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could be approximated within ± 0.05 as percent slope (a CV of 3.65%). The mean slope for Area 3 was 0.77%, while the mean slope for Area 1 was 1.30%.

6.2.3

Longest Flow Path

Longest flow path results produced errors greater than slope or area errors for all three study areas. However, this error decreased from 8.42% to 3.22% as the study area size increased from Area 1 to Area 3. For the largest area, longest flow path was calculated within ± 0.22 miles, with a mean value of 6.67 miles. For the smallest area, longest flow path was calculated within ± 0.13 miles, with a mean value of 1.58 miles.

6.2.4

Perimeter

Watershed perimeter length, although not a hydrologic parameter, was

examined

to

evaluate

trends

in

line

variation

among

methods.

Automated

methods using DEMs produced greater values for perimeter

methods for all three study for perimeter. For Area 1, value was 14.99%.

areas. the CV

This resulted in consistently value was 10.28%, and for

than traditional high CV values Area 3, the CV

6.2.5

Curve Number

The SCS runoff curve number obtained by combining land use and soil types in GIS for Area 2 was 91.7, while the curve number determined by an independent TxDOT study was 85.8. A range of curve number values, using the

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