of various types are being examined, with an eye to their effect on the 
fronting and adjacent shores, and their stability. A particular type of 
block resulting in a stepped seawall has been designed and is being in- 
vestigated at the Board Laboratory. Run-up tests have been made, and are 
discussed earlier in this report (see paragraph b), and stability tests 
are now underway. Stability tests are being carried out for two beach 
conditions, one a normal condition with a beach fronting the seawall and 
the wave breaking somewhat offshore, and the other an extreme storm con- 
dition at which considerable scour is hypothesized to have taken place in 
front of the seawall, and the wave breaks directly on the wall. A pre- 
liminary report discussing the data to date "Interim Report on Interlocking 
Precast Concrete Block Seawall Study" by R. A. Jachowski and J. R. Byerly 
has been given rather limited distribution. Testing is continuing, and a 
more comprehensive report will be prepared when more conclusive data are 
available. 
(0) Propagation of Mechanically Generated Waves. 
A short series of tests have been made on the propagation down a wave 
tank of the first waves generated by a wave generator. Normally used 
methods predict each wave to move down the tank at a constant speed de- 
pendent on the period of the generator and the water depth. In each wave 
length of travel, each wave leaves behind it a particular portion of its 
energy (again dependent only on the wave period and depth), transmitting 
the rest forward with the wave form. Such has not been found the case. 
The waves are more dispersive in character, the first wave having a longer 
period than that of the generator, and travelling at a greater velocity. 
The velocity of each successive wave decreases until finally the velocity 
appropriate to the period of the wave generator is reached, after which 
both wave period and speed remain constant. The wave height at a point 
increases with each successive wave until its full height is reached, 
after which time it also remains constant. The rate increase is faster 
than would be predicted in the way discussed above, and the energy front 
arrives earlier. When the wave generator is stopped abruptly (so that no 
extraneous longer period waves are generated by "coasting" of the generator 
blade), the waves do not die down gradually, but cease relatively abruptly. 
XV Publications 
Technical Memoranda published by the Board during fiscal year 1963 
are listed below. Copies can be furnished on request to persons within 
the United States to the extent of a limited printing. 
ee MiemNoO Title and Date 
131* Littoral Studies Near San Francisco Using Tracer Techniques , 
November 1962, 
632) Waves in Inland Reservoirs (Summary Report on Civil Works 
Investigation Projects CW-164 and CW-165) November 1962. 
*This number is already out of print. 
te 
