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" 002831 @ 1991 by S.E.L. &: Associates Ecological and Geomorphological Concepts for Instream and Out-of-Channel Flow Requirements Mark T. Hill and William S. Platts DOli Chapman Consultants, Inc. 3653 Rickenbacker Boise, Idaho 83705 Robert L. Beschta Department of Forestry Oregon State Ulliversity Corvallis, Oregon 97330 ABSTRACT: Healthy fish populations are dependent on streamflow regimes that protect the ecological integrity of their habitat. Fish habitats are the con- sequence of linkage among the stream, floodpLain, riparian and upland zones, and watershed geography. Fluvial~geomorphic processes form and control fish habitat. Because of this, multiple in-channel and out-of-channel flows are needed to maintain these processes. We present a conceptual methodoLogy for measuring four types of streamflow regimes: instream flows, channel maintenance flows, riparian maintenance flows, and valley maintenance flows. The combin<;ttion of these four streamflow types is designed to protect fish and their habitat. Using a case study of the Sillmon River neilr Whitebird, Idaho, we demonstrate how the methodology could be used to develop a multiple flow recommendation. KEY WORDS: Ecology, floodplain, flow management, geomorphology, in- stream flow, Instream Flow Incremental Methodology, riparian. INTRODUCTION A Iteration of streamflow for power production, irrigation, flood control, and other purposes adversely affects aquat- ic resources. The question of how much streamflow is required to protect aquatic resources has been examined over the years from several perspectives including fish- eries, channel maintenance, and riparian zone. Instream flow requirements for fish- eries have been extensively studied and many technical approaches have been ad- vanced (Stalnaker and Arnette 1976; Wesche and Rechard 1980), Instream flows to maintain channels and geomorpholog- ical processes have also been investigated (Beschta and Platts 1986; Rosgen et al. 1986; Reiser et al. 1989). Other investigations II~ 198 have focused on out-of-channel flows nec- essary for riparian vegetation and flood- plain processes (Franz and Bazzaz 1977; Harris et al. 1987; Junk et al. 1989; Strom- berg and Patten 1991), However, no mod- els or approaches have been suggested that link the instream and out-of-stream flow requirements of all aquatic resources. Con- sequently, streamflow management typi- cally focuses on one or two critical resource values rather than the simultaneous pro- tection of multiple resources. Our purpose is to suggest a conceptual or theoretical method for evaluating both instream and out-of-stream flow require- ments within a holistic streamflow management framework, We combine Rivers' Volume 2, Number 3 Pages 198-210