Combined Sewer Overflow (CSO) spills in the UK: how software can help solve this hardware problem

Combined Sewer Overflows (CSOs) discharge raw, untreated sewage directly into rivers and seas during heavy rainfall events. This untreated sewage has environmental impacts and poses a risk to public health, depleting oxygen in the water, causing fish kills, and (if it gets bad enough) spreading disease. It’s become a hot-button issue in the UK.

Download the report

How are hydraulic models used to predict CSO incidents? Do utilities need specific in-house expertise to make use of sewer modelling technology? To help answer these big questions (and 9 more!) we’ve partnered with Utility Week to develop a downloadable report about CSOs in the UK, which also includes two mini case studies that show how Thames Water and Anglian Water are tackling the issue. You can download it from their site.

This issue won’t go away without action, and regulators in the UK have been increasingly promoting and mandating regulations to help solve this pernicious problem. We know it’s important to both water professionals who are tasked with helping solve these problems and everyday people who rely on clean water to function and thrive.

It’s not the CSOs – it’s the infrastructure

The good news about CSOs is that sewerage systems are usually designed to remove both wastewater from buildings and surface water from rainfall by including CSO outlets in their networks. This allows for discharges when the system is overloaded. If the CSOs weren’t there, sewage would simply back up into homes.

But the UK infrastructure has a very long history. Many 19th-century sewerage systems were designed to combine both foul and drainage systems into a one-piped network that leads to a wastewater treatment works. Truth be told, even Victorian-era combined systems can still work, but not if they are continually overloaded. With the infrastructure increasingly showing its age and rainfall levels seemingly already increasing due to climate change, UK water professionals will need to act quickly to ensure they design their sewerage networks with these facts in mind — or adapt existing infrastructure to help prevent CSO spills.

SuDS to the rescue?

The first step to solve this problem is to reduce the volume of rainfall in a combined system by holding onto storm water before discharging to rivers. You could install new, larger storage structures to store water and reduce the peak of the flow, or install pipework to separate stormwater from wastewater flows but, of course, it’s not always practical to dig up roads and install hard-engineered solutions to separate the stormwater drainage from the wastewater network. In fact, it’s quite expensive and time-consuming. With most of the infrastructure in England and Wales being built to last 60-80 years, at the current rate of replacement, it might take 800 years to accomplish full rehabilitation.

Instead, Sustainable Drainage Solutions (SuDS) are increasingly being adopted to mitigate the impact of increased surface water. SuDS is based on the concept that rainwater should go back into the ground closest to the point where it falls to alleviate flooding, replenishing groundwater supplies and improving water quality. Not only does it reduce the chance of a CSO spill, but it reduces road runoff which carries polluting heavy metals and petroleum residues. That’s another benefit to SuDS. Well-designed SuDS can actually help filter many types of residue and pollutants.

These green infrastructure features also improve the biodiversity value and appearance of urbanised areas. None can deny that SuDS are a lot more pleasant to look at than a landscape covered in concrete. Greenery matters, and SuDS often brings about the unexpected benefit of revitalising community spaces. It simply makes the people who live there happier. That might be the best benefit of all.

How software can help solve this hardware problem

We strongly encourage the use of SuDS (“LIDs” in the US; Low-Impact Development) in your planning, and you’ll find lots of SuDS-friendly tools inside apps like InfoWorks ICM and InfoDrainage. But so much more can be done to prevent CSOs beyond designing larger pipes and incorporating SuDS:

• Real-time data: You can inject weather data into ICMLive and monitor sensors to see how it behaves during heavy rainfall to predict where and when CSO spills are likely to occur and prevent them from happening with capacity planning and proactive maintenance.
• Spill alarms: You can set up CSO Spill Alarms in ICMLive to alert you of emergency situations. This is, of course, very forward-thinking – we strongly recommend it.
• See inside: You can incorporate more rigorous CCTV surveys to find and prevent blockages using Info360 Asset.
• What happened, exactly? If a spill happens, you can use InfoWorks ICM with current and historical data to understand why and prepare environmental remediation.
• Measure your success: You can analyse all of the data you collect using Info360 Insight so that everyone knows what is working (and what should be working better).

Do you want to design in a SuDS-friendly way?

Download a 30-day free trial of our stormwater drainage design software InfoDrainage – no credit card required – and follow along with our Introduction to InfoDrainage learning series.

What’s your use case for controlling CSOs?

We’re hearing more and more questions from different types of customers (and potential customers) about working with SuDS inside our products, and we think that’s a good sign.

• Wastewater operations directors are responsible (in a court of law, in some situations) for reporting breaches of environmental permits as a result of the inability to fully treat wastewater. They may be interested in InfoWorks ICM for planning and InfoWorks ICMLive for situational monitoring. 
• Drainage designers at engineering, construction, and housebuilding firms often use InfoDrainage for both traditional sewer and SuDS design, which is now mandated for new developments in Germany. All signs point to the UK and France following suit. Both InfoWorks ICM and InfoDrainage are integrated with Civil 3D, which many existing Autodesk customers already use. 
• Local authorities and municipalities responsible for surface water drainage are increasingly incorporating SuDS to alleviate road flooding through retrofits. This is an excellent use case for InfoDrainage. One of the best.
• Flood and water basin management authorities and environment agencies do like to use SuDS, but they are often more interested in measuring the betterment offered by SuDS on a catchment scale and assessing the flood risk to establish interventions to reduce it. InfoWorks ICM is the solution for integrating the water cycle processes and creating a dynamic view of the river basin and its drainage and land use characteristics to simulate how it will react to storms of varying intensity and duration. It can be used for flood risk awareness as well as to plan flood defences, both engineered and natural.

What’s your use case? What do you need to accomplish to alleviate unplanned CSO spills? Download the new Utility Week report and hone your CSO strategy.