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<br />OJl;)(;5 <br /> <br />31.2--3 <br /> <br />WATER INFORMATION MANAGEMENT SYSTEM HANBBOOK <br /> <br />Baseflow discharge helps to prevent vegetation encroachment into the active <br />channel and transports sediment when energy is sufficient for the available <br />sediment size and supply. <br /> <br />9. The natural concentration and yield of sediment of a channel are <br />dynamic properties and fluctuate about mean values. <br /> <br />10. The maintenance of existing channel capacity requires the "run of <br />the river" or all naturally occurring discharges of a water arid sediment <br />mixture. <br /> <br />11. Approximate channel equilibrium can be achieved with less than the <br />"run of the river" through a range and duration of flows including rise, <br />bankfull, recession, and baseflow components. <br /> <br />In view of assumptions 3 and 7, and as a practical matter, some change to <br />channel form from artificial activities must be expected. However, the <br />maintenance flows calculated in this procedure are intended to minimize the <br />adverse effects of artificial modifications of the normal flow regime. <br />Furthermore, the calculated maintenance flow will result in sediment <br />transport at a level which lies within the range of expected fluctuation <br />about a mean value (assumption 7). This assumption appears to be congruent <br />with the intent of both Congress, as defined.in the Organic Administration <br />Act [Act of June 4, 1897 (16 U.S.C. 475)], and the Supreme Court, as <br />expressed in United States v. New Mexico [98 S. Ct. 3012, 8 ELR 20564 (July <br />3, 1978)]. . <br /> <br />12. National Forest maintenance flow requirements will be no more than <br />those determined to be necessary for the achievement of the objective of <br />securing a favorable condition of water flows. <br /> <br />13. Maintenance flows .in ungaged watersheds can be determined through <br />methods other than direct discharge measurement. <br /> <br />14. Gaged station flow-duration curves can be extrapolated to nearby, <br />similar, ungaged watersheds. <br /> <br />15. The discharge regime of an erodible bed/bank channel can be <br />characterized by, at least, the channel's hydraulic geometry. <br /> <br />16. Channel width at bankfull stage is the best single variable, among <br />those available through measurements of a channel's hydraulic geometry, for <br />estimating bankfull discharge. <br /> <br />17. Other frequently occurring discharges can be described as <br />percentages of bankfull discharge. <br /> <br />, <br />\ <br /> <br />) <br />