Lake Brownwood Watershed - Texas State Soil and Water ...

Brush Removal Simulations
All watersheds showed an increase in water yield and streamflow as a result of removing brush.
Average annual water yield increase varied by watershed and ranged from about 111,000 gallons
per treated acre in the Fort Phantom Hill watershed to about 178,000 gallons per treated acre in
the Palo Pinto watershed (Figure 1-2). As in previous studies (TAES, 2000; COE, 2002) water
yield increases were higher for watersheds with greater annual precipitation.
Streamflow increase at the watershed outlet (Figure 1-2) ranged from about 32,000 gallons per
treated acre in Fort Phantom Hill to about 127,000 gallons per treated acre in Arrowhead.
Average annual streamflow increases were less than water yield increases because of channel
transmission losses that occur between each subbasin and the watershed outlet, and capture of
runoff by upstream reservoirs. Streamflow increases for Fort Phantom Hill and Palo Pinto were
significantly less than water yield increases because these two watersheds had higher channel
transmission losses and upstream reservoirs had a greater effect on streamflow.
Average annual inflow increases for lakes at each watershed outlet were higher for watersheds with
greater drainage area (Figure 1-3). One exception was Fort Phantom Hill, which had less inflow
increase than Palo Pinto, even though the drainage area of Fort Phantom Hill was slightly greater.
This was most likely due to lower annual rainfall and higher channel transmission loss in Fort
Phantom Hill.
Water yield increases for watersheds in this study were similar to COE (2002), but slightly
higher than TAES (2000) (Figure 1-4). In TAES (2000), removal of all brush was simulated,
and in COE (2002) several scenarios of partial brush removal were simulated. The data for
COE (2002) shown in Figure 1-4 are for Scenario I – removal of all brush on slopes less than
15 percent.
Water yield increases for the current study and COE (2002) were higher than TAES (2000)
because of SWAT model changes after the TAES (2000) study was completed, especially a
reduction in calculated PET.
The higher water yield for Arrowhead (Figure 1-4) was likely due to the higher percentage of
hydrologic group “D” soils in this watershed (54% vs. 39, 21, 38 for Brownwood, Phantom
Hill, and Palo Pinto, respectively) that produced a greater difference in annual runoff volume
between brush and no-brush conditions.
SUMMARY
The Soil and Water Assessment Tool (SWAT) model was used to simulate the effects of brush
removal on water yield in four watersheds in Texas for 1960 through 1999. Landsat 7 satellite
imagery from 1999 was used to classify current land use and cover for all watersheds. Brush
A1-9