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Water as Leverage in Khulna

Khulna: From Sponge to Brick

Water as Leverage
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Khulna is located in coastal Bangladesh, at the intersection of the Rupsha and Bhairab Rivers on the alluvial soils of the Ganges Brahmaputra delta.

The landscape is crossed by dozens of tidally-influenced rivers, canals, and creeks. The main source of fresh water is the Gorai River, a branch of the mighty Ganges. Khulna City is located approximately 40km from the largest mangrove forest in the world: Sundarbans. The mangrove forest, together with the Mosque City Bagherat, are listed as UNESCO heritage sites and are mainly accessible by boat from the Mongla port. Early settlements in Khulna often excavated the extremely permeable ground to reach superficial aquifers and provide direct sources of freshwater. This common practice combined with heavy seasonal rains generated a series of water ponds that are now a unique part of Khulna’s urban fabric.

Today, Khulna is the third-largest city in Bangladesh and the third-largest economic center in the country. Beginning in the 1960's, large-scale industrialization spurred population growth and urbanization along the river's north-south axis, by which contact with the water was maximized to empower new economic activities. Today, the city is facing serious water resilience issues including saltwater intrusion, "dying" rivers, and coastal flooding from lack of adequate drainage and sea level rise. Interventions at multiple scales are needed to bring improve water resilience in Khulna.

Rivers Running Dry

Water as Leverage
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Almost 50% of the canals and rivers that historically composed Khulna’s drainage system have disappeared in the last 30 years.

While natural sedimentation processes are partly to blame, the major causes of these "dying" waterways are human related: many canals and ponds have been choked with solid waste or filled to create more habitable space. Originally, these ponds were constructed as systems for water retention and were used as drinking water supplies, wash basins, and space for aquaculture. Rising land values have largely contributed to the filling of ponds for development - hundreds of ponds in Khulna have been filled with sand and waste material so that people can settle on the new land.

The disappearance of these water bodies from the landscape makes water drainage more difficult, exacerbating floods and waterlogging in the city. Ponds also play an important part in the social structure of Khulna as central public spaces where people can meet. Without their presence, open and green spaces in central Khulna are becoming more and more scarce.

Drinking Water Salinization

Water as Leverage
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The relatively small Gorai River, a tributary of the Ganges, is the only significant source of freshwater in Khulna, and it's getting saltier.

Salinization poses a serious threat to the city's water supply. Salt water from the coast intrudes up to 160 kilometres inland. The degree of intrusion is worsened by dams and water consumption upstream which reduces the flow of the Ganges in the dry season (February - May). Although the city is located in a water-rich river delta, only 64% of Khulna’s population has access to potable water, with many relying on public tube pumps. Recenty, salinity levels in the upper aquifer and the Bhairab-Rupsha river have forced the Khulna Water Supply and Sewerage Authority (KWASA) to turn to a remote surface water source to meet the city’s increasing demand.

The lack of fresh water also threatens food production. Areas that are flooded by salt water (from the sea or from broken embankments of shrimp farms) lose their agricultural value, especially if means are lacking to drain the area and irrigate with fresh water. Large areas of southwestern Bangladesh have become uninhabitable due to salinization of the soil, forcing many to leave their homes.

Centralized water supply solutions are under construction in Khulna. The local water supply authority KWASA is constructing a water production plant that relies on fresh river water from upstream. A series of overhead tanks and distribution reservoirs will store and distribute the fresh water throughout Khulna. In addition, a large storage basin will contain enough fresh water for two weeks in case the river water is too salty in dry times. In rural areas, the focus is on making better use of rainwater, especially for irrigation, and on small reversed-osmosis plants ("drinking water ATM’s"), where people can buy five liters of fresh water with a prepaid card.

Sea level rise will worsen salt water intrusion in the coastal zone, and, if the base flow in the Gorai does not increase, the saline zone will extend further north over time.

Flooding

Water as Leverage
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Khulna is extremely vulnerable to coastal flooding from cyclones and inundation from heavy monsoon rains.

Tidal flooding in Khulna occurs on an almost monthly basis during the wet season. The combined effects of storms and high tide result in storm surges that inundate large parts of the city. Thousands of people are affected: mobility is impaired and stagnant floodwaters contribute to the spread of waterbourne diseases such as diarrhea, ringworm and dysentery. Cyclones are projected to become more severe (though perhaps less frequent) due to climate change, while rainfall is expected to become more erratic and severe. Floods in rural areas increase the pressure on informal settlements in Khulna: 40% of the inhabitants of slums are climate refugees.

The people in Khulna have learned how to live with floods and are taking measures to reduce flood risk. Along the main rivers of the city, embankments have been fortified and raised to reduce tidal flooding from cyclones. Maintenance projects have been set up to remove elements that block water flow in the low-lying canals and rivers. The removal of solid waste, sediment, encroachments, landfill, and buildings helps to restore the drainage capacity of these waterways. Unfortunately, some drainage measures and embankment fortifications increase land subsidence, which, in conjuncton with erosion of the river banks and sea level rise, is actually exacerbating flood risk in Khulna.

Urban Expansion

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The availability of fresh water for Khulna is largely dependent on upstream developments like the Gorai river offtake project.

Throughout its history, most of the urban area of Khulna has beem located on relatively high grounds, where approximately 10-15% of the excessive water from rainfall can be stored in ponds and khals. Most water is drained to the Moyur river, but congestion, encroachment of khals are causing local flooding.

In the near future, population growth will force the city of Khulna to expand to the low-lying areas west of the Moyur river. There are opportunities to transform this mainly agricultural area in a resilient way by enforcing new regulations for construction projects. For example, developers of multi-level buildings should reserve 25-40% of their properties for water storage to prevent flooding in the new urban area. Additionally, new developments should integrate storage facilities for fresh water into the buildings and designate permeable groundwater recharge zones to restore the supplies in the aquifers during the rainy season.

Wastewater and Drainage

Water as Leverage
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Technical studies, projects by municipal and national agencies, and feedback from affected communities all confirm that Khulna's wastewater and drainage systems are dysfunctional.

There are several main issues: flaws in design and construction; lack of maintenance; unregulated dumping of sewage and solid waste in drains, streams and the Mayur River; encroachments upon surface water bodies; filling of hundreds of small ponds; and increased hard surface area in the city.

Currently, Khulna does not have a sewer system, so sewage is discharged directly into waterways. This practice poses health risks and makes water unfit for use. Meanwhile, only 25% of solid waste is collected by the city - the remainder is dumped into the rivers and canals where it becomes pollution and blocks critical drainage infrastructure. As a result, flooding and prolonged waterlogging inflict physical and economic damage to households and businesses, especially in congested slums.

Created in partnership with: FABRICations, 100 Resilient Cities and Architecture Workroom Brussels