This project applies the urban design principles of “Sponge City” in the context of Khulna, Bangladesh. It advocates for an absorbent urban environment to cope with excess rainfall and water-related disaster. It uses nature-based infrastructure to bring environmental and socio-economic benefits. The sponge city programme is currently in place as a key planning approach for urban developments across China.

Khulna, a low-lying city in the Ganges-Brahmaputra delta,  is located on the south-western coast of the Bay of Bengal. Water, being the source of life and hazards, has a large impact on this region. Over the last several decades, the region is experiencing notable changes in local human and natural habitats. Experts often explain this as an effect of climate change.  Rising sea level coupled with an increasing amount of rainfall is causing frequent waterlogging and flooding in urban and rural areas of Khulna. Moreover, the soft surface to absorb the rainwater is disappearing fast due to continuing urbanization and river encroachment. The objective of this project is to explore sustainable design strategies for managing urban stormwater that would potentially perform as a catalyst for regenerating the landscape of the city.

An online survey among different groups of people from Khulna city, which was conducted as a part of the study, has identified different aspects of waterlogging, flooding, and climate change. Human interventions are commonly identified as causes of waterlogging and flooding. Moreover, climate change is playing a driving role in water management and natural drainage systems. The Mayur  River that passes through the urban and peri-urban areas of the city, is heavily suffering from illegal encroachment, lack of waste management, and planning policy. Whereas in the past, the Mayur  River used to be the main stormwater flow path in this area. Further, due to rapid urbanization, public and private open spaces such as courtyards, gardens, and ponds are disappearing at an alarming rate, thus making the urban area vulnerable to stormwater flooding.

Under these circumstances, a water-sensitive landscape design solution- Sponge City- holds promises to alleviate the situation. In a conventional city, development disrupts the natural water balance, by rapidly discharging the stormwater to the waterways. Sealed concrete surfaces of the city also create heat islands. The concept of ‘sponge cityscape’ enables the application of certain different strategies in a unified way. According to this concept, a large part of rainwater would be retained in the city and slowly discharged into the waterways. Many small retention storage spaces would be created at the street and building levels which would collectively reduce the urban runoff. At the same time, it would help to improve the urban microclimate through evaporative cooling.

The proposed strategies include the retention of stormwater both underground and above the ground to restrict the runoff water. Other strategies include rainwater harvesting, implementing bioswale area in the streetscape, securing the remaining ponds and lakes in the city.

Uncovering and unsealing are the ways to revive the old natural canals or water sources which was channelized or covered by the pipe system. The use of water-permeable materials in public plazas, outdoor markets, and parking spaces would absorb the excess water and recharge the aquifer.

Moreover, the proposal also applies the idea of multifunctionality which plays a vital role in riverside landscape regeneration. A water park around the Moyur  River area is proposed following this idea.  Strategies include reclamation of the river edge from illegal encroachment with the help of the local community. In the dry season, the proposed multifunctional open space along the riverbank will perform as a  recreational space while in the rainy season it will become an active part of the river. In this way, the water park would enhance the interaction between the community and the natural ecosystem.

© Nafiz Rahat

International Masters of Landscape Architecture

Nürtingen-Geislingen University of Economics and Environment (HfWU), Germany

Hochschule für Wirtschaft und Umwelt Nürtingen-Geislingen (HfWU), Germany