2006

DEVELOPING A LOW RETURN PERIOD REGIONAL IDF RELATIONSHIP USING GENERALIZED PARETO (GPA) DISTRIBUTION

Mohd Nor Mohd Desa, M. Z. M. Amin, Asnor M., F. Mohamed
Humid Tropics Centre (HTC) Kuala Lumpur
National Hydraulic Research Institute of Malaysia (NAHRIM)

At site frequency analysis is often hindered by lack of sufficient data with high resolution both in space and time. As a basic for economical and efficient urban drainage design some kind of method to estimate design rainfall at low return periods are to be provided to designers. In order to overcome this limitation regional frequency analysis is often resorted to estimate flood quantiles in a region where inadequate amount of data are available. This study made use of available convective storm data collected over period of 11 years in Sungai Kayu Ara urban catchment which covers an area of 23.5 km2. This paper proposes an approach to estimate design rainfall depth at low ARI using the Partial Duration (PD) data series of short duration high quality rainfall data obtained from seven gauges. Partial Duration Series (PDS) of maximum intensities for durations 3, 5, 10, 15, 20, 30 and 60 minutes are used. Applicability of the proposed approach is performed for at-site and regional frequency analysis; whereas the ability of Bernard’s empirical IDF equation is also examined. Areal reduction factor (ARF) as defined the ratio of areal to point design rainfall. Applicability of the proposed approach is performed for at-site and regional frequency analysis; whereas the ability of Bernard’s empirical IDF equation is also examined. Areal reduction factor (ARF) as defined the ratio of areal to point design rainfall depth is derived for the region. Generally, this paper shows relatively simple application to estimate design rainfall depth or rainfall intensity particularly with the workability of Bernard’s empirical equation which is relevant for the at-site and regional IDF relationship.