[A-HW23] Isotope Hydrology 2021

[AHW23-03] Stable Isotope Dynamics of Hydrological Interactions in The Chao Phraya River System in Thailand

*Jeerapong Laonamsai¹, Kimpei Ichiyanagi¹ (1.Deaprtment of Earth and Environmental Sciences, Graduate School of Science and Technology, Kumamoto University)

Keywords:Hydrology, Isotopic interactions, Tropical catchment, Water transit time

The present study focuses on a detailed seasonally varying interaction study and flux quantification between the river and monsoon precipitation and groundwater in the Chao Phraya River system which is the main river system that feeds an enormous population. Contributing parameters to the total river discharge on a temporal scale are estimated through three-component hydrograph separation and end-member mixing analysis using high-resolution water isotope (δ¹⁸O and δ²H). This model reports groundwater discharge in the river to be the highest in monsoon (30%), whereas the contribution lowers to 15% during the dry season. During peak monsoon, the monsoon precipitation directly generates river runoff which is also justified using isotopic amplitude damping approach of both river water and precipitation. The mean water transit time is about 26 days. Furthermore, hydrological interaction reflects quantitative variability depending on river morphometry. The current study also provides insight into aquifer vulnerability due to chemical mixing through interaction and reasonable water resources management efforts.