can be calculated automatically. A longest flow path is also digitized from the DRG and its length calculated by the GIS.
Table 4.2 outlines the results of Area 1, Area 2, and Area 3 from digitization.
Table 4.2: On-Screen Digitizing Results
Longest Perimeter Flow Path
Watershed Area 1
No Hwy/ Hwy No Hwy Hwy No Hwy Hwy No Hwy Hwy
CASE III: AUTOMATED METHODS USING A DEM
Case III is divided into two parts. The first part describes using ArcView GIS 3.2 and CRWR-PrePro to delineate the watersheds and extract watershed parameters using two different spatial resolution DEMs. The second part explores using the Watershed Modeling System (WMS) to also delineate the watersheds and extract watershed parameters at the same two spatial resolutions as with ArcView GIS 3.2.
The most widely available grid DEMs in the US are distributed by the USGS and are of 7.5 minute resolution (same coverage as a standard USGS 7.5 minute map series quadrangle), with a grid spacing of 30 x 30 meters. These