. r. , ^ ^(14,15,16,17.18) . ... 



recently been completed » » • ©r are now under way which 



should serve in the development of a quantitative understanding of 



this phenomenon. A laboratory study at Massachusetts Institute of 



Technology^ 1^^ ddals with the sorting action of waves on beach sands 



which results in the pulling of the fines into deep water; a laboratory 



study at the University of Calif ornia(20) deals with the problem of 



fundamental mechanics of movement of sand particles by wave action. 



A field study at Scripps Institution of Oceanography deals with the 



seasonal changes in bottom depths from the shore line out to about 



the 100-foot depth contour. These studies are sponsored by the 



Beach Erosion Board of the Corps of Engineers and should lay the 



foundation of a quantitative understanding of sand movement by wave 



action. 



Littoral Drift . The mass alongshore movement of sand by wave 

 action is generally the key to shore erosion problems as well as many 

 inlet navigation problems. The actual design of a shore protection 

 plan frequently hinges on a proper estimate of the net rate jind 

 direction of littoral drift. At present this rate can usually be 

 estimated accurately only where some structure, such as a breakwater 

 or jetty, has created an impoundment area which enables a volumetric 

 computation to be made. Some method of accurately estimating the rate 

 of drift where no impoundments have taken place is needed. Attempts 

 have been made along this line both in the laboratory (17, 21) and in 

 the f ield^^^*^^^^^' by working out a correlation of net wave energy 

 upcoast or downcoast with the resulting rate of littoral drift; the 

 results are promising but as yet too fragmentary to justify adoption 

 as a basis of engineering design. 



Effect of Natural Features . The effects of promontories and of 

 inlets and submarine canyons in modifying the littoral drift and 

 thereby the shore processes have only recently been subjected to intensive 

 study. Studies at Scripps Institution of Oceanography(22) have led 

 to a definition of the effect of submarine canyons on shore processes. 

 Studies at the University of California (Berkeley)(23) have shown that 

 rocky promontories extending out into as much as 30 feet of water are 

 not barriers to the alongshore drift of beach sand. Small-scale studies 

 at the Waterways Experiment Station are demonstrating the influence 

 of littoral drift on tidal inlets and of tidal inlets on shore processes. 

 Analytical studies of actual inlets and estuaries are also being made 

 to develop a quantitative understanding of the part that inlets play 

 in shore processes. These particular studies are sponsored by the 

 Beach Erosion Board and other agencies of the Corps of Engineers, 



Geologists are devoting an increasing amount of attention to the 

 inshore area and their contributions are helping to clarify many 

 aspects of shore behavior. '^4, 25) 



From the broad viewpoint, however, the activity in the shore zone 

 at a tidal inlet or the mouth of a large river presents a very complex- 



20 



