How can ponds protect us from flooding? Attenuation ponds This may not be a term that you’re familiar with but basically, they are ponds which fill with water in times of flood and let it out slowly, helping with drainage and flood alleviation while also providing a wildlife-friendly space.

You could say I’ve seen attenuation ponds from both sides: on the one hand as an engineer trying to persuade developers to agree to them as part of surface water drainage design; and as someone with a keen interest in their ecological and flood alleviation benefits. Developers are torn between wanting to be seen to do the “right” thing and maximising their profits, and sadly all too often the tendency is to see giving over a sizeable patch of house-building land to water only in terms of lost profit.

It is so difficult to put an accepted financial value on the health of the environment.

But attenuation ponds are built to as an integral part of sustainable surface water drainage systems; they store excess water during particularly heavy rainfall to slow the run-off into watercourses and allow more water to percolate into the ground – both of which reduce the risk and or severity of flooding downstream.

Increasingly now, it seems that the health and environmental benefits of open space around housing developments – and space for wildlife – are being more fully appreciated. Attenuation ponds, and the green spaces which often surround them, are a perfect example of combining an essential function (drainage and flood alleviation) and wildlife-friendly space. The ponds are designed to hold water all of the time – which allows the wetland habitats to survive – but the water level rises at times of heavy rain. Take Cumbria Wildlife Trust’s Thacka Beck reserve in Penrith: on the edge of an industrial estate, it contains attenuation ponds which take excess water from the town, and the presence of a number of species of dragonflies, and plants such as water avens, great burnet, meadowsweet and knapweed proves its benefit to wildlife. Many bird species visit to feed on the sloes and haws (and dragonflies!) there.

Another place I’ve long wondered about is the pond entirely enclosed by the Northbound exit slip road from the M6 at junction 38: if not built as an attenuation pond for motorway drainage I’m sure it does serve that purpose. And being inaccessible to people in the middle of that loop of road, it is likely a haven for wildlife.

SAs well as providing habitat for water plants and creatures, such ponds also improve the quality of floodwater before it reaches the watercourses, which of course has benefits for fish and other life downstream too. In the first instance the rainwater has a chance to settle in the pond, which removes sediment (and some chemical pollution with it); next, whilst it is in contact with plants some pollutants will be absorbed by their leaves – one of the reasons it’s not a great idea to harvest watercress from such sources! Finally, there’s biological cleaning which happens both in the pond itself and as the water filters through the ground and back to watercourses or aquifer.And that’s before we have even started on the mental and physical health benefits to humans of being able to spend time in a green space set right next to their houses. All in all, the profits from a couple of houses seems like a small price to payfor all the good things that come with ponds.