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Green River Floodplain Inundation 18 June 2005 Figure 6 illustrates how lowering the magnitude of the connecting flows, while maintaining the instantaneous peak flows identified in the Muth et al. (2000) flow recommendations could allow the duration of connecting flows to be extended. The hydro graphs in Figure 6 present hypothetical spring runoff flows at the Jensen gage that might be achieved during an average water year (1) using 527 m3/s (18,600 cfs) as the connecting flows, (2) using 424 m3/s (15,000 cfs) as the connecting flow, (3) using 396 m3/s (14,000 cfs) as the connecting flow, and (4) using 368 m3/s (13,000 cfs) as the connecting flow. All scenarios in Figure 6 use the average mean daily flow for the Yampa River for each date and all scenarios include an instantaneous spring peak of 527 m3/s (18,600 cfs) for at least 3 days. The volume of water that passes the Jensen gage during the period is identical under the four scenarios. The number of days indicated for each line is the duration that flows of at least 368 m3/s (13,000 cfs) could be maintained under each hypothetical scenario (Figure.6). If it was determined that the appropriate connecting flow was 396 m3/s (14,000 cfs) instead of 368 m3/s (13,000 cfs), a connection could be maintained for 19 days under the Muth et al. (2000) recommendations, 28 days under the 396 m3/s (14,000 cfs) scenario, and 25 days under the 424 m3/s (15,000 cfs) scenario. Thus, depending upon the specific connection flows required to allow larval entrainment to occur, 1 to 2 additional weeks of connection could be provided compared to the Muth et al. (2000) recommendations. Note again that all four scenarios shown achieve the instantaneous peak flow magnitude recommended by Muth et al. (2000) for at least three days. Providing peak flows that are much higher than those required to inundate depression floodplains may provide no increase in available nursery habitat once flows recede. Thus, for a given volume of water, it may be more beneficial to native fishes to provide a lower magnitude, longer duration connecting flow rather than a higher magnitude, shorter duration peak flow. We recognize, however, that somewhat higher flows may be needed to provide adequate depths at the floodplain-main channel interface for entrainment of larvae and out-migration of reared juveniles. In addition, different magnitudes of flow may affect rates of larval entrainment. These and other uncertainties that should be investigated are identified in Section 6. Once larvae are entrained into suitable depression floodplain habitats, recession of flows will break the connection to the main channel and the larvae may mature in the floodplain depression. At some point, it is necessary for juvenile razorback suckers to return to the main channel. Studies and observations indicate that razorback sucker juveniles will remain in floodplain habitats for up to two years, even when reconnection to the main channel would allow them to leave. Consequently, it is appropriate that the reconnection frequency of the majority of suitable depression floodplains should occur in most years. The proposed connecting flow target of 368 to 396 m3/s (13,000 to 14,000 cfs) would provide two weeks or more of connection to most priority depression floodplain habitats in 60% to 70% of years. As with the Muth et al. recommendations, connection between floodplains and the main channel would not occur in dry years and in some moderately dry years. Occasional drying is consistent with the desire to reset the system periodically by eliminating nonnative fishes. The utility of connecting floodplains that connect only at very high peak flows (e.g., Sportsman's Lake and Sheppard Bottom) should be considered carefully. The relatively low