(4) Lateral tank oscillations — long waves (with a period other 

 than the period of the generator) resulting from critical combinations 

 of wavelength and tank width, which occurred in some experiments and 

 could not be controlled. These waves can be identified by examining 

 the deviation of the running average wave height, D m , along ranges 

 other than the center range. 



(5) Wave instabilities--vaTia.tions in wave shape, which result 

 from nonlinear shallow-water waves propagating in the tank. 



2. Variations in Wave Reflection . 



Reflection coefficients varied noticeably throughout the LEBS experi- 

 ments (Table 2), and an important part of the experiments is the attempt 

 to identify the causes of this variation. 



Each of the two tanks had an adjacent control tank situated so that 

 the same generator simultaneously produced the waves in both the test 

 tank and the control tank. The control tank had a 0.10 smooth concrete 

 slab instead of a movable bed. K^ variability in the fixed-bed tank 

 is a measure of the K^> measurement accuracy in the movable-bed tank. 



Table 2. Average reflection coefficient and limits of values 

 in each LEBS experiment. 



Experiment 



Movable-bed tank 



Fixe 



d-bed tank 





Avg K R 



Limits of K^> 



Avg K R 



Limits of K^> 



72C-10 



0.05 



0.02 to 0.12 



0.01 



0.01 to 0.02 



70X-06 



0.08 



0.04 to 0.14 



0.05 



0.05 to 0.06 



70X-10 



0.09 



0.00 to 0.15 



0.05 



0.03 to 0.07 



71Y-06 



0.08 



0.01 to 0.23 



0.05 



0.03 to 0.06 



71Y-10 



0.07 



0.01 to 0.13 



0.05 



0.04 to 0.07 



72D-06 



0.12 



0.04 to 0.27 



0.05 



0.04 to 0.07 



72B-06 



0.08 



0.03 to 0.14 



0.04 



0.03 to 0.06 



72B-10 



0.17 



0.10 to 0.21 



0.05 



0.02 to 0.09 



72A-06 



0.26 



0.17 to 0.31 



0.08 



0.06 to 0.08 



72A-10 



0.30 



0.24 to 0.36 



0.05 



0.02 to 0.07 



a. Processes . Three processes are involved in wave reflection from 

 a movable-bed profile. These are the conversion of potential energy 

 stored in runup on the foreshore into a seaward-traveling wave, the sea- 

 ward radiation of energy from a plunging breaker, and reflection of the 

 incident wave from the submerged profile, particularly where the depth 

 over the movable-bed changes significantly (Chesnutt and Galvin, 1974). 



17 



