Rainfall depth-duration-frequency studies for Sri Lanka

Rainfall depth-duration-frequency studies for Sri Lanka were carried out with data available for 19 stations spread over the country. The data are in the form of historic records of annual maximum rainfall depths with 3-, 6-, 12- and 24-h durations. The extreme-value type-1 distribution fitted with maximum likelihood estimates was utilised to derive the required relationships. The analyses for the individual stations were treated as a prelude to a regional study covering the whole country. The regions were defined taking rainfall and topographical characteristics into consideration, and the regional data sets were formed using the station-year concept. Satisfactory results were obtained for both phases of the study. However, owing to the relatively short length of the individual station records, the regional results have been recommended for use in engineering design.