Paul Davies, Global Surface Water Skills Leader, Arup outlines why a radical change in approach is needed  to translate stormwater drainage into stormwater management.

Paul Davies: As cities take over as the dominant way of life, continuing to use drainage as a waste disposal system is a recipe for disaster - stormwater drainage needs to become stormwater management.

 I think drainage has always been looked upon as a poor relation in engineering and unsurprisingly it’s not a common topic of conversation in polite circles. However, I think it should be – because we need to radically rethink our approach to drainage if we want to live sustainably in cities.

The volume of water we drink is insignificant compared to the volume of water we consume. See embedded water thought, this is not sustainable. For some time, I have believed that turning rainwater into a waste product to be discarded down the drain, whilst at the same time using treated water to water the lawn or irrigate land has got to be some form of insanity.

The drainage industry has evolved over the last millennium to take our discarded water away from us in the most efficient manner. Its main purpose is to enhance our convenience by making our waste products disappear.

Drainage is making flooding and droughts worse

Over time, drainage has become very efficient as a waste disposal system, which hides many of the problems we are creating by moving them downstream, out of sight. Yet drainage is not protecting us from flooding or droughts. In fact, it’s making flooding and droughts worse.

Currently stormwater drainage aims to take water away from us as quickly as possible. So the system collects water together, which concentrates both the flow and whatever it picks up on the way. Then we transfer these flows to the receiving system much earlier than they would have arrived naturally. Effectively dumping these concentrated flows into rivers more quickly makes it much more likely the river will be overloaded – in terms of both water quantity and quality.

Considering the other side of the coin, large areas of low permeability (such as streets and buildings) reduce the amount of stormwater that can get into the ground. Drainage disposes of this water very efficiently too, transferring it to the receiving system and depriving the aquifers of this water, depleting them.

Stormwater - a precious resource

What’s the answer? Stormwater drainage needs to become stormwater management. Stormwater should be captured, recycled, and stored for a (not) rainy day. The Hunters point area in New York is a good example of what can be done, as is Greener Grangetown in Cardiff. Keeping water local in this way could also save some of the huge costs incurred moving it around.

 Achieving this requires a change in mindset. We must think of stormwater as the most precious resource we have, and not something to be discarded as a waste product. Stormwater management should not just be a way of making water go away; stormwater is what keeps us alive.

Cities do not yet manage water very well and need to do better. As cities take over as the dominant way of life, continuing to use drainage as a waste disposal system is a recipe for disaster. If cities do not become more self-sufficient they will suck the drinkable water out of the rest of the planet.

This article first appeared in Arup's thought leadership blog - visit www.thoughts.arup.com