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<br />001G03 <br /> <br />., , <br /> <br />31.2--1 <br /> <br />WATER INFORMATION MANAGEMENT SYSTEM HANDBOOK <br /> <br />At present the procedure can only be applied to watersheds where streamflow <br />is perennial and dominated by snowmelt runoff. Methods applicable to <br />rainfall dominated perennial, and ephemeral and intermittent streamflow <br />have not yet been developed. <br /> <br />The procedure is generally applicable only to channels that can adjust <br />their dimensions, shape, pattern and/or gradient in response to changes in <br />streamflow. It'may also be applied to those channels which cannot adjust <br />to changes in streamflow where deposition of sediment or encroachment of <br />vegetation threaten potential changes in base level or a potential <br />reduction in channel capacity. <br /> <br />31.2 - Assumptions. The procedure to secure a favorable condition of water <br />1TOW assumes the following: <br /> <br />1. The failure to maintain the capacity of a river, stream, or creek <br />channel to pass frequent flows without flooding results in an unfavorable <br />condition of water flows. <br /> <br />. I <br /> <br />The objective of maintaining a favorable condition of water flows is not <br />served by a reduction in the capacity of a channel to pass frequent flows <br />without flooding. Neither is it served if other flood flows are passed at (')' <br />higher than normal stages. For the purpose of this procedure the magnitude <br />of change in such flood impact is not addressed. Increases in flooding due <br />to diminished channel capacity therefore constitute an unfavorable <br />condition of water flows. <br /> <br />2. The dynamic balance between discharge, sediment concentration, and <br />channel morphometry results in a channel form which tends to be <br />self-maintaining. <br /> <br />This assumption best applies to those channels whose form is modifiable by <br />the forces of moving water. It does, however, also apply to resistant or <br />essentially immobile channels insofar as changes in sediment Or water <br />delivery can result in changes in bedform and channel capacity through <br />deposition. <br /> <br />! I <br />I <br /> <br />The self maintenance of the channel is especially important in achieving <br />the desired favorable flow objective. The use of artificial means to <br />.maintain channel capacity, while possible, may not be technically or <br />economically feasible, or environmentally acceptable. Therefore', a flow of <br />water in the channel most generally will be the most practical means of <br />achieving and/or maintaining channel form. <br /> <br />I <br />