Development of Rainfall Intensity-Duration-frequency Relationships from Daily Rainfall Data for the major cities in Bangladesh Based on Scaling Properties

The rainfall Intensity-Duration-Frequency (IDF) relationship is one of the most commonly used tools for various engineering projects against floods. It is important in water resources engineering, either for planning, designing and operating of water resource projects. For estimation of runoff especially for urban areas short duration rainfalls are necessary. Developing countries like Bangladesh short duration rainfall is scarce and data available is mostly for daily rainfall data. In such cases, design rainfall is estimated by approximation and thus leading to frequent failure of drainage network. The purpose of this paper is to develop an empirical formula to estimate design rainfall intensity for seven major cities based on simple scaling properties. This method allows for the estimation of the design value of rainfall of selected return period and durations shorter than a day by using only the daily data. The assumption of simple scaling implies in direct relationships between the moments of different orders and the rainfall durations, which can be used to derive IDF relation¬ships from larger durations.