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

Ponds and Reservoirs
Surface runoff is the principal source of water for all purposes, due to the low water table and poor
quality of underground water. Seven storage reservoirs in this watershed furnish water for
municipal and industrial uses. Lake Scarborough, Hords Creek Reservoir, and Lake Coleman
furnish water to Coleman. Old and New Lakes Santa Anna, supplemented by a pipeline from
Lake Brownwood, furnish Santa Anna’s water. Lake Novice supplies Novice, and Lake
Brownwood supplies Bangs, Early, and Brownwood. Three PL-566 watershed protection and
flood prevention projects (Jim Ned Creek, Pecan Bayou, and Turkey Creek) are in the Lake
Brownwood watershed with 74 installed structures. Farm ponds supply a majority of the farmers
and ranchers with water for domestic and livestock uses. Figure 3-3 shows the distribution of the
major lakes and inventory-sized reservoirs.
Surface area, storage, and drainage area were obtained from the Texas Natural Resource
Conservation Commission (TNRCC) for existing inventory-sized ponds and reservoirs in the
watershed, and input to the SWAT model. Withdrawals from reservoirs for municipal and other
uses were estimated from data obtained from the City of Coleman, Brown County Water
Improvement District Number One, and the Texas Water Development Board (TWDB).
Model Inputs
Significant input variables for the SWAT model for the Lake Brownwood Watershed are shown in
Table 3-1. Input variables were adjusted as needed to calibrate flow at the applicable USGS
stream gage or reservoir. The calibration simulation represents the current “with brush” condition.
Model Calibration
SWAT was calibrated against measured streamflow and reservoir volumes by varying selected
model parameters (Table 3-1). The model was calibrated for flow at four USGS stream gages
(08141500 – Hords Creek near Valera, Texas; 08142000 – Hords Creek near Coleman, Texas;
08140800 – Jim Ned Creek near Coleman, Texas; and 08140700 – Pecan Bayou near Cross
Cut, Texas) (Figure 3-2) and for storage volume at two reservoirs (08140100 - Hords Creek
Reservoir and 08143000 - Lake Brownwood) (Figure 3-3).
Brush Removal Simulation
The input variables for the no-brush condition, with one exception, were the same as the calibration
variables, with the change in landuse being the only difference between the two simulations. The
exception is that we assumed the shallow aquifer re-evaporation coefficient would be higher for
brush than for other types of cover because brush is deeper rooted, and the opportunity for reevaporation
from the shallow aquifer is higher. The re-evaporation coefficient for all brush
hydrologic response units (HRU – combinations of soil and land use/cover) is 0.4, and for nonbrush
HRU’s is 0.1.
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