Thursday, October 10, 2019

A case study of the UK flooding: the river Uck, East Sussex, October 2000

During the wet season of October the Sussex the Uck-Ouse basin burst it banks and caused major flooding in the surrounding towns mainly a small town called Uckfield. Upstream of the town of Uckfield slopes are very steep and so runoff happens very quickly after rainfall. However the River Uck flood plain is relatively undeveloped, with natural flood plains remaining. Here land management practices are well adapted to flooding. The flooding in the central part of the Ouse catchments on Thursday 12th October 2000 was preceded by 3 days of storms and heavy rain across the whole area. The ground became increasingly waterlogged, and there was widespread, localised flooding from surface water run-off. Uckfield flooded dramatically from about 5.00am on the 12th October, with river levels rising rapidly to a peak between 9.00am and 10.00am, at which point a torrent of water up to 1.9m deep, was flowing through the town centre causing considerable damage. Barcombe and Lewes filled up and widespread flooding in Lewes started at about 1.00pm, as the rising river backed up behind the Cliffe Bridge and overtopped the flood defences at a number of locations. Within about an hour or so the flood defences throughout the town were completely overwhelmed and the town centre rapidly filled with floodwater. Many hundreds of people were stranded and had to be rescued by the Emergency Services in boats. By the time the floodwaters peaked at about 9.30pm, some parts of Lewes were less than 3.6m of water. As the flows passing downstream from Barcombe continued to increase at a rapid rate, the floodwaters weired over the river walls and surged through the streets and open areas in Lewes, rapidly filling up sections of the urban floodplain to a depth of 1m in about half an hour. The Police abandoned the centre of town, and the evacuation turned into a rescue operation as the RNLI and Emergency Services used inflatable lifeboats to reach people suddenly trapped in their homes or businesses. The flood devastated the centres of Uckfield and Lewes, as well as causing significant damage to surrounding rural properties and the farming community. * long periods of drying out and repair mean that many homes have remained uninhabitable for many months after the event, with residents having to live in alternative, temporary accommodation; * similarly, many businesses remain closed months after the flood, and a small number are believed to have closed permanently; * a long term loss of trade, both for the flooded businesses, and for the wider business community; * widespread concerns about property values and insurance; * losses of agricultural crops and livestock; * impact on County Council Social Services provision due to the loss of day centres and buses; * long term damage to road surfaces, and widespread blockage of highways drainage systems; * impact on Lewes District Council's housing provision due to temporary re-accommodation of flood victims; * disruption to the Fire Brigade and Ambulance Service due to the temporary loss of several of their buildings, including their control centres, and loss of vehicles; * in Lewes, 118 Listed Buildings and 230 other ‘traditional' buildings within the Conservation Area were damaged, requiring specialist repair; * long term needs for emotional support amongst some. This means that the upper and middle sections of the catchments become quickly saturated following heavy rainfall. During wet periods a large proportion of the rainfall will quickly run-off into the river system rather than drain through the ground, and this effect is exacerbated by the hilly nature of the upper parts of the catchment. * increasing the amount and rate of surface water run-off, thereby increasing flows; * reducing the area available for flood storage, thereby increasing peak levels; * reducing the area available for flood flow conveyance, thereby increasing peak levels, contributing to rapid inundation and high flood velocities, and extending the period of flooding. * River flows were increasing very rapidly at this time and continued to do so for several hours after the flood defences were overtopped. * The upstream flood storage areas were already ‘full' so that the majority of the flood flows passed straight downstream to Lewes with little attenuation. * Once overtopped, the flood defences acted like weirs allowing large volumes of water to pass over them in a short space of time, rapidly filling the low lying areas behind them, with high velocities being witnessed where flows were channelled through narrow gaps. * The natural narrowing flood plain as it approaches Lewes, together with the artificial obstructions across its path in Lewes (Phoenix Causeway, Mayhew Way, Cliffe High Street shops) severely reduces the ability of the flood plain through Lewes to convey flood waters, causing levels to rise higher still. *  It is an obvious point, but maybe worth stating, that the 12th October 2000 flood inundated the floodplain – so named for a good reason. The devastating impact of the flood was because large numbers of properties have over the years been built on the floodplain, and although artificial flood defences or river improvement works have protected those properties from more frequent flooding events, all property constructed on the flood plain is at risk of flooding occasionally. The Environment Agency's Flood Warning slogan of â€Å"You cannot prevent flooding, you can only prepare for it†. The existing flood defences were overwhelmed by the 12th October 2000 flood flows and it may be possible to justify future improvements to raise the current standards of defence to protect against an event of similar magnitude. A number of options are likely to be considered in the forthcoming Catchment Strategy Plan being commissioned by the Environment Agency. However, given the extreme severity of 12th October 2000 event, and the nature of the long-standing government rules and arrangements for project appraisal and flood defence funding, we do not believe that it is reasonable to assume that they should already have been of such a standard. Nevertheless we believe that there are a number of important issues relating to the existing flood defences in Lewes which need to be urgently addressed, in particular the apparently poor condition of many of the river walls through the town, and the long term settlement in the upstream flood embankments. The floodwalls were breached or damaged in at least 8 locations through the town, and the sudden failure of the river wall at Phoenix Industrial Estate is particularly worrying. The flooding took many residents by surprise, and it is clear that the Environment Agency and a significant number of affected residents have very different perceptions about the performance of the flood warning system. This is partly an issue of communication and education. We believe that it is important that the Environment Agency vigorously continues its efforts to educate local residents, and that it is explicit about its actual responsibilities and capabilities. With the benefit of hindsight, we also believe that a number of important improvements in the flood warning and forecasting service can be identified, and should be undertaken. These would not have had any impact on the extent, speed or depth of the actual flooding, but they may have meant that for many, vehicles, stock, or precious personal possessions might have been saved.

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