littoral processes remain unaltered, and 

 thus fills can only be regarded as a temporary measure. Although requiring 

 maintenance at regular intervals and after severe storms, beach fills have 

 been successful in many instances such as Miami Beach, Florida; Virginia 

 Beach, Virginia; and Wrightsville Beach, North Carolina. 



The greatest effect of long-term sea level rise on beach fill design 

 is to increase the volumetric requirements of the fill and so increase 

 costs. Attempting to hold the shoreline in one location will necessarily 

 require a steeper beach profile as sea level rises. This means increased 

 volumes of placed sand are necessary to satisfy the offshore transport 

 demand, or else placing material of coarser grain size than the native 

 sediment. 



An example of a successful beach nourishment project is that at 

 Harrison County, Mississippi, shown in Fig. 6.12. Constructed in 1951-1952 

 of 4.6 million m^ of fill, the project provided 280 hectares of new beach 

 which was 90 m wide with a berm height of 1.5 m, and fronted the seawall 



