Appendix 6.4(3). Continued. 



for areas in southeast Louisiana and once again by participants of this 

 project for selected areas in the Chenier Plain. A comparison of the two 

 methods indicates that results were within 3% of each other for the area 

 covered by one 1:24,000 U.S.G.S. topographic sheet. 



Habitat Changes 



Having established a habitat base map for the year 1974, a second habi- 

 tat map representing some time in the past was sought in order to determine 

 habitat changes through time. The availability of air photo coverage was 

 the limiting factor in determining any habitat changes. 



Examination of black and white aerial coverage revealed that 1952 was 

 the earliest year in which sufficient coverage was available. This coverage, 

 flown by the United States Navy, covered the entire Louisiana portion of 

 the Chenier Plain and approximately 50% of the Texas portion. Habitat 

 changes by basin, therefore, were measured from 1952 to 1974 with the ex- 

 ception of the East Bay area where changed were measured from 1954 to 1974. 



In addition to the above coverage, 1953 to 1954 1:72,000 scale air photo 

 mosaics and ~ 1:20,000 scale air photos mission flown by Edgar Tobin Aerial 

 Services for the Humble Oil and Refining Company covering coastal Louisiana 

 were used as a supplement. United States Navy air photos of the Texas coast 

 flown in 1961 to 1962 was also used as supplemental coverage. 



Variability in scale of the black and white air photos was significant. 

 In mapping habitat changes, therefore, the areas of change were plotted on 

 a scale of 1:24,000. These areas of change were then computed using the 

 Calma Digitizer. 



Shoreline Changes 



Shoreline changes were represented in the habitat change matrices by 

 either a change from Nearshore Gulf to Marsh (indicating shoreline advance) 

 or from Marsh to Nearshore Gulf (shoreline retreat) . While the shoreline 

 may be advancing or retreating, it was not felt that the area of the beach 

 changed significantly; rather the change was at the expense of the habitat 

 either seaward or landward of the beach, depending on the direction of move- 

 ment of the shoreline. 



These changes were determined by use of unpublished data (Morgan, Lou- 

 isiana State University) for the Louisiana coast and Seelig and Sorensen's 

 (1973) data for the Texas coast. The former source included changes between 

 1954 and 1969. Thus, shoreline changes for the Louisiana portion of the 

 Chenier Plain are in a close time frame with other habitat changes. The lat- 

 ter source, however, lists shoreline changes from the latter part of the 

 nineteenth century to the early to mid 1960's. The data are reported as 

 linear changes per year. The long time period covered gives one a misleading 

 nature of the change, (i.e. , most of the change could have occurred over a 

 much shorter time period). As these were the only data available they were 

 used by taking the reported linear change per year and multiplying by the 

 time period covered for other habitat changes. For the East Bay area this 

 was 22 years (1954 to 1974) and for the Texas portion of the Sabine Basin 24 



370 



