An Analysis of a Methodology for Generating
Watershed Parameters using GIS
By David Mason, MSE, and David R. Maidment
ABSTRACT
A basic methodology is presented for generating watershed parameters
in a GIS format. The calculation of drainage area, average curve number,
and average precipitation parameters were made for water right locations
as part of the TNRCC´s Water Availability Modeling project for the Nueces,
Guadalupe, San Antonio, and San Jacinto river basins. The effectiveness
of the methodology was analyzed. The study showed that 90-meter (1:250,000
scale) DEMs alone could not be used to accurately delineate watersheds.
However, 30-meter (1:24,000 scale) DEMs were used to accurately delineate
watersheds ranging from a size of 10,000 square miles to 0.15 square
miles in areas with well-defined drainage. The limitations of using
30-meter DEMs were a 10-fold increase in both file size and processing
time. Also, the increased resolution of the DEMs still had difficulty
defining accurate watersheds in areas with an average slope of less
than 0.002 m/m.
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2000 Center for Research in Water Resources.
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