Storm-Water Predictions by Dimensionless Unit Hydrograph

Abstract

This paper presents a theoretical derivation of a dimensionless unit hydrograph using the kinematic wave approach. The dimensionless kinematic wave unit hydrograph (KWUH) is normalized by the parameters associated with the equilibrium condition and can be generated according to the selected rainfall duration. For comparison, a KWUH whose rainfall duration is equal to the time of equilibrium produces good agreement with the Soil Conservation Service dimensionless unit graph (SCSUH). Both the KWUH and SCSUH are kinematic in nature and have a 37.5% runoff volume that occurred before the time to peak. To verify the applicability of the KWUH derived in this study, a set of hypothetical rectangular watersheds ranging from 20 to 200 acres was investigated. The predicted 100-year peak flow rates from these five hypothetical rectangular watersheds are compared with the SCSUH method and the Colorado Unit Hydrograph Procedures (CUHP). In general, the KWUH produces good agreement with the CUHP when the catchment has an area between 60 and 120 acres. Based on the study of hypothetical rectangular watersheds, it is recommended that the KWUH be applicable to urban catchments with a drainage area of up to 120 acres.