Cave Monitoring of Recharge Rates in the Edwards Aquifer Recharge Zone – Before and after Juniper Removal

Enhancing recharge in the Edwards Aquifer is critical for the water supply of the city of San Antonio. In addition, municipalities, industry and agriculture in the region surrounding San Antonio all depend on the Edwards Aquifer for water. The objective of this research was to assess the effects of juniper removal on recharge in the Edwards Aquifer. Recharge rates in the Edwards Aquifer recharge zone were monitored in a shallow cave during simulated rainfall events. The cave is beneath a hillslope covered with a dense juniper – hardwood forest. A baseline series of simulated rainfall events were conducted with the trees in place. The baseline tests found that for simulated rainstorms of around 50 mm, about 20% of water applied was intercepted, except for wet and cloudy conditions, in which case interception was close to zero. Stemflow accounted for between 5% and 10% of the water reaching the ground surface and was highest under the wettest conditions. There was little surface runoff. Recharge accounted for between 6 and 11% of the water applied and was highly responsive to rainfall. The juniper trees have been cleared and the same simulated rainfall events will be applied to the cleared site this summer. The changes in recharge rates due to the removal of the juniper will be presented. The effects of canopy interception on recharge and surface runoff will be discussed.