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<br />eM lUo-2-U08 <br />. 1 Marek lKO <br /> <br />15 <br /> <br />10 <br /> <br /> <br />w <br />l.:) <br />a: <br /><( <br />- <br />U <br />(/) 5 <br />Q <br /> <br />o <br />o <br /> <br />!) <br /> <br />10 <br />TIME <br /> <br />15 <br /> <br />20 <br /> <br />Figure 7 <br /> <br />2-11. SELECTION OF REACH LENGTHS. The ends of routing reaches should he chosen with refer- <br />ence to the storage characteristics of the river valley. A section should be located at any channel control <br />which creates relatively large storage upstream. 'In the extreme case the storage outflow relation for <br />such a reach is the reservoir type, for which X equals zero, and the reach in which the reservoir-type <br />storage is located should not be subdivided. A section should be located at the upstream end of pool- <br />type storage reaches, If a long stretch of river intervenes between the pool-type reaches, the stretch <br />should be subdivided at convenient section" including gaging stations, according to the criteria requiring <br />K to approximat.ely equal 6t. Water-surface profile charts are useful in locating channel controls and <br />inflow sections to pool.type reaches, If a major tributary jcins the stream, the downstream end of the <br />routing reach should be at or near the confluence. <br /> <br />CHAPTER 3 <br /> <br />FLOOD ROUTING THROUGH USE OF WORKING VALUE R <br /> <br />3-01. GENERAL. The device of using working values has been used in various flood-routing procedures. <br />The method discussed hcrein has been described hy Gilcrest' and is a variation oj a procedure previously <br />described by Steinberg." This method utilizes a working value R, representing an index of storage, <br />which is (I-X) times the similar index utilized in the procedure described by Steinberg. Both methods <br />utilize a working discharge D that is related to the value X used in the coefficient method. Either of <br />these two methods is considered more advantageous than.the coefficient method if a variable K must he <br />considered or if an independent variable, such as tributary inflow or controlled discharge through a <br />gated low dam, is involved. <br /> <br />H2. THEORY. The method is based on the assumption that <br /> <br />D=XT+(I-X)O. __.. _ _.. _____u___ _ ___ ___.__nn (24) <br /> <br />11 <br /> <br />I <br />\ <br />