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<br />i time of rise (t r) of the inflow hydrograph. <br /> <br />5 <br /> <br />At :S t <br />-r <br /> <br />(5) <br /> <br />3. MUSKINGUM METHOD. The Muskingum method was developed by the Corps <br />of Engineers in connection with studies of the Muskingum Conservancy District Flood <br />Control Project to directly accommodate the looped relationship between storage and <br />outflow that exists in rivers. With the Muskingum method, storage within a reach is <br />visualized in two parts: Prism Storage and Wedge Storage. Prism storage is <br />essentially the storage under the steady-flow water surface profile. Wedge storage <br />is the additional storage under the actual water surface profile. As shown in figure 1 r <br />during the rising stages of the flood wave the wedge storage is positive and added to <br />the prism storage. During the falling stages of a flood wave the wedge storage is <br />negative and subtracted rom the prism storage. <br /> <br />FIGURE 1 <br />Muskingum Prism and Wedge Storage Concept <br /> <br />3.1. Development of the Muskingum Routing Equation. prism storage <br />is computed as the outflow (0) times the travel time through the reach (K). Wedge <br />storage is computed as the difference between inflow and outflow (1-0) times a <br />weighing coefficient X and the travel time K. The coefficient K corresponds to the <br />travel time of the flood wave through the reach. The parameter X is a dimensionless <br />value expressing a weighing of the relative effects of inflow and outflow on the <br />storage (5) within the reach. Thus, the Muskingum method defines the storage in the <br />reach as a linear function of weighted inflow and outflow: <br /> <br />5 '" prism storage + wedge storage <br /> <br />5 '" KO + KX(I-O) <br /> <br />(6) <br />(7) <br /> <br />5 = K [XI+(1-X)0] <br /> <br />(8) <br /> <br />7-42 <br />