Protecting the aquatic environment from urban runoff pollution: StopUP

Background & challenges

The problem with European freshwaters

European freshwaters need to be protected. The Urban Waste Water Treatment (UWWTD) and other directives have already made a big impact towards protecting the European freshwaters. However, urban pollution still poses a big threat to the water quality. The biggest culprits are stormwater overflow from combined systems and surface water runoff. And with climate change we can expect these conditions to get even worse. Expected sequences of 1) extended dry periods, 2) hotter temperatures, and 3) intense rainfalls will put a huge stress on the flora and fauna in the European freshwaters.

Regarding the climate change, when we look at the projected increase in rainfall intensity, then there is an associated wash off of a wide range of pollutants: e.g., suspended solids, nutrients, hydrocarbons, heavy metals, trace organics, and microbial contaminants. Good solutions are needed to successfully cope with this.

Figure 1 shows the assessment of avoidable loads from various emission sources and highlights the importance of addressing the polluting effects of urban runoff and combined sewer overflows – according to a JRC study.

Figure 1: Remaining loads that can be avoided (SD=agglomerations <2 000 p.e., CSO=combined sewer overflows, IAS=individual or other appropriate systems); p.e. = population equivalent. Coliforms are bacteria that can cause diseases. By comparison, the total urban wastewater generated is currently about 612 million p.e. Source: JRC (2019).

What is needed to protect our European freshwaters?

So, it’s needless to say that new ways need to be developed to effectively address and combat this pollution. There is a need for effective load reduction that is affordable and acceptable to the end-users and society.

Once these new methods are developed, it’s important that they are taken up by the planners and drainage practitioners, along with of course the already existing sustainable drainage systems (SuDS) and good practice, whether designing new drainage or retrofitting on existing sewer systems.

What are possible solutions to reduce urban runoff pollution?

Something that comes up a lot as a possible first solution is to locally retain and infiltrate stormwater, so that the risk of sewer overflow is under control, but this bears a new risk and that is the risk of groundwater pollution when it is not properly managed or treated.

The existing sewer infrastructure has limited capacity due to the ever-increasing paved surfaces that they need to serve. This results in many spills.

Increasing hydraulic capacity is difficult and expensive. But the pollutant loads can be reduced by a combination of treating runoff at the source and at the discharge locations, as well as improving the operation of the drainage infrastructure.

As you can read, a range of different interventions will need to take place to protect our freshwaters.

What will be the best approach?

In the current surface water management of towns and cities there are significant knowledge and implementation gaps to effectively apply urban runoff pollution control.

We need a better and clear understanding of pollution loads and pollution pathways from different types of roads, other paved surfaces, industrial and commercial estates, and roof runoff into urban catchments. That’s how we can create effective targeted interventions through source control, retention, and treatment measures.

This better understanding can be gained by utilizing the newest advances in monitoring methods, like online sensors in the field and data processing, appropriate models, and data sciences.

Model-based assessments are particularly relevant to assess the impact of projected global climate change and to check if the taken measures are effective or not.

Important criteria to be considered:

When technical and managerial interventions and operating techniques are embedded in urban development processes, the following criteria must be considered: environmental impact, cost-effectiveness, low carbon footprint, and social acceptability. Certain existing solutions, like large retention tanks or basins do not meet these criteria and they are not effective enough for a broad spectrum of contaminants. Other nature-based solutions such as planted soil filters or innovative retention materials are much more effective, but to become mainstream options they lack great case studies and consolidated design criteria. The design and implementation of solutions also must consider the case-specific contexts including geography, climate, land use and receiving waters.

The goal of this European Horizon project StopUP

Stop urban pollution (StopUP) aims to fill this need and proposes to provide new methods, information, tools, and guidance on how to limit the impact of urban diffuse pollution more effectively. A conceptual outline of the project scope is shown in Figure 2:

Figure 2. Scope of the project StopUP, including sustainable urban drainage (SUDS), rain water (RW) and combined sewer overflow (CSO) management options also in conjunction with optimised use of wastewater treatment plants (WWTP).

StopUP will consider the full urban context of each case study. The StopUP project will assess the diffuse pollution from urban surfaces through different types of drainage systems – such as combined sewers and separate systems – and monitor their impact on the receiving waters. The SUDS concept is of particular importance to the project. It aims to reduce stormwater volumes from entering combined systems by using harvesting, treatment, retention, and infiltration. This approach will reduce the pollutant load.

The enhancement of the operation of the wastewater treatment plant can reduce the volume and number of untreated spills from the system. Overall optimization of the interplay between the sewer system and the wastewater treatment plant is essential for successful pollution control. This holistic approach will be investigated and applied in StopUP.


In summary, the goal of StopUP is to minimise pollution from urban runoff by better understanding pollutant sources and pathways. StopUP will provide innovative monitoring, treatment technologies and tools to enable end-users to apply existing and new SUDS practices. Progressing the use of SUDS with a focus on water quality supports achieving ambitious environmental quality targets as required by the Water Framework Directive (WFD). In particular, StopUP will equip drainage engineers and supporting experts with better solutions for managing urban surface water runoff, while taking into account the project pressures due to climate change.