Environmental impacts of re-ex-cavation of the Kapotaksha river

Abstract

The river Kapotaksha is located in the southwest part of Bangladesh. Due to reduced cross section and siltation, annual flooding and drainage congestion is a common phenomenon in this area. To offer a short-ternl relief, Bangladesh Water Development Board (BWDB) has undertaken a decision of re-excavating a portion of the river named Kapotaksha River Re-excavation Project (KRREP). The present study is aimed at carrying out a detail Environmental Impact Assessment (EIA) and prepares an Environmental Management Plan (EMP) so that the dredging activities can be carried out in an environmental friendly and sustainable manner. To carryout the Environmental Impact Assessment (ErA), primary and secondary data and information were collected by field visit and from different relevant sources. Environmental Evaluation System (EES) was adopted to assess the impacts due to re-excavation. The net impact due to the re-excavation of the Kapotaksha River is assessed as positive. The impact assessment shows that the re-excavation offers not only a short-term relief from flooding and drainage problem but also a long-term beneficial option for an extended program of re-excavation. During dredging work, water quality and sedimentation will experience negative effects, but this situation will improve gradually with time. Water level and salinity will improve significantly (Environmental impact value, EIV was found +20 to +40 for water level and +100 to +175 for salinity). Incase of flood control, high EIV (+900) shows that more than 90% of flood control is expected due to re-excavation. Navigation situation will also improve (about 90%). Among the ecological parameters, fisheries resource shows zero impact during dredging. But it will experience a large-scale positive impact (EIV +280) after the completion of the re-excavation. The situation of partly terrestrial- partly aquatic ecosystem will worsen (about 10%) during dredging. However, the situation will improve with time. The re-excavation project will offer employment opportunity to the local people. Around 30% of unemployed persons can be involved in manual re-excavation work. After re-excavation, about 40- 50% employment is expected to increase due to better situation in agriculture, irrigation and transport communication sector. Noise level and dust pollution will be a major problem during dredging. However, this problem will be diminished after completion of the project. A complete EMP has been prepared to reduce and mitigate adverse effects at three phases of the project i.e. during dredging, for a short period after dredging and for a long period after dredging. During dredging, an extensive mitigation measure should be undertaken for maintaining ground water quality and sedimentation. Moreover care should be taken to minimize land loss. After short period of dredging, mitigation measures should be taken for ground water level, sediment quality and soil quality. A restricted use of ground water for irrigation can ensure a sufficient ground water level. Prohibition of extensive use of agricultural land and limited use of fertilizer and pesticides may reduce the degradation of soil quality. Moreover, limited movement of engine driven vehicle on the Kapotaksha River may limit the deterioration of the sediment and water quality. For long run, a good control on use of land and fertilizer are essential to ensure good soil and sediment quality. A monitoring plan has also been provided which would enable to detect any changes in the physical, ecological, and social sectors due to the implementation of the project. Salinity, water level and river cross-sections, fisheries, flooding and drainage situation is suggested to be closely monitored. Some special aspects such as occupation and employment, agriculture and fisheries activities, waterway navigation, land loss due to riverbed erosion etc. should be monitored throughout the year. Some enhancement plan like re-establishment of connectivity of the river with neighbouring beels and baors, fish friendly operation of fish pass etc. are provided in the EMP to ensure improved benefit from the project. The impact assessment of the Kapotaksha River Re-excavation (KRREP) conducted in the present study, showed that the re-excavation activity would definitely lessen the siltation on the riverbed to a great extent glvmg a sustainable solution to drainage congestion occurring every year in this area.