Synthetic Storm Pattern and Run-off for Gauhati, India

One of the most important factors which is generally not considered in the rational method, is the effect of antecedent rainfall as well as the location of peak intensity during the time of concentration. It is known that the rainfall intensity duration curve for a particular frequency indicates only average intensity for a given duration corresponding to the time of concentration which is one of the basic assumptions of the rational method. But to determine at what time within the duration of storm the said average intensity may have occurred, the knowledge of storm pattern is necessary. Without this, proper application of the rational method is not possible, especially in evaluating the effect of antecedent precipitation. The purpose of this study is to determine a synthetic storm pattern from the rate duration curve with particular reference to the city of Gauhati in Assam, India, and the application of this storm pattern in the determination of the run-off coefficient in the Rational Method.