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| On April 18, Dr. Bradford Wilcox, Texas A&M University, presented a talk on his study of brush control and the its effect on the recharging of the aquifer. He wanted to determine how much affect brush control has on the amount of water reaching the aquifer after a rain event. He said he got the idea for his study from observing water pouring out of the rocks on a highway cut on Interstate 10. Since it does not rain very often in West Texas, Dr. Wilcox and his assistants decided to build a rainfall simulator at the Sonora Experiment Station. By using PVC pipes and sprinklers, they are able to simulate any type of rainfall event on a small plot (30 feet by 30 feet). They dug a trench down hill from the plot to determine what happened to the water that was absorbed by the ground. Traps covered the trench to prevent any rain from the sprinklers from directly entering the trench. During the first part of their study, a large cedar tree dominated the plot. They studied simulated rain events from .3 of an inch to flood type rains. After the data was collected over a period of one year, they cut the cedar tree down and started the test over. On small rain events (less than or equal to .3 inches), they found some disturbing data. When rain lands on a cedar tree, the rain can be trapped on the leaves of the tree, or fall through the canopy of the tree and reach the ground. On small rains, most of the water is trapped by the canopy and evaporates. As the rain continues and the leaves become saturated, the water flows to the stem (stem flow) of the tree. When it reaches the stem, it runs to the base of the tree where it is used by the tree. As the rain intensity increases, more of the rain reaches the ground under the tree. There, it is absorbed by the ground under the tree or runs off. In West Texas, a very large majority of our rain events are less than .3 of an inch. So, on cedar-covered land, nearly all of the water from most of our small rains evaporates or is used by the cedar trees. They were surprised to learn where the water goes after the ground is saturated, and how fast the water penetrates the rocky soil. When the simulator was set to simulate a 2 inch rain on saturated ground, the water began to flow into the trench six feet below soil level in as little as ten minutes. They found that up to 70% of the rain fall enters the ground and flows to the aquifer. At the time of the test, they had not yet made any conclusions on the differences from the cedar tree covered plot to the cleared plot. Dr. Wilcox also pointed out that the most significant recharging of the aquifer occurs during floods. From this, he feels that his research will show that brush control will have a small impact on the recharging of the aquifer. This comment lead to some heated debate. Most of the long time ranchers present, related their experiences with cedar control and the improvement of grass production. Long time rancher, George Wallace said, "I don't know where the water goes once a cedar tree is cut down, but I do know that the cedar tree is no longer using it."
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