water availability modeling in the state of texas
DESCRIPTION
Water Availability Modeling in the State of Texas. CE 394 K.2 - Surface Water Hydrology University of Texas at Austin David Mason. Outline. Project Objectives Source Data Collection Analysis of Data Presentation of Results Possible Solutions Conclusions Future Work. Project Objectives. - PowerPoint PPT PresentationTRANSCRIPT
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Water Availability Modeling in the State of Texas
CE 394 K.2 - Surface Water HydrologyUniversity of Texas at Austin
David Mason
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Outline
• Project Objectives• Source Data Collection• Analysis of Data• Presentation of Results• Possible Solutions• Conclusions• Future Work
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Project Objectives
• Use GIS utilities to create a spatial water rights database
• Compile watershed data for each water right and stream gage location in selected basins – Drainage area, avg. precip, avg. CN, flowlength to
outlet• Compare GIS results with established USGS
values• Study the effects of using higher resolution DEMs
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Selected Basins
Nueces San Antonio
Guadalupe
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Source Data Collection
• Digital Elevation Models (USGS)• RF3 Coverages (EPA)• Water Right and Diversion Locations (TNRCC)• Primary Control Points (Relevant Contractor)• Precipitation Grid (Oregon State)• Curve Number Grid (CRWR)• Digital Raster Graphics (TNRIS)
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Process the DEMs
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Download and Edit RF3
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Water Rights and Diversions
-The San Antonio Basin had 488 water right locations when it was sent to TNRCC
-When I got it back….488 turned into 788!!
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Primary Control Points
• Primary control points are mainly stream gage locations used to distribute naturalized flows throughout the basin
• Control points and locations were provided by HDR
• Arc/Info was used to create an Arcview theme of these control points
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Precipitation and CN Grid• The precipitation grid
received from Oregon State was resampled to the same size as the DEM
• Once resampled, a calculation was preformed in Arc/Info to produce a grid of the average precipitation across the basin
• The same basic procedure was used to produce the CN grid
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Flow Length Grid
• The flow length grid is calculated using the Hydrologic extension in Arcview
• The extension calculates the distance to an assigned outlet for each cell in the grid
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Calculating the Parameters• Once all the grids have been produced, the next step is to place the points on the flow accumulation grid in order to assure the accurate calculation of the parameters
• After the points are in place, a script is run that selects the value of each grid cell “under” a point and attributes those values in a table
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End Result of a Very Long Process
• The result is a coverage with avg. CN, avg. precip., flowlength and # of cells in the flow accumulation grid
• The # of cells are then converted to an equivalent drainage area
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Results - Nueces
Average Error in Area = 1.36%
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Results - San Antonio
Average Error in Area = 3.44%
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Results - Guadalupe
Average Error in Area = 3.57%
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Possible Problems• DEM Resolution
– Currently using 90m, just received 30m• Degree of Terrain Relief
– Guadalupe is somewhat of a coastal basin• God Forbid! USGS May Be Wrong!!
– Numbers based on old maps– No one’s perfect!
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Conclusions
• GIS can be used effectively to compute watershed parameters for a large number of control points
• Although some of the results are somewhat different than USGS values, the new 30m data sets should help to reduce this error
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Future Work
• Find a way to use the new 30m DEM data sets in an efficient manner– the current file sizes are far too large
• Apply some quality control techniques to assure more accurate results– hand-delineate some of the smaller watersheds to make
sure the larger ones aren’t masking discrepancies