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Flow Restoration: <br />Using Science to Anticipate Ecosystem Needs of Colorado's Mountain Streams <br />by Julia M. McCarthy, Christine M. Albano, David M. Pepin, and N. LeRoy Poff <br />Department of Biology & Graduate Degree Program in Ecology, Colorado State University <br />w ater remains a scarce resource in Colorado and <br />throughout the and West. The U.S. Bureau of <br />Reclamation (2003) projects continuing conflicts, with <br />potential water shortages along the Colorado Front <br />Range by 2025. One common approach to provid- <br />ing water to the Front Range (and elsewhere) is via <br />streamflow diversion. Indeed, in Colorado there are <br />approximately 109,000 active points of diversion on <br />streams (CDSS 2000). Many of these diversions occur <br />on small streams on the Western Slope of the Rock- <br />ies, where water is transported by tunnels to the Front <br />Range population centers. This movement of water <br />provides a valuable <br />resource, but at what <br />cost to the aquatic <br />ecosystems that are <br />deprived of their <br />native flows? The <br />question of ecologi- <br />cal damage caused by <br />extensive streamflow <br />diversion is one that <br />has received very <br />little attention, but <br />one that we expect to <br />become increasingly <br />important in the f i- <br />ture. Many scientific <br />studies show that the <br />ecological integrity <br />(or health) of streams <br />and rivers declines <br />when too much water <br />is removed from the <br />channel (Poff et al. <br />1997, Richter et al. 1997), but what is "too much "? <br />While there is a growing scientific literature on how <br />streamflow alterations below larger dams impair <br />stream and riparian ecosystems, this question has not <br />been resolved for diversions on mountain headwater <br />By providing clear definitions of ecosystem needs, <br />scientists can aid in the policy - making process and <br />help to balance the sometimes competing demands <br />of ecosystems and stakeholders (Doff et al. 2003). <br />Accordingly, the research conducted by our group at <br />CSU focuses on quantifying the ecological effects of <br />stream diversions. Specifically, we are investigating <br />how aquatic ecosystems respond to differences in op- <br />erational mode of diversion structures, the magnitude <br />of diversion, and the location on the landscape. Ad- <br />ditionally, we are trying to better define the flow needs <br />for these ecosystems. We envision that our results <br />will further <br />streams. <br />Management and policy decisions on restoring river <br />flows should be guided by the best available science. <br />14 <br />improve <br />diversion <br />manage- <br />ment by <br />helping <br />managers <br />and stake- <br />holders <br />operate di- <br />versions in <br />a way that <br />maintains <br />and restores <br />the system's <br />ecological <br />integrity. <br />Mode of <br />Diversion <br />Operation <br />The Fraser <br />River is at <br />the headwaters of the Colorado River where it drains <br />the western slope of the Arapaho National Forest's <br />continental divide. The City of Denver diverts water <br />from streams in the Fraser basin under the continen- <br />tal divide through the Moffat tunnel and into Gross <br />Reservoir on South Boulder Creek. Diversion dams <br />in the basin are operated to either take all the water <br />from a stream or to allow some "bypass" or "fish <br />flow" around the structure. Dams that dewater <br />