TRANSPORT PATTERNS IN THE CHAP PHYA ESTUARY

Abstract

Present day's society asks for ever larger engineering works to be carried out in estuaries. The developing techniques of dredging and construction allow for great interventions in the natural phenomena with often far reaching consequences. The whole intricate system of transports of water, salt and sediments may be drastically changed,affecting the existing quasi-static equilibria between sedimentation and erosion. For the planning of such works a thorough knowledge of the estuarme hydrology is indispensable. The port of Bangkok, the mam gateway for traffic into Thailand, is situated in the estuary of the Chao Phya river (figure 1). Increasing navigation demands improvement of the harbour and its 55 km long approach channel but the interests of agriculture and municipal water supply must also be taken into account. The Netherlands Engineering Consultants (NEDECO) m combination with the Delft Hydraulics Laboratory have made a four-years study of the estuary covering a field survey and a hydraulic model test. The observations in nature served to obtain insight into the estuarme transport pattern m relation with the boundary conditions given by the regimen of the river and the state of the sea. The small scale tests gave indications of the changes in these phenomena to be expected from alterations of the situation m the estuary and of the discharge characteristics of the river. The field survey was carried out from 1961 to 1965 with four fully equipped survey vessels to measure current velocities (60,000 times) to take samples of water and sediments, to measure wave heights and for echo-soundings. In a laboratory the samples of water (70,000) and sediments were tested as to silt concentration, salinity and soil-mechanical properties. Together with meteorological, oceanographical and hydrological data from cooperating local authorities a picture was obtained of the phenomena in the estuary and the causes of the siltation m the dredged channel.