Taking the rise

FLOODS are natural. Man's impact on flooding is not. Consider this statistic: in the last 50 years, flood events have doubled. For every thing man does to alleviate the effects of floodwater, he does something else that makes matters worse.

Alan Ervine, professor of water engineering at the University of Glasgow, said there are three key reasons for the increasing incidence of flooding.

"One is global warming. That tends to raise more moisture into the atmosphere.

"Two, we have got much more Tarmac and concrete everywhere. Rainfall runs off to rivers far more quickly than in the past.

"In the past it had time to infiltrate down into the soil. Now it comes into the rivers straight away."

The third reason, he said, was riverside development,

"If you build flood banks at the edge of the river, that tends to cut the river off from its flood plain.

"Flood plains have always been used by God, if you like, to check the peak of the flood. Part of the flood went into what they call temporary storage. The flood peak tended to be reduced.

"Part of the problem is that everyone wants to buy their house at the edge of a river because it's quite attractive.

"But if you live at the edge of a river you are basically building your house in the river. Every flood plain tends to flood about once a year, or possibly once every two years naturally."

Prof Ervine is critical of the planning policies that have exacerbated the problem. "I still think that local authorities have been highly remiss in that they have, in the past, let people build on the flood plain.

"This means there's less temporary storage. The flood peak tends to be higher and further down the river."

Barry Potter, chairman of the York Natural Environment Trust, says this has environmental implications.

"Flood plains are interesting and valuable habitats. If you build on them, you are taking away environments which are relatively rare. Wetland areas are becoming more and more scarce."

In recent years there have been moves to discourage development on the flood plain.

Both the Environment Agency, responsible for the management of Britain's major rivers, and the Department of the Environment have issued guidelines to councils.

The agency says that development on flood plains has more than doubled since 1950. The rivers continue to flood, and that means more flood defences have to be built.

It says: "Development on flood plains can impact on both the ecological and archaeological value of the land, and may divide linear habitats such as river corridors.

"Any new developments on flood plains increase the risk and financial burdens for present and future generations.

"The risk is often most easily removed by not building within the flood plain in the first place."

The agency is spending £22 million between 1996 and 2001 mapping flood plains, to give planners more accurate information.

After floods earlier this year, the Department of the Environment issued new guidelines to local authorities on flood plain development.

This places the burden of determining whether land is suitable for development on the developer.

They are responsible for assessing whether any new buildings will be affected by flooding or will increase flood risks elsewhere. They must also "satisfy the local planning authority that any flood risk can be successfully managed with the minimum environmental effect to ensure the safe development and secure occupancy of any site".

The department also states that "local planning authorities should guide development away from areas that may be affected by flooding and give due weight to the case for refusing development that would itself increase the risk of flooding locally or elsewhere".

Responding to these guidelines, City of York Council changed its draft local plan. Originally this stated that "account will be taken of any increased risk of flooding that a proposed development may cause".

That has been amended to read: "Proposals for development within flood plains or other areas liable to flood will only be permitted where the proposal will not be at risk from flooding and/or significantly increase the risk of flooding elsewhere."

Roy Templeman, the council's director of environmental and development services, goes further. He said: "We don't allow any building on the flood plain. The council's policy is to preserve this important area."

Anglers have long been traditional river conservationists. John Lazenby, from Acaster Malbis, is Yorkshire regional representative of the Salmon and Trout Association. "Modern farming and development methods do tend to mean that water runs off the land quicker and doesn't get held," he said.

Trees have been removed and fields are replanted immediately. Previously they were left to lie fallow allowing rainwater to collect in the plough furrows.

"This all increases flooding of the rivers," he said.

Mr Lazenby said farmland drainage schemes, supported by government grants, date back to the Sixties and maybe beyond. Water now runs off straight into the rivers, speeding up the rise in water levels and increasing the flood risk.

It is too late to turn the clock back, Mr Lazenby admits. But we can do something about the future. "We are going to get more rain. We are going to get greater changes in the river patterns."

So farmers, planners and environmentalists must make a concerted effort to ensure that rivers are managed to minimise future flooding.

Prof Ervine praised the work already completed to make York safer from the flood threat. But he added: "There are probably three future measures they can take in York which might be helpful.

"One is they could aim to build more temporary flood plain storage areas - temporary basins. Part of the flood is then directed into the basins. As the flood peak passes they can let it out again.

"Secondly I think they could designate corridors at the edge of the river and say there isn't any building there. They can be used as pathways and cycleways which make the place more attractive."

Thirdly, he said, where the heaviest rainfall occurs, Tarmac and concrete could be replaced by a permeable surface "so the rain can go through it and into the ground".

The message from flood experts, environmentalists and anglers alike is simple. Worse is to come. We'd better start preparing for it.

Three steps to a flood...

1 Global warming

2 Too much Tarmac and concrete, pushing rainfall into rivers too quickly

3 Riverside development