Phreatic surface fluctuations within the tropical floodplain paddy field of the Yom River, Thailand

Abstract. The fluctuation of phreatic surfaces in tropical floodplain was studied for the lower part of the Yom's river basin at Phichit Province in Thailand. The simple water balance budget model was applied to estimate the groundwater recharge. The hydrologic components i.e. average rainfall, surface runoff, and deep percolation were calculated by using climatologically recorded and measured data. The Penman-Monteith's evapotranspiration method was used to estimate potential evapotranspiration for crop water requirement based on climatic data. The 49-points of field infiltration and theirs distribution over the floodplain were measured using ring-infiltrometers. The surface water and phreatic surface deviations from the existing 22-observation wells nearby the Yom River daily observed continuously for 3 years. The observed river water levels and phreatic surface water levels were agreed very well with R² approx. 0.90. The rising or recessing of those fluctuations was depended on the inundated depth over floodplain or the amount of groundwater withdrawal for crop consuming. Understanding and quantifying the phreatic surface fluctuations in lowland paddy field is crucial for further floodplain management.