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<br />minimum depth to water) to 131 % (average fall rate) for the individual attributes, while the <br /> <br />average absolute difference for the five groups ranged from 18% (Group 1: monthly means) to <br /> <br />64 % (Group 5: rate and frequency of rises/falls). For individual attributes, the relative <br /> <br />difference between CVs ranged from -45% (average rise rate) to 61 % (mean June level); the <br /> <br />range for the five groups was 20 % (Group 2: magnitude and duration of annual highs and~ <br /> <br />lows) to 44 % (Group 3: timing of annual minimum and maximum). <br /> <br />, .,!,srl~) <br /> <br />The well data:;clearly:convey'the,impacts:oNncreased well pumpage in the EdwanljUI' <br /> <br />Aquifer in the recent20-year period as compared to the 20-year period at the start ofdataiWn-tl <br /> <br />collection. Monthly means have all shown increases, reflecting. greater depths to water (larger <br /> <br /> <br />values in Tahle4 represent lower water levels), ranging from 11-26% in deviation(Grou~. <br />In addition, the annual maximum 1-, 3-, 7-, 30-, and 9O-day depths all have increased"l~i:,~~.!,~, <br />substantially (30-37%), and the number and duration of low pulses is greater due to pumplrigr- <br /> <br />stress~ Annual minimum depths have also increased, but not to the degree that maximulll"l hIT-ii; <br /> <br />drawdowns have, suggesting that pumpage has not yet severely affected the aquifer's ability"to' <br /> <br />recharge during rain-y.,periods::However;the-rate'of'-drawdown (due to water withdrawals,lias <br /> <br />increased by 131 %, yet the average rise rate has decreased by 107 %, suggesting that well F>nl <br /> <br />pumpage may be restticting the rate at which water levels are recharged. <br />, , <br /> <br />. " oV' ,.l4".i:i ,.u <br /> <br />This Edwards Aquifer case study illustrates how cumulative impacts accruing fronrjh.,q <br /> <br />large numbers-of individually small hydrologic alterations such as wells can put ecosystenlslUti. ' <br /> <br />jeopardy. Thesubterranean channels and caverns within just the' southern portion of this .; 001 <br /> <br />limestone (karst) aquifer'support more than 40 endemic aquatic species (Longley 1992), ~lM <br /> <br />including the federally endangered Texas blind salamander (Ty.phlomolge rathhuni), the fIfst. <br /> <br />21 <br /> <br />,,".' <br /> <br />