Agricultural water-gate management for operational flood protection in low-lying paddies

Abstract

It is essential to assess in influence of water-gate operations on inundation processes during the wet season to mitigate inundation damage. Here, a numerical analysis method for modelling regional drainage through water gates was developed by integrating the Distributed Water Circulation Model incorporating Agricultural Water Use (DWCM-AgWU). The inundation process was reproduced using an H–V curve (flooding water level verses area volume). The developed model was applied to the low-lying paddy areas of the Nam Cheng River basin in the Lao PDR. This study area is a sub-basin of the Nam Ngum River, with which the Nam Cheng River merges downstream of the Nam Ngum 1 dam. Fourteen agricultural water gates of slide-type at the river outlet function as a storage facility for irrigation water for the paddies during the dry season and as a flood protection measures against backwater effects from the main stream of the Nam Ngum River during the wet season. However, current gate operation is based on empirical knowledge without reference to filed observational data. The simulated results revealed that the outer water level did not exceed the inner level, if the difference between the inner and outer water levels was > 4 m on operational days. Several feedback control strategies combined with gate opening heights, the number of open gates, operation intervals, and the threshold inner and outer water level differences were examined focusing on inundation damage within the area and drainage volume through the gates.