or engineer in charge o£ a model study. Field engineers should also be 

 aware o£ these results when analyzing model studies for coastal engineer- 

 ing projects. 



The data in this study (particularly the profiles) may have other 

 uses. The researcher can use these data, after consideration of the 

 laboratory effects, to analyze short- and long-term changes in profile 

 shape. After an analysis of the scale and laboratory effects, the field 

 engineer may use these data to determine generalized shoreline recession 

 rates. 



II, RESULTS 



1. Wave Height Variability . 



a. Incident Wave Heights . 



(1) 1.90-Second Wave . Wave height measurements from the con- 

 tinuous recording of water surface elevation along the center range at 

 station +25 during the first 10 minutes of each experiment are shown in 

 Table 4. The wave heights in the movable-bed tanks varied from 0.26 to 

 0.52 foot (7.9 to 15.8 centimeters) in experiment 71Y-10, and from 0.20 

 to 0.41 foot (6.1 to 12.5 centimeters) in experiment 71Y-06. Ignoring 

 the first group of waves, the range of wave heights within the first 10 

 minutes was 0.11 foot (3.4 centimeters) in experiment 71Y-10 and 0.10 

 foot (3.0 centimeters) in experiment 71Y-06„ In the fixed-bed tanks, 

 again ignoring the first group, the range of wave height variation was 

 0.12 foot (3.7 centimeters) in experiment 71Y-10 and 0.07 foot (2.1 

 centimeters) in experiment 71Y-06, The range of wave height variation 

 was as great in the fixed-bed tanks as in the movable-bed tanks. 



The average wave height in the movable-bed tank for each record was 

 determined by averaging the average of the last 10 waves in the last 

 20-second interval for each of the 10 minutes. In experiment 71Y-10, 

 the average wave height was 0.33 foot (10,1 centimeters) in experi- 

 ment 71Y-06, the average wave height was 0.36 foot (11.0 centimeters). 

 Because the waves were recorded at the same distance from the profile, 

 the difference in the average wave height is likely due to the difference 

 in the initial test length which affects the development of secondary 

 waves or re-reflection from the wave generator. During the first 10 

 minutes, there was little difference in the average wave height between 

 the movable- and fixed-bed tanks for either experiment, even though the 

 gages in the fixed-bed tanks were 7 feet farther from the profile. 



The average incident wave heights in the fixed-bed tanks from the 

 two experiments are shown in Table 5. These heights were determined as 

 part of the manual method for determining the reflection coefficient, K^ 

 (see Vol. I). This variation is probably caused by generator operation 

 variation, measurement errors, and all errors not caused by a changing 

 profile in both movable- and fixed-bed tanks. The range of variation 

 was 0.03 foot (0.9 centimeter) in experiment 71Y-10 and 0.04 foot (1.2 

 centimeters) in experiment 71Y-06. 



15 



