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Developing Flood Vulnerability Index for the Imrpovement of Knowledgebase for Flood Preparedness

Anjuma Tabassum Khan*
Institute of Water Modelling, Dhaka-1206, Bangladesh

A. K. M. Zeaul Hoque
DHI Australia,Sydney,

Abu Saleh Khan
Institute of Water Modelling, Dhaka-1206, Bangladesh,

Abstract/ Executive Summary:

Bangladesh’s unique geography and topography contribute to frequent flooding, with serious consequences in terms of losses in lives and property. Flood and disaster risk management are recognized as critical components for development and poverty reduction. Knowledge and information that improves understanding about where floods are most likely to occur, and which populations are most likely to be affected, is critical for risk reduction and preparedness efforts. Two recent floods of 1998 and 2004 have been taken into consideration to select the most flood-prone areas. The regions, which are inundated by more than one meter from a normal flooding condition during an extreme flooding condition, have been taken as flood-prone areas. Comparing the flood maps of normal and extreme scenarios during 1998 and 2004, four regions of Bangladesh have been initially identified as most flood-prone areas. Mapping of flood depth, depth duration and duration of flooding have been performed for the four Vulnerable Areas. The results extracted from various flood maps for the Vulnerable Areas have provided the necessary data for further analyses and detail investigation to identify the vulnerable localities.Criteria for flood vulnerability have been established both in terms of flood depth and flood duration. Methodologies have been developed to calculate vulnerability index based on both duration and depth of flooding. This index is then used to rank the unions of the four vulnerable areas to represent the vulnerability to flooding.

Keywords: Vulnerability, Flood, Food map, Union level and Bangladesh

Location:

Start Date:

End Date:

Program Area: Risk Management in Agriculture

Non-commodity: Impact, Flood,

Objectives:

This effort has been undertaken to generate critical information that better informs risk reduction and preparedness efforts for reduced vulnerability in future.

Methodology:

The objective was to identify the most flood-prone areas within a district. For identifying flood-prone areas, a number of flood maps were required during different flooding conditions. This investigation includes simulation of one dimensional river model for selected flood events, flood map preparation, selection of vulnerable areas, more focused mapping for selected areas and calculations based on the maps. Hydrodynamic Simulation In the current investigation, a hydrodynamic river model was required to estimate water levels on the major rivers of Bangladesh at any time instant. One dimensional hydrodynamic models are already developed in MIKE 11 both at regional scale and national scale and these models are being regularly updated and validated. The hydrodynamic model of Flood Forecasting and Warning Centre (FFWC) was used for the current study. FFWC uses this model for real-time flood forecasting during the monsoon in Bangladesh. FFWC model covers all major river system of Bangladesh except the eastern hilly part of Chittagong area and some parts of southeast and southwest regions. Selection of Flood Event Two most recent extreme flood events of 1998 and 2004 were considered to identify the vulnerable areas to flooding within Bangladesh. Flood maps for both extreme and normal flood conditions have been developed for the flood event of 1998 and 2004. A normal flood condition was considered as the instant when the water level in neighbouring FFWC station(s) remain 1 (one) meter below the “Danger Level” as used by FFWC. The extreme condition was considered as the time instant when most of the major rivers have attained the peak of that flood season. However, it is unrealistic that a normal or the extreme flooding condition would occur on the same date for all locations. For this reason, normal flooding date was selected based on the observed water level of some important routine flood forecasting stations. Then a representative date was considered for the whole country’s normal flooding situation. Similarly for the extreme flooding situation a representative was selected when water level at important flood forecasting stations reached to its peak value. Identification of Flood Prone Areas Flood depth maps were generated using MIKE11 GIS tool on dates of normal and extreme flooding situation. The regions of Bangladesh, which are most vulnerable to flooding, were identified by comparing these flood depth maps. During flood mapping, flood protection embankments or road cum embankments were considered to be serving as full flood barrier. Flooding due to any accidental breach or overtopping of these embankments was not reflected in the flood maps prepared under the current study. These flood maps were produced using land level information from the national Digital Elevation Model (DEM), which has some flaws in and around the city areas where remarkable changes due to city development has undergone. It is very likely that the areas which get inundated during a normal flooding scenario are expected to be inundated every year. Therefore, the regions, which are inundated by more than 1 (one) meter from a normal flooding condition during extreme flood events of 1998 and 2004 were taken as flood prone areas. Chalan beel in the northwest region and the haor areas in the northeast region of Bangladesh were been taken into consideration as vulnerable areas since these low-lying areas are deemed as water bodies during the monsoon season. Four areas have been identified as vulnerable areas (VA1, VA2, VA3 & VA4).

Source of Information: 2nd International Conference on Water & Flood Management (ICWFM-2009), BUET, Dhaka, Bangladesh

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

The 10 most vulnerable unions ranked by Vulnerability Index based on duration of flooding are: Suagram (Kotalipara, Gopalganj), Singa (Kashiani, Gopalganj), Nizra (Gopalagnj Sadar, Gopalganj), Kandi (Kotalipara, Gopalganj), Ujani (Muksudpur, Gopalganj), Balla (Kaliganj, Tangail), Sadullapur (Kotalipara, Gopalganj), Kasalia (Muksudpur, Gopalganj), Radhaganj (Kotalipara, Gopalganj), Puisur (Kashiani, Gopalganj).

The 10 most vulnerable unions ranked by Vulnerability Index based on depth of flooding are: Kaundia (Savar, Dhaka), Shyamsiddhi (Sreenagar, Munshianj), Paurashava (Amin Bz W-07p) (Savar, Dhaka), Churain (Nawabganj, Dhaka), Agla (Nawabganj, Dhaka), Baraikhali (Sreenagar, Munshianj), Galimpur (Nawabganj, Dhaka), Paschim panchgachhia (Daudkandi, Comilla), Kanchanpur (Basail, Tangail), Sholaghar (Sreenagar, Munshianj).

Finally, the combined Vulnerability Index of individual union calculated by taking the average value of two Vulnerability Indices (for duration and depth of flooding). Thus equal weights have been assigned on both the Vulnerability Indices during the calculation of combined vulnerability. The 10 most vulnerable unions ranked by combined Vulnerability Index are as follows: Kaundia (Savar, Dhaka), Shyamsiddhi (Sreenagar, Munshianj), Paurashava (Amin Bz W-07p) (Savar, Dhaka), Paschim panchgachhia (Daudkandi, Comilla), Agla (Nawabganj, Dhaka), Goalmari (Daudkandi, Comilla), Isibpur (Rajoir, Madaripur), Chitrakot (Sirajdikhan, Munshiganj), Balla (Kalihati, Tangail) and Kanchanpur (Basail, Tangail).

Knowledge Management: Report/Proceedings