A model for optimisation of water management in rice polders in Thailand

This paper presents a mathematical model for the determination of optimal values for the main components of water management systems in rice polders in Thailand. The aim of the water management system in a rice area is to create good growing conditions for the crops. Under the hydrological conditions of Thailand the average rainfall during the rainy season is more than enough for growing rice or other crops. However, during the dry season there is a very small amount of rainfall. Thus the farmers are confronted with two quite different conditions and water management has to deal with irrigation and drainage issues. The main components of the water management system in a rice polder are the water level in the canals, the percentage of open surface water, discharge capacity from the field and discharge capacity of the pumping station or sluice. A model has been developed that takes into account damage due to flooding and drought as well as construction and maintenance cost for irrigation and drainage systems based on the hydrological conditions. Optimising of such a water management system means determining the main components in such a way that the equivalent annual costs are minimal. A case study has been done for a rice polder in Suphanburi province. It was found that the polder water level for rice under rainfed conditions could be kept above ground level to minimise loss of water from the rice field, whereas under irrigated conditions the polder water level has to be kept below ground level to get good drainage condition