(d) The shoreline recession rate was a constant 0.025 foot per hour 

 uniformly across the tank after 15 hours in experiment 71Y-06. In experi- 

 ment 71Y-10, the shoreline recession rate was a constant, uniform 0.016 

 foot per hour between 15 and 205 hours; for the last 130 hours, the rate 

 along the outside ranges of the tank increased to 0.025 foot per hour 

 (Fig. 18). 



(e) The slower development of the inshore shelf across the full width 

 of the tank and slightly slower shoreline recession rate in the wider tank 

 indicate that even wider beaches (closer to an infinitely long beach) 

 would develop more slowly. Until tank width effects can be quantified, 

 engineers should be careful in extrapolating shoreline recession rates 

 from two-dimensional laboratory tests to field problems (Fig. 44). 



(f) Changes in the sediment-size distribution along a laboratory 

 profile appear to be measurable, even for fine, well-sorted sand. The 

 median size along the initial profile was 0.27 millimeter. At the end 

 of the experiments the mean median was 0.32 millimeter in the foreshore 

 zone, 0.29 millimeter in the inshore zone, and 0.26 millimeter in the 

 offshore zone (Tables 10 and 11) . (Sand sizes are RSA values which tend 

 to average 0.04 millimeter higher than sieve analyses of the same sample.) 



(g) The long, low wave run near the end of experiment 71Y-06 on the 

 steep wave profile quickly began the natural healing process of the beach, 

 which occurs after storms in nature (Figs. 33, 34, and 35). 



2. Recommendations . 



(a) Becaiise of varying reflectivity of the profiles, incident wave 

 measurements to characterize a three-dimensional coastal engineering 

 experiment should be based on calibration of the wave generator rather 

 than isolated wave measurements during the experiment. 



(b) Experimenters should be cautious in defining equilibrium profile 

 conditions and should consider the possibility of using other means for 

 characterizing steady-state conditions in coastal processes experiments 

 and models. 



(c) In conducting two-dimensional studies of profile development, 

 the tank width should not be too gre^t, probably less than half the 

 incident wavelength. But extrapolation of narrow tank results should 

 assume variability in profile development in the longshore direction. 



3. Further Analysis . 



These experiments were essentially the same as the experiments dis- 

 cussed in Volume II except for the 7- foot difference in initial test 

 length. These results will be compared with results from Volume II in 

 Volume VIII. 



100 



