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<br />31.11 <br /> <br />WATER INFORMATION MANAGEMENT SYSTEM HANDBOOK <br /> <br />,1.11 - ~at~. The application of these procedures does <br />not result in a description of any special purpose flows such as <br />those for fishery, streamside habitat maintenance, water <br />quality, recreational, or esthetic considerations. The <br />calculated flows are designed to maintain only the active <br />channel. <br /> <br />At present the procedures can only be applied to watersheds <br />where streamflow is perennial and dominated by snowmelt runoff. <br />Methods applicable to rainfall dominated perennial and ephemeral <br />and intermittent streamflow have not yet been developed. <br /> <br />The procedures are generally applicable only to channels that <br />can adjust their dimensions, shape, pattern and/or gradient in <br />response to changes in streamflow. They may also be applied to <br />those channels which cannot adjust to changes in streamflow <br />where deposition of sediment or encroachment of vegetation <br />threaten potential changes in base level or a potential <br />reduction in channel capacity. <br /> <br />~ - Assumntions. The procedure to secure a favorable <br />condition of water flow assumes the following. <br /> <br />1. The failure to maintain the capacity of a river, stream, <br />or creek channel to pass frequent flows without flooding results <br />in an unfavorable condition of water flows. <br /> <br />The objective of maintaining favorable conditions of water flow <br />is not served by reducing the capacity of a channel to pass <br />frequent flows. Neither is it served if other flood flows are <br />passed at higher than normal stages. The procedures that follow <br />in Sections 32 through 34 do not address changes in occurance of <br />such flood impacts. Increases in flooding rusulting from <br />diminished channel capacity, therefore, constitute an <br />unfavorable condition of water flows. <br /> <br />2. The dynamic balance between discharge, sediment <br />concentration, and channel morphometry results in a channel form <br />which tends to be self-maintaining. <br /> <br />This assumption best applies to those channels whose form is <br />modifiable by the forces of moving water. It does, however, <br />also apply to resistant or essentially immobile channels insofar <br />as changes in sediment or water delivery can result in changes <br />in bedform and channel capacity through deposition. <br /> <br />The self maintenance of the channel is especially important in <br />achieving the desired favorable flow objective. The use of <br />artificial means to maintain channel capacity, while possible, <br />.~ <br /> <br />. <br /> <br />*-FSH 4/89 AMEND 3-* <br />