Eastern watershed analysis of alternate approaches to delineation in Austin, TX

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Title: Eastern watershed analysis of alternate approaches to delineation in Austin, TX
Author: Vermillion, Elizabeth Lauren, 1982-
Abstract: Drainage area is a measure of the number of acres feeding into a creek . Drainage area threshold is the amount of acreage required for the creek to be included on a map . Watersheds mapped according to higher drainage area thresholds will show creek systems that are shorter and concentrated at the bottom of the watershed . Watersheds mapped according to lower drainage area thresholds show creek systems that are longer and extend further up the watershed . Since all watersheds are subject to different land uses , soil types , geology , etc . , they should be mapped according to different drainage area thresholds . Headwaters are where creeks begin . There is empirical evidence that properly functioning headwaters significantly reduce erosion , improve water quality , slow stormwater flows , and provide habitat . If municipalities use lower drainage area thresholds to define their creeks , they can include more headwaters in their creek setback requirements . This professional report identifies the Harris Branch watershed as being under relatively more pressure to develop and exhibiting more environmental risk than other watersheds in Austin , Texas’ Desired Development Zone . Creeks in the watershed are redrawn according to reduced drainage area thresholds using a simple ArcGIS analysis . The analysis reveals a critical mass where creek setbacks appear to be too extensive . If creeks with a drainage area of 5 acres are protected by development code , the setbacks created have excessive branching that could be too restrictive for development . A critical mass ratio should be considered when determining which drainage area threshold is most appropriate for a watershed . The critical mass ratio is equal to the number of branches allowed per a specified distance of creek centerline . The process of identifying this critical mass ratio can help growing cities find a balance between the need to encourage development in designated areas and the need to protect natural creek systems everywhere . I recommend that municipalities review the effects of reducing drainage area threshold for each watershed , and then identify the drainage area threshold that , when protected by setback requirements , allows for extended and connected greenways as well as an increase in density .
URI: http : / /hdl .handle .net /2152 /ETD -UT -2010 -05 -1296
Date: 2010-11-24

Citation

Eastern watershed analysis of alternate approaches to delineation in Austin, TX. Master's thesis, University of Texas at Austin. Available electronically from http : / /hdl .handle .net /2152 /ETD -UT -2010 -05 -1296 .

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