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Generally speaking, the most frequent channel response after the construc- tion of a dam is degradation of the reach downstream of the dam. Sometimes the change in bed elevation exceeds 6 m, and the effect may extend downstream for 150 to 300 km (Lane 1955). Clearly, one necessary action in evaluating changes in microhabitat due to dam construction is to predict what the channel will look like in its new equilibrium state. Channelization (or channel realignment) increases the slope of the stream in the channelized reach. This gives the available discharge more energy with which to carry sediment. The result is frequently degradation of the channel- ized reach and of unchannelized upstream reaches as well. As the water proceeds downstream from the channelized reach, it often carries more sediment than can be transported by the discharge in the unchannel i zed downstream reaches. This results in aggradation downstream of the realignment. This series of events is one of the reasons that channelization tends to be a self-perpetuating activity. Microhabitat studies which concentrate on the reach of stream physically altered by the bulldozer fall short of documenting the full impact of the channel ization. Removal of seasonally accumulated sediments in streams generally occurs during high discharge periods associated with snowmelt or storm runoff. Diversion of large amounts of this high discharge can cause aggradation of the channel by not providing enough flow to remove previously deposited sediments. The high discharge period is also highly correlated with the peak watershed sediment yield, and more sediment may enter the channel than the discharge can transport, causing deposition. Diversion during high discharge might be expected to remove a proportionate amount of sediment along with the water. However, diversion works are commonly designed in such a way that most of the coarse sediment remains in the stream. Step 3, the determination of the channel structure with and without the project, is summarized in the bottom half of Figure 3. The outputs from this step are a measure of the channel structure as it currently exists and an estimate of the future structure. The existing and future channel structures are assumed to be the same only if: The watershed and channel are currently in equilibrium; The project will not directly or indirectly affect the channel; and 3. The flow/sediment load relationship (particularly during high flows) remains the same. 1.3.4 Step 4: Determine Length of Stream Having Suitable Water Quality and Temperature Water quality is related to streamflow in an intriguing number of ways. Water quality considerations can be classified into three general types: conservative and nonconservative constituents and temperature. Conservative water quality constituents do not decompose or significantly react with other chemicals in the water. Many inorganic salts fall into this category. The concentration of these materials is related to discharge only through dilution. 11