became more compact under continued wave action, whereas near the toe of the 

 slope, the bed surface became looser. In early runs, the survey rod was 

 attached to a pulley; this was later converted to a crank system attached to 

 the movable instrument carriage. 



17. Depth surveys were made in 4-ft increments and at prominent breaks 

 in slope at irregular time intervals from 1 to 16 times, not including the 

 initial profile. The resultant beach profile change under wave action proved 

 to be highly two-dimensional. In the experiment conducted during 1956-1957, 

 surveys were first made along three lines parallel to the axis of the tank, 

 but no significant lateral differences were found. Because of the observed 

 lateral uniformity, subsequent surveys were limited to the center line of the 

 tank. In the 1962 experiment, surveys were made along three lines, although 

 they too exhibited lateral uniformity. If sand was transported seaward of the 

 location of the initial toe of the beach, surveys were usually extended to a 

 point where the horizontal floor of the tank was reached. Profile elevations 

 were recorded in 0.1 -ft increments. 



Wave height and period 



18. Wave height was usually measured with a stepped resistance gage 

 placed seaward of the toe of the beach. It is believed that the spacing 

 between resistance gage elements was 2 in. in earlier work and 1 in. in later 

 work, but the date of change between element types is not known. Accuracy of 

 wave height measurements is limited by this spacing, both at the crest and the 

 trough, but the errors would tend to cancel since a difference is taken to 

 obtain the wave height. Visual estimates of wave height were also made by use 

 of markings painted on the wall of the tank. Wave period was set through the 

 gearing mechanism of the wave generator. The period is exact because it was 

 produced by a constant speed motor connected to a specific gear. 



Wave reflection 



19. The wave generator was run continuously between depth surveys (not 

 in the burst mode) and the amount of reflection in the tank was not quanti- 

 fied. Reflection in tests with structures was apparent as large nodal points 

 along the walls of the tank (Figure 2), whereas nodal points observed in the 

 movable-bed experiments were smaller. Based on experience with many kinds of 

 tests performed in the tank, including tests with rubble-mound structures for 

 which notable reflection did occur, it is believed that reflection from the 

 beach was small, particularly for the shorter period tests (3.75 and 



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