A case study of a flood management scheme in the UK - The Morpeth Floods
Morpeth is an ancient market town situated in a loop of the river Wansbeck in the northeast of England about 15 miles north of Newcastle upon Tyne and 12 miles west from the North Sea. Following a flood in 1963, a flood defence scheme was established. Flood walls were erected on the north bank to protect the main business district. Housing properties at Middle Greens on the south bank were also protected by flood walls. When the River Wansbeck swelled on the 6th and 7th September 2008 (see photo below by Tzdelski via Wikimedia Commons), the floodwater simply flowed over the top of the defences, which were not high enough to hold back the volume of water. This resulted in a new flood defence scheme being required.
Causes of the 2008 Floods
The flood of 2008 was estimated to have been a 1 in 115 year event. It was caused by;
1. Prolonged rainfall - The Environment Agency recorded a HUGE 150 millimetres of precipitation falling in the Wansbeck catchment between Friday 5 September and Saturday 6 September.
2. The River Wansbeck Valley is narrow and steep and as a consequence has exaggerated amounts of surface runoff.
3. The soil was already saturated as a result of the wet summer, the effect of surface runoff was greatly enhanced.
4. Increased urbanisation since the 1960s in Morpeth meant that most water falling on the town would have drained directly to the river channel.
5. Other tests investigating the catchment lag time (time lapse between the mid point of storm rainfall and peak river level) indicate that the Wansbeck has a LAG time of only 8 hours. This means that any water falling in the catchment area would have been rapidly converted into channel flow by surface runoff and to a lesser extent by throughflow.
This resulted in a peak water level of 3.99 metres recorded in the river channel, the biggest flow ever recorded in the Wansbeck.
During 6 September 2008, more than 400 residents were evacuated. Shelter was provided in the Town Hall, King Edward VI High School and County Hall. An error made by the Environment Agency's warning system meant that 198 properties in the Middle Greens area of the town did not receive a flood warning. Fire fighters, ambulance crews, the RAF, the RNLI and the British Red Cross were among the emergency services involved in rescue and recovery operations over the weekend. Many residents had to be forced from their homes, and lived in caravans or with relatives as rebuilding took place.
995 properties in Morpeth town centre were directly affected by the flood water. Early estimates suggested that damages could be over £10 million, but the Journal Newspaper later claimed it was £40 million. On Sunday 7 September, Morpeth Lions Club and the Red Cross launched the Morpeth Flood Disaster Fund and by Wednesday 10 September had raised over £20,000.
At the peak of the flood, Morpeth High Street (Bridge Street) was under 60 centimetres (2.0 ft) of water. Not since 1963 had the main street been flooded. The library suffered severe structural damage due to the heavy debris transported by the river. Such was the extent of the damage that structural engineers were required to test its safety. Houses were full of mud and sewage.
THE NEW FLOOD MANAGEMENT SCHEME
Morpeth already had a system of flood defences (flood walls and low embankments) in place following the 1963 flood event, but these were overtopped by the high flood waters in 2008.
NEW plans were developed to;
1. Have a system of higher flood walls along weak spots in the town – walls were raised by 30cm in the most vulnerable areas
2. Poles were placed in the River Wansbeck to catch debris upstream, it is hoped that this will stop debris clogging up the bridges in the town which caused some of the flooding.
3. Clear out the culverts that drain water in Morpeth so that areas within Morpeth are well drained
4. Construct a huge upstream reservoir - which would hold over one million cubic metres of water- would only allow through a volume of water manageable by the town centre defences.
5. Build new flood walls in areas that had none
6. Add an earthen embankment to protect the housing estate of High Stanners
The social, economic and environmental issues involved with the flood management scheme.
This flood management scheme has many issues, which can be viewed as social, economic, and environmental. Overall, the scheme cost £27 million pounds, a massive sum of money to protect residents in a small town in the North of England. The flood walls were also raised to a height of 1.8m, which obscures the view of the river for many residents and which intrudes in the natural landscape. The walls are also a barrier to some forms of wildlife. The culvert clearance is a good thing, as this provides areas with faster flowing drains for some fish and birds, and the reservoir will reduce the flood risk significantly.