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<br />OJ1245 <br /> <br />8 <br /> <br />The oscillations appear to be related to the time periods selected for the <br />quantizing of the observed rainfall and runoff data. If the intervals <br />are too small, the oscillations are more prevalent. If the time <br />intervals are made to large, desired accuracy about the response time <br />is lost. <br />There are several other computer based procedures for deriving a <br />unit hydrograph from the observed rainfall runoff pairs. They all appear <br />to suffer from the same difficulty of oscillations when computing values <br />of the recession limb. Kavvas and Schulz (1972) described a procedure <br />for the removal of the unit hydrograph oscillations by means of filtering. <br />It was demonstrated that the undesireab1e oscillations could be removed <br />by applying a low pass filter to the derived unit hydrograph. It was <br />shown that the actual watershed behaves as a low pass filter. <br />T~e-A!lea ~~togllam6 - An instantaneous unit hydrograph can be <br />computed from watershed characteristics using Clark's method, Clark <br />(1945). Clark's method is a parametric system synthesis method where <br />the instantaneous unit hydrograph (IUH) is derived by routing the time- <br />area curve of the particular basin through a linear reservoir whose <br />storage constant, K, is determined from the recession side of the <br />runoff hydrograph. Isochrones of travel time are drawn on a map of the <br />watershed. The time-area curve is obtained by p1animetering the area <br />between adjacent isochrones. The method reflects the influences of the <br />watershed shape and utilizes the basin storage concepts to find the <br />translation time of a flood wave through the stream pattern of the <br />basin. This translation time is called the travel time. Clark (1945) <br />defined the travel time as a ratio of the storage to discharge, <br />