30 



20 - 



10 - 



10 - 



•20 - 



30 - 



-40 



- 



i 1 





1 1 1 1 1 1 1 1 1 





\ 





1st Survey Sta. 28 + 60 (inlet) - 





^\ 



« v.\<^* — --^ — °" — — °~^ ^-°' 

 "-"■"•<£» 5th Survey Sta. 28+60 (inleTT 









/^ * "■ ■» « « « « x __ x 



1st Survey Sta. 141 + 50 (updrift) 





1 1 





l l 1 - 



-200 200 400 600 800 1,000 1,200 1,400 1,600 1,800 2,000 

 Distance Offshore (ft ) 



Figure 36. Updrift beach profile superimposed on the profiles near 

 Murrells Inlet, South Carolina. 



X. DESIGN OF UPDRIFT BEACH 



Several methods are available to predict the realinement of the updrift 

 beach after construction of a jetty complex. None of the methods are entirely 

 satisfactory because they have not been verified by comparison with the behav- 

 ior of actual beaches. Characteristics of the weir jetty that determine the 

 response of the updrift beach are the length and orientation of the sandtight 

 section landward of the weir, the length and elevation of the weir itself, and 

 the orientation of the entire jetty system. The location of the landward end 

 of the weir generally fixes the location of the shoreline at the weir and to a 

 certain extent the planform of the updrift shoreline. The elevation and pro- 

 file of the weir determine the beach profile near the jetty; this also influ- 

 ences the location and alinement of the updrift beach. The alinement of the 

 overall jetty complex and the variability of direction of wave approach deter- 

 mine the amount of sheltering that the jetty affords to the updrift beach. 

 The degree of sheltering or protection from wave action determines whether 

 sand in the fillet adjacent to the jetty can be moved up the coast during 

 periods of transport reversal. 



The simplest method of predicting updrift beach response is to extrapolate 

 the curvature of the existing shoreline into the region of the inlet. The 

 landward end of the weir is then established at the intersection of the 

 extrapolated shoreline and the proposed jetty alinement. Figure 37 shows an 

 example shoreline which is updrift of Murrells Inlet. The use of the extrap- 

 olated shoreline for the design of the weir jetty at Murrells Inlet would have 

 resulted in an extremely long sandtight section landward of the weir. Judg- 

 ment must be used in interpreting the results of extrapolating the shoreline. 



55 



