13 



THE USE OF HISTORICAL SURVEYS IN BEACH 

 EROSION STUDIES 



Harold A. Ward 



Chief , Drafting and Reproduction 



Branch, Beach Erosion Board 



The long-term behavior of the shore line and offshore depths is one 

 of the important factors considered in devising a solution to beach erosion 

 problems . Suitable historical topographic and hydrbgraphic surveys are 

 superposed to delineate the movement of the shore lines and offshore depth 

 curves o The relative positions of the shore lines and depth curves at the 

 times of the various surveys show the area of erosion or accretion, whether 

 the movement has been constant, and how the introduction of other factors 

 such as man-made structures, breaches of barrier beaches and the migration 

 of inlets, etc. have altered the regime of the area under study,, 



The purpose of this article is to point out some of the cartographic 

 problems that must be considered when old surveys are used to determine 

 the long-term behavior of the shore lines and offshore depths. These 

 valuable sources of information when properly used will give a factual 

 history of the changes that have occurredc The past behavior of the beach 

 is a tool in the analysis of the forces acting upon the shore, the amount of 

 material in motion, etc., and can determine the most feasible means of harness- 

 ing the forces to solve the problem,, 



The U. S. Coast and Geodetic Survey in Washington, D. Co, is the primary 

 source of general historic surveys for this purpose for the U. S° Coast of 

 the Gulf of Mexico, Atlantic and Pacific Oceans „ The vault of this agency 

 contains approximately 15,000 original field sheets dating back to 1834- • 

 The high standards of accuracy of work performed over the period of record 

 makes the field sheets invaluable for use in beach erosion studies. 



In addition an incomplete file is preserved of "Descriptive Reports" 

 carrying the registry number of the survey it describes Of times the old 

 descriptive reports give a graphic description of conditions found by the 

 survey party, and of particular interest to the engineer studying erosion 

 problems is "on the spot" comparison of circumstances with former surveys. 

 The report for example, may mention changes caused by severe storms which 

 have preceded or interrupted the work. To the engineer this means the 

 shore line or depth curves as shown may be abnormal and must be appraised 

 carefully. 



It is important that superposed surveys be accurately placed on a 

 common geodetic datum and in handling old historic surveys this sometimes 

 presents a problem. The polyconic projection is used for practically all 

 field sheets . Due to recomputations of the dimensions of the spheroid at 

 various times the coordinates of triangulation stations have been adjusted; 

 which, of course, necessitates replotting the latitude and longitude lines. 

 In the earlier periods when there were relatively few field sheets in the 



