Sediment dispersion from offshore TIN dredging along Andaman sea coast using satellite data
Resamee Suwanwerakamtorn, Anong Paijitprapaporn,
Darasri Downreasng, Prakmard Suwanasing
National Research Council Department of Mineral Resources
Bangkok, Thailand.
Abstract
The study on sediment dispersion from offshore tin dredging along the Andaman sea coast was performed by the use of three time-series Landsat-5 TM data acquired on Feb 04, Feb 20 and May 11, 1989. The main purpose was to study the effect of the sadiment dispersion resulting from tin dredging on the coral reef along Ko Ka--- Island and Bang Sak beach, Phangnga province, North and East of the dredging area . The data were analysed on the Meredian Image Analysis System by using contrast stretch enhancement technique of bands 1, 2 and 3 incorporation with mining concession map, number of dredges and oceanographic data.
The results of the study showed that during the North East Moonsoon which is the dredging period, the current circulation along the Andaman seashore in the Northern hemisphere moved from North to South and then inclined southwest somewhat parallel to the Equator. This caused the sediment from tin dredging to disperse from the shoreline in elingate pattern when the diffuser was not installed. In the contrary, after installation, the sediment dispersion was changed to become patchy or circular pattern. However, in both cases, it was found that the tin dredging has only slight effect on the coral reef environment around Ko Ka Island and Bang Sak beach and vicinity area. The study will be continued in order to monitor such effect on a long term basis to obtain a better understanding of the sediment dispersion process.
Intdoduction
With the proposal from the tin company to increase the dredging activities to about 200 dredges in the mine concession area in Bang Muang - Ko Khor Khao, Takua Pa district, Phanganga Province, the Department of Mineral Resources (DMR) with its responsibility in the control of off shore tin dredging has put more efforts in finding appropriate means to protect the sea environment. This is because the unefficient dredging may cause damages to the marine ecology due to the sediments that are drained directly from jig to sea and could have effect on teh coral reefs along Ko Ka Island and Bang Sak beach which are the tourism spots. These two areas are about 5 and 7 kilometers (km.) lying in the North and East of dredging area. Basides that reason, the protection of mineral resources with marginal return is also important. Therefore DMR has set out regulations that every dredge must have a specific dredging system and a diffuser.
The activities began with the first four dredges that had been inspected and approved to dredge in February, 1989. So far, 120 dredges have been approved to dredge in the Andaman seashore.
In order to control the dredge to follow the government specifications, to verify the efficiency of diffusers as well as to protect and to reduce the impacts resulting from tin dredging, the detection and monitoring scheme has been programmed by the use of satellite data. The work has been carried out by the Division of Environment and Mineral Resource of DMR with support from the National Research Council for the satellite data and the digital image analysis facilities.
Objectives
- To study the pattern and direction of sediment
dispersion from tin dredging sites.
- To detect and monitor the bounderies of sediment
dispersion before and after diffuser installation.
- To study the impacts of sediment dispersion on the coral reef environment along Ko Ka Island , Bang Sak beach and vicinity area.
