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Parameter Sensitivity in Hydrologic Modeling - page 135 / 163

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6.1

ERROR SOURCES AMONG PARAMETER EXTRACTION METHODS

This study examines parameter extraction methods in three drainage areas

of different size in Austin, Texas. Area 1, the smallest area, is approximately 0.5

mi2. Area 2, the medium-sized area, is approximately 1.7 m2; and Area 3, the

largest area, is approximately 8.8 mi2.

Errors associated with each of the four

levels of parameter extraction, in addition to the influence of drainage area size on

parameter extraction method, are evaluated.

6.1.1

Parameter Extraction using Paper Maps

Traditional hydrologic parameters from paper maps.

modeling involves calculating watershed Calculation of terrain-based hydrologic data

involves delineating the watershed by hand using map contours as guidelines. Once the perimeter of the watershed has been established, a planimeter is used to measure its area. Perimeter and length of the longest flow path are measured

using a map wheel. between map contours.

Slope

is

calculated

by

taking

the

difference

in

elevation

Variations in traditional, paper map-based methods were most apparent in Area 3. This drainage area, the largest area under investigation, yielded hand measurements for area and longest flow path, 0.29 mi2 and 0.39 miles below the mean, respectively. These area and longest flow path values were smaller than any of the other area or longest flow path measurements for Area 3. The length of perimeter, although not normally used as a hydrologic parameter, was 3.57 miles

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