Modification of DWCM‐AgWU Model Applied to A Paddy‐Dominant Basin with Large Dams

The Distributed Water Circulation Model incorporating Agricultural Water Use (DWCM‐AgWU) was modified and the revised model was applied to assess water use in the Chao Phraya River basin in Thailand for the years 2008–2011, during which there were droughts and floods. A reservoir management model was introduced to incorporate two large dams (Bhumibol and Sirikit dams), with several remote irrigated areas in water allocation/management, and performed special treatments of flood peaks to account for agricultural practices. In the system, the two dams are the main sources of irrigation water during the dry season and they are used to control floods during the rainy season. Moreover, for the lower Chao Phraya River from Nakhon Sawan to the sea, another special water management was applied on rainy days to keep the release at the Chao Phraya Diversion Dam at or below a certain threshold. That is, when discharge exceeded the threshold, water was diverted to main irrigation canals on the western and eastern sides of the Greater Chao Phraya Irrigation Project. According to the simulation, the average relative error between the calculated and observed daily discharge was 21% at the Nakhon Sawan station, which is located below the confluences of the four main tributaries of the Chao Phraya River. The modified model will enable continuous calculations for mitigating the impacts of extreme events, such as the 2011 flood in Thailand, managing the use of irrigation water, and proposing adaptive countermeasures to climate change. Copyright © 2016 John Wiley & Sons, Ltd. Résumé Nous avons modifié le modèle (DWCM‐AgWU) de circulation et de distribution de l'eau avec intégration de l'utilisation de l'eau agricole, et appliqué ce modèle modifié en vue de l'évaluation de l'utilisation de l'eau dans le bassin versant de Chao Phraya en Thaïlande pendant les années 2008 à 2011 et durant lesquelles des sécheresses et des inondations se sont produites. Nous avons introduit un modèle de gestion de réservoir afin d'intégrer deux grands barrages (barrages de Bhumibol et de Sirikit) comportant plusieurs zones d'irrigation éloignées pour la répartition et la gestion de l'eau et eu recours à des traitements spéciaux des pointes de crue pour représenter les pratiques agricoles. Dans ce système, les deux barrages représentent les sources principales de l'eau d'irrigation pendant la saison sèche et sont utilisés afin de contrôler les crues pendant la saison des pluies. Par ailleurs, nous a