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<br />R2 = Rl + (11 + 12) I 2 - OlAt <br /> <br />(7) <br /> <br />O2 = f (R2) <br />O2 = D2 - X (12 - O2) I (1 - X) <br /> <br />(8) <br />(9) <br /> <br />in which: <br /> <br />Rl = working storage index at start of interval <br /> <br />R2 = working storage index at end of interval <br /> <br />01 = working discharge index at start of interval <br /> <br />O2 = working discharge index at end of interval <br /> <br />x = same as in the Muskingum routing method <br /> <br />A curve of D vs R can be established from the following equation: <br /> <br />R = D (K-KX + .SAt) <br /> <br />(10) <br /> <br />in which K is the variable used in the Muskingum method but need not <br />be constant for different discharges. Routing procedure consists of <br />applying equations 7 to 9 for each computation interval, usually assum- <br />ing that outflow equals inflow at the start of the computation. <br />The straddle-stagger method of flood routing is an artificial and <br />empirical technique that might be satisfactory in many applications and <br />is very simple in concept. This technique consists of averaging a fixed <br />number of successive inflows to obtain the outflow that would occur some <br />time after the mid-time of the inflows averaged. Straddle refers to the <br />number of inflows to be averaged. Stagger refers to the number of ordi- <br />nates of time delay between the mid-time of the inflows averaged and the <br />time that such average becomes the outflow. This method is also referred <br />to as the progressive average-lag method. In order that timing at the <br />downstream point coincides with timing at the upstream point. stagger <br />should be an integer if the straddle is an odd number. If straddle is <br />an even number, the stagger should be an odd multiple of .5 time intervals. <br /> <br />2-18 <br />