Urban flooding calls for urgent measures

Kathmandu, Aug. 16: Every year, in the heart of cities, a familiar and unwelcome visitor returns - urban flooding. The blame rests on a foursome of factors including concretisation, rapid urbanisation, waste mishandling, and the looming presence of climate change. These tangled elements flood our streets annually, demanding our attention and action. The chaos unfolds for a few weeks or a month during the monsoons, only to retreat and then reappear with the next rainy season. This pattern repeats, leaving a quieter period of eight to 10 months in between.

Who is at fault? Both unplanned urban development and human choices share the blame. Consider the Kathmandu Valley – once natural wetlands and rivers, now paved with roads and settlements. Nature adapts, but human actions push limits, experts say.

Mandira Shrestha, Senior Water Resources Specialist at International Centre for Integrated Mountain Development (ICIMOD), said that over the last 20 years, the Kathmandu Valley has been built up rapidly and most of these settlements are very haphazard with little planning. 

Between 2000 and 2018, the built-up area of Kathmandu Valley more than doubled. In Bhaktapur, the urban areas quadrupled during that period. The transformation in land use over the past several decades has heightened the vulnerability of urban centres like Kathmandu and Bhaktapur to regular flooding, Shrestha said. The amount of impervious area has rapidly increased by many folds. There are now many settlements along the river corridor which have further increased the vulnerability.

In Kathmandu, chaotic urbanisation and expanding impervious surfaces spell disaster. Urban settlements have replaced the green fields, Shrestha said. “When the rain falls, the impervious surface does not allow water to percolate into the ground. So, all the water is directly going out as direct run-off which quickly enters the rivers and is obviously going to increase the water volume in the rivers,” she informed. 

According to Shrestha, the rivers have been encroached to the extent that no floodplains exist. During a high rainfall event, it is inevitable that the rivers overflow their banks into the settlements as there is nowhere else for the waters to retreat except into the urban settlements.

Shrestha also mentioned that improper disposal of wastes – such as plastics – block the drains, resulting in greater surface runoff in the urban areas. The poor maintenance of these 

pipes without proper treatment and segregation of waste has led to water accumulation in the urban centres. Inadequate small drainage pipes with no maintenance struggle with floodwaters from impermeable areas. Plastics, 

cartons, clothes, glass, and untreated human waste mix into rivers, clogging these pipes and escalating the risk of urban floods, she mentioned.

Low-lying zones, such as Sankhamul, Kapan and vegetable markets, remain continually vulnerable to flooding within Kathmandu, she added. Just think of the amount of rainfall like that was in 2002 in the Bagmati River, what will happen in present Kathmandu?

Shrestha said, “Climate change is a reality. There is increasing variability of rainfall with the occurrence of the large volume of rain in a short span of time.”

Mani Nepal, Programme Coordinator and Lead Economist at South Asian Network for Development and Environmental Economics (SANDEE), said that low-income countries are grappling with growing issues of waterlogging and water contamination due to mismanaged solid waste. 

Several factors play into this problem, such as the rapid urban population increase that pushes cities into flood-prone areas, the intensifying impact of climate change that leads to heavier rainfall, overwhelming drainage systems, and the improper dumping of solid waste, which can clog drains and result in waterlogging, according to Nepal.

A study by the SANDEE and the Asian Centre for Development (ACD) between 2017 and 2020 in Bharatpur (Nepal) and Sylhet (Bangladesh) revealed that rapid urban population growth leads to cities spreading into flood-prone lowlands. Additionally, climate change intensifies rainfall, overwhelming drainage systems, and careless solid waste disposal clogs drains, causing waterlogging.

How to minimise the risk

As Shrestha mentioned, the adverse impact can be minimised. “We require implementation of land use policy, risk mapping and impact-based forecasts that not only predict the weather but also inform how it will affect our communities, environment, and economy. Understanding the impacts can trigger quicker and more effective preparatory measures,” she informed. 

Timely impact-based early warning may be provided to the people living in populated and at-risk areas for which coordination at various levels needs to be strengthened. While the science behind forecasts is getting better, the government still needs to invest in increasing the accuracy and ensuring the forecasts reach everyone so that no one is left behind, she added.