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rapid periods of scour and fill, the rating curve approach will not work as well because the cross section itself will be-different each time it is measured. What was a pool is now a sandbar. In this situation, the use of two or three replications of the Manning equation, with data collected at different flows, would be preferred for hydraulic simulation, each addressing the various channel configurations. Under the condition of dynamic equilibrium, it is immaterial that pools are converted. to sandbars. In order for this to happen, a sandbar somewhere was converted to a pool. Therefore, if a dynamic equilibrium has been assumed or determined, the relative proportion of pools and bars should remain fairly constant even though their positions change with time. SUMMARY OF POTENTIAL SITUATIONS AND RECOMMENDED APPROACHES The preceding discussions are designed to help the field investigator select a hydraulic simulation technique which is consistent with the type of study being conducted and the type of river being studies. Several different settings (type of study, type of river) which could confront the investigator, and the suggested hydraulic simulation approach for each situation are summarized in Table 6. Additionally, Table 6 includes the page numbers in the text which discuss a particular simula- tion approach or its limitations. The approaches suggested in Table 6 are given with the caveat that the stream is in equilibrium, or very nearly so. If the stream is currently in dis-equilibrium, or a change in equilibrium states is anticipated due to some change in watershed characteristics, stream flow pattern, land use, etc., it is necessary to predict what the channel will be like under new equilibrium conditions. Given this situation, the only way to simulate the hydraulic characteristics of the new channel is to use the Manning equation, preferably using the gradually varied flow (step-backwater) computation procedure. Finally, the level of field intensity required depending on the potential for conflict with other water uses is considerably different. One would prefer to assume that the conflict with other water-uses will be small, so that the cost of data collection could be minimized. However, unless there is clear evidence to the contrary, one should assume that there will be some conflict with other water uses, and that an instream flow recommendation will be contested. The approach used should be selected accordingly. 57