Geo-environment and effect of sea level rise in the Chao Phraya Delta
Masatomo Umitsu1
1 Dept. of Geography, Nagoya University, e-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.
Abstract: Landforms and sediments of the Chao Phraya Delta are analyzed, and the effect of future sea level rise in the delta is discussed in relation to the geoenvironment. Landforms of the Chao Phraya Delta are classified into the deltaic floodplain in the north, the deltaic plain in the central and south, and the tidal plain in the southernmost regions of the plain. Elevation of the tidal lowland in the southernmost region is around 1 m a.s.l., and its surface is very flat and low. Most of the region is originally lower than high tide level, and the sediments of the region are thin tidal flat silt or clay over thick marine sediments. The deltaic plain with elevation 2- 3 m has been formed as a tidal and deltaic plain since the Holocene high stand around 6000 years BP. The surface sediments of the region which cover marine sediments are soft silt and mostly consisted as tidal flat origin. There are a little fluvial landforms and their sediments in the deltaic plain. Fluvial landforms as natural levees and flood basins develop in the region of deltaic fluvial plain. Surface sediments of the region are characterized with fluvial silt or clay that cover tidal silty sediments. The tidal plain of the delta is the region where the direct impact of the sea-level rise may occur. Coastal erosion is already in progress, and there is a possibility of submergence of the region according to the sea level rise. Acceleration of badly drainage condition is anticipated in the deltaic plain, because the surface gradient of the region is very low and the relative gradient of the drainage is going to decrease according to the sea level rise. As there is a little relief in the deltaic plain region except the artificial reclaimed land, the impact of sea level rise might effect widely. Land subsidence of the region also accelerates the effect of sea level rise. In the deltaic floodplain, difference of flooding condition can be seen in relation to the micro landforms. Natural levees and other higher places suffer a little flooding or escape from floodings. On the contrary, swampy areas of a flood basin suffer severe flooding. Most of them develop in the area surrounded by natural levees. The flooding condition has possibility to be accelerated according to the future sea-level rise.
