Water, water, everywhere
Recent floods have raised questions about where we build.But have environmental worries exacerbated the problem?
Flood control of rivers has been vital to development and economic growth in Britain over the past couple of centuries and this has gone hand in hand with the development of storm catchments and sewer systems. As AJwent to press, deputy prime minister John Prescott was considering powers to veto flood plain developments in the government’s new planning policy guidance.
To blame the developers and river catchment modellers now, and seek to limit or even ban building on flood plains, is a knee-jerk reaction. It demonstrates an ignorance of the lessons of history and a contempt for real engineering possibilities.
Engineers looking at flood defences and modelling catchments, sewer systems and watercourses, have to take many factors into consideration. With lifestyles and demographics becoming increasingly varied during the past 25 years, the demand for river courses to be safely accessible as sites for leisure, as well as habitation, has grown. Living with nature does not stop the sensible desire to control it, and so, understandably, flood defences remain top of the list of homeowners’ priorities.
But ecological obligations have led to a change in the type of flood defences proposed. Environment Agency officers now advocate soft ‘green’ flood defence measures. Hard concrete channel solutions for river bank protection tend to be overlooked in favour of stone gabbions, gravel banks, reed beds and willow trees. The current aim is to hold up the river’s flow when it is in spate, as opposed to quickly moving the flood waters on.
However, while York suffered badly from inadequate defences last month, the solutions that saved a large part of that city, and many others, from the worst effects of the flooding, were hard structures. Soft defences would have been totally useless. And yet some environmentalists argue that hard concrete solutions should be excluded from future flood defence solutions in favour of more ‘natural’, less intrusive proposals.
Developers also like ‘natural’ solutions because they prettify access to river plains. The heightened leisure and amenity value of willow trees in green field settings, as opposed to grey concrete channels, adds value and attracts housebuilders to build on the flood plains.
Trickle down effect There is no single cause of the different behaviours of various river catchment areas. Each decision - whether to build on an existing flood plain or not - must be made on the merits of the specific case. But localised flood prevention solutions often have implications for other areas and political expediency should not determine the solution.
Developing river plains involves handling the increased rate of runoff from the new hard surfaces and building in local and network buffer capacity. In some new build areas groundwater infiltration to existing sewers is as high as 20 times the dry weather flows. Upstream pressures from new developments increase the strain on existing sewer networks and often require the replacement of crumbling and outdated sewer infrastructures in the lower catchment areas. But limits on capital spending preclude this. Projections given at the recent global environment summit at The Hague suggest that the costs of flood damage will outstrip the combined total of every country’s gross domestic product. Maybe spending by government and utilities companies would be a worthwhile investment.
Antediluvian prospects Resources are too short to both improve treatment to meet Urban Wastewater Treatment Directive works and carry out fundamental improvement works on the combined sewer systems to avoid premature spilling and prosecution. The already over-stretched funds cannot deal with serious infrastructure solutions to facilitate the development of flood plains. It is therefore easier to prevent development on the basis of the precautionary principle, rather than look for possible solutions.
A major problem is that such solutions require inter-agency dialogue. Water companies currently have a duty to prevent properties flooding from sewers; and funding is available for this key function.
But with government bodies such as OFWAT and the Environment Agency prioritising financial interests, and with the utilities companies only patching the problem, the possibility of an integrated, rationalist approach to infrastructure, river management and flood prevention seems unlikely.