At 115 hours along range 9 the bar in the inner inshore began to erode 

 and a flat shelf began to develop. This pattern continued progressively 

 across the tank: progradation of the offshore zone, erosion of the long- 

 shore bar, and development of the flat shelf in the outer inshore region. 



With the profile along range 9 closer to the generator, the waves began 

 to refract and break first along the range 9 side of the tank, draining 

 energy along the wave crests toward range 9 (see Fig. 41, a at 135 hours). 



Deposition in the offshore along range 1 began at 170 hours. Erosion 

 of the bar and development of the shelf were completed by 215 hours. Depo- 

 sition in the offshore zone along the other ranges continued, thus main- 

 taining the refraction pattern and the skewed breaker position. By 265 

 hours the refraction had decreased the wave energy (and wave height) 

 along range 1 so that the breaker position was even farther inshore at 

 a shallower depth where the smaller wave would break. At 280 hours the 

 waves along range 1 did not break as part of the continuous breaker line 

 between ranges and 2, but broke separately at the base of the foreshore 

 (Fig. 39). The refraction increased the mass transport along the range 9 

 side and the return flow was concentrated along range 1 where the incident 

 wave energy was least. 



The concentration of energy along range 9 due to refraction also 

 accounts for the increased shoreline recession along the range. The 

 increased shoreline recession along range 1 may have been the result of 

 the wave breaking closer to the foreshore, thereby increasing the tur- 

 bulence at the foreshore (Fig. 18) . 



Water temperature and shoreline position for experiment 71Y-10 are 

 compared in Figure 43. For the first 15 hours the shoreline recession 

 rate was 0.133 foot per hour; from 15 to 205 hours the rate was 0.016 

 foot per hour. At 205 to 335 hours the shoreline recession rate varied 

 across the tank, from 0.016 foot per hour along the center to 0.025 foot 

 per hour along the outside ranges of the tank. The water ten^ierature rose 

 sharply during the first 2 hours and then remained fairly high and constant 

 until 125 hours. The temperature dropped gradually between 125 and 280 

 hours, then dropped sharply between 280 and 300 hours. The increase in 

 the recession rate along the outside ranges occurred during a period when 

 the temperature was gradually dropping, but the sharp drop in temperature 

 at 280 hours was not accompanied by an increase in recession rate. 



c. Comparison of the Two Experiments . The general shape of the pro- 

 files and the sequence of events during the development of the profiles 

 appeared to be similar in the two experiments, and neither experiment 

 reached equilibriiom. Significant lateral variations in the rate of pro- 

 file development, which occurred in the wider tank, did not occur in the 

 narrower tank. 



(1) Shoreline Recession Rate . In experiment 71Y-06 the shoreline 

 retreated at a uniform (across the tank) rate of 0.025 foot per hour after 

 15 hours. In experiment 71Y-10 the shoreline recession rate was lower 

 (0.016 foot per hour) and more uniform across the tank between 15 and 205 



