Development of IDF Curves for Colombo

Rainfall Intensity-Duration-Frequency (IDF) relationships usually play a major role in the designing and building of water infrastructure. The main purpose of this paper is to show the procedure that need to be followed in the development of IDF relationships using rainfall data collected in Colombo, Sri Lanka. Short duration rainfall data of Colombo recorded over a 30 year period by the Department of Meteorology were used for the study. The procedures to be adopted in screening rainfall data, carrying out frequency analyses, and finally developing the IDF relationships are described. The IDF curves have been developed for 2, 5, 10, 25, 50 and 100 year return periods for durations ranging from 15 minutes to 24 hours. The developed IDF relationships were compared with the IDF relationships presently available for Colombo. The results indicate that the rainfall intensities of Colombo have recently increased. It is recommended that the IDF relationships for other stations in the country also be updated.