A CASE STUDY OF STABLE ISOTOPE FINGERPRINTING FOR SURFACE WATER AND GROUNDWATER ORIGIN AND DYNAMIC INTERACTIONS IN THAILAND

摘要

Water stress is rapidly increasing in many parts of Thailand, especially during drought season, due to expansion in agriculture and industry. In this paper, we focus on the Upper Chao Phraya River and a part of Naan river basins in order to assess the capability of using water stable isotope analysis (8D-518O) to refine the understanding on precipitation spatial and temporal distribution as well as the recharge process for the aquifer system underneath the study area. Surface water and groundwater were sampled along the main river course and irrigation canals in combination with the precipitation data in this catchment gathered from the public IAEA database. Meteorological maps were employed to detect the origin of precipitation that generated the majority of runoff in the study area. The preliminary results were compared to published literature data on local and regional precipitations. The use of oxygen and hydrogen isotopic compositions was proven to be a useful tool to explain the spatial and temporal distribution of the rainfall in the study area and also gave some valuable insights in the dynamic sources of groundwater for the aquifer system of interest. The precipitation signature predominated the shallow aquifer, reflecting that the rainfall produced the local runoff sampled in the study. On the other hand, the surface water signature predominated the deeper groundwater, indicating the possible effects from past extreme rainfall events from connected basin upstream. The existence of a degree of spatial separation of groundwater characteristics in the study area demonstrated that groundwater flow in a complex alluvial system in Upper Chao Phraya basin was not always continuous.