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t ,--~ ~ ~ ~~ i~-~ Boulder's planning process accounted for tributary and mainstream water and dealt with land planning issues so the city could predict its water needs at the time of complete build- out. Boulder may be unique in that, by 1988, the city had acquired sufficient rights to supply all anticipated development, even in the case of drought. Boulder Creek, Colorado Boulder Creek, Colorado, provides another example of the use of water rights transfers to maintain instream flows for fisheries and, as a collateral benefit, for urban aesthetics. Boulder Creek arises as North, Middle and South Boulder Creeks in the mountains west of the City of Boulder. The city- owned Arapahoe Glacier and the Silver Lake watershed, which feed the Boulder creeks, supply about 40%~ of the water used by the city's 125,000 water customers via diversion points on North Boulder Creek. Another 40% of the city's water supply is diverted from Middle Boulder Creek at Barker Reservoir. South Boulder Creek runs a gauntlet of headgates east of the city to provide water for the cities of Denver, Louisville and Lafayette and for numerous irrigation ditches. Historically, diversions on all three branches have dried up the creeks at various locations during periods of low flow -mostly in late summer and winter. Protecting Instream Flows In 1987, the City of Boulder began in earnest to consider ways to maintain streamflow in the creeks to preserve fish 12 habitat and enhance the aesthetics of the stream corridor. Since 1973, the Colorado Water Conservation Board (CWCB), the only agency under Colorado law allowed to hold water rights for instream purposes, had held a 1S cubic feet per second (cfs) right for instream flow for the portion of Boulder Creek flowing through the city (from Orodell gauging station to 75th Street). While this junior right prevented conditions on the stream from worsening, it could not secure flows during dry periods because calls of senior rights - held by both agricultural interests and the City of Boulder -could dry up the stream during low flow periods. In 1988, the city completed a planning process resulting in the Raw Water Master Plan, which called for a goal of maintain- ing a 5 cfs minimum flow in main Boulder Creek during droughts and the winter low flow season, as well as 15 cfs during normal or above-normal flow periods. The plan also established a goal of achieving instream flows in the tributaries of Boulder Creek outside of the city.