Regional Comparison of Flood and Lowflow Characteristics in Southeast Asia and the Pacific

Abstract

The specific discharges of the mean annual flood and the mean annual lowflow were compared in different rivers in Southeast Asia and the Pacific. It was found that the specific discharges of the mean annual floods have two groups, relatively high and relatively low while they as a whole show a decreasing trend with the size of catchment. Most rivers that belong to the relatively low group are under the influence of reservoir regulation upstream. The specific discharges of the mean annual lowflows have also two groups, one concentrated around 0.1-1.0m³/s/100k²and the other below that range, both decrease slightly with the catchment area. They were found dependent on the dryness of the region and the reservoir regulation. Few unregulated rivers seem to show the influence of land cover such as forests, paddy fields and base rocks. A dryness index, m/n, the number of months that have the mean monthly rainfall less than 10mm and 30mm, was introduced and shown operational.