Utilization of the SWAT Model and Remote Sensing to

Demonstrate the Effects of Shrub Encroachment on a

Small Watershed

Jason Afinowicz

Department of Biological and Agricultural EngineeringTexas A&M University

Shrub Encroachment

• Replacement of herbaceous growth with woody species

• Active process over the past century

• Potentially caused by a number of human factors and climate change

• Shrub species such as Juniper and mesquite are assocaited with increased water consumption and transpiration

Brush Control

• Factored into many water quantity BMPs

• Reducing new-growth cedar in the Edwards recharge zone may lead to increased recharge

• Studies have been conducted to determine the effects of these techniques

• Methods include mechanical removal as well as more environmentally friendly manual methods

Overview of Project

Hydrologic simulation of a watershed with brush cover

Electronically remove the brush and determine the changes on the modeled

hydrology

The SWAT ModelThe Soil and Water Assessment Tool (SWAT) is a basin and watershed scale model for estimating the effects of management practices on water quantity and quality.

The SWAT 2000 model was integrated into the EPA’s Better Assessment Science Integrating point and Non-point Sources (BASINS) package.

SWAT can incorporate many factors into the simulation, including land cover, soil types, weather, and crop growth.

Honey Creek• Located in western Comal County

• Part of the Upper Guadalupe watershed (HUC 12100201) and is in the contributing region of the Edwards Aquifer

• Drains approximately 6000 acres

• Remains active throughout the year due to the activity of several springs

• Site of an in-progress brush control study utilizing two upstream branches of the creek

DataSurface Elevation

Hydrography

Soil Distribution

Land Cover

Weather Data

30-meter Resolution DEMs for Anhalt and Bergheim Quads

Provided by TNRIS

RF3 Reach Files for Upper Guadalupe Basin

Provided by EPA

SSURGO 2.0 Data for Comal and Hays Counties

Provided by USDA-NRCS

Landsat ETM+ Image: 20 October 1999 (LE7027039009929350)

Provided by TNRIS

Rainfall, Temperature, Solar Radiation, PET, and Windspeed

Provided by Texas ET Network, San Antonio Station (1/96–10/98)

DEM and Reach Data30-m DEMs of the Anhalt and Bergheim quads were mosaiced to produce an elevation grid which covered

the entire Honey Creek area

SSURGO DataSSURGO provides a

high-resolution alternative to

STATSGO soil data

Data for Comal County is provided in the new SSURGO 2 format

SWAT is built to read data found in STATSGO datasets

A User Soils table obtained from the Texas A&M Spatial Sciences Lab aided in the integration of this data

Landsat DataBand 1: Visible Blue

Band 2: Visible Green

Band 3: Visible Red

Band 4: Near Infrared

Band 5: Middle Infrared

Band 6: Thermal Infrared

Band 7: Middle Infrared

Band 8: Panchromatic

ClassificationScheme

Using ENVI

ClassificationScheme

Using ENVI

Land Cover Classifications

Landsat Data

Original DOQQ Parallel Piped Mahalanobis Distance

Maximum Likelihood Minimum Distance1-m DOQQ courtesy of TNRIS

Unclassified 0.69%

FRSE 43.06%

RNGB 31.83%

RNGE 24.42%

Climate Data

SWAT allows for the input of historical rainfall, temperature, solar radiation, and windspeed data, as well as the ability to name a user defined weather generator.

Potential ET can also be read into the simulation.

Climate data is entered in two separate dbf tables

Pre-Analysis with BASINS

Delineate the Honey Creek basin using the DEM and RF3 datasets

Assign spatial data pertaining to land cover and soil distribution

Control Simulation

Experimental Simulations

Experiment 1: Replace RNGB land cover with RNGE to demonstrate complete removal.

Experiment 2: Replace RNGB land cover with RNGE to demonstrate complete removal AND replace FRSE with RNGB to demonstrate partial clearing of dense areas.

Water YieldTotal Water Yield Results

Without October 1998 Data

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October-95 May-96 December-96 June-97 January-98 July-98 February-99

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Control Run

Experimental Run 1

Experimental Run 2

Change In Water YieldChange In Simulated Water Yield

-150

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-96

Apr-9

6

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96

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6

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97

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7

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7

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Experimental Run 2

Groundwater RechargeAquifer Recharge ResultsWithout October 1998 Data

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Experimental Run 2

Change In RechargeChange In Simulated Groundwater Recharge

-350

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96

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-97

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7

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-97

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97

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7

Aug-9

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Sep-9

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97

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Experimental Run 1

Experimental Run 2

ETEvaoration-Transpiration

0.0000

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October-95 May-96 December-96 June-97 January-98 July-98 February-99

Month

ET

(In

ches

of

Wat

er)

Control Run

Experimental Run 1

Experimental Run 2

Change in ETChange in Simulated Evaporation-Transpiration

-0.8

-0.6

-0.4

-0.2

0

0.2

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0.6

0.8

1

Jan-

96

Feb-96

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-96

Apr-9

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-97

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-97

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ET

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Experimental Run 1

Experimental Run 2

Future Goal:

Creation of a GIS

system for targeting

brush removal

1. Calibration of the model with gauging data now being recorded2. Enhancement of satellite land cover techniques3. Increased integration of available data