10:45 〜 11:00
[AHW20-01] Groundwater and surface water interaction revealed by multi-tracer method in Klang River Watershed, Kuala Lumpur, Malaysia
キーワード：マルチトレーサー手法、酸素・水素安定同位体比、複雑な地質構造
This study aims to investigate the groundwater and surface water interaction using stable isotopic compositions and inorganic constituent concentrations as tracers in a basin, namely the Klang River watershed located in a humid tropical area with a complex geological setting. We conducted intensive sampling campaigns of river water and groundwater during three different time periods in the relatively dry season (September 2019, January-March 2020, and August-September 2022). The 17 river water samples and 24 groundwater samples were taken from the upper-stream area with an altitude of 527 m to the downstream area with an altitude of 10 m. The oxygen-18 (δ18O) and deuterium (δ2H) stable isotopic compositions and inorganic ion concentrations were determined on all water samples. We used the monthly rainfall amount and stable isotopic compositions of rainwater at the location 15 km apart from the Klang River basin, which is provided by the Global Network of Isotopes in Precipitation database (GNIP), IAEA. We also obtained the static water level in 144 groundwater wells from the Jabatan Mineral dan Geosains Malaysia (JMG), Ministry of Science and Technology and Innovation, Malaysia. These chemical compositions of rainwater, river water and groundwater, and static water levels were used to investigate the groundwater and surface water interaction in this study area.
The δ18O of river water increases with a decrease of sampling altitude from 70 to 26 m, however, it reaches the maximum value at the elevation of 26 m, then decreases with the flow toward downstream. The elevation of 26 m corresponds to the boundary of geology between sedimentary rocks and alluvial deposits. The shallow groundwater table contour lines constructed by observation of the static water level show a clear change from the losing stream to the gaining stream at an elevation of approximately 26 m. This suggests that the discharge of groundwater with higher δ18O seems to cause a maximum value of δ18O in the river at the elevation of approximately 26 m.
The deep groundwater shows a lower δ18O than the volume-weighted mean of rainwater and higher inorganic ions concentrations, whereas the shallow groundwater shows a higher δ18O and lower inorganic ions concentrations. This suggests that the deep groundwater with low δ18O seems to be recharged in the mountainous area with an altitude ranging from 70 to 1421 m. This shows that the deep groundwater in the downstream area is recharged mainly in the mountainous areas with the highest altitude of 1421 m, and the shallow groundwater is recharged partly in the hilly areas with the highest altitude of 250 m.
The δ18O of river water increases with a decrease of sampling altitude from 70 to 26 m, however, it reaches the maximum value at the elevation of 26 m, then decreases with the flow toward downstream. The elevation of 26 m corresponds to the boundary of geology between sedimentary rocks and alluvial deposits. The shallow groundwater table contour lines constructed by observation of the static water level show a clear change from the losing stream to the gaining stream at an elevation of approximately 26 m. This suggests that the discharge of groundwater with higher δ18O seems to cause a maximum value of δ18O in the river at the elevation of approximately 26 m.
The deep groundwater shows a lower δ18O than the volume-weighted mean of rainwater and higher inorganic ions concentrations, whereas the shallow groundwater shows a higher δ18O and lower inorganic ions concentrations. This suggests that the deep groundwater with low δ18O seems to be recharged in the mountainous area with an altitude ranging from 70 to 1421 m. This shows that the deep groundwater in the downstream area is recharged mainly in the mountainous areas with the highest altitude of 1421 m, and the shallow groundwater is recharged partly in the hilly areas with the highest altitude of 250 m.