Determining the Water Budget in Comal County’s Honey Creek
By April Smith
Current and projected water needs for the state of Texas are rapidly growing. The Edwards Aquifer Area and upstream “contributing zone” exemplify those needs. Population pressures, in-stream flow, endangered species and irrigation are putting pressure on regional water resources.
One potential management strategy for increasing stream flow and ground water recharge in the area is vegetation management. Much of the region is covered by a dense canopy of juniper and oak, which has increased substantially during the last century. For this reason there is a high level of interest in using brush control as a mechanism to increase recharge.
“We want to know if vegetation management can increase the amount of stream flow or recharge,” said Dr. Brad Wilcox, associate professor in the Texas A&M University Department of Rangeland Ecology and Management.
Wilcox is conducting a field study in the Edwards Plateau with Dr. Clyde Munster, associate professor in the Texas A&M Department of Biological and Agricultural Engineering. Their research will help determine management strategies to increase water recharge by using brush control.
Wilcox and Munster have set up a research area seven meters wide and 14 meters long in the Guadalupe State Park’s Honey Creek Natural Area to conduct rainfall simulation. Their research group dug a trench approximately eight feet deep in order to view and measure subsurface water flow. The group also measured surface runoff, interception, transpiration and interflow to document how water flows through the system.
In August 2003, approximately eight inches of rainfall, which translates to 6, 980 gallons, was applied to the site during a period of 51 minutes using rainfall simulation equipment. There was no observed surface runoff during or after the rainfall simulation, which is unusual. The theory behind this is that the water moves below the surface, potentially promoting recharge into the aquifer.
“We saw a lot of water coming out at different faces in the trench,” said Shane Porter, a biological and agricultural engineering graduate student working with Wilcox and Munster. “It flowed predominantly from soil areas and places with heavy limestone or root fractures.” According to Wilcox, this kind of rapid water movement through the system is called preferential flow.
“This field study will allow us to quantify a water budget for the area in real time,” said Porter. “We can determine how much water brush species use, and whether brush control is necessary.”
Wilcox and Munster have also designated a paired plot that resembles the first research area in slope and soil type, but does not have any brush growth. Doing field studies allows comparison of surface and ground water flow with and without brush. The group’s field study in the paired plots began in March, and they have already seen a larger amount of surface runoff without brush present. Long-term plans include removing brush on the first plot and measuring the resulting flow patterns through simulation.
