Areal Rainfall Reduction Factor and Areal Flood Peak Reduction Factor for Upper Chao Phraya River Basin

Abstract

This research work consists of the study of areal rainfall reduction factor (ARF) for the upper Chao Phraya river basin from maximum rainfall depth–area–return period relationship, and the study of areal flood peak reduction factor from flood peak–area–return period relation. For maximum rainfall depth, considered duration is from 1 to 7 days, and for variation of areal rainfall reduction and areal flood peak reduction factors, considered return period is from 2 to 10,000 years. The data used in this study were annual maximum rainfall depth for duration of 1 to 7 days, and daily rainfall data. In the analysis, 35 subbasins located throughout the upper Chao Phraya river basin were selected as representative. The catchment areas of these subbasins vary from 30.23 to 12,866.00 square kilometers and watershed parameters were measured. Regarding to the study result of areal rainfall reduction factor varies from 100 percentage for the point rainfall of any duration to 43.81, 48.83, 52.58, 53.63, 54.92, 55.15 and 55.67
percentage for area of 13,000 square kilometers and for duration of 1, 2, 3, 4, 5, 6 and 7 days, respectively.