Appendix 6.4(3). Continued 



years (1952 to 1974). The linear distances were converted to area by multi- 

 plying by the sum of half of the distance to the next data point to the west 

 and to the east. 



Canals 



Canal length was digitized by type of canal. Area occupied by canals 

 could not be digitized due to resolution problems in determining widths at 

 1:24,000 scale. An average width value for each type of canal was determined 

 by general field observations, and a limited amount of U.S.A.C.E. dredge 

 data. These width values, along with the digitized length values, were used 

 in computing canal areas. 



Canal types were defined according to their initial intended purpose. 

 This was necessary in order to place a canal under a single category, al- 

 though it may have multiple uses. For example, Stack's canals in and around 

 the Sabine National Wildlife Refuge were constructed for trappers. This 

 places these canals under second order navigation canals although the re- 

 sulting spoil is also used for wildlife management impoundment. Definitions 

 of the various canal types are listed below: 



First Order Navigation Canals 



- those major canals dredged and maintained to facilitate both 

 interstate and intrastate navigation. 



Second Order Navigation Canals 



- canals dredged or dug to a low passage of small craft, or short deeper 

 water spurs to allow movement of large craft from a first order canal 

 to an industrial site. 



Agricultural, Industrial, and Urban Drainage Canals (Wetland and Upland) 



- canals whose primary purpose is to convey water to or from a site, 

 or canals which were dug to isolate an impounded agricultural area. 



Agricultural Access Canals and Borrow Pits 



- canals and typically staggered borrow pits flanking an embankment 

 which is used solely for the purpose of cattle access. 



Oil Activity Canals 



- canals dredged for exploration and production of oil and gas. 



Canals dredged principally for a water-based oil/gas extractive 

 operations were listed as oil field navigation canals. Canals and 

 borrow pits flanking embankments which extended into the marsh to 

 enable a land-based operation were classified as oil field embank- 

 ment canals and borrow pits. 



371 



