bi-modal size -frequency distributions. The contract has been extended to 

 study, both experimentally and analytically, the formation of littoral 

 currents along straight beaches. Initial experiments involve wave-induced 

 currents along a beach with a smooth impermeable 1 on 10 slope. The initial 

 work has been to establish experimental techniques to maintain uniformity 

 of flow along the test beach, and to measure satisfactorily wave height, 

 elevation of mean water surface, and current velocities and distribution. 



III. University of California, Contract DA-49-055-eng-17. Fundamental 

 Mechanics of Sand Movement by Waves 



A report "Sand Movement by Wind Action (on the Characteristics of 

 Sand Traps)" was published as Technical Memorandum No. 119 of the Board. 

 This report discusses the calibration of various types of sand traps in a 

 wind tunnel; efficiencies of these various traps have been checked and 

 compared with each other. As a result of the tests, a trap giving an 

 efficiency close to 100 percent has been developed. Some field tests were 

 made using this portable sand trap, during which the vertical velocity dis- 

 tribution was determined both with a bank of anemometers and a group of 

 Pitot tubes. A report describing these tests is being prepared. Under 

 that portion of the contract dealing with sand movement by waves, the model 

 tests -..'ith three-dimensional roughness were concluded. Analysis of the 

 data has shown that the velocity distributions are similar to those for 

 smooth surface and two-dimensional roughness. However, attempts to relate 

 the sediment transport rate to the shear stress obtained from integration 

 of the velocity profile have so far been unsuccessful. A new approach 

 similar to Jhat for unidirectional flow is now being considered, wherein 

 it is proposed to calculate the instantaneous lift force acting on the 

 individual grain, and establish criteria of stability depending on the 

 direction of the resultant of this force and the submerged weight of the 

 grain. 



IV. University of California, Contract Ifl-49-055-eng-44. Laboratory 

 Study of Wave Refraction . 



Ripple tank tests were completed on the refraction, reflection, and 

 energy dissipation characteristics of a solitary wave at oblique incidence 

 to an inclined beach. A report "Experimental Study on the Solitary Wave 

 Reflection Along a Straight Sloped Wall at Oblique Angle of Incidence" was 

 published as Technical Memorandum No. 124 of the Board. In these tests it 

 was found that curved ripples developed when incident waves hit a wall with 

 a slope less than approximately 65°. As the angle of incidence increased, 

 an envelope of these ripples formed and became large enough beyond a certain 

 angle of incidence, depending on slope, to look like a reflected wave but 

 remained curved as were the ripples. For a relatively steep wall slope, 

 larger than 65°, reflection was regular, but the angle of incidence at which 

 a straight reflected wave occurred depended on the slope of the wall. For 

 a wall with vertical or negative slope Mach reflection took place for wave 

 incidence angles between 30° and 35°. Mach reflection ceased and regular 



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