In Nepal’s weather, erratic is the new normal

The 2019 monsoon was an erratic one. Sadly, erratic seems to be the new normal.

There were storms in April, causing floods, and it seemed as if a large monsoon was on the way. This was followed by a couple of very dry months and delayed onset of the actual monsoon. From July it was as if the monsoon was playing catch up.

Heavy rainfall creates havoc in the Kathmandu Valley, as streets turn into flowing sewage. Across the country, landslides and floods claim more lives and livelihoods. Now, dengue outbreaks lengthen the list of monsoon dangers. The unjust and devastating impacts of flooding across the country have brought to the surface the failures of current development practices.

One area that is often overlooked is the management of stormwater infrastructure. Poor maintenance, encroachment along riverbanks, improper waste disposal that clogs sewage outlets and rivers, and rampant enclosure of open land leave people vulnerable to threats that go beyond flooding. With its current wastewater infrastructure, even if the existing systems were fully functioning Kathmandu could handle less than 100 million litres per day of wastewater.

Treatment plants are inadequate. While development-as-usual tends to focus on building bigger and better pipes, drainage is often overlooked, especially of stormwater after major rainfall events. Conventional practice transports stormwater to wastewater treatment systems. Yet, these systems are often overburdened and difficult to maintain, which causes sewage system overflows.

Stormwater that overflows drains and runs down roads, streams and rivers carries with it more and more pollutants the farther it travels. Poorly managed stormwater is thus a major source of water pollution worldwide. Climate change projections are of more erratic and increased intensity storm events placing additional pressures on drainage infrastructure. Many cities are looking to overhaul this practice.

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They have found that the costs of transforming drainage systems and building green infrastructure has significant benefits. Green infrastructure is a set of practices that utilise and revitalise ecosystems within and between watersheds, urban areas, neighbourhoods and households. Permeable pavement, rain gardens, bioswales, and household-level rainwater harvesting are common examples of green infrastructure solutions for stormwater.

As cities elsewhere have found, green infrastructure saves. Financially, green infrastructure reduces the capital investment and operational costs of urban infrastructure. For cities like Philadelphia in the US, the cost of implementation has been four times lower than conventional stormwater drainage and wastewater treatment system upgrades. New York will see significant savings over the lifespan of its project, both in capital and operational costs.

A review of over 400 green infrastructure initiatives by the American Society of Landscape Architects showed that three-quarters of these investments were as cost-effective, or more so, than alternatives. Moreover, these examples were primarily on-site initiatives and not at the city-scale, which can be more cost-effective.

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In Kathmandu, 150 billion litres of rain fall on rooftops and paved surfaces in one year. Spread over 365 days this would be 420 million litres daily, but during the monsoon rainfall is much more concentrated. A 50mm storm produces 5.5 billion litres of stormwater, more than 50 times what wastewater treatment systems could handle if they were completely functional. The same storm would produce 5,000l of water on a normal household rooftop, 15 times their daily wastewater production.

If much of this water was retained and recharged on-site the cost reductions, additional groundwater supply available, and the reduced pollution of the Bagmati and its tributaries would be enormous. 

Green infrastructure already exists in this growing city. Ancient water infrastructure and management systems continue to function in the Valley. Historians, archaeologists, engineers and architects have found that each area of the Valley has a water system that is not only suited to the local environment but that also integrates ecology with Newa social and cultural practices. These social and ecological interconnections between ponds, aquifers, porous brick surfaces, green space, channels and stone spouts still help to move, store and treat stormwater.

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Sustainable development means moving away from cement solutions to promote and integrate green infrastructure in ways that suit Kathmandu’s social and ecological landscape. This could include protecting the city’s few remaining green spaces or providing meaningful support of local efforts to revitalise ancient water systems. It could also include reimagining rainwater harvesting as more than an alternative water source for households, but a city-wide infrastructure for sustainable stormwater management.

It is time for the city and its residents to rethink stormwater management. It is time to look beyond dated development practices of more pipelines and channelised rivers towards those that are not only cost-effective and enhance local social and ecological systems, including restoring the Kathmandu Valley’s traditional water infrastructure.  

Olivia Molden, PhD, has studied Kathmandu’s water infrastructure since 2013. Tyler McMahon is Co-Founder of SmartPaani Pvt Ltd and President of One Planet Solution LLC.