COMPARATIVE STUDY OF CONVENTIONAL AND INSTANTANEOUS UNIT HYDROGRAPHS

Abstract

This thesis is concerned with a comparative study of the results from instantaneous unit hydrograph and the conventional unit hydrograph. The primary objective of the study was to see the influence of the nonuniformity of rain-fall on the DRHS derived using conventional unit hydrograph and the departure of these DRH f rom those derived using IUH Storm-runoff records for three different catchments have been selected and used for the computation of It I by Nash model and unit hydrographs of full and one-third duration of effective rainfall. Nine different rainfall patterns were assumed arbitrarily and two indices of nonuniformity of pre-cipitation viz. P and d1/d2 were used in the analysis. The variation in DRHS developed from IUH, UH of full rainfall duration and UH of (1/3rd) rainfall duration have been studied with respect to nonuniformity indices. The following significant conclusions have been drawn 1) Nearest integerised value of n ( to make it physically meaningful in Nash model as no. of reservoirs) with modified value of storage coefficient K (maintaining nK constant) can be used without loss of accuracy in .preference to use non-integer value of n. 2) The use of unit hydrograph of full or one-third effec-tive rainfall duration underestimates the peak dis-charges if the results from the ITJH are used as basis a.. for comparison. The time of peak discharge as given by conventional unit hydrograph is either same as that given by IUH or is somewhat delayed with res- 0 pect to it. 3) The unit hydrograph of, one-third rainfall duration can be used without much loss of accuracy in case sufficient data for development of IUH are not available.