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February 2003 ECOLOGICALLY SUSTAINABLE WATER MANAGBMBNT 211 T ABL.E 1. Federal environlT.lent~l agencies have defined ecosystem flow requirements thought necessary to sustain viable populations of endangefed species in the Apalachicola.-Chatta.. hoochee-FliJlt River basin in Alabama, Flodda, alld~ Georgia. . Gl.lidelin~s based on pre...dam flows exceed the lniniro,um In all years ex.ceed ~he 25th percentile in 3 out of 4 years exceed the n1edi~n in half of the years do not exce,ed th~ nlaxiqlUlU in all years , do not exceed th~ 75th percentile in 3 out of 4 years do not exceed the: median in half of the years maintain the monthly n1eall flow within .the range of the 25th and'75th pel'centile values in" hatf of the years ' , ex.ceed the mini 'I'l1Un1 in all years exceed the, 25th percentile in 3 out of 4 years exceed the nledian in half of the years exceed the miniJll.unl in all yea1'S ex.ceed the 25th ~ercenti1e in 3 OLlt of 4 years exceed the medi~n in half of the years "Fl,?w pSrE\1ueter Monthly. ] ..day lninima Annual1ow..flow duration Monthly average flow Annual ) ..day maxinla Annual 11 i gh-flow duration the influence of the prescribed flow characteristics (e4g., Table 2). These ecosystem indicators becoll1e part of the mOllitoring program (Step 6) that tracks the suc- cess of the water management plan in achieving eco. logical sustainab~lity. . _ , Initial estimates t)f ecosysteul flow requirements should be defined without regard to the p~rceived tea... sibility of attain ing them through near-term changes 'in water TIlartagelnent. We reiterate our assertion that eco- logical sustainability Sh01.11d be presulned to be attain- able over the long"run, until conclusive evidence sug- gests otherwise. We have been involved in" numerous water manageme:nt conflicts ill which initial petcep- tion~ of unfeasibility were OVerCQll1e through creativity and deeper analysts~ or a change in the socioeconomic or political landscapes that made possible what had seen1.ed impo'ssible ~ decade or two earlier~ " 350D 3000 2500 ..-.. ~ 12000 ~ rt 1500 Q) :~ a: 1000 SOD Inviting water managots and otner interested parties to Q 'bserve the process 0 f defining ecosysteln flow re- quirements can have inlportant benefits (J4 King. ocrrr [oJqo ITlD 0 ooa:nonoO). Water managers can help sci- ellti.~ts .understand how to prescribe flow _targets -in _ a manilet that can be i1nplemel1ted. Water managers can learn a lot about the possible effects of water manage- nlent on river ecosystenls, thereby incl"easing their eco... logi6allitera.cy. Perhaps more imporrant~ watet man... ager~ . will gain insight into the nature of the LOOq:m OOODOIm 00 [][]([J moo ornoo~ thereby helping tbe~ un- derstand the need fot 'ex.periments and flexibility in water ~lanagement. It is important (01.._ water ll1a.nagers) -. " conservationists, and water users to understand that scie~tists .will not be able to" 'provide comprehensive al'ldiexact estimates of the flows l"equired by pa.rticular speQies, aquatic and ripalian communities, or the whole ~-----...- . 0 Jan Feb Mar Apr May Jun ~UI A~9 Sep Oct Nov Deo FlO. 4. One of the ecosystem flow requirelnents identified for t~'e Apalachicola. River in Florida is to maintain daily flows above targeted minimunllevels during each month of the year; Eqosystem flow requirements (thin line) are compared with , nlodel simulated daily flaws (thick line) for the drought year of I ~85.. River flow is in cubic meters per second (In)/s),