Subsidence in the lower deltaic areas of Bangladesh
Titel:
Subsidence in the lower deltaic areas of Bangladesh
Auteur:
Hoque, Monirul Alam, Mahmood
Verschenen in:
Marine geodesy
Paginering:
Jaargang 20 (1997) nr. 1 pagina's 105-120
Jaar:
1997
Inhoud:
The lower deltaic area of Bangladesh is located on two active troughs, Faridpur Trough and Hatiya Trough. Although most of the Bengal Basin is slowly subsiding, the troughs are subsiding more rapidly. The area shows evidence of three different types of subsidence: tectonic, anthropogenic, and that resulting from the compaction of peat layer. Under natural conditions the subsidence of the area is compensated by sediment brought into the system by rivers, tides, and coastal currents. However, man-made projects, especially the coastal embankment project and polder projects, are altering the sedimentation pattern of the area. Areas being protected by embankment and polders from salt water intrusion and flood water are receiving very little to no sediments from outside. In most of the lower deltic area, tidal processes play the most important role in sedimentation: The main objective of polder projects is to protect the project area from the intrusion of tidal water, which at the same time prevents sediments from reaching the protected area. Uncompensated subsidence is causing widespread waterlogging and drainage problems in the lower deltaic area of Bangladesh. There are not enough accurate and quantified data on the rate of subsidence in the area. There are no field stations to measure the rate of subsidence. Field evidence suggests that the rate of subsidence is not uniform throughout the area. The areas underlain by peat layers are often undergoing rapid subsidence. The rate of subsidence obtained from carbon-14 dates and well log data shows considerable variation. The rate of subsidence obtained from the Hizla-Muladi well suggests that the area is subsiding at a rate of 2.0 cmlyear. However, carbon-14 dates often indicate a rate of around 2—4 mm/year.
Tijdschrift beschrijving