Section III. ANALYSIS OF PIPE PROFILE DATA 



1. Basic Data 



The basic data of this study are the sand elevations at the 

 pipes; these are tabulated in Appendix A with reference to local datum 

 Then, for each profile, the sand elevations at the pipes, referenced to 

 MSL, were plotted against time in two ways: plots of individual observa- 

 tions (Appendix B) , and plots of three-point running averages against mean 

 dates (Appendix C) . The three-point running averages were computed in 

 order to better indicate mean trends. They are obtained by plotting the 

 average elevation of three successive sand elevations, at a given pipe, 

 against a date midway between the dates of the first and third observations, 

 According to this process, each observation in Appendix A, except for the 

 first and last two of any series, will contribute to three successive 

 points on the plots in Appendix C. In addition to plots of the basic 

 data, histograms were constructed to show the frequency distribution of 

 the sand elevations (Appendix D) and the frequency distribution of the 

 1-week changes in elevation (Appendix E) . The histograms of sand eleva- 

 tions (Appendix D) are, in effect, plots of the pipe profiles, and the 

 histograms of sand elevation changes (Appendix E) are plots of all 1-week 

 changes in sand level. 



2. Profile Shape 



The approximate weighted averages of the histograms of each pipe 

 in Appendix D have been combined into time-averaged beach profiles in 

 Figure 6. The 10 average profiles obtained in this way (Figure 6) show 

 a progressive flattening of the profile shape, from the most northern 

 (Westhampton Beach) to the most southern (Ludlam Island) of the five 

 beaches studied. 



On a smaller scale, physical features of beach profiles, such as 

 beach faces, scarps, or berms, can be interpreted from the basic data 

 plots (Appendix B) and the 3-point running average plots (Appendix C) . 

 Closely spaced lines on these plots indicate a nearly flat surface; widely 

 spaced lines indicate an abrupt change in elevation or a steeply dipping 

 surface. For example, at Jones Beach there is a scarp on profile 07, at 

 approxir ^ly 8 feet above MSL which appeared near the end of February 

 1968. Atlantic City, profile 07, there is a berm at approximately 

 7.5 fe ibove MSL (see Appendix B) . 



6 Maximum Single-pipe Erosion and Accretion 



By examining data from each pipe in Appendix A, the maximum 

 i-week and 3-month values of erosion and accretion were determined for 

 each of the 10 pipe profiles. This resulted in four maximum changes at 

 each profile for the 3-month period (Table II) : the greatest 1-week 

 erosion at any one pipe on the profile; the greatest 3-month erosion at 

 any one pipe on the profile; the greatest 1-week accretion at any one pipe 

 on the profile; and the greatest 3-month accretion at any one pipe on the 



