Dhaka / The Action Plan for flooding
The disastrous 1987 and 1988 floods have stimulated considerable international interest in helping Bangladesh deal with its flood problem. In June 1989, the World Bank agreed to a request from the Government to help in coordinating the international efforts. It outlines an Action Plan which would be the first step in the implementation of a comprehensive long-term program for flood control and drainage in Bangladesh.
In 1987 and 1988, Bangladesh experienced two of the most severe floods on record. Widespread damage was caused to crops, roads, railroads, cities and towns, and more than three thousand people lost their lives. These floods were a major setback to the country’s economy and this thus stimulated the Government to undertake a comprehensive review of flood policy and, soon after the 1988 flood.
The first systematic study of the Bangladesh flood problem was followed by a Master Plan prepared in 1964 which proposed a large number of projects combining the functions of flood control, drainage and irrigation. Subsequently, some major embankments were built along parts of the main rivers, including the World Bank-financed Brahmaputra Right Embankment. In those pre-Independence days, major water control works were seen as a requirement to advance the agricultural production. However, by the early 1970’s, the advent of low-lift pumps, tube wells, and the spread of dry-season cropping led to a strategy based more on small-scale, quick-yielding projects rather than major flood control works. Thus, the flood control debate had receded into the background until the floods of 1987 and 1988. Strategies and options for flood control in Bangladesh have been debated for many years. On one side is the argument that periodic flooding in Bangladesh is largely unavoidable because the works needed to eliminate flooding from the rivers are, in some areas, technically and economically infeasible and, moreover, tend to create as many problems as they solve.
The above figure shows the existing and proposed flood control and management infrastructure in Dhaka
Planning and Design Issues
Since the interception of flood waters by upstream storage is infeasible, measures to limit overbank flooding must rely on embankments. The planning and design of embankments in Bangladesh faces various problems. Foremost among these is that embankments tend to obstruct drainage from the areas they protect. During the flood season, most of Bangladesh receives 2,000 to 5,000mm of rain and this in itself can cause flooding unless it can be drained away from the land to the rivers. Thus, any embankment scheme must include provision to remove excess rainfall. This may be by controlled openings in the embankment (where gravity drainage is possible) or by drainage pumps where differences in level inside and outside the embankment are too small to allow gravity flow. Embankment schemes must also be designed to allow controlled inflow of water from the rivers for irrigation and to recharge the groundwater. Provision must also be made to avoid harmful effects on fisheries and river transport. Embankments must therefore be seen as elements of a comprehensive water control system planned and designed to modify the water regime in the interests of more profitable land use in an environmentally sound manner.
The ‘compartment’ was then proposed. With this approach, a section of river embankment forms one side of a block of land enclosed by embankments and provided with the various structures necessary to ensure water control over a wide range of hydrologic conditions. The experience with the embankments has been mixed; a few have been successful but others have not worked as intended. The reasons range from design deficiencies, failures to complete the works as designed, and weaknesses in operation and maintenance. Thus, the compartment approach will require a higher standard of planning, design, construction and operation than has generally been practiced to-date in Bangladesh.
Another important planning issue is the location and alignment of embankments. In terms of economics and engineering, the embankments should ideally be placed far enough from the main river channel to avoid attack from the river and to maintain the conveyance capacity of the river. In such cases, the land between the embankment and the river can be, used for rice, jute and a variety of dry-season crops which can be protected. Loss of benefits can therefore be greatly reduced from more intensive wet- season cropping needs to be more than balanced by the savings in construction costs and by the much lower recurrent costs for river training and maintenance.
The main features of the Action Plan are:
- Strengthening of the Brahmaputra right embankment and improvementof flood control and drainage in the north-west region;
- Measures to control flooding on the left bank of the Brahmaputra and the
developmentof the protected area by means of drainage and water control works, particularly in the north-central region; measures to control flooding on the right bank of the Ganges, the Padma and the Lower Meghna, and improvements in water control and drainage in the south-west and south-central regions;
- Measures to control flooding on the left bank of the Meghna, including improvementsin water control and drainage in the south-east region;
- A study of the north-east region leading to a regional water management program;
- Rehabilitation of the coastal embankments to protect against cyclones and tidal surges, and to include provision for drainage outlet structures;
- Flood protection and drainage works for the Greater Dhaka area, and bank protection for towns such as Chandpur, Sirajganj, and Bhairab Bazar,
- Strengthening of the flood forecasting and early warning system;
- Development of a flood preparedness program. In addition, the Action Plan includes the following activities to support the Plan components and the preparation of future projects:
- Surveys of the operation and maintenance, agricultural, social and environmental aspects of existing flood control projects;
- Provision of topographic mapping, satellite imagery, and geographic information systems;
- Pilot projects in compartmentalization, bank protection, river training, fisheries and flood proofing;
- Expansion of hydrologic data collection such as discharge and sediment measurements, water level recording, and observations of changes in river regimes on all the major rivers;
- Adaptation of existing surface water simulation models to provide inputs to flood management, project design and project operation;
- A study of the institutional arrangements required for implementation of the Action Plan.
Flood Control in Bangladesh: A Plan for Action