Source: Texas State Soil and Water Conservation
The Texas State Soil and Water Conservation Board (TSSWCB) and HDR Engineering, Inc., recently finalized the project final report Brush Management in Gonzales County as a Water Management Strategy. This study was conducted by HDR with funding from the agency’s Water Supply Enhancement Program.
The purpose of the Water Supply Enhancement Program is to increase available surface and ground water supplies through the targeted control of water-depleting brush in areas in need of water conservation. The State Conservation Board allocates program funding to landowners giving priority to projects that balance the most critical water conservation need of municipal water user groups with the highest projected water yield from brush control.
Following discussions with the San Antonio River Authority, the State Conservation Board approached the South Central Texas Regional Water Planning Group (Region L) about the potential inclusion of a brush management project in Gonzales County as a water management strategy in the 2016 South Central Texas Regional Water Plan. Working with the regional water planning group’s consultant (HDR), a water management strategy was conceptualized for areas of the Carrizo-Wilcox Aquifer in Gonzales County. In the regional water plan, the Carrizo-Wilcox Aquifer in Gonzales County is fully allocated, as usage and permitted pumpage are greater than the modeled available groundwater; therefore, any enhancement to groundwater yield would be additional water supply available to water user groups.
“This study was able to quantify the benefits of brush management for water supply enhancement in a way that could meet the Texas Water Development Board requirements for inclusion as a water management strategy in the regional and state water plans,” said Steve Raabe, director of technical services for the San Antonio River Authority. “The study utilized a dynamic ecological model to simulate changes in the landscape characteristics due to brush management and coupled those results with the groundwater model for the Carrizo-Wilcox Aquifer to estimate changes in recharge and potential increases in modeled available groundwater. This is the first time these two models were linked to provide information for the regional water planning process.”
Brush has invaded millions of acres of rangeland and riparian areas in Texas, reducing or eliminating streamflow and aquifer recharge through interception of rainfall and increased evapotranspiration. Brush control has the potential to enhance water yield, conserve water lost to evapotranspiration, recharge groundwater and aquifers, enhance spring and stream flows, restore native wildlife habitat by improving rangeland, and improve livestock grazing distribution.
If brush management were conducted over the Carrizo-Wilcox Aquifer outcrop in Guadalupe, Gonzales, and Caldwell Counties, increases in recharge to the Carrizo-Wilcox Aquifer would result in increases to the amount of water in aquifer storage in Gonzales County. This study utilized information from a brush control feasibility study for Gonzales County, completed by scientists at Texas Tech University (McLendon et al. 2012; available on the agency’s website), to approximate recharge to the aquifer outcrop. Using a groundwater availability model, this study then determined the increases in the modeled available groundwater in these counties.
“Brush management as a water management strategy could potentially benefit entities utilizing the Carrizo-Wilcox Aquifer in Gonzales County,” said Brian Perkins, formerly with HDR Engineering, Inc., now with Black and Veatch. “Assuming cooperation amongst those that use the Carrizo-Wilcox Aquifer, regulators, and landowners, the project could be a cost-effective way to incrementally increase the water supply from the aquifer.”
The study demonstrates that about 17 to 19 percent of the enhanced recharge produced from brush management is translated to an increase in the modeled available groundwater estimates in Gonzales County. The model scenarios show that implementing a brush management program in Gonzales, Caldwell, and Guadalupe Counties over the Carrizo-Wilcox Aquifer outcrop could potentially increase the groundwater levels and the subsequent modeled available groundwater in these counties by 1,370 acre-feet/year to 13,910 acre-feet/year depending on the landowner participation levels, while maintaining the existing desired future condition.
“When private landowners ably manage our natural resources, we enhance and sustain the availability of water for everyone in the state, including those living in urban areas,” said Phil Breitschopf, chairman of the Gonzales County Soil and Water Conservation District. “Effective land stewardship increases the ability of open land to absorb rainfall, replenish aquifers, and ensure that water drains slowly and steadily into springs, streams, rivers, and lakes.”
With 100 percent landowner participation, the modeled available groundwater in the Carrizo-Wilcox Aquifer in Gonzales County could increase by 25 percent. This level of participation is probably impracticable; however, 30 percent landowner participation may be attainable and would increase the modeled available groundwater by 4,631 acre-feet/year. Annual unit cost estimates for this brush management strategy range from $937 to $1,209 per acre-foot of water, depending on the level of landowner participation, which is fairly reasonable when compared to other more expensive water management strategies such as brackish water desalination, aquifer storage and recovery, or off-channel reservoirs.
“Voluntary land stewardship, on a grand scale, is a cornerstone solution for water supply issues in Texas. The efforts of private landowners to control water-depleting brush are vitally important to the ecological health of our productive rangelands across the state,” said Rex Isom, TSSWCB executive director. “Many Texans today, especially those in urban areas, enjoy the public benefits, such as clean plentiful drinking water, they derive from the voluntary land stewardship provided by private landowners and agricultural producers throughout the state.”
For more information about the TSSWCB’s efforts to enhance public water supplies through the targeted control of water-depleting brush, please contact Johnny Oswald at 325-481-0335 or [email protected]. Additional information on the agency’s Water Supply Enhancement Program, including the project final report Brush Management in Gonzales County as a Water Management Strategy, is available at http://www.tsswcb.texas.gov/brushcontrol.
Source: Texas State Soil and Water Conservation