Using GIS to visualise sewage spills

Written by one of our Ambassadors, Kieran Bird.

Matthew Woodard


There is plenty of data about our rivers out there. Lots of it is free to use, but that doesn’t always mean that it is easy to access or interpret. Thankfully there are people within the Rivers Trust doing great work to make this data easier to access.

GIS data

GIS stands for Geographic Information Systems. And rightly or wrongly, I like to think of it as giving data a specific place, so you can see its location. It has lots of uses, for example when you are in a new place and trying to find a restaurant on google maps. Within the Rivers Trust the sewage map is an excellent example of how the raw (sewage) data has been developed into a neat user-friendly map to explore. The sewage map has been described as a crucial place for public and recreational river users to investigate where the nearest know sewage outfall is and how often it spills – all about making the data more accessible.

Learning about GIS

While it may not be worth recreating the sewage map, there may be some GIS skills that you think may be helpful for some of your local river projects. Thankfully the Rivers Trust has produced a series of 5-15 minute tutorials, on the Catchment Based Approach website, outlining how to carry out tasks on GIS software. Some of the software used in the videos may require purchasing a licence but here are free open-source alternative GIS desktop programmes.

Applying this data further

Sewage overspill data has been applied and visualised even further by modelling a hypothetical spill in a real-world river. Using modelling software, such as TUFLOW FV that myself and Duncan Kitts has used here, it is possible to predict how the sewage would behave in the flow of a river. It doesn’t make for such pretty viewing, particularly at low flows!

This shows the sewer spill data is only part of the story, there is potential for multiple simultaneous spills could make the water quality worse! Although flowing downstream and off the end of this image, it is not out of sight out of mind. Every river flows to the sea where fragile ecosystems, wildlife and human activity continue.

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