HC Deb 09 January 2001 vol 360 cc522-3W
Ms Kingham

To ask the Minister of Agriculture, Fisheries and Food what quantity of water was released as a result of the opening of the Leigh barrier on the Medway on(a) 12 and (b) 13 October and over what period of time; what estimates were made by the responsible staff at the time of the opening of the barrier as to the effect on the village of Yalding and its surrounding area; what assessment he has made of the level of flooding in the Yalding area had the barrier not been opened; and what evidence he uses to support his assessment. [144450]

Mr. Morley

[holding answer 8 January 2001]: The Leigh Barrier provides relief from flooding in the Upper Medway valley, by allowing floodwaters to be stored in 6km of river valley. This reduces the risk to life and property downstream which would otherwise be exposed to an uncontrolled natural event. The benefit is to all communities downstream of the barrier, including Yalding and its surrounding area, although the degree of flood mitigation reduces downstream due to inflow from unrestricted lengths of the Medway and its tributaries. The Barrier is operated by dedicated and qualified staff of the Environment Agency.

The release of water from the Barrier is a normal function in a flood event as the operation of the Barrier is not to stop outflow but to throttle the flood to an extent which is appropriate to its size, available storage and the capacity of the downstream channel. In extreme events the discharge may exceed the capacity of the downstream channel, and hence flooding occurs, but the extent of this flooding will be reduced by virtue of the stored volume of floodwater.

The flood event of mid-October produced the highest flood peak since the scheme was constructed with peak inflows between 250 and 300 cubic metres per second. The Leigh Barrier was operated from 10.30 on 12 October until 16.00 on 14 October. During this time nearly 5 million cubic metres of floodwater were stored. In the 16 hours from the onset of the flood on 12 October the throttled flow leaving the Barrier varied between 55 and 160 cubic metres per second, a total of 5.76 million cubic metres. On 13 October the throttled flow varied between 155 and 80 cubic metres per second, a total of 8 million cubic metres in 24 hours.

The Environment Agency staff recognised that while the Leigh Barrier could give some relief to downstream communities from the floodwaters in the Upper Medway, floodwaters from the rivers Beult and Teise and the Middle Medway catchment would severely affect Yalding. The peak flood from the River Teise reached Yalding first, followed by the flood peak from the Beult causing extensive flooding through the early hours of 13 October. The floodwaters from the Upper Medway, which had been moderated by the Leigh Barrier, would not have reached Yalding until late evening on 13 October.

The Environment Agency is to produce a full report on the Autumn flooding, in co-operation with local authorities and the emergency services. This will include the way that flood defence control structures, such as the Leigh Barrier, were operated and will identify any lessons to be learned.

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