Summary 



The ratio of the rate of sand transport without groins to the 

 rate of sand transport with groins perhaps is the best criterion for 

 evaluating the effectiveness of a particular groin system. In this 

 series of experiments, once the equilibrium rates were established 

 the shore line was considered to be in a stable position. The intro- 

 duction of fixation works produced a rate of change peculiar to that 

 particular type of structure. These rates in turn developed the sub- 

 sequent volume changes that were computed on a percentage basis using 

 the stable profiles of the beach without any structures in place as a 

 reference . 



A review of the experimental data for the tests made with the 

 s$rstems using three permeable groins indicates that where there is 

 proper nourishment to the beach s the permeable structures have a small 

 but effective influence on the beach. Significantly, for both sets 

 of tests the runs made with one groin in place produced a marked 

 scour area in the region downcoast from the structures. The tests 

 substantiate the fact that for sand trapping purposes the perneable 

 groins should not be used as individual units isolated along the beach 

 but in a group, i.e., in a system of groins. Care also must be taken 

 when placing the groins in the beach s for if they are placed further 

 apart than their influence area, each would act as an undesirable in- 

 dividual unit. 



With a constant -£••* input to the surf zone, the first set of 

 tests made on the permeable groins showed that there was a 26 per cent 

 deposit of sand on the beach, with the structures in place, over the 

 base condition, with a straight unobstructed beach. The second set 

 of tests on the permeable groins, made with a different set of wave 

 conditions, showed only an 11 per cent beach fill. Comparison of the 

 data on the types of fixation works tested, where the littoral 

 current is a significant factor, showed that the impermeable groins were 

 more effective in the accretion of sands that the permeable groins. 



The retention, or holding power, of the impermeable groins is re- 

 latively large. In a particular series of tests where there was no 

 feed material introduced, the total decrease or the amount of scour 

 that occurred from the base reference volume (taken at the start of a 

 test) amounted to a reduction slightly less than 20 per cent in a 

 run that exceeded 54 hours in duration. 



The experiments show that, when the beach is adequately nourished 

 and the littoral current is an effective force, the impermeable groins 

 rapidly accrete the sediment. The building or filling -up of the area 

 between groins follows a very definite pattern. In general, the sand 

 begins to move around the seaward tip of a groin and fills in the 

 space near the downcoast side of the groin. Then the sand moves at an 

 angle across to the next groin and fills in the upcoast face. Then the 



