Climate change could overwhelm our sewers – here’s how green infrastructure could help

In addition to warmer summers and melting glaciers, climate change is transforming how, when and where rain falls. This poses a challenge to much of the world’s sewage systems, particularly with the added pressures of population growth and increased urbanization.

The sewerage systems of the Victorian era were simply not designed for the climate we are heading towards. This has major implications for public health, water quality and urban life.

The growing population means that sewers are sometimes clogged without any rain. Then add climate change to the mix. Heavier downpours are becoming more frequent, causing problems for sewage systems that simply cannot cope with increasing volumes of water. One type of system, called a combined sewer system – the predominant type in the UK and Europe – is particularly vulnerable.

These systems carry wastewater from homes and stormwater from streets in the same pipes. When it rains heavily, pipes can become submerged, resulting in permitted discharges of untreated wastewater from combined sewer overflows (CSOs). These untreated overflows flow into the ocean, rivers and streams, polluting the environment, threatening wildlife and harming public health.

And this problem will only get worse. The results of my doctoral research show that climate change could triple wastewater discharges into waterways by 2099.

But there is a silver lining: “green infrastructure,” which mimics nature by retaining or slowing the flow of rainwater into the environment, allowing it to evaporate or absorb . Examples include green roofs, permeable pavements and rain gardens which already exist in many UK cities, including London and Sheffield.

Instead of relying solely on traditional pipes and tanks to carry away rainwater, green infrastructure solutions manage rain where it falls. Green roofs retain rainwater and help increase evaporation. Permeable sidewalks allow water to seep into the ground instead of flowing into sewers.

Bio-retention cells or “sumps” are landscaped areas like rain gardens that collect and filter stormwater before slowly releasing it into the ground or drainage systems. Wetlands and rainwater tanks also reduce the total amount of water entering the sewers or delay the entry of water into them.

My team’s research explores the effectiveness of these solutions and highlights how best to plan for green infrastructure improvements and cope with increased precipitation.

Our study simulated the operation of sewer networks with and without green infrastructure under future precipitation regimes, using climate models. We found that green infrastructure improves resilience to climate change but has limitations: while reducing the severity of combined sewer overflows, it cannot fully offset the effects of climate change, even with maximum deployment. However, different combinations of green infrastructure show promise.

Our study highlights that these solutions must be carefully designed to fit context and context. Poorly placed, they can increase the duration of rainwater drainage following a storm, because they release retained water into the network while the sewers are still overflowed, and can thus extend the sewer drainage period.

The effectiveness of green infrastructure varies across different parts of the sewer system. Solutions must be tailored to specific locations and conditions.

Measurements are also essential, because what is measured is managed. The scale of the problem can only be accurately understood by measuring both the sewer overflow flow and what is happening in our sewer systems. Otherwise, we are trying to solve a problem for which we have no parameters.

Good computer models play a crucial role in helping researchers and planners understand how our system works. Models provide a cost-effective way to test different interventions, but they must be representative of reality. An inaccurate model can cause large differences in the effectiveness of these solutions, affecting decisions about how to manage stormwater.

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Read more: Water companies must now publish live data on sewage spills – here’s why more transparency is key to cleaner rivers

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Future precipitation patterns are also crucial. Sewer performance is highly dependent on precipitation characteristics, which are influenced by climate change. More intense and longer storms could overwhelm even the best-designed green roofs or permeable sidewalks.

How to build resilient sewers

To address the growing challenges facing the UK’s sewage system, towns and cities need to invest in green infrastructure to reduce run-off and improve water quality. It also has other benefits, such as keeping urban areas cool and providing green spaces for communities.

Traditional infrastructure must be upgraded to upgrade existing pipes and treatment facilities to handle higher volumes of water. This not only means bigger pipes, but also smarter systems.

Local plans should depend on the specific needs of each neighborhood. Solutions can be adapted accordingly, while considering the watershed as a whole.

More accurate computer models need to be developed and adopted by infrastructure managers, researchers and consulting firms. With reliable and robust models, we can prepare better and prioritize resources more effectively.

Future climate scenarios are uncertain, so plans must be flexible and aim for a safe approach. Urban planners, policymakers and communities must work together to implement well-designed solutions.

The challenges posed by climate change are vast, but not insurmountable. By embracing innovation and careful planning, cities and their sewers can adapt to the new realities of our changing world.

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