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. 11 2.2.2 Qualitative Response of River Systems . Many rivers achieve a state of approximate equilibrium throughout long reaches. Conversely, many streams contain long reaches that are actively aggrading or degrading. Regardless of the degree of channel stability, man's . local activities may produce major changes in river characteristics both locally and throughout an entire reach. Predicting the response to channel development is a very complex task. . There are a large number of variables involved in the analysis that are interrelated and can respond to changes in a river system and in the continual evolution of river form. To predict the response to channel development, an . understanding of the direction and magnitude of change in channel character- istics caused by actions of man and nature is required. This understanding can be obtained by: (1) studying the river in a natural condition; (2) having . knowledge of the sediment and water discharge; (3) being able to predict the effects and magnitude of man's future activities; and (4) applying to these, a knowledge of geology, soils, hydrology, and hydraulics of alluvial rivers. . Because such a prediction is necessary, useful methods have been developed to predict both qualitative and quantitative response of channel systems to change. . 2.2.2.l Prediction of General River Response to Change Prediction of response can be made if all of the required data are known with sufficient accuracy. Usually, however, the data are not sufficient . for quantitative estimates, only for qualitative estimates. Past studies and investigations conclude that: . l. Depth of flow Y is directly proportional to water discharge Q. 2. Channel width W is directly proportional to both water discharge Q and sediment discharge Q . s .