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biological response thresholds to streamflow diversion
<br />would aid greatly in determining what proportion of
<br />natural flow is needed downstream of diversions to
<br />maintain ecological integrity during baseflow periods.
<br />Downstream recovery gradients
<br />As the above studies illustrate, negative impacts of
<br />diversion on the integrity of aquatic habitat and bio-
<br />logical communities can be ameliorated by re -entry of
<br />water to diverted reaches. In addition to groundwater,
<br />water is restored to diverted reaches from inflow -
<br />ing tributaries, which are likely to contribute to rapid
<br />recovery of aquatic habitat and communities. In
<br />recognition of this, a third component in our research
<br />program aims to quantify how quickly downstream
<br />diverted reaches may recover as a function of differ-
<br />ing degrees of groundwater and tributary inputs. We
<br />are examining this question at a broad scale, sampling
<br />diverted streams from multiple basins across northern
<br />Colorado, all with varying degrees of flow diversion
<br />and recovery. With this approach, and with the aid
<br />of a geographic information system (GIS), we plan to
<br />design a multi -basin model to predict the number of
<br />stream miles impaired by diversion dams. This land-
<br />scape -scale perspective on the biological impairment
<br />caused by diversion dams is important for furthering
<br />management and restoration efforts, as it provides sci-
<br />entific information at a scale relevant to river manag-
<br />ers and policy makers.
<br />Implications for restoration and management
<br />Maintaining some flow below diversion dams is
<br />necessary to sustain a viable aquatic community. Our
<br />initial, and preliminary, data suggest that maintenance
<br />and/or restoration of stream ecosystem integrity may
<br />be achieved by providing a relatively small volume of
<br />water to pass through diversion structures. Based on
<br />our ongoing research, we expect to gain a better un-
<br />derstanding of how the "landscape setting" influences
<br />the magnitude of diversion impact — for example,
<br />diversions in proximity to groundwater recharge areas
<br />or having downstream tributaries could potentially
<br />be managed differently than those having a slower
<br />recovery of flow.
<br />Further, determining a threshold of impact in sub -
<br />alpine and montane streams can advance restoration
<br />efforts, especially for water users with permits on
<br />multiple structures in one area. For example, our
<br />research could eventually suggest that collecting small
<br />amounts of water from multiple streams would have
<br />fewer impacts upon stream biota than collecting large
<br />amounts of water from just a few streams. In the cases
<br />of large water diversion projects, where structures on
<br />several streams are already in place, incorporation of
<br />this knowledge into water management could enable
<br />th same amount of water to be collected, with fewer
<br />ecological impacts.
<br />With growing populations on the Front Range, there
<br />is increasing interest to divert more water for human
<br />consumption. An opposing tension, however, may be
<br />the value that our modern society places on managing
<br />resources for ecosystem health. Good science is need-
<br />ed to determine how much alteration ecosystems can
<br />withstand and still remain "healthy." Our preliminary
<br />research on the impacts of diversion location, operation
<br />and magnitude can help shape management and policy
<br />decisions about our shared water resources. Furthering
<br />the conversation with water users, managers and policy
<br />makers on our research and restoration initiatives can
<br />improve the future of water management for all water
<br />users, human and aquatic.
<br />References
<br />CDSS. 2000. Hydrobase Database, Colorado Water
<br />Conservation Board.
<br />Pepin, D.M. and N.L. Poff. 2001. Flow regime analysis
<br />of 7 Colorado trout streams. Report prepared for
<br />Trout Unlimited.
<br />Poff N.L., J.D. Allan, M.B. Bain, J.R. Karr, K.L. Pre -
<br />stegaard, B.D. Richter, R.E. Sparks and J.C. Strom -
<br />berg. 1997. The Natural Flow Regime: A paradigm
<br />for river conservation and Restoration. Bioscience
<br />47(11). 769 -784.
<br />Poff, N.L., J.D. Allan, M.A. Palmer, D.D. Hart, B.D.
<br />Richter, A.H. Arthington, K.H. Rogers, J.L. Meyer
<br />and J.A. Stanford. 2003. River Flows and water
<br />wars: emerging science for environmental decision
<br />making. Frontiers in Ecology and Environment 1:
<br />298 -306.
<br />Rader, R.B. and T.A. Belish. 1999. Influence of mild
<br />to severe flow alterations on invertebrates in three
<br />mountain streams. Regulated Rivers: Research and
<br />Management 15: 353 -363.
<br />Richter, B.D., Braun, D.P., Mendelson, M.A. and L.L.
<br />Master. 1997. Threats to imperiled freshwater
<br />fauna. Conservation Biology 11: 1081 -1093.
<br />USBR. 2003. Water 2025: Preventing crises and con-
<br />flict in the West. U.S. Bureau of Reclamation.
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