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

The soils database currently available for all of Texas is the State Soil Geographic (STATSGO)
1:250,000-scale soils database, which covers the entire United States. In the STATSGO
database, each soil delineation or mapping unit is made up of more than one soil series. Some
STATSGO mapping units contain as many as twenty SSURGO soil series. The dominant
SSURGO soil series within an individual STATSGO polygon was selected to represent that area.
The GIS layer representing the soils within each watershed was a compilation of CBMS,
SSURGO, and STATSGO information. The most detailed information available was selected for
each county and patched together to create the final soils layer. SSURGO data was available for
approximately 90 percent of Phantom Hill and 75 percent of Palo Pinto watersheds. CBMS soils
were used in about 90 percent of Brownwood and essentially all of Arrowhead watersheds. Very
little STATSGO soils were used in any of the watersheds.
SWAT used the soils series name as the data link between the soils GIS layer and the soils
properties database. County soil surveys were used to verify data for selected dominant soils
within each watershed.
Topography. The United States Geological Survey (USGS) database known as Digital
Elevation Model (DEM) describes the surface of a watershed as a topographical database.
The DEM available for the project area is a 1:24,000 scale map. The resolution of the DEM is
30 meters, allowing detailed delineation of watershed boundaries (Figure 1-1) and subbasins
within each watershed (Table 1-2).
Table 1-2. Watershed area, number of subbasins, and average annual precipitation.
Watershed Total Area Number of Subbasins Average Annual
(acres)
Precipitation (inches)
Lake Arrowhead 529,354 28 28.0
Lake Brownwood 997,039 48 26.5
Lake Fort Phantom Hill 301,118 17 25.4
Lake Palo Pinto 296,398 22 30.4
Climate. Daily precipitation totals were obtained for National Weather Service (NWS) stations
within and adjacent to the watersheds for 1960 through 1999. Data from nearby stations were
substituted for missing precipitation data in each station record. Daily maximum and minimum
temperatures were obtained for the same NWS stations. A weather generator was used to
generate missing temperature data and all solar radiation for each climate station. Average
annual precipitation decreased from east to west (Table 1-2 and Figure 1-1).
Model Inputs
Required inputs for each subbasin (e.g. soils, land use/cover, topography, and climate) were
extracted and formatted using the SWAT/GRASS input interface (Srinivasan and Arnold,
1994). Specific values used in each watershed are discussed in the individual chapters.
A1-6