San Juan Dolores Draft Instream Flow Recommendation

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Attachment 3 -Dolores River Instream Flow Recommendation Biological Flow Recommendations Overview of Recommended Flow Rates The recommended flow values were determined using the best professional judgment of CPW and BLM biologists and hydrologists. The CDOW and BLM professionals reviewed and evaluated the results of the Physical Habitat Simulation (PHABSIM) Methodology and RHABSIM software PHABSIM/RHABSIM analysis. They also reviewed the R2CROSS analysis, using the criteria set forth in the previous section of this letter. These initial flow recommendations were based on the physical and biological data collected to date and do not incorporate any water availability constraints. The PHABSIM/RHABSIM data analysis shows that the maximum amount of usable habitat for bluehead suckers is produced at a flow of 1200 cfs and for flannelmouth suckers at a flow of 875 cfs. BLM and CPW staff determined that a flow rate of 900 cfs would adequately protect the flannelmouth sucker habitat while protecting more than 90% of the usable habitat for bluehead sucker. BLM and CPW staff also noted that this usable habitat is typically available for only two months of the year. Accordingly, the initial biological recommendation for the snowmelt period between March 15 and August 14 is 900 cfs. The R2CROSS analysis indicated that a fall/winter flow rate of approximately 100 cfs was necessary to meet two out of the three of the critical hydraulic criteria in the cross section selected by the BLM and CPW. This flow rate is an average of the R2Cross results collected in five different riffles. BLM and CPW personnel also determined that a flow of 100 cfs would also protect other habitat types, such as pools and glides, during the base flow period. According, the initial biological recommendation for the base flow period between August 15 and March 14 is 100 cfs. Consideration of Water Availability After developing flow initial recommendations based exclusively upon maintenance of usable habitat and hydraulic characteristics, BLM and CPW reviewed the initial recommendations in light of water available during various times of the year. The BLM and CPW consideration of water availability was based upon an initial water availability analysis conducted by the CWCB staff. The initial water availability analysis by the CWCB staff is described in a separate attachment. Consideration of water availability is very important for this recommendation because the amount of time (number of days in a calendar year) that habitat is available for the critical life functions of fish directly affects the health and viability of those populations. After considering water availability, the original flow recommendations were modified as follows: