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I I I [RM 203-240]); (2) Grand Valley reach of the Colorado River between Loma and Palisade, Colorado (RK 245-298 [RM 152-185]); (3) Colorado River between McGraw/Hotel Bottoms and the Cisco boat landing (RK 159-177 [RM 99-110]); and (4) the Gunnison River near Delta, Colorado (RK 81-87 [RM 50.2-54.2]). Floodplain habitat sites in the Colorado River Subbasin consisted of 37% terraces, 21% gravel-pit ponds, and 20% side channels. Natural levees separated 23.6 km (14.6 mil of the 158 floodplain habitat sites along the Colorado and Gunnison rivers while 56.3 km (34.9 mil were separated by levees constructed by humans. I I I The 1998 evaluation of river reaches identified RK 204 (RM 127; Westwater Canyon) to RK 386 (RM 240; Rifle, Colorado) on the Colorado River and RK 80.5 (RM 50; Escalante State Wildlife Area) to RK 120.7 (RM 75; North Fork of the Gunnison River) as high priority reaches based on the three criteria described above (P. Nelson, 1998, personal communication) . J I AI.rangements are being made with state and federal agencies that have floodplain habitat in public ownership along the Colorado and Green rivers to experimentally remove levees to evaluate zooplankton and benthic invertebrate production and responses by endangered as well as other native and nonnative fishes. Acquisition of floodplain habitat sites in private ownership is being explored to protect areas that flood with present streamflows and to reconnect other sites with the river by breaching levees (U.S. Bureau of Reclamation and U.S. Fish and Wildlife Service 1998) . I I VI. CONSIDERATIONS IN ENHANCING OR RESTORING FLOODPLAIN HABITATS IN THE UPPER COLORADO RIVER BASIN I The principles of hydrology, fluvial geomorphology, and systems ecology must be integrated into planned river enhancement to prevent inadequate analysis of water and sediment transport, morphology of the channel and its associated floodplain, and ecological requirements of organisms (National Research Council 1992). Such planning must recognize the ongoing physical processes in the river and work with these processes rather than against them (Heede and Rinne 1990). Important concepts in river enhancement planning are that (1) a river is the product of the drainage basin or watershed, (2) the integrity of river systems is influenced by watershed management practices, and (3) the terrestrial environment closest to the river (i.e., riparian zone) has the greatest impact on potential responses in the floodplain. Many past failures in ecological enhancement of rivers and streams resulted from inadequate analysis of physical 'conditions and establishment of realistic and measurable objectives for biological responses (National Research Council 1992). I I The dynamic equilibrium of a physical system in a river creates various ecological habitats that results in a corresponding dynamic equilibrium of the biological system. River enhancement should begin with improved land management practices in a watershed that will allow the river to re-establish the dynamic equilibrium of its physical system. The goal of ecological enhancement of rivers is to improve the dynamic equilibrium of the physical, chemical, and biological systems together (National Research Council 1992). I I The basic ecological requirements of space, water quality, streamflow, cover, and food must be reviewed by life stage for each endangered fish species in recovery efforts since all are important in producing and maintaining self- sustaining populations. Various biological, chemical, and physical factors must be considered in evaluating floodplain habitats that have the potential for enhancement or restoration (Table 5). Because rivers have a one-way downstream movement, preservation or enhancement efforts requires careful planning and management of the entire stream network and the surrounding landscape (Shelton 1988) . I I I 27 I