Comparative Seasonal Surveys 



Seasonal surveys made in April, July and October 194-8 were used 

 as a basis for determining changes in the position of the high-water 

 shore line and the 12, 24, 30, 36 and 4.2-foot depth contours . The 

 April survey was made prior to the first dump; the July survey near 

 the end of the dumping period and the October survey after all dumping 

 had been completed. The purpose of these surveys was to aid in 

 detection of any realignment of the depth curves and shore line 

 resulting from the movement of the dumped material «, 



An examination of the high-water shore line showed that in general 

 accretion had taken place on the beach during the periods April-July 

 and July-October, except during the latter period in the area north 

 of the jettied section adjacent to the pier. Here there had been a 

 general shifting of the sands with a relative balance between accretion 

 and erosion« Seaward from the shore line, excluding the area where 

 the dredged material had been deposited, there had been a general 

 oscillatory shifting of the depth curves. The changes in shoreline 

 and depth curves, exclusive of the dump area, do not show a detectable 

 movement of the dumped material. Such changes as did occur are con- 

 sidered to be the result of natural seasonal changes in o ceanographic 

 conditions. 



Discussion 



An examination of all waves recorded during the course of the 

 study, including the three severe storms, showed average waves 

 available to move the sand to be 12-foot waves of 10-second period, 

 6-foot waves of 8 second period, and 2-foot waves of 6-second periodo 

 The bottom orbital velocities for these waves were computed for two 

 depths; 40-feet at the seaward toe of the pile and 28-feet as the 

 minimum depth at the crest of the pile. These velocities, applied to 

 Filip Hjulstrom's curve "Lower Limit of Eroding Velocities" with a 

 graph of the sand particle size distribution of the dumped. material, 

 show that in all but one instance (velocity of the 2-foot wave with 

 6-second period over a 4-0-foot depth) wave velocities were sufficient 

 to erode material from the bottom. However these eroding forces on the 

 bottom are not unidirectional but oscillatory. 



In view of the nature of these forces and the assumption that 

 other transporting forces are extremely weak or even non-existent, it 

 is believed that the sand will merely be shifted about, filling the 

 depressions and flattening the pile in general. That this action did 

 occur was confirmed by an examination of the comparative dump area . 

 profiles covering the period after all dumping had been completed to 

 the date of the final survey of the study. 



