7843 - Laserfiche WebLink

Home Browse Search

r subjectivity, and judgement. It is something that can only truly be learned by doing. Trust and credibility are essential to the implementation of IFIM, and they must appear in every application. Our knowledge about rivers, biology, and human nature will never be perfect, nor will our imple- mentation of IFIM. We can, however, control the quality of our own work. We can be craftsmen. Approach IFIM is an adaptive system composed of a li- brary of models that are linked to describe the spatial and temporal habitat features of a given river regulation. In addressing a river system problem, one must keep in mind the matter of scale. Table 4.1 describes a river system at five levels of resolution, from the river basin scale down to microhabitats (similar to that offered by Frissell et al. 1986). When addressing a river regulation problem, it is necessary to bound the area of in flu- ence and to stratify your approach so that observa- tions can be expanded from the micro-scale up to at least the river segment scale, if not the stream network or full sub-basin scale. Most experience and application of IFIM techniques have been at the micro- and meso-habitat levels, focusing on one or a few river segments. Consequently, the great- est improvement in field techniques and the most tested concepts relate to (1) river hydraulics and microhabitat utilization by aquatic species and (2) longitudinal analysis of water chemistry and temperature through long river segments com- posed of many mesohabitat types. THE INSTREAM FLOW INCREMENTAL METHOLDOLOGY 23 Recent emphasis on reservoir operations and stream network analysis has linked habitat models with engineering models for water routing and reservoir storage and release (Waddle 1992). The combined effects of severe ramping rates associated with peaking hydropower operations and the re- evaluation of large storage reservoir operations have elevated the instream flow management issue in the United States to the stream network and even the river basin scale (Lubinski 1992; Hesse and Sheets 1993). A thorough understanding of the hydroperiod, the water supply, and the management capabili- ties is essential to IFIM studies in regulated riv- ers. The most common instream flow problems being addressed today throughout the United States require the aggregation of habitat data at the stream network or sub-basin level and focus fishery managers' attention to the population level. The inherent need to describe the within-ba- sin movement and life history periodicity (Fig. 4.1) establishes the utility of computer-based modeling for tracking and summarizing informa- tion throughout a stream network (Bartholow et al. 1993). It is no longer sufficient to argue for flows to maximize the habitat value for one life stage (adult) at a few isolated spots in a river. Computer simulations provide the mechanism for 'gaming' with various river regulation schemes. Allocated water budgets for fish production and decisions on storage and release from reservoirs are now becoming the responsibility of the fishery manager (Waddle 1991; Bartholow and Waddle 1994). Table 4.1. Major factors influencing habitat of river ecosystems based on spatial scale of the processes. Scale Major factors influencing habitat River basin Climatic change; climax vegetation; geologic disturbances (earthquakes, volcanos); catastrophic floods and droughts. Stream network Valley gradient; local geology (natural or man-made barriers to fish migration); watershed vegetation and land use activities; runoff patterns; groundwater flow; soils and sediment yield; location of dams and diversions. River segment (macro-scale) Longitudinal gradients of temperature and water quality; habitat types and proportions (more similar within segments than among segments); canyons, floodplain segments, bedrock controlled reaches, alluvial reaches, etc. Periodic floods can reshape floodplain contours and reroute channels. Mesohabitats (meso-scale) Unique channel width/depth ratios: Pools, runs, chutes, oxbows, cutoff .backwaters, riffles, pocketwater, plunge pools, side channels, navigation pools, channelized reaches. Cross sections (micro-scale) Channel geometry; stage/discharge relations; substrate material distribution; % fine materials; cover objects (instream, undercut banks, overhead vegeta- tion, ledge rock, woody debris, root wads); depth and velocity distributions.