Combating flood risk in future
Climate change models predict more intense storms and a higher frequency of flooding in some parts of the world. So what can be done to mitigate the threat from floods? Roger Falconer, from Cardiff University, takes Chris Smith through some scenarios...
Chris - First of all Roger, what do you think of what Nigel was suggesting about the way we just retrofit our cities and also encourage people to just have more gardens instead of tarmac?
Roger - Well in principle that's fine, I would support that but if you look at the Somerset levels area, the groundwater was pretty saturated anyway and I know from living in Cambridge some years ago, the same occurs in the Cambridge area as well. So, when you have big floods like we've had recently, the groundwater is usually at ground level and in that case, changing the ground conditions wouldn't make a lot of difference.
Chris - So, the water goes in and it's got nowhere to go so it just runs straight off anyway.
Roger - That's exactly what happened in the Somerset levels area.
Chris - Indeed. So instead, what might we be able to do? What sort of strategies could we explore?
Roger - One of the arguments is we shouldn't build houses on flood plains. But if you look at almost every major city, near the coast, London, Cardiff and so on, most of the city is on a flood plain. So, you have no choice, but to build on the flood plain in the future. You wouldn't build any houses in York, Cardiff, London, and a long list of other cities if you adopted the policy of never building anything on the flood plain. But I think we can look more at how we build our houses. If you look at houses in the States for example, it's quite common for the garage to be on the ground floor, but most of the living area is on what we would call here the first floor and possibly a floor above. And I would be perfectly happy to buy a house which had a garage on the ground floor and a play room for the kids for example. But no real power of any significance there, and then on the first floor, have my living area. Then at least if my house was flooded, the garage would be messed up, but the living area and probably then the second floor would be fine. So, I think this is a solution which look more to.
Chris - Good for new development. Obviously, something to bear in mind. What about actually things we could do to try to mitigate with the housing stock that we currently have? What about for instance trying to tether the way in which we handle flooding and turn it to our advantage so we can use the water that we accumulate in other ways because water is a pretty precious resource these days, isn't it?
Roger - Well, one of the things that's been proposed at the moment and many proposals on the table, to build large, coastally attached lagoons to generate power. So, these are marine renewable energy projects. They're not for flooding as such, but if you look at many of the attractive sites such as for example, Bridgewater Bay, and the North Wales Coast, these are communities very prone to flood problems. If we were to build large coastally attached impoundments, similar to barrages, around these embayments, we would have a huge opportunity to alleviate a lot of the flood risk.
The problem in the Somerset levels and the reason why dredging is not a solution in my view, as things stand at the moment is basically the flow in the river is governed by the water surface slope. And in the Somerset levels, you almost have flat land similar to Cambridge. Therefore, the flow in the canals and the rivers, and so forth is extremely low velocity. Dredging doesn't really change that. I live in Cardiff and we have a bay here. If you dredge Cardiff Bay, it wouldn't make any difference to the flow with through the bay.
Chris - So lagoons might be one answer.
Roger - Well, if you want to increase the water surface slope, we either want to raise the land, that's a nonstarter, or we drop the sea. If you build a lagoon, close off the sea from the land, use it most of the time to generate power and then when you need it for flood mitigation, you would not generate power on the incoming tide.