HYDROLOGIC ANALYSIS OF SURYANAGAR WATERSHEDS USING IDF CURVES AND RUNOFF MODELS

Abstract

Quantification of short duration high intensity rainfall is generally done using IDF (Intensity-Duration-Frequency) curves, based on historic rainfall data of significant years.Due to non-availability of short duration rainfall data, an attempt is made to derive short duration empirical reduction formula to understand urban hydrology.Bangalore is a rapidly growing city in terms of population and intense urban growth.Today about 70 per cent of the 262 water tanks in 1961 in Bangalore have disappeared leading to surface flooding.Daily rainfall data of5 stations for the years 1998 to 2011 collected from Indian Meteorological Department (IMD) were used in the study.The missing rainfall data, during this period was interpolated by Airthematic_mean method.The IMD empirical reduction formula was used to estimate the short duration rainfall.The rainfall depth for various return periods were predicted using different probability distributions and analyzed.The Chi-Square goodness of fit was used, to arrive at the best statistical distribution among Normal, Log-Normal, Gumbel and Pearson.Chi-Square test showed that lognormal is the best probability distribution for the 5 stations considered.The IDF curves were plotted for short duration rainfall of 5, 10, 15, 30, 60, 120, 720 and 1440 minutes for a return period of 2, 3, 5, 10, 25, 50, 100 and 200 years for stations with peak rainfall values.The use of IDF curves becomes cumbersome; hence a generalized empirical relationship was developed for the Study Area Suryanagara -Urban Bangalore, through method of least squares.