The recent heavy rainfall with slow-moving weather systems in September 2024 caused dramatic floods on highways, property and farmland across the UK. The ongoing response is underway for some regions with further flood alerts. It was another reminder of the need for flood resilience and to have flood preparedness in mind when it comes to drainage systems.
Schemes need to be designed that are resilient to climate change and have maintenance planned in to retain pollution control capacity. While some cases saw nervous residents on flood alert, plenty of existing and new developments did not flood – the drainage systems working as planned.
Some of these systems are hard engineering, underground pipes and work well when designed for the right capacity and maintained to deal with blockages. Other nature-based solutions have the name: Sustainable Drainage Systems (SuDS) whereby the local recharge of soils and aquifers can hold waters, slowing up floodwaters. Beyond providing flood prevention services by dealing with the water flows and hydraulics, well-designed SuDS start with the premise that rainfall is a resource and should benefit the local natural area. They improve water quality, provide amenity and encourage biodiversity. Then when the scheme is in the ground, a maintenance schedule is needed for its long-term effective operation. These include agreements in place about adoption (ownership) and who pays for and carries out the long-term maintenance.
Options for housing developments
The question of whether drainage for larger new housing developments operates as designed can be attributed to site-specific reasons. Generally, at the design and approval stage the scheme should be able to retain a rainfall event with, say, an annual probability of a one in a hundred years (including an allowance for climate change). This can be achieved through a mixture of capturing rainfall and runoff from roofs and paved surfaces with infiltration paving, grassland swales, attenuation ponds and dams that provide storage and slowly release water after the event.
Even though these features are not mandatory in England (at least until the long-expected Schedule 3 of the Flood and Water Management Act 2010 is enacted) many developments built over the last 20 years do have SuDS included. Having been shown to deliver flood prevention and all the other benefits, they are coming up as a requirement in some local neighbourhood plans.
Upskilling the industry with the knowledge to design and approve operational, resilient, well-maintained schemes is a crucial step in delivering these plans.
Highways design, maintenance and upgrades
An example of a (mainly) hard-engineered system that are heavily maintained are the highways on both local and major motorway routes. There is a reason local authorities and national highways agencies put effort and budget into the fleets of gully tankers out keeping the road gully pots’ drains clear throughout the year, with more frequent activity coinciding with leaf fall over autumn and winter. Blockages reduce a drain’s capacity and can cause flooding. What’s more, drains do not operate as designed to (i.e. capturing sediments and reducing downstream water quality pollution) when the highway overflows into the water environment.
Poor maintenance is too easy to blame after roads flood, however the root of the problem lies with sites that continue to flood even with regular emptying. These scenarios build the case for upgrading a local drainage system to include SuDS that would fit that site - infiltration on kerbs and blockwork, underground sediment separators, swales and ponds are some of the options.
Drainage systems for housing developments and highways are just that, systems, that need to be designed to take account of rainfall with an allowance for climate change, using the SuDS principals.
Systems need to be maintained regularly, and when that maintenance is not delivering the flood protection and environmental benefits, then it is time for an upgrade.
Upgrading through upskilling
Expertly designed systems require expertly trained practitioners who have the skills to design and approve schemes that meet site requirements, are cost-effective, bring long-term local benefits, are resilient to extreme weather and adaptive to climate change. Build sustainable capability within your team through WRc Academy’s SuDS & Hydrosystems Engineering Training.
Use the form below to get in touch with WRc’s engineering specialists about your SuDS solutions. Also, find out more about our training relating to drainage, urban pollution, climate change and beyond.