(m) Development of Sediment Density Probe. 



A report "Development and Tests of a Radioactive Sediment Density 

 Probe" will be published in September 1960 as Technical Memorandum No. 121 

 of the Board. In this report, the development of an in-place sediment 

 density probe utilizing a (3-miilicurie ) radium source is described, as 

 well as its calibration by laboratory tests. Field testing in estuary, 

 reservoir, and bay sediments is discussed. The gage has demonstrated 

 satisfactory results and has the advantage of giving an indication of 

 densities at successive depths without withdrawing the probe. 



(n) Hurricane Studies. 



The staff of the Board has continued to support the hurricane study 

 work of the Corps of Engineers. Considerable work has been done by the 

 staff in developing and improving simplified methods for estimating storm 

 surge elevations and wave heights under a variety of shore line conditions. 

 Wave forces, wave ruh-up, and wave-overtopping phenomena connected with 

 seawall, dike, and barrier design under hurricane conditions have also 

 been studied. A generalized study of the effect of offshore slope on the 

 amount of wave set-up observed with high hurricane waves has been initiated. 

 These tests have indicated that a rough approximation of the wave set-up 

 at the shore line may be obtained as 1/10 the incident wave height, 

 although this value varies somewhat with the offshore, and particularly 

 the nearshore, slope. Testing in a flume has also indicated that a 

 submerged offshore breakwater or high bar or barrier may significantly 

 increase this set-up by preventing, or making more difficult, seaward 

 return flow along the bottom. The test results for these barriers, 

 however, would be expected to be considerably higher than set-up observed 

 in nature, as the barrier in the tests extended across the full width of 

 the channel and consequently alongshore escaping flow parallel to the 

 submerged barrier, such as would occur in nature, was prevented. 



(o) Wave Pressure Attenuation with Depth. 



A series of measurements using pressure gages on the bottom of the 

 large wave tank has been made with waves several feet in height in an 

 attempt to determine more accurately the attenuation of wave pressure 

 with depth. These tests and their results are discussed in an article 

 in this Bulletin. 



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