Blog: How to reduce flood risk in urban areas of Bangladesh?

By Rafia Anjum Rimi and Addri Attoza

Introduction

If you live in a town, what do you see around you? Among your neighbours, how many of them are now living in cities and their previous generation lived in the same cities? You will see a good number of them have migrated from their ancestors' route for many reasons but the main goal is to have “a better life, better job”.

For the same reason, cities are now the home of 55 per cent of the world's population. By 2050, approximately 7 out of 10 people on the planet will live in cities, more than tripling from its current level. More than 80 per cent of global GDP, urbanization can contribute to long-term growth if properly managed through enhancing productivity. 

Today, Bangladesh is facing various problems in the urban area like urban poverty, socioeconomic inequality, substandard housing and roads, inadequate institutional capacity, polluted air and water, lack of open space or playground etc. These problems have made the life of urban people very difficult. In addition to that, there are natural hazards and calamities which have added extra suffering for the people. So, urban development should be done in a way that can help the people at their best capability.

Over the past decade, the cities of Bangladesh have turned into urban societies. The changes in arrival are related to urban advancement and influence flooding in numerous ways. Expelling vegetation and soil, evaluating the arrival surface, and building seepage systems increment runoff to streams from precipitation. As a result, the crest release, volume, and recurrence of surges increment in adjacent streams. Changes to stream channels amid urban advancement can restrain their capacity to communicate floodwaters. Roads and buildings built in flood-prone ranges are uncovered to the expanded surge risks, counting immersion and disintegration, as unused advancement proceeds. Data almost stream flow and how it is influenced by arriving utilize can offer assistance communities diminish their current and future powerlessness to surges. 

Climate change increasing flood risks

Bangladesh is a riverine country and consistently bears the results of its space in the low-lying deltaic floodplain of the Ganges-Brahmaputra-Meghna (GBM) stream bowl. Around 80 per cent of the spot that is known for Bangladesh falls under the flood plain and whatever amount 34 per cent of its region locale goes lowered for about five to seven months in reliably. 

Floods are devastating and have become the most economically damaging issue for this country. It breaks down the ordinary components of life, impacting homes, agrarian land, step-by-step workout, water supply and sanitation conditions, and economic development. Losses of human lives, assets are the most common damages in flooding issues. In this densely populated nation, land assets are scant and because of the pressing factor of the developing populace, individuals, particularly the provincial poor are compelled to get comfortable in the flood-prone zones. 

Impacts in urban areas

Though every year in monsoon, at least a few districts suffer from a flood, inundation but the flood of 1998 was the longest lasting and deadliest flood that Bangladesh has experienced in 100 years. In total, 53 of 64 districts of Bangladesh were affected by another scale flood. About 50 per cent of the country was underwater for a maximum of 67 days, and the submerged depth is estimated to be a maximum of 3 meters. Especially, districts including Comilla, Chottogram, Cox`s Bazar, Faridpur, Feni, Gaibandha, Habiganj, Jamalpur, Khagrachari, Kurigram, Lalmonirhat, Manikganj, Mymensingh, Natore, Nilphamari, Pabna, Rajbari, Rajshahi, Rangpur, Sirajang, and Tangail were severely affected.

The scarcity of water bodies in urban areas has made rain a curse for urban people. Less rainfall creates inundation in the urban areas. The reason behind this as urban areas are mostly covered with the cemented top layer, so water cannot go under the soil. Sewage and water drainage systems have less water retaining capacity than rainfall. 

Dhaka, the capital city of Bangladesh, always suffers from this waterlogging and flooding problem. Due to poor discharge capacity of existing drainage pipes and canals, clogging of existing drainage is a regular phenomenon because of disposal of wastes into roads, inefficient labour forces for cleaning streets and lack of maintenance, Impediment of canal waters due to encroachment of buildings, insufficiency of drainage pipe length, and encroachment of the natural drainage channels in Dhaka, the city get logged by few minutes of rain only, like in greater Mirpur area. The flood causes disruption of traffic movement and normal life, damage of roads and underground service lines, household goods, water pollution, waterborne diseases, damage of trees and vegetation, and also increase of construction and maintenance cost.

During heavy rainfall, waterlogging, flood, salinity, scarcity of potable water, siltation of river beds are common hazards in Khulna city. A significant part of this city is exposed to flooding during heavy rain. Production of rice and other crops in peri-urban areas are ruined at the same time. 

The Government of Bangladesh (GoB) has taken The Flood Damage Rehabilitation Project in 1999 which was formulated in response to the Government’s request to the Asian Development Bank (ADB) for rehabilitation assistance following floods of unprecedented nature, extent, and intensity, which inundated 68% of the land in Bangladesh for 11 weeks from 20 July to 30 September 1998. Under this project the Government worked in the transport sector which includes increasing the height of roads and railways, cross-drainage structure as well as in the infrastructure sector similar projects have been undertaken like increasing the height of coastal polders, erosion control programs, etc. The project was completed in December 2002. 

Way forward 

Rainwater harvesting

Harvesting rainwater includes collecting water from surfaces on which rain falls and saves it for later uses. For this purpose, water is gathered from the roofs of buildings and stored in a tank. We can encourage more rooftop rainwater harvesting systems for proper groundwater recharging through these techniques will reduce flood impacts.

If we use rooftop rainwater harvesting techniques in buildings, and if it rains excessively, the rainwater will accumulate in the rainwater tank without going directly to the ground level. In this way, the problems of waterlogging, flood, and clogging of drainage pipes can be reduced. The rainwater reserve tank can also be utilized to flatten the rainwater runoff.

Increase green roofs

Green roofs mean the roof that is covered with plants. The larger green roofs of an urban area can act as a larger catchment of rainwater and help to slow down the spread of heavy rain into the ground. Such more benefits of green roofs are - it is stormwater management equipment for the building owner; for the community, and for the environment. It prevents combined sewer overflow, neutralizes the effects of acid rain, and removes nitrogen pollution from rainwater.

Construction of permeable roads

In some flood-prone regions, green space is viewed as an extravagance. On the ground and housetops, there is a lot of cement. Concrete is not penetrable and it does not retain water, rather it blocks the water on the surface and sidetracks. As a result, waterlogging and floods occurred on the roads and walkways. As a component of ecological drives that are in progress in Europe and across the globe, the suggestion is that impermeable surfaces be supplanted with porous materials like grass and gardens. This will permit the water to deplete into the dirt. The interaction, known as invasion, likewise serves to support the vegetation.

Improved drainage system 

The improved drainage system can support reducing the flood impact in flood-prone urban areas. Segregating sewer, rainwater discharge drains can avoid clogging of water and sewerage discharge channels. Proper discharging of rainwater also improves rainwater infiltration into the ground. Thus, the groundwater can be recharged as we know that the water table is decreasing day by day. Also, advanced technologies for detecting damaged pipelines, regular maintenance of water and sewage lines can help to fix the problem before it gets bigger and more difficult for the urban people.