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3.0 Scientific Basis And Underlying Principles 3-13 April 2004 3.7.1 Floodplain Connection Connection of the floodplain to the river channel is critical to this management strategy. Historically, the river flooded during spring and the area of connected floodplain habitat depended on the magnitude of runoff. Flow regulation and concomitant geomOlphic changes in the river channel have altered the magnitude, frequency, duration, and timing of floodplain connection and inundation. The foundation of this strategy is to enhance floodplain connection and inundation through mechanical modification (e.g., levee removal or breaches) and flow re- regulation (e.g., Green River flow recommendations; see section 3.3). Despite modification and flow re-regulation, floodplain connection will not be possible for most floodplain sites in dry years (90-100% peak exceedence) and moderately dry years (70-90% peak exceedence; Figure 3-6). Connection of key modified floodplains should occur in most average years (30-70% peak exceedence), and connection of most or all floodplains should occur in moderately wet (10-30% peak exceedence) and wet years (0-10% peak exceedence). The goal of this Plan-to provide adequate floodplain habitats for all life stages of razorback sucker-will be accomplished by modifying floodplains to inundate with flows identified in the Green River flow recommendations. It is recognized that not all floodplains will connect to the main channel in given years, or if connected may not function as desired. Hence, the greatest number of connected floodplain depressions possible will increase the likelihood of success of this strategy. Green River Neilr G reet1 Rivet', utah 2200 - 211GB " .,- 18GB E 16GD - 14&0 , 1200 S 111GO Ui. 800 .. 6&0 : 400 A. 2GO 0 0 10 20 3D 411 5D &0 70 3D 911 1DD Probability of Exceedance Figure 3-6. Peak flow exceedance curves for regulated (solid line) and unregulated (dorted line) flows in the Green River, near Green River, Utah, 1963-1996 (excerpted from Muth et al. 2000). Horizontal dashed line shows flow recommendation of 527 m3/s (18,600 cfs).