VII. Massachusetts Institute of Technolo Contract No. DA=-)9-055-eng-16. 
th Progress Report dated 12 February 195h. 
dhe To determine the proper statistical sample size of the test sedi- 
ments, a study was made of the motion of 1/8" cellulose acetate spheres 
in individual sample sizes of 20, 30, 40, 50, and 60 spheres under the 
action of the same wave. On the basis of the derived set of distribution 
curves as a function of time and distance, a sample size of 50 was 
selected as being the smallest having the correct statistical distribu- 
tion. 
2. Three more tests were carried out to check reproducibility of 
results with this sediment sample size, and also the effect of the last 
wave generated in each increment of time. It appears, on the basis of the 
first increment where all samples had the same starting position, that 
a number of runs will have to be averaged to give the correct velocities. 
36 It was found that for each combination of wave geometry, beach 
and particle properties, there is a point on the beach slope at which 
the gravity force is in balance with the drag forces on the sphere. This 
point divides motion of the particles into onshore and offshore trans- 
portation. 
Lh. Recording the transverse positions of the particles shaal a 
steady migration of the center of gravity of the sample toward one wall. 
This may be due to the effect on the wave motion of slight misalignments 
in the channel walls. 
VIII. Waterways Experiment Station, Vicksburg, Mississippi. - 
Wave Run-up on Shore Structures - Overtopping tests on a step-faced 
seawall with a seaside slope of 1 on 13 and a beach slope of 1 on 10 
were completed for the 25 and 3h-foot depths, and for the 3- and 6-foot 
crest elevations for the 29.5 foot depth. Testing was then discontinued 
due (1) to lack of funds, and (2) to permit initiation of testing on a 
1 on 3 smooth slope similar to the Lake Okeechobee levee section. An 
expanded program of wave conditions will be used in these new tests. 
Effect of Inlets on Adjacent Beaches - This test, having in 450 tida) 
cycles successfully reproduced several cycles of migration of the tidal 
inlet, was discontinued, and the results of the test are now being 
analyzed. 
IX. Beach Erosion Board, Research Division, Project Status Report for 
Quarter ending 15 March 195]. 
In addition to the research projects under contract to various 
institutions which are reported on above, the Research Division of the 
12 
