wave action is a significant factor. As part of the research program 

 on this contract;, a study was made of two types of groins; one, 

 the sloping, impermeable groin; and second, the high, permeable groin. 

 This investigation was intended to determine the relative influence 

 of the high permeable groins and the sloping impermeable groins for 

 stabilizing a beach where littoral transport occurs. 



In this study a sand beach was placed at one end of a model basin. 

 Waves were generated at the opposite end of the basin and moved toward 

 the beach. Those waves breaking along the shore induced a current 

 which caused a littoral movement of the sand. The relative effect of 

 a particular type of groin was determined by comparing the topography 

 of a straight, unobstructed beach which had reached an equilibrium 

 profile with the topography of a beach which had reached equilibrium 

 after a groin or system of groins were installs d e 



The experimental program for studying the groin influence on the 

 littoral sand movement was carried out under the following conditions; 



a. with no groins in place (for establishing the base equili- 

 brium condition); 



b. with one high, permeable groin in place; 



Co with a system of two high, permeable groins in place j 



do with a system of three high, permeable groins in place; 



e„ with a system of ten sloping , impermeable groins in place; 



f „ with a system of ten high, permeable groins in place; 



go introducing dyed sand particles in the bed of the beach to 

 study currents . 



Prior to placing a particular groin, or groins, in position, the 

 littoral transport rate was determined (i.e. for the steady state con- 

 ditions obtained with a specific set of wave characteristics). The 

 sand composition was the same throughout the tests. The stable profile 

 of the beach then became the base for evaluation of subsequent changes 

 in the beach configuration. The effects of tide were not studied. 

 (For complete details see the report Issue No. 6, Series No. 14, as 

 listed in Part VI). 



* O'Brien, M. P. and Mbrison, J. R.; The Forces Exerted by Waves on 

 Objects; Transactions, American Geophysical Union, (In Press). 



