ANALYSIS OF SHORT-TERM VARIATIONS IN 



BEACH MORPHOLOGY (AND CONCURRENT DYNAMIC PROCESSES) 



FOR SUMMER AND WINTER PERIODS, 1971-72, 



PLUM ISLAND, MASSACHUSETTS 



by 

 Ralph Warren Abete, Jr. 



I. INTRODUCTION 



Continuous bihourly measurement of beach processes variables was 

 carried out on Plum Island, Massachusetts (Fig. 1) during a 6-week 

 period in July and August 1971, and a 4-week period in January 19 72. 

 These measurements included meteorological variables, i.e., barometric 

 pressure, windspeed and direction; and wave parameters such as breaker 

 height, breaker depth, breaker angle, breaker type, and wave period. 

 Wave steepness and breaker power were calculated for each set of wave 

 measurements. In addition, longshore current velocity, and, in July and 

 August, ground water elevation were measured. 



A series of 12 profile lines, spaced at 60-meter intervals and extend- 

 ing from a base stake on the foredune ridge to a point seaward of spring 

 low water, was surveyed daily for 42 days in July and August 1971 and 24 

 days in January 1972. Also, 12 daily profiles were run for an 8-day 

 period following the "northeaster" of 19 February 1972. The southern- 

 most profile, PL-0 (Fig. 1), was located near the position of an original 

 Plum Island profile (PLB) that was measured at biweekly intervals between 

 September 1965 and July 1971 (Coastal Research Group, 1969). The other 

 11 profile locations (PL-1 to PL- 11) extended in a northerly direction 

 from PL-0. Bimonthly aerial photos of the study area and offshore pro- 

 files (linked to beach profiles) augmented data gathered during the study 

 period. 



A computer program developed by W.T. Fox (Davis and Fox, 1971) was 

 used to process and plot the large numbers of beach profiles measured. 

 Vertical changes were measured every 3 meters on each profile; the pro- 

 gram converted these data to elevations with respect to mean low water 

 (MLW) and made a linear interpolation of elevation changes every 50 cen- 

 timeters between data points. These interpolated data were plotted at 

 2-meter horizontal intervals. Linear interpolation was also calculated 

 between each of the profile lines at 1-meter intervals. A 2 to 1 exag- 

 geration normal to the shoreline was shown on computer printouts (Davis 

 and Fox, 1971). From these two-dimensional data, erosion-deposition maps 

 were constructed by comparing individual profile lines at any specified 

 interval of days. The results obtained from these maps, contoured at 

 10-centimeter intervals, may be used to delineate zones of erosion and 

 deposition through time. 



Beach process measurements were analyzed by using CALCOMP plots of 

 the observed data and visually comparing trends evident between different 

 process variables. 



I I 



