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Are groundwater inputs into river‐dominated areas important? The Chao Phraya River — Gulf of Thailand
Author(s) -
Dulaiova H.,
Burnett W. C.,
Wattayakorn G.,
Sojisuporn P.
Publication year - 2006
Publication title -
limnology and oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.7
H-Index - 197
eISSN - 1939-5590
pISSN - 0024-3590
DOI - 10.4319/lo.2006.51.5.2232
Subject(s) - hydrology (agriculture) , groundwater , submarine groundwater discharge , estuary , discharge , river mouth , groundwater discharge , environmental science , radium , shore , river delta , delta , groundwater flow , geology , drainage basin , aquifer , oceanography , sediment , geography , geomorphology , geotechnical engineering , physics , cartography , engineering , aerospace engineering , nuclear physics
We used the natural geochemical tracers radon‐222 and radium isotopes ( 223 Ra, 224 Ra, 226 Ra, 228 Ra) to assess exchange rates between the Chao Phraya River and the Gulf of Thailand, and the magnitude of groundwater discharge in the estuary. We performed tracer surveys during two periods in 2004, in January (dry season, gauged river discharge 47 m 3 s ‐1 ) and in July (wet season, 430 m 3 s ‐1 ). The isotopic data suggested that there are at least three different sources of these tracers in the estuary: river water, seawater, and groundwater. We estimated the extent of each input via a mixing model using 222 Rn, 223 Ra, and 224 Ra activities and 224 Ra : 223 Ra ratios. Our analysis showed that the largest groundwater outflow occurs near the mouth of the river. Our groundwater discharge estimates based on the mixing model are 10 and 16 m 3 s ‐1 for January and July, respectively. An independent estimate of groundwater discharge in July using a mass balance of excess 226 Ra together with our estimated water exchange rates based on 224 Ra : 223 Ra ratios resulted in a range of 14‐19 m 3 s ‐1 , depending upon the estimated amount of desorbable radium. Our estimated groundwater inputs therefore represent about 20% of the river flow during low flow in January and 4% during high flow conditions in July 2004. The unit shoreline flux (~200 m 3 m ‐1 d ‐1 in July) for the area around the river mouth is over one order of magnitude higher than two other areas of the Gulf of Thailand where groundwater fluxes have been evaluated.