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<br />Evaluation of the <br />Standards and Methods Used for <br />Quantifying Instrellm Flows in Colorado <br /> <br />" <br /> <br />e <br /> <br />Colorado's Instream FlowlNatural Lake Level Program ("ISF Program") was initiated in <br />1973 with the passage of Senate Bill 97 (SB 97) which vested the Colorado Water Conservation <br />Board (CWCB) with statewide authority to appropriate instream flow and natural lake level water <br />rights. SB 97 was subsequently amended by sa 414 in 1981, SB 91 in 1986, SB 212 in 1987, SB <br />181 in 1989, and SB 64 in 1996. Colorado's instream flow legislation is contained within S 37-92- <br />102(3) of the Colorado Revised Statutes (1997). <br /> <br />Colorado's ISF Program is administered under the guidance of the "Rules and Regulations <br />Concerning the Colorado Instream Flow and Natural Lake Level Program" which were adopted by <br />the CWCB on November 10, 1993, and amended on September 13, 1994 (Colorado Water <br />Conservation Board (1994). The "Rules" were amended again in 1998 to reflect the legislative <br />changes that resulted from the passage of SB 64. <br /> <br />Instream flow rights are held by the CWCB on behalf of the people of the State of Colorado <br />to "preserve the natural environment to a reasomlble degree." The CWCB currently holds more than <br />1,800 water rights covering approximately 8000 miles of Colorado streams and almost 500 of the <br />state's natural lakes. <br /> <br />In Colorado, instream flow appropriations are generally based on biological e <br />recommendations provided to the CWCB by various state and federal agencies. To date, the <br />majority of the Board's appropriations have been on coldwater stream reaches or high elevation <br />lakes. Biological flow recommendations have generally been based on the premise that the amount <br />of water needed to preserve an aquatic indicator species, like a trout, is the same amount of water <br />necessary to preserve the entire natural environment. The most frequently used methodology for <br />developing biological flow recommendations for Colorado's coldwater streams has been R2CROSS <br />(Nehring 1979; Espegren 1996). <br /> <br />The R2CROSS methodology has proven to be advantageous because (1) it requires data from <br />only a single field visit, (2) the procedures are very easy to learn and implement, and (3) data <br />interpretation is simple. In addition, recommendations from R2CROSS output are generally more <br />representative of site-specific stream conditions than non-field methods. R2CROSS <br />recommendations have also been found to be quite similar to, and more cost effective than, <br />recommendations developed from more data intensive techniques (Nehring 1979). Finally, the <br />hydraulic criteria that are used to develop R2CROSS-based instream flow recommendations are <br />specifically designed to protect the biologic flow needs of coldwater fish species within riffle <br />habitats (Nehring 1979). Consequently, the R2CROSS methodology has been, and will continue <br />to be, an important quantification technique for developing instream flow recommendations on <br />coldwater stream segments throughout the state of Colorado. <br /> <br />I <br /> <br />e <br />