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Britain's longest river (350km, catchment covering 11,000km 2 )
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Source: in Welsh Mountains on Plynlimon (at 741m)
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In the Upper Course the river quickly falls through steep-sided incised valleys to 198m by the time it reaches
Llanidloes, a distance of just 19km.
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Then flows through Shropshire, then flows South-East to its mouth at Avonmouth near Bristol.
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The geology and climate of the River Severn's catchment help explain the pattern of flooding.
Geology
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Upper catchment: Ordovician and Silurian shales; hard rocks, resistant to erosion with many steep slopes.
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Also impermeable, allowing rapid runoff into the river so increase the flood risk further downstream.
Climate
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Annual precipitation in the upper catchment (Welsh mountains) is over 2,500mm but most of the rest of the catchment area is close to the average for Britain at less than 700mm per annum.
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Rainfall in summer is mainly caused by convective storms.
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Precipitation during autumn and winter is generally due to depressions and tends to be of higher volume.
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This, together with the topographic (mountains) effect, can result in heavy rainfall falling on a near-saturated upper catchment during autumn and winter.
Land Use
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The River Severn catchment is mainly rural, with agriculture the main land use.
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Severn Uplands: o Sheep farming (1/3 of hills) o Dairy farming – valleys
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Middle Severn: o Fertile plains - arable faming, (46%), mainly wheat and barley farming. o Other land uses include dairy, poultry and pig farming.
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Severn Vale o Pasture - 43% o Arable farming for 34% of rural land use o Woodland makes up approximately 10% , mixture of commercial forestry (primarily coniferous), mixed, deciduous and ancient. o Other land uses include wind farms o Mining and quarrying have declined in recent years although soft limestone is extracted along the
Cotswold escarpment.
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The main communities currently at risk of flooding from the Severn are Shrewsbury, Ironbridge, Bridgnorth,
Bewdley, Stourport on Severn, Worcester and Tewkesbury.
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The risk of flooding in these towns is affected by rural land use elsewhere in the catchment and how it is managed. For example, increased run off results wherever vegetation is removed, or when arable fields are left bare. Forests and pasture normally help to reduce flooding.
History of Flood Events
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Documented history of flooding since 1258.
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Heavy rainfall in the Welsh mountains and a large catchment lead to regular flooding of the river
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Size of the catchment means different areas can be affected during different flood events: it is uncommon to have one event affecting the entire catchment, as happened during the 1947 floods.
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Most settlements along the Severn are well adjusted to this flooding, but less so to exceptional events (large magnitude low recurrence interval).
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There were six high profile flood events within the Severn catchment between 1998 and summer 2007:

1) Easter 1998: occurred in the Avon catchment, caused extensive flooding in a number of communities including Leamington, Stratford, Evesham and Worcester.
2) October 1998: largest event in the Severn Uplands region for 30 years. Communities affected included
Shrewsbury, Ironbridge, Bridgnorth, Bewdley and Worcester.
3) Autumn 2000: was the wettest recorded in England and Wales for 270 years. Rainfall was prolonged throughout the catchment from October to December and this compounded runoff and flooding problems.
Communities were affected from Shrewsbury to Gloucester. This was the largest flood on record in the
Severn Vale reach, estimated to be a 2% chance event at Ironbridge and a 1.11% chance event at Upton on
Severn.
4) February 2002: flooding affected communities along the Severn, including Shrewsbury, Bewdley, Upton on
Severn and Kemspey. The event was estimated to be a 20 – 50% chance event at Shrewsbury.
5) February 2004: this was a smaller event than October/November 2000, but caused flooding in areas of
Shrewsbury and Bewdley.
6) June and July 2007: a series of depressions tracked over the UK, bringing very high falls of rainfall and record totals in some areas. In the Severn catchment, record rainfall caused the biggest floods on record in
Worcestershire and Gloucestershire, affecting settlements including Tewskesbury and Gloucester.
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Worcestershire
Population of 9178
Town Centre located on the western bank of the River Severn
It has an 18th Century listed quay (dock), next to twelve listed properties and a Thomas Telford Grade I bridge
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The main commercial area is Load Street just across the Bridge on the West Bank
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The river has a typical range of height from 0.21m – 3.30m (Current 1.11m)
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The highest on record has been 5.56m
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Regularly suffered from floods and this affected many houses and commercial properties
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Approx. 175 properties are at risk from flooding in a 100 year flood event (1%)
The 2000 Floods
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The autumn of 2000 - September to November - was the wettest on record in UK
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Wet weather brought widespread flooding to England and Wales as rivers rose to record levels and burst their banks.
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The worst flooding was in mid-October and then from late October into early November.
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The disruption was compounded by some very strong winds at the end of October, damaging buildings, trees and power lines and cutting road and rail links.
Impacts
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The flooding that occurred across much of England and Wales in the autumn and early winter of 2000 was the most extensive since the snowmelt-generated floods of March 1947.
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In all, 10,000 homes and businesses were flooded at 700 locations.
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Peak flows on five major rivers - the Thames, Trent, Severn, Wharfe and Dee - were the highest for sixty years, and the River Ouse in Yorkshire reached its highest level since the 1600s.
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The October-November 2000 flood was the largest on record in the Severn Vale reach (prior to 2014!).
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It was estimated to be a 2% (1 in 50) annual probability flood at Ironbridge and a 1.11% (around 1 in 90) annual probability flood at Upton on Severn.
Impacts in Bewdley
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Extensively flooded three times in the space of six weeks
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Worst flooding for over 50 years (since 1947).
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More than 140 properties were flooded, many to a depth of over 1.5 metres
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Section of the stone quay wall in Severnside North collapsed.
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Many of the buildings affected in this area are listed.
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Immediate problems include: interrupting business and causing evacuation of residents
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Long term: transport disruption and problems renewing insurance for property owners

Managing the Floods
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After the 2000s flooding, the aim was to construct an effective flood defense for Bewdley, which would also enhance the Georgian town and its 18th Century quay.
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Suggestions for management included: o Afforestation upstream o Embanking areas of the floodplain as emergency flood storage areas o Building weirs (structure across river which changes flow characteristics) o Clearing debris from river channels. o Flood storage reservoir o Tunnel to bypass the town.
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The Environment Agency believed that in the longer term, changing rural land management would be the most environmentally acceptable type of response.
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However, floods have become more frequent and more devastating in Bewdley, with some properties being affected almost every other year.
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Prime Minister (Tony Blair) visited the town and promised urgent action after 2000s flood
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The Environment Agency consulted local people about the best solution to the flooding problem and they produced a strategy to compare the different options.
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Engineering solution was the most cost-effective solution that had the least impact on the environment.
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Innovative demountable aluminum barrier system called 'the invisible defence' was decided on
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Constructed to protect properties in the town. The barrier works with a below-ground wall, which acts as a cut-off to underground flow during flood events.
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Solved conflict of building a 21st Century flood defence system along an 18th Century listed quay, next to twelve listed properties and a Thomas Telford Grade I bridge.
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About 450m of demountable flood defence has been built, with 150m of permanent flood defence wall.
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When a high river flow is forecast the Environment Agency's Flood Warning gives at least 24 hours to bring in and put up the barriers.
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There was the added bonus of a new open space with handrails, steps, ramps and walkways, which conceal the line of the flood defences, but give easy access during flood events.
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The scheme cost £7 million.
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The first part of the system was proved in real flood conditions in February 2004.
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Once the Severnside North section was completed, work started in March 2004 to build the larger
Severnside South section and complete protection of the town.
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Construction work was completed in time for the system to be live tested in November 2005.
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The final parts of the scheme were completed in March 2006
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In the major flooding of July 2007, the barriers were put in place before river levels rose and the town was saved from serious damage.
The Future
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In the future (already is), flooding will be influenced by climate change, changes in land use (for example urban development) and rural land management.
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In the River Severn catchment, climate change will have the greatest impact on flood risk. The following future scenario for climate change was used in the River Severn CFMP:
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20% increase in peak flow in all watercourses. This will increase the probability of large scale flood events.
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Using river models we estimate that by 2100, around 68,000 people and 33,000 properties across the catchment may be at risk from a 1% annual probability river flood.