Probably the most visible signs of flood risk management are flood defences. We build ‘hard defences’ of concrete, metal or other construction but we also try to use natural processes wherever possible to reduce flood risk.
Throughout England and Wales there are some 24,000 miles of flood defences. In 2010/11 we plan to spend £161 million maintaining existing flood defences and £270 million building new and improved ones.
Typical hard defences include embankments, walls, weirs, sluices and pumping stations. Of these, some may only be brought into operation when a high tide or flood is forecast or in progress. An example is the Thames Barrier in London.
However, we are increasingly trying to use more natural methods to deal with floodwater. Sometimes called 'soft defences’, they use mudflats and saltmarshes to provide space for floodwater and prevent flooding from occurring elsewhere. At the same time, this method can benefit wildlife by providing areas of habitat.
Soft defences are becoming more common as climate change drives the need for flood defence measures. While they generally occupy a larger area of land than a hard defence, they require less investment and maintenance. In coastal and estuary areas saltmarshes also help break the power of incoming tides – a saltmarsh can reduce the impact of a wave by up to 95%.
Managed realignment
Managed realignment is the deliberate process of altering flood defences to allow flooding of a currently defended area.
Many guidance documents, including advisory notes, government policy and national and international legislation, have been written concerning our legal obligations and the use of managed realignment. These have been written from a variety of perspectives including flood risk management, conservation, habitat creation and mitigation for development and have now been collated into one single source.
All this information is now stored in our managed realignment online guide.
