Office-Based Premapping Clause Samples

Office-Based Premapping. Initially, scientists premapped wetlands in a broad project area encompassing the area of all the potential alternatives. This mapping entailed stereoscopic interpretation of color aerial photographs (with a scale of 1” = 400’). Initial wetland/upland boundaries and boundaries between wetland types were drawn on mylar overlays of the photos. Wetland areas were delineated based on vegetation characteristics (e.g., small plant size and low-density stands), hydrologic indicators (such as stream locations and ponding), and topographic clues (such as concave topography). Upland locations were based on the lack of surface water visible on aerial photographs, the presence of tall and dense forest, and steep topography that would allow good surface drainage. Several information sources were examined initially: • Aerial photographs from AeroMap U.S. (taken 7/2/99, scale 1” = 400’; and taken 8/15/97, scale 1” = 1000’), true color. • Detailed topographic maps. • National Wetlands Inventory (NWI) map for quadrangles Ketchikan B-5 and B-6. The NWI maps are based largely on interpretation of aerial photographs and are presented at a coarse scale. • The detailed preliminary wetland determination prepared by ▇▇▇▇ Environmental Services for the Alaska Department of Transportation & Public Facilities in July 2000. The report provides wetland mapping and a wetland function assessment specifically for the current update of the Ketchikan International Airport Master Plan. • Existing GIS layers including streams, water bodies, NWI mapping, soil data, slope, and elevation data. Wetland/upland boundaries drawn in the office were used to plan the field efforts and determine potential problem areas. Initial mapping showed that most of the project area on ▇▇▇▇▇▇▇ Island is wetland.