own facilities. Many of these projects have been described in previous 

 numbers of the Bulletin, and progress on the major projects during the 

 last year is summarized below. 



(a) Measurement of Suspended Material in Laboratory Wave Tanks 



Development of a laboratory sampler and sampling techniques 

 is discussed in a report by Fairchild in this Bulletin. For samples 

 taken relatively close to the sand bottom, the exact positioning of the 

 sampler intake relative to the ripple crest or trough appear to be quite 

 important. Additional testing on the effect of water temperature is 

 underway, and indicates that considerably greater amount of material 

 are placed in suspension in colder water. One test on resultant equilibrium 

 profile under two different temperature conditions indicates that the 

 same eventual profile results, but adjustment occurs faster with the 

 colder water. 



(b) Laboratory Study of Effects of Groin Field on Littoral Drift 

 Passing Field 



Certain preliminary tests were run in the Shore Processes Test 

 Basin to determine probable range of sand transport rates. A new and more 

 precise sand trapping and measuring system is being installed, with an 

 eductor system to transfer the trapped material back to the upbeach end 

 of the test area. 



(c) Equilibrium Profile Tests 



Temperature effects are discussed under (a) above. Two tests 

 have been run in the prototype tank involving waves of 2.5 and 4 feet 

 in height with 1 to 10 and 1 to 15 scale models run in small flumes 

 utilizing the same sand and a 1 on 15 initial slope. The tests indicate 

 that the sometimes used "critical" value of wave steepness of 0.02 to 

 0.025 found in some small model tanks as the dividing point between beach 

 erosion and beach accretion for comparable sands possibly does not apply 

 for larger waves; that with large waves, waves having steepness consider- 

 ably less than 0.02 may erode rather than accrete the beach. This 

 possibility has been previously indicated by Rector reporting (Board 

 T.M. #41) on small scale tests where it was shown that the "critical" 

 steepness possibly also depended on a sand-wave size parameter (as grain 

 diameter - wave height ratio). 



(d) Forces on Piling 



A 12-inch pile with a 3-foot sensitive (instrumented) section 

 has been mounted in the prototype tank, and force measurements are being 

 taken for depth and wave conditions — including breakers. 



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