Urban Flood Framework for Dhaka

Posted: 2011-11-22

The Center for Environmental and Geographic Information Services (CEGIS), supported by GWP Bangladesh, has conducted a study on managing flood risks for Dhaka in the face of climate change. The study resulted in a concept note on Climate Resilient Urban Flood Risk Management Framework for Dhaka.

Dhaka experiences about 2,000 mm of rainfall annually, of which almost 80% falls during the monsoon. The main natural hazards affecting Dhaka include floods, which are associated with river water overflow and rain water stagnation.

Dhaka is the capital of Bangladesh with a population of around 20 million. The city is surrounded by a network of rivers: the Buriganga on the south-west, the Turag on the north-west and the Balu on the north-east and the Shitalakhya on the south. The city is more vulnerable to flooding due to heavy and unpredictable rainfall but also because its drainage capacity is decreasing due to unauthorized settlements and illegal occupation of wetlands by land grabbers.

The problems, consequences and cause effects relations are given in the matrix below:

Problems in the Dhaka drainage system Causes of Urban Flooding Effects of Urban flooding

- unplanned urbanization and expansion of the urban areas within the urban fringe,

- increase of in built-up areas and metal roads and accelerate land run-off,

- filling up of low-lying areas of surrounding the Dhaka city to construct buildings, with no or little provision of drainage,
- the main drainage systems of the urban area (khals) are blocked by unauthorized constructions,
- insufficient  capacity of storm sewers constructed in the extensions of the urban area and lack of maintenance of the storm drainage system,
- lack of co-ordination among different organisations engaged in development and management of Dhaka,
- solid waste and poly bags disposal in the storm sewer.

- Excessive Rainfall due to climate change
- Population growth and unplanned development
- Lack of Waste management system
- Encroachment of surrounding wetlands by different developers for new residential area.
- The average elevation of the ground levelof Dhaka city is 0.5-12 meter with 70% of the total area within 0.5 to 5m. Due to this low topography, a large portion of concerned area is inundated during monsoon.
- Capacity and gradient of existing natural drainage systems have been reduced due to siltation.
- Unplanned rehabilitation and maintenance of development works during rainy season.
- Lack of public awareness
- Poor application and practices of existing policy and regulations.

- Trouble in traffic movement
- Disruption of normal life
- Damage of roads
- Damage of katcha houses in the low lying areas and substructure of the pucca houses
- Damage of household goods
- Damage of underground service lines
- Water pollution
- Water borne diseases
Increase of mosquito
- Damage of trees and vegetation
- Increase of construction and maintenance cost
- Disruption of societal facilities such as reduction in attendance of students in primary level.

In the study a flood risk management framework has been developed which include pre-flood prevention, risk mitigation and flood preparedness. Adaptations to climate change and to economic development are important drivers in designing flood management schemes. Flood risk management is strongly related to spatial planning: the location of new developments, flood proof structures and space for rivers. Risk communication is considered as a valuable way to promote flood awareness and to improve flood preparedness of the citizens.

The study synthesized the relevant information from different available plans, programs, reports and scientific literature. To explore the existing situation of flood protection and storm water drainage management system, a field survey was conducted by a team consisting of multidisciplinary professionals.

(Photo: Prince Roy)

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