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Parameter Sensitivity in Hydrologic Modeling - page 103 / 163





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larger portion of the flow path was already marked with a blue line on paper maps and on the DRG, whereas for Area 1 the blue line was not drawn on the map. It should also be noted that longest flow path using traditional paper map-based methods for Area 3 (6.28 miles) is 0.39 miles below the mean of 6.67 miles, well below the measurements using other methods of longest flow path extraction.

Perimeter measurements become less precise as the drainage area increases (the CV for Area 1 is 10.28%, while the CV for Area 3 is 14.99%). In addition, the perimeter values found using traditional methods and on-screen digitizing of raster graphic maps are smaller than those found using DEMs. Part of the reason for this large variation in perimeter could be due to the subjective nature of traditional paper map-based methods and on-screen digitizing of raster graphic maps, in addition to the more tortuous path created by digital data.

Table 5.3 shows that automated methods using CRWR-PrePro, WMS, and on-screen digitizing produce more consistent results than using manual hand delineation techniques on paper maps to determine area, longest flow path and perimeter for large areas. The values for area, longest flow path, and perimeter

determined using traditional paper map-based methods for Area smaller than those determined using more automated methods. outlines the CV results from Table 5.1, Table 5.2, and Table 5.3.

3 are much Figure 5.2


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