Platte River Channel Becomes a Focus for Platte River Cooperative Program Studies2001

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Messrs. Lochhead, Simpson, and Robotham Based on the above, Dr. O'Brien recommended that the targets for the mean annual peak flow over a 10 -year running period should be in the 8,300 -cfs to 10,800 -cfs range. Dr. O'Brien also noted that island and bar attachment through vegetation establishment is the primary mechanism of channel narrowing, that slightly exceeding bankfull discharge 1 out of every 3 years is beneficial in terms of reworking the alluvial channel, and he recommended that bars (macro- forms) should be active with an 8 -inch to 2 -foot depth over the bars to maintain movement. Based on these observations and the Overton gage record, he recommended a 2.5 -year to 3 -year event of 12,000 cfs and a 5 -year event of 16,000 cfs. Dr. O'Brien recommended a duration pattern for the peak flow (i.e., daily flows of the pulse) based on computations of the early flow records for the central Platte River. Several of the experts, though they did not provide specific numbers, indicated that the natural pattern should provide guidance in the pattern selected. How do these recommendations relate to the functional needs of listed species? Many of the habitat needs of listed species are summarized in the Biology Work Group Report (1990) of the Platte River Management Joint Study (Joint Study), in Service biological opinions, and in the scientific literature. For example, for least terns and piping plovers, Sidle et al. (1992) described the observed function of flow peaks for maintaining sandbar nest habitat. The preference for wide channels demonstrated by whooping cranes is given by the Joint Study (1993 at Figure A1(c)). The recommended pulse flow would contribute to saturation of the soil profile in wet meadows, which are inhabited by or a foraging area for several listed species. Paae 6. 2.2. Late Winter Pulse Flows Comment: "What data, for example, are available to substantiate the Service's view that soil organisms and aquatic food organisms require the stimulus of rising groundwater in the late winter to be of benefit to listed species ?" Along the Platte River, ground water levels are closely and most frequently influenced by river stage (Hurr 1983; Wesche et al. 1994), and the Service regards the relationship of soil saturation and wetland biota as basic wetland science. For example, activity and migration of soil organisms (e.g., frogs and earthworms) in early spring are typically associated with soil temperature (frost) and moisture. Sandhill crane foraging in wet meadows in late winter /early spring is typically associated with depressions where ground water intersects or is near the soil surface. Whooping crane foraging is generally regarded to be more closely associated with aquatic habitats than is sandhill crane foraging. The Platte River Whooping Crane Habitat Maintenance Trust (1990) also reported that soil thawing in low meadows in spring occurred from the bottom up.