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.
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.
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