Planning for the Next Flood
Civil engineer and transport planner Karen McShane reflects on lessons from Madrid, Venice and Belfast, and why long-term flood planning must now shape how we design and build to protect our towns and cities.
This month I had the pleasure of visiting the Manzanares River in Madrid, which has been significantly impacted by heavy rainfall and widespread flooding, in particular during a major flooding event about a year ago. It can also be affected by melting snow in the Sierra de Guadarrama.
The authorities now monitor rising flow levels in both the Manzanares and Jarama rivers and use this to control the release of water from the upstream El Pardo Dam, helping to regulate the river and manage reservoir levels in anticipated flood events.
The river features several locks as part of its historical and architectural character. Each has a gate controlling the upstream water level, which can also be used to hold back water during known flood events. They are very similar in nature to those at the River Lagan as it joins Belfast Lough.
The use of gates is a primary flood control measure in many areas, and even in Venice the city is protected from high tides by the MOSE system, a mobile network of 78 floodgates that temporarily seals the lagoon from the Adriatic Sea. It provides protection against high tides and storm events. The gates remain submerged under normal conditions, allowing navigation in the shallow lagoon.
Construction began in 2003 and was completed in 2020, with its first real deployment in October 2020. Low-lying areas such as Piazza San Marco are now protected. In 2017 I visited the model with various Chartered Institution of Highways and Transportation colleagues to better understand how flooding in this historic city would be controlled.
Within Northern Ireland, many current schemes are being designed to look ahead 100 years, taking climate change into account and considering what new measures need to be implemented. There is a real expectation of sea level rise, more intense rainfall and more frequent extreme events. With this in mind, we should expect the raising and upgrading of existing defences over time.
I have written about new localised flood schemes across Northern Ireland, including the new glass walls along the Lagan and flooding at Newcastle and Downpatrick. We need to ensure that government can allocate a budget so these features are maintained and upgraded as required.
As we write our new Local Development Plans for the future, we need to ensure that we consider flooding across entire river catchments, not just city sections. It will be important to have measures in place to hold back flood water upstream before it ever reaches our more built-up areas. This will include a system-wide approach.
This will include avoiding development in flood risk zones and using up-to-date mapping in planning decisions.
As part of new developments, we need to consider more appropriate sustainable urban drainage systems that store water locally rather than releasing it straight into our watercourses. Maintenance of these systems will be essential for the future. Measures being employed locally include permeable surfaces and green roof technology, helping to hold back water at individual properties.
We need to consider better water management powers, improved communication and stronger demand management during extreme events so we can all learn, adapt and be prepared for when the next flood arrives.
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