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A Water Quality GIS Tool for the City of Austin
Incorporating Non Point Sources and Best Management Practices
By Katherine Grace Osborne, Michael Barrett and David Maidment
ABSTRACT
Estimating pollution contributions from non-point sources is always
difficult. Calculating pollution due to runoff into urban creeks and
waterways is no exception. In an effort to model non point source pollution
in Austin, a Geographic Information System (GIS) grid based hydrology
model was developed for the City to aid in the development of a citywide
Water Quality Master Plan. There are three primary objectives for the
model: 1) compute current pollutant loadings for seventeen constituents
at Environmental Integrity Index (EII) sites; 2) estimate future loadings
for the year 2040 for the same constituents; and 3) model the influence
of Best Management Practices (BMPs) on reducing pollution loads. Initial
work completed in 1997 by researchers at the Center for Research in
Water Resources (CRWR) was a substantive first step; however, many limitations
and recommendations were also identified. This paper discusses the next
manifestation of the model that was developed at CRWR during 1999-2000.
The three main modifications made in the second phase concern increasing
both model accuracy and accessibility. First, significant improvements
were made to improve datasets used as input to the model. Second, corrections
for both flow and load calculations were made on a cell-by-cell basis
within the GIS environment instead of corrected separately in a spreadsheet.
Third, future impervious cover projections, the basis for flow calculations,
were tied more closely to undeveloped land parcels. Lastly, to make
the model more accessible to a variety of policy makers, reliance on
ArcInfo has been minimized; ArcView is now the platform for the model.
In addition to these changes, new City assumptions were incorporated,
especially with regards to base flow and storm flow separation. With
these modifications in place, City objectives were met, and improvements
in accuracy and accessibility were realized.
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These materials may be used for study, research, and education, but
please credit the authors and the Center for Research in Water Resources,
The University of Texas at Austin. All commercial rights reserved. Copyright
2000 Center for Research in Water Resources.
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