degree of evaluation of wave direction - at least to the extent of permit- 

 ting separation of those waves which are from the southerly quadrant from 

 those which are from the northwesterly quadrant. Coordination with Palm 

 Beach County officials was continued in compiling data and information from 

 the operation of the sand transfer plant at Lake Worth Inlet, Florida. 



A report "Mechanical Bypassing of Littoral Drifts at Inlets" was pre- 

 pared and published in the Waterways and Harbors Division Journal of the 

 American Society of Civil Engineers. It presents a brief examination of 

 the general processes of littoral drift movement at both uncontrolled and 

 controlled coastal inlets. The report indicates the principal factors to 

 be evaluated when mechanical bypassing of littoral drift past an inlet is 

 considered, and examines the general techniques of bypassing. The report 

 also presents a summary of all completed and active bypassing projects in 

 the United States. 



Specifications for the purchase of a mass-flow density meter (utilizing 

 a radioactive source) to measure flow of sand through a 3-inch pipe were 

 completed, and submitted for bids. The meter will be tested in conjunction 

 with model work on littoral drift rates at the Board's laboratory and evalu- 

 ated as to feasibility for use in the field to measure quantity of material 

 pumped in bypassing operations. 



(e) Laboratorv Studv on Relation of the Littoral Drift Pate to 

 Incident Waves. 



A report "Laboratory Determination of Littoral Transport Rates" was 

 published in the Journal of the Waterways and Harbors Division, American 

 Society of Civil Engineers. This report discusses previous littoral drift 

 studies, adds data obtained at the Beach Erosion Board, and presents a 

 figure relating the value of alongshore littoral transport to the value of 

 the alongshore component of wave energy summed over the period of interest. 

 The report also discusses techniques of laboratory studies of the littoral 

 transport rate, indicating some problems and solutions for measurement, 

 feeding and trapping mechanisms, end effects caused by refraction at the 

 ends of the test beach, and wave variability (perhaps superimposed basin 

 surges) over the test area. A series of additional laboratory tests were 

 made in the Shore Processes Test Basin to obtain further data on the re- 

 lation of littoral movement to incident wave characteristics. One of 

 these involves a maximum movement rate of about 19,000 to 20,000 pounds 

 of sand per hour (dry weight) obtained with the highest wave tested of 

 about 11 inches. This rate of movement is the equivalent of about 60,000 

 cubic yards per year. Testing was also continued on the effect of local 

 variation in wave period on the rate of littoral movement. In general, it 

 was found that varying the wave period over a short range about the mean 

 period (plus or minus 10%) at lesser and lesser time intervals increases 

 the rate of littoral movement. However, a single test in which the wave 

 period was varied continuously (sinusoidaly) over a one-minute cycle showed 

 a decrease in transport rate from the test in which the period was varied 



68 



