The Washington State Department of Transportation (WSDOT) has a need to inventory wetlands along highway rights of way. Aerial photo interpretation was determined to provide a reasonable compromise between accuracy and cost, so several forms of aerial photography were tested. Two test areas were photographed with both true color and color infrared film in three scales: 1:24,000 (1 in.=2000 ft), 1:12,000 (1 in.=1000 ft), and 1:6,000 (1 in.=500 ft). Photo interpreters classified wetlands and delineated their boundaries, and these interpretations were compared with data from field delineations performed by a wetland biologist. A method using aerial videography was also analyzed.
Based on test results and other factors, the preferred inventory method will use color infrared film at 1:12,000 scale. WSDOT devised techniques to plot wetland boundaries on existing base maps and is developing an Oracle database that will be linked with the map files. When this is completed, it will be possible to print maps that depict wetland boundaries and classifications. A variety of modeling tasks and data analyses will also be possible.
The inventory will cost approximately $658,000 for 7,030 miles of WSDOT right-of-way. The end product should improve early project planning, eliminate problems resulting from late discovery of wetlands within project boundaries, and reduce biologist field time.