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<br />.' <br /> <br />.' <br /> <br />geomorphology and channel slope. If data needed to calculate sediment mass balance are available <br />and are coupled with detailed topographic information, derived either from air photos or surveys <br />over the period before and after regulation, the morphological dynamics of the channel can be <br />documented (cf., Andrews 1986, Lyons and Pucherelli 1992) and informed approaches to flow <br />negotiations can proceed. However, regime analyses too often rely on untested assumptions that <br />some flow volume and rate relationship, usually bankfull flow, is the dominant channel-fonning <br />flow. Determination of bankfull flow is problematic owing to local variations in channel <br />morphology coupled with usually too few data on hydraulics of the reach during peak flow events. <br />The preferred approach in my view is a thorough, empirical understanding of sediment <br />gradation, channel geomorphology and channel slope, with which movement of sediment, and hence <br />the dynamics of many physical habitats important to aquatic biota, can be estimated as a function of <br />the amplitude of peak flow events. Andrews and Nelson (1989) used this approach to document <br />topographic responses of a large bar complex in the Green River over a history of flow events. A <br />major advantage of the model is that, although it is deterministic, flows, sediment supply and to <br />some extent the topography can be stochastic. The model is being used to predict dynamics of <br />sediment transport and channel topography in response to flow variation elsewhere in the Colorado <br />River system. Model development and verification is greatly assisted by recent improvements in <br />automated field surveying equipment (total stations) that allow rapid and very accurate <br />measurements of local topography (E. D. Andrews, U.S. Geological Survey, Boulder, CO, personal <br />communication). However, as concluded by Reiser et al. (l989b), the most certain method to <br />determine relationships between peak flow events and channel features in a regulated river is to tag <br />an array of bed materials, carefully sUIvey channel topography (sensu Andrews and Nelson 1989) <br />and relate movement of materials and changes in topography to different flow events carefully <br />controlled by reservoir releases. However, the flow peaks have to be high enough to move the <br />tagged bed materials, which can be approximated a priori using standard hydraulic calculations. <br />From a more biological perspective, a number of alternative approaches are possible. Binns <br />and Eiserman (1979) predicted trout biomass in Wyoming streams with a habitat quality index <br /> <br />51 <br />