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Water Availability Modeling in the State of Texas

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.

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Water Availability Modeling in the State of Texas

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  1. Water Availability Modeling in the State of Texas CE 394 K.2 - Surface Water Hydrology University of Texas at Austin David Mason

  2. Outline • Project Objectives • Source Data Collection • Analysis of Data • Presentation of Results • Possible Solutions • Conclusions • Future Work

  3. 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

  4. Selected Basins Guadalupe San Antonio Nueces

  5. 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)

  6. Process the DEMs Guadalupe Nueces San Antonio

  7. Download and Edit RF3 Talk to Brad!

  8. 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!!

  9. 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

  10. 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

  11. 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

  12. 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

  13. 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

  14. Results - Nueces The GOOD Average Error in Area = 1.36%

  15. Results - San Antonio The BAD Average Error in Area = 3.44%

  16. Results - Guadalupe The UGLY Average Error in Area = 3.57%

  17. 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!

  18. 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

  19. 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

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