Author(s): E. Venkata Rathnam; K. V. Jayakumar; C. Cunnane
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Abstract: Most hydrological studies require short duration rainfall-runoff data and generally in developing countries, such short duration data are not available. However, daily data are collected and are available; hence efforts have been made to develop short duration data from daily data to aid in hydrological studies in general, and urban stormwater management in particular. In the present study, an attempt has been made to estimate the generated runoff from an urban watershed for design storms of different return periods. The fast growing city of Hyderabad in South India has been taken up for the study. A record of observed daily rainfall values, of length 17 years, were available. From each annual maximum value, corresponding values of 1-hr, 2-hr, 3-hr, 6-hr and 12-hr rainfall values were obtained using an Indian Meteorological Department (IMD) empirical reduction formula and this series is used in the absence of observed data (t-hour rainfall). Frequency analysis was then carried out to establish Intensity-Duration-Frequency (IDF) relationships. Design storm hyetographs for various return periods (2-yr, 5-yr, 10-yr and 20-yr) were derived from the IDF relation and assumed time profiles. Two approaches, viz., the Rational method and NRCS Curve Number method were used to estimate the generated runoff. The results obtained from the study can effectively be used to design storm sewers and detention facilities for urban stormwater management.
Year: 2001