Monitoring of the environmental action plan during the construction of Bhairab Bridge over the Meghna River

摘要

A study was carried out with the objectives to assess the existing environmental conditions to establish baseline conditions of the Bhairab Bridge project and to monitor the environmental action plan implemented during the construction of the Bhairab Bridge project. The bridge was constructed on the Dhaka-Sylhet National Highway in Bangladesh over the Meghna river at a distance of 110 m upstream of the existing Bhairab railway bridge. The project consists of three main components such as a bridge with the length of 1.23 km, river training works with the length of 1.07 km and bridge connecting approach roads with the length of 1.43 km. The study was carried on the basis of available secondary and field monitoring data. The secondary data pertaining to this study were collected from different sources. Field data on water (surface, ground and drinking) quality and quality of dredged materials were collected from the various monitoring points in the project area during the construction stage of the bridge. Data on vibration impact on the existing Bhairab railway bridge due to pile driving activities were also collected from the site. The results of the analyses of the available data showed the parameters that were tested from the collected surface water samples of the monitoring points in the project area revealed that all the water bodies except the Meghna river were polluted due to untreated waste, toilet and public ignorance but not due to project activities. Groundwater quality test results showed the presence of arsenic (As) which was not due to project activities. Drinking water from the hand tube wells contained high level of arsenic (As) and therefore deep tube wells were installed at the depth of 200 m to supply pure drinking water. The test results of the water samples showed that all the parameters were within the standard values and suitable for drinking. Most of the parameters of the quality of dredged materials were within the acceptable limit and hence used for fill materials of the project area. The vibration level on railway bridge prior to pile driving of the road bridge did not exceed the base value. It showed that no vibration impacts were occurred on the railway bridge due to pile driving of the newly constructed Bhairab road bridge. Th monitoring on air and noise pollutions, navigation, drainage and waste management was carried out regularly to avoid any environmental damage. About 3000 trees have been planted in the project area to compensate 35 trees lost which would also enhance the positive environmental impacts in the project area. It can therefore be concluded that the Bhairab bridge project constructed over the Meghna river is environmentally friendly and sustainable.