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3.0 Scientific Basis And Underlying Principles 3-1 April 2004 3.0 SCIENTIFIC BASIS AND UNDERLYING PRINCIPLES 3.1 Scientific Basis For Plan This Plan is based on scientific principles derived from research on floodplains throughout the Colorado River Basin, as well as from other systems. The fundamental basis of this Plan is that floodplains provide nursery habitat for razorback sucker, and restoration and appropriate management of these floodplains will assist the recovery of this and other endangered fish species. Floodplains develop along rivers with valley floors that are extensively covered with alluvium and/or sand. The river flowing through this substrate carves an active channel that is flanked by low relief bottomlands that may have groundwater connection with the river and/or become inundated during high-flow periods. High-flow periods of most western rivers are usually associated with snow-melt runoff in spring (Poff et al. 1997). The timing and frequency of flooding, magnitude of flows, and duration of peak flows determine the degree of floodplain connection to the river. Considerable scientific research has been conducted to better understand the complex inter-relationships associated with formation, inundation, maintenance, and desiccation of riverine floodplains (Ward 1989). Flow regulation can disrupt hydrological and ecological connectivity between the river channel and alluvial floodplains (Ward and Stanford 1995). Reduction in spring peaks can reduce connectivity and lead to geomorphic channel changes and vegetative encroachment that may exacerbate this disconnection (Andrews 1986; Graf 1978). Floodplain reconnection is vital to restoring some of the structure and function of floodplains disrupted by flow regulation (Stanford et al. 1996). Flow of the middle Green River is largely regulated by Flaming Gorge Dam. This flow regulation has reduced the frequency of connection of the river to floodplains, as well as the duration of connection (Stanford 1994), and is believed to be a major factor in the endangerment ofthe razorback sucker (Tyus and Karp 1990; Modde 1996, 1997). Tributary inflow, especially from the Yampa River, can periodically affect flows of the middle Green River during spring snow-melt runoff or from late-summer monsoonal rain storms. The relationship of flow regulation and floodplain inundation in the middle Green River is sufficiently understood to predict numbers, acreage, and types of floodplains at given river stages, but individual floodplain dynamics are not well understood; e.g., flow and particle entrainment rates, sedimentation, water retention. These inter-relationships are often confounded by physical, chemical, and biological attributes and linkages that are unique to each floodplain site (Flo Engineering 1997; Crowl et al. 1998b). Given this complexity and dynamic character of floodplains and river flows, predictions in floodplain formation and maintenance, as well as management plans for these floodplains, must be considered provisional and subject to ongoing modification with new information from scientific findings.