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. . . ", ", .- t,' OJ.... ~ UJ~JJo Colorado's ISF Program is also expanding downstream into cool and warmwater aquatic habitats. Biologic instream flow recommendations can be difficult to quantify in low elevation stream reaches because the complex aquatic species assemblages that typically inhabit these reaches often have very divergent streamflow requirements. The task of developing cool and warm water biologic flow recommendations may also be complicated by the social and political issues associated with recommending instream flows that will "preserve the natural environment to a reasonable degree" in areas that may be the subject of significant water development pressures. The R2CROSS methodology may also prove useful in cool and warmwater habitats assuming that the hydraulic criteria, which drive the biologic instream flow recommendations, can be adapted to reflect the streamflow requirements of the aquatic species that inhabit these cool and warmwater water environments. However, more sophisticated models may be required in areas of high water development pressure or when habitats other than riffles need to be modeled. In 1996, the CWCB assembled an Instream Flow Subcommittee to gather input on the public's desires for the future direction of Colorado's ISF Program. The ISF Subcommittee was comprised of several CWCB Board members, representatives of Colorado's water development and environmental communities, and interested members of the general public. ISF Subcommittee discussions were far-ranging, but one of the most recurrent issues was the public's desire for the CWCB to consider other "in-channel" and "over-bank" indicators of the natural environment when quantifying a stream's instream flow requirements. "In-channel", the public suggested that the Board consider (1) quantifying channel- forming/channel maintenance flows, (2) integrating water quantity with water quality and water temperature parameters, and (3) considering flows for recreation purposes. "Over-bank" , it was suggested that the CWCB take a more holistic, ecosystem management approach by recognizing the importance of appropriating flows to maintain riparian and side-channel habitats that are capable of sustaining avian and mammalian species living along the stream corridor in addition to the various life stages of aquatic species that live within the stream. Recent articles on a few of these issues include Brown (1991) on wilderness area water rights, Hill et al. (1991) on out-of-channel flow requirements, and MacDonnell (1991) on wetlands protection. In some instances, the CWCB has appropriated instream flow rights based on meeting the needs of cool and warmwater aquatic habitats or to protect other "in-channel" or "over-bank" natural environments. For example, the CWCB' s recovery flow filings on the I5-mile reach of the Colorado River and on the Yampa River were based on various biologic studies conducted by United States Fish and Wildlife Service (USFWS) biologists. On Little Dry Creek, located near the Denver metropolitan area, the CWCB and CDOW staffs utilized the Instream Flow Incremental Methodology (IFIM) and Physical Habitat Simulation Model (PHABSIM) to develop an instream flow recommendation to protect the habitat requirements of wannwater fish species like creek chub (Semotilus atromaculatus) and white sucker (Catostomus commersoni). The CWCB also appropriated the entire unappropriated flow of Deadhorse Creek to preserve the unique hydrologic characteristics and the water-dependent natural environment associated with that drainage. As Colorado's ISF Program expands, biologic flow recommendations based on new methodologies or 2