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<br />For example, if straddle is 5 computation intervals, stagger can be an <br />integer of 2 or larger such as 2, 3, 4, etc. If straddle is 4, stagger <br />should have a value such as .5, 1.5, 2.5. etc. <br />The Tatum method, also known as the successive average lag method, <br />consists simply of a number of successive straddle-stagger routings <br />where straddle is 2 and stagger is .5. The number of successive routings <br />is usually taken as twice the time of travel through the reach divided by <br />the computation interval. <br />The multiple storage routing consists of a succession of reservoir- <br />type storage routings (where outflow is a direct and unique function of <br />storage) using a time-of-storage factor as an index of the linear storage- <br />outflow relationship. The equation used is: <br /> <br />O2 = <br /> <br />(I, + I2) I 2 - 01 <br />At <br />T 01-0.2 + At 12 <br /> <br />(11 ) <br /> <br />in which: <br />T = time of storage in the same time units as At. <br /> <br />The exponent in the denominator may vary somewhat from -0,2, but this <br />value usually gives satisfactory results if sufficient data in a stream <br />system are not available for empirical determination of this exponent. <br />The routing computation is accomplished by successively computing the <br />outflow at the end of each computation interval using equation 11, as- <br />suming that outflow equals inflow at the start of the computation. The <br />time of storage, T, is derived empirically through reconstitution of <br />recorded flood hydrographs for the stream. Usually 4 or 5 successive <br />storage computations are used per reach. <br />Routing techniques described in this section are contained in com- <br />puter programs described in Appendix 2 of this volume and Appendix 1 of <br />Volume 1. Automatic derivation of routing coefficients from recorded <br /> <br />2-19 <br />