nesses. The data obtained so far are now being organized so that a 



final conclusion may be reached that will describe the motion in the 



general case. The contract work has been expanded during the next year 



to include seme preliminary field work on the transportation of sand by 

 wind. 



IV. University of California, Contract DA -4 9 -05 5 -eng -31, Wind Action 

 Over Shallow Water . 



Wind set-up in shallow water was studied in a laboratory channel 

 with a reef, with various widths of openings, located near the center of 

 the channel. Measurements were also taken with various slopes of the 

 channel bottom other than horizontal. Data indicate that the set-up was 

 increased by a factor of as much as two over a smooth bottom condition 

 with the installation of a solid reef, and somewhat less than this if the 

 reef had an opening. Data were also gathered on the motion of water 

 particles with various wind velocities and water depths under steady- 

 state conditions. In addition, certain data were taken to determine such 

 questions as: (1) is there an overshoot of set-up, and if so, what is its 

 magnitude compared with the steady state condition; and (2) does the water 

 circulation follow the water set-up exactly. These data are now being 

 analyzed. The funds for this study were provided to the Beach Erosion' 

 Board by the U. S. Army Engineer District, Jacksonville. 



V. University of California, Contract DA -49-055-eng-44, Laboratory 

 Study of Wave Refraction . 



Laboratory studies to determine the application of Snell's law to 

 wave refraction were continued, and a report "Model Study of Wave Re- 

 fraction" was published as Technical Memorandum No. 103 of the Board. 

 This report showed that Snell's law was valid over most of the range 

 tested, which involved deep water angles of incidence between 10 and 70 

 degrees and four slopes ranging from vertical to 1 on 10. Occasional 

 wide discrepencies were, however, observed. Some of these discrepencies 

 may be associated with the formation of multiple crests from a single 

 wave crest as the wave moves into shoal water. Additional laboratory 

 data were therefore taken on the criteria for the formation of multiple 

 crests. From these, it appears that the critericai f or their formation 

 developed by Miche is valid. 



VI. University of Florida, Contract DA-49-055-eng-55, Analysis of 

 Existing Data on Tidal Inlets . 



Additional tidal data have been examined, and a final report pre- 

 pared. This report investigates existing data on a number of tidal 

 entrances in the United States and abroad and examines conditions for 

 the stability of cross-sections in light of existing theory on cross- 

 section stability of rivers and canals, in particular utilizing Bretting*s 

 approach. A stability shear stress is defined and compared with values 

 recommended by Lane. This study is administered by the Beach Erosion 

 Board for the Corps of Engineers' Tidal Hydraulics Committee. 



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