CWCB San Miguel PHS Final - Laserfiche WebLink

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Enclosure 2- San Miguel River instream Flow Recommendation Flow Quantification Methodology PHABSIM and R2Cross Methodology The Colorado Division of Wildlife (CDOW) and the Bureau of Land Management (BLM) evaluated all of the data collected to date and determined that best flow recommendation would come from using the results from a combination of methods. Physical Habitat Simulation (PHABSIM) is a widely accepted method for quantifying the suitable versus unsuitable hydraulic habitat attributes of selected species and life stages as a function of discharge. The R2CROSS is best suited for identifying flows with specific hydraulic criteria across riffle type habitats. The State of Colorado has used the R2CROSS extensively in the past to appropriate instream flow water rights. The CDOW and the BLM were concerned that exclusive use of the standard R2CROSS method may not be appropriate for this reach of the San Miguel River due to its major width (over 75' wide in most places), type of fish species present (warm /cool water species) and its big river channel hydraulics and characteristics. The CDOW and the BLM collected transect and flow data for seven different cross- sections within an 815 -foot reach of stream. The transect data was collected at a site approximately 1.5 miles upstream from the confluence of the San Miguel River with Tabeguache Creek. These seven transects incorporated different mesohabitat types including riffles, runs, pools and glides. These seven different cross - sections formed the basis for the PHABSIM /River Habitat Simulation ( RHABSIM) study conducted by the CDOW and the BLM. The PHABSIM is widely used in North America to quantify instream flow regimes and consists of two modeling components, These initial recommendations are designed to address the unique biologic requirements of this stream reach without regard to water availability. In addition to the criteria developed using the PHABSIM Methodology and the RHABSIM Software, the three standard instream flow hydraulic parameters used in the R2CROSS (average depth, percent wetted perimeter and average velocity) were also used to calculate and predict the biologic instream flow recommendations. Application of Habitat Suitability Criteria Habitat Suitability Criteria (HSC) were developed from the 2003 Riverine Fish Flow Investigation Study Report (Federal Aid Project F- 289 -R6) written and performed by Richard Anderson, CDOW Aquatic Researcher, and Gregory Stewart, Department of Geosciences Oregon State University'. The basis for this study was a 1999 request from the Colorado Water Conservation Board (CWCB) for the CDOW to provide biologically justified instream flow 1 See "Impacts of stream flow alterations on native fish abundance and native fish habitat and the use of native fish population data to support instream flow recommendations made using a 2D instream flow methodology."