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<br />, <br /> <br />r<n.""7~ <br />ui.,dU '. <br /> <br />31.2--1 <br /> <br />, <br /> <br />WATER INFORMATION MANAGEMENT SYSTEM HANDBOOK <br /> <br />may not be technically or economically feasible, or environ- <br />mentally acceptable. Therefore, a flow of water in the channel <br />most generally will be the most practical means of achieving <br />and/or maintaining channel form. <br /> <br />3. In energy limited systems, a change in any variable in <br />the relationship Q d - Q S results in a compensatory change <br />in one or more of ~he re~aining variables. <br /> <br />Channel responses can be anticipated in kind and magnitude <br />whenever there is a change in one or more of these variables. <br />Some such change occurs naturally from the normal variance in a <br />heterogeneous environment. However, such change is generally <br />limited in magnitude, random in occurrence, of a temporary <br />nature, and has produced a channel form capable of accommoda- <br />tion. Artificial changes in these variables, especially <br />discharge, tend to be long term, systematic, and of substantial <br />consequence. <br /> <br />ij. The quantity of sediment delivered to the point of <br />quantification will not change appreciably. <br /> <br />The procedure calculates the water discharge needed to maintain <br />the dynamic equilibrium between sediment discharge, particle <br />size and stream slope. A change in the quantity of sediment <br />which must be transported would necessitate a change in the <br />required flow if equilibrium is to 'be maintained. <br /> <br />5. There is an effective discharge that forms the active <br />channel in erodible bed/bank channels. <br /> <br />6. The effective discharge is approximately equivalent to <br />the discharge which occurs at bankfull stage. <br /> <br />7. Bankfull discharge is frequently occurring and can be <br />characterized by the flow with a recurrence interval of 1 to 5 <br />years and reasonably estimated using the flow associated with a <br />1.5 years recurrence interval (log-Pearson type III analysis of <br />annual peak series). <br /> <br />This procedure is designed to maintain the capacity of the <br />active channel only. Therefore, the use of an effective <br />discharge (also called the formative or dominant discharge) will <br />achieve the desired capacity maintenance objective. <br /> <br />This assumption is necessary to allow for the application of the <br />procedure to numerous diverse drainages for which little or no <br />field data are available. This particular return interval (1.5 <br />years) is the one most frequently encountered in the literature <br /> <br />*-FSH ij/89 AMEND 3-* <br />