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Description:
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Increasing demand for water supplies in semi -arid regions , such as San Antonio ,
has sparked an interest in potential recharge management through brush control . Two
shallow caves under woody plant cover in northern Bexar County , Texas were chosen as
study sites where a detailed water budget would be developed . The Headquarters Cave
site measures natural rainfall and cave recharge while the Bunny Hole site is
instrumented to measure throughfall , stemflow , surface runoff , and cave recharge . Large
scale rainfall simulation was used at Bunny Hole to apply water directly above the cave
footprint allowing us to determine how recharge differs between natural and simulated
rainfall events . Under natural conditions , Headquarters Cave recharged 15 .05 % of the
annual rainfall while Bunny Hole received 4 .28 % . Natural canopy throughfall measured
59 .96 % of the water budget ; stemflow accounted for 0 .48 % and canopy interception was
39 .56 % ; no surface runoff was measured . Rainfall simulations conducted at Bunny Hole
resulted in an average of 74 .5 % throughfall , 5 .3 % stemflow , 20 .2 % canopy interception ,
2 .8 % surface runoff , and 6 .9 % cave recharge ; simulation intensities were typically
higher than natural event intensities . General water budgets across the Edwards Plateau have concluded that evapotranspiration represents 65 % of total annual rainfall while
percolation and storage accounts for 30 % and the remaining 5 % is runoff . These studies
have been focused on broad water budget parameters while this study looks at more
detailed components . No other study to date has been able to combine throughfall ,
stemflow , surface runoff , and vertical recharge monitoring to quantify the water budget
in the Edwards Plateau ; these parameters are instrumental in determining a detailed
water budget in juniper rangelands . Results from this study illustrate the significance of
all aspects of the water budget and are the first to yield a firm measurement of actual
upland recharge . |