Bangladesh is considered to be a country worstly affected by recurring floods with devastating dimensions exposing the national economy in the hands of nature. Complete flood control in the geographical context, particularly in the deltaic form of Bangladesh is not at all a feasible option. Structural methods of flood protection are neither economically viable nor these are environment friendly. Therefore, non-structural methods are becoming popular in mitigating flood disaster. A good way to prevent/ reduce damages occurred from flood is to develop a Flood Forecasting and Warning System in the affected area. This study aims to fulfill such requirement by the extensive use of GIS, providing spatial information for assessment of flood vulnerability.

Flood warning system was developed by integrating flood-forecasting results from Hydrodynamic Model MIKE 11 and GIS. The MIKE 11 flood forecasting system comprising of three modules of NAM, HD and FF is used for flood foresting. Geographic Information System (GIS) is a powerful tool for describing, analyzing, modeling and integrating spatial data with other related information such as topographic, thematic and attribute information. It offers new opportunities to develop and implement a user-friendly, interactive decision support system for flood forecasting and identifying the affected areas using dynamic spatial modeling to find out safer location for evacuation. The study concludes that an effective Evacuation System can release warning in advance, say 72hrs, 48hrs and 24hrs. It can change the existing scenario substantially and render informed decision making in adopting proper measures towards disaster preparedness, mitigation, control, planning and management.

Floods in Bangladesh

The consequences of flood event in Bangladesh are hazardous in terms of loss of lives and property. Comprehensive large-scale flood protection is neither economical nor environmentally friendly. Non-structural measures such as flood forecasting and flood preparedness are highly cost-effective to alleviate flood impacts to a great extent. Warning is the critical “hinge factor” in disaster management, which provides the vital link between preparedness measures and response action. It gives information on a hazard, identified at a distant threatening of a particular area and allows the authority to take precautionary measures effectively.

Identifying the problem

In Bangladesh, mostly, the people living in towns (small city) and villages are vulnerable to flooding. As the basic infrastructure of Bangladesh is very fragile and the flooding is frequently widespread, the affected people themselves have to take action to mitigate the damaging effects of flood for their survival.

In determination of Decision Support System for flood risk assessment, it is of utmost significance to apply the most efficient technique in flood forecasting and warning system linked with real-time data collection system.

Preparedness and mitigation

Complete flood control in the geological context of Bangladesh is not a feasible solution. It is important to think at in a way that it is better not to go for the complete control of flood instead accepting its reality and formulate a master plan so that it is possible to save life and property from its devastation. Simultaneously, day-to-day life and economic activities can easily be maintained and utilizing the floodwater can benefit the nation. In a nutshell, it will be such a master plan, which will limit the devastating effect and at the same time, will bring prosperity to the country.

The existing systems of collecting information on floods extent and their effects are not very reliable. The system depends heavily on field information, which sometimes is erroneous and at times cannot even be collected until the recession of the floodwaters (EGIS, Dhaka, June 1998). Information from GIS can be used to extract some types of information, which are otherwise difficult to access by traditional methods, particularly for flood-forecasting and floodwater movement. This present study employs Geographic Information Systems to develop a new model for warning of floods rather than flood mapping for flood risk assessment for regular monitoring of damages integrating hydrodynamic model MIKE 11 and GIS.

Use of GIS will provide supplementary data in Hydrology for such analysis and will lead to easier interpretation and understanding of flood phenomena and characteristics. The use of Digital Elevation Model (DEM) can be effectively used for simulation to get a complete model of the study area.

Discussion

The objective of flood mapping is to describe the spatial linear variations (rise and fall) of the water level data and to classify regions within the model area depending on the depth and extent of flooding. The accuracy of flood maps depends on the correctness of the water surface generated and more importantly, the available DEM.

Flood Forecasting and Warning is a continuing activity, but the operational emphasis is on effective dissemination of warnings at grass-root level. Warning needs to be disseminating in time and in simple, understandable manner to clearly indicate for action to be taken. Their aim is to expand a user-friendly decision support evacuation system in an appropriate state to make possible use of arrangement of resources at any warning period up to the union level. In every union, there is a flood and disaster management committee, which is the lowest institutional tier of national flood management. Among the different levels of local government, Union Parishad (Council) is the most stable and functional in terms of continuity. Government and also development partners are gradually recognizing the importance of strengthening union parishads and contributing towards local level planning, community participation and good governance.

However, this study will be useful in the future for the decision makers to arrive at decisions quickly and promptly related to issues of flood preparedness, mitigation, relief and rehabilitation, if data required for the model are available.

Future perspectives

This dynamic model can be automated fully to be accomplished with the existing flood warning system to provide warning for the people without the knowledge of GIS to identify the possible inundated areas to take initiative to evacuate people to the safe places in time. It can help to promote public awareness in disaster management activities as a part of focusing the dissemination of forecast at the grass-root level.