Appendix 6.4(3). Techniques employed in habitat and canal inventory. 



Habitats 



The purpose of the inventory was to locate and determine the total areas 

 occupied by each of the fourteen habitats. In addition, the inventory was 

 to assess any temporal changes in the distribution and amount of the habitats 

 and features. 



Sources 



The entire area is mapped by the U.S.G.S. at 1:24,000 scale. This repre- 

 sented the best resolution of published maps that were easily accessible. Where 

 available the U.S.G.S. 1:24,000 orthophoto sheets were used. Approximately 60% 

 of the area was covered by this set. For the remaining area the latest edition 

 of U.S.G.S. 1:24,000 topographic maps were used as a base. 



In mapping the present habitats in the 1:24,000 base the following re- 

 mote sensing coverage was used: 



1. 1969 U.S.A.C.E. uncontrolled photo mosaics. 



2. 1974 U.S.G.S. orthophoto quadrangle sheets. 



3. 1974 NASA High Altitude Color IR, missions 

 174, 191, 194, 197, and 289. 



Differentiation between marsh types was based on Chabreck et al. (1968), 

 Chabreck (1972), and the Texas Bureau of Economic Geology (1976). Updating 

 those previous works was accomplished through low altitude overflights. The 

 overflights along with ground reconnaissance served to evaluate the remote 

 sensing interpretation. 



Since field work was conducted in 19 76 to 19 77 and aerial coverage 

 varied from 1969 to 1974, it is impossible to put an absolute date on the 

 finalized habitat map. A reference date was needed in order to determine 

 temporal changes in habitat distribution. Over 90% of the area was covered 

 by a combination of color IR missions and the U.S.G.S. or the photo quads 

 for the year 1974. Thus, except for the differentiation between marsh types 

 the finalized habitat map represents habitats in 1974. 



Areas 



Areas of 1974 habitat units were derived from the 1:24,000 scale 



maps using the point-counting (grid sampling) method developed by Gagliano 

 and van Beek (1970). This method was compared to digitizing areas by means 

 of a Calma Digitizer (computerized planimeter) by Gane (in Adams et al. 1976) 



369 



