Why puddles are the latest in a long list of obstacles to building the homes we need

In the list of Britain’s most popular pastimes, talking about the weather and finding excuses not to build new homes must come pretty near the top. The latest of a long line of planning absurdities combines the two - we’re now being asked to design homes around puddles.

“Surface water flood risk,” as puddles are called in planning policy, has always existed but never used to be a problem. There was a good reason for that - new developments were already required to include sophisticated surface water drainage schemes to take account of the expansion of impermeable areas that typically results from new development.

The simple, sensible approach was for the design of those drainage schemes to deal with any pre-existing surface water flood risk too.

Sustainable Drainage Systems (SuDS) comprise chains of drainage features - like swales, rainwater gardens, storage basins and ponds - ensuring that surface water run-off from the site was no higher than before the development was built.

These SuDS schemes were even designed with surplus capacity - sometimes as much as 50% - to take account of the wetter weather we’re likely to experience as a result of climate change. As a result, new developments were not at risk of flooding from surface water, nor would they increase the risk of flooding elsewhere. If anything, they reduced the chance of flooding compared to the pre-development risk.

Puddles, the courts told us, should be treated in exactly the same way as the risk of flooding from rivers or the sea

But then, last year, a legal judgement revealed that we’d been misunderstanding flood risk policy. Puddles, the courts told us, should be treated in exactly the same way as the risk of flooding from rivers or the sea. That means directing development away from the areas of highest flood risk towards those with the lowest risk.

This change was compounded earlier in the year when the Environment Agency (EA) updated its flood risk maps, dramatically increasing the areas at risk of flooding from surface water - of puddles forming.

No one would dispute that it is a worthy aim to avoid building homes in areas where they might flood - but this new approach makes no difference to that goal.

Rivers are very different to puddles. They’re much harder to move, for a start. And the amount of flood water they produce is a consequence of a whole range of factors - from rainfall levels to land-use - across a very large catchment area. Puddles simply form in low points when the amount of rain falling exceeds the ability of the land to absorb it.

It seems sensible to treat flood risk from rivers differently - by avoiding the most sensitive development in those areas as far as possible. That’s what the EA Flood Map for Planning has helped us do for years, by splitting the whole country into three zones depending on their flood risk. The planning system no longer recognises the difference between rivers and puddles.

 Instead, if a site shows any risk of surface water flooding - of puddles forming - developers have three options.

The first is to produce a site-specific model showing where puddles might form. Although the EA has surface water flood risk maps, they aren’t hugely accurate. A bespoke model, using more accurate data, can show puddles in different locations or of different sizes to the EA mapping. Those models take time of course - around four months - in large part because of the time it takes the EA to approve the various steps in the modelling process. It’s expensive too, costing tens of thousands of pounds. This approach might show the surface water flood risk isn’t real; but it’s also possible it won’t.

Whichever choice a developer makes, the result is a slower and more expensive planning permission that delivers few homes

The second option is to carry out a “sequential test” to show there are no other sites at a lower risk of flooding that could accommodate the development. That’s very hard to do. You must look across the whole of the local authority area - not too bad if your site is in Rutland (382km2), but good luck if it’s in North Yorkshire (6,189km2) - and must consider combinations of sites that could deliver the development. Again, this takes time, is expensive, and might not deliver a helpful result.

>> See also: Nutrient neutrality: How sustainable drainage systems can help housebuilders find the right balance

The final choice - and by far the easiest - is to simply design around the puddles, locating homes and roads elsewhere on site. To avoid the sequential test, however, the ground level of those surface water flood zones can’t be changed either, leaving them as low points prone to flooding forever. And whereas designing around flood zones from rivers creates attractive, river-side green space, puddles are usually scattered across sites producing an oddly fragmented layout that reduces design quality and layout efficiency.

Whichever choice a developer makes, the result is a slower and more expensive planning permission that delivers few homes. And this approach, remember, doesn’t actually deliver any greater reduction in flood risk than the previous approach of simply reflecting it in surface water drainage designs. If anything, it’s worse for flood risk than the way it used to be dealt with.

It’s just one example of the grit in the system which must be remedied to get the planning system operating as efficiently as possible.

The good news is in this case it is really very easy for the government to fix. All they need do is make it clear that existing surface water flood risk should be taken into account in the design of drainage schemes, but that it doesn’t trigger the sequential test.

And then we’ll all need to find some other way of passing the time.

 Paul Smith, managing director, Strategic Land Group