WSPC111 - Laserfiche WebLink

Home Browse Search

. . . U'.. ,-- . h . ..., ;,~ I'j" .r i,j l , U " ,J It , split-flows" on streams with coldwater fisheries around 1981. While the concept of seasonal split- flows is intuitively reasonable, the biological basis for CDOW's seasonal split flow has never been fully documented. CDOW's biologic justification for recommending seasonal flows should be researched and documented. R2CROSS may also be useful in warmwater and coolwater environments, if a relationship can be established between the hydraulic parameters estimated in the R2CROSS staging table and the biologic requirements of the species that inhabit these types of environments. This relationship may be explored through a review of the existing biologic literature (e.g.., USFWS habitat suitability curves) or it may require additional research on warm and coolwater species. The CWCB and CDOW staffs should investigate the possibilities of expanding the use ofR2CROSS into cool and warmwater environments. Finally, the CWCB and CD OW staffs should attempt to address public concerns that the Board's decreed instream flow water rights, which were quantified utilizing the R2CROSS methodology, may not be providing reasonable protection of the natural environment. This concern is likely to be very difficult to either prove or disprove due to the subjectivity ofthe question and the plethora of flow and non-flow related factors that may inhibit strict interpretation of the data. One possibility for making this determination would be to design a study that would evaluate fish population characteristics above and below major diversion structures that frequently reduce streamflows to the amounts of the Board's instream flow water rights. Differences in fish population characteristics between natural flow, "control" sections (above diversions) and depleted flow, "test" sections (below diversions) could be evaluated to determine the effectiveness of the Board's instream flow rights in preserving the natural environment to a reasonable degree. Other research possibilities also exist, but staff time and budgetary constraints may prohibit an extensive study. IFIMI PHABSIM IFIMlPHABSIM is a more general model than R2CROSS. Whereas R2CROSS is most applicable for modeling riffle and run habitats, IFIM/PHABSIM can be used to model almost any stream habitat type. In addition, IFIM/PHABSIM habitat suitability indices exist for a variety life stages of common aquatic species, including cold, cool, and warmwater fish species, reptiles, and amphibians, as well as for recreational uses like wading and rafting. However, instream flow recommendations based on IFIM/PHABSIM studies are generally more expensive and time consuming than those based on R2CROSS studies. This extra expense can be attributed to the additional data requirements of the IF 1M model and the technical complexities of running the model. The methodology has also been criticized because a relationship between WUA and a population response has never been established and because it cannot model competition between sympatric aquatic species. In Colorado, IFIM/PHABSIM may an appropriate, and necessary, methodology for developing recommendations on highly controversial stream segments and on streams with fish 13