FLOOD DEFENCES ALONG THE R. MEDWAY AROUND TONBRIDGE.

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FLOOD DEFENCES ALONG THE R. MEDWAY AROUND
TONBRIDGE.
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The Problem

• The R. Medway flows through Tonbridge, before
  joining the R. Thames at Rochester.
• The river is prone to flooding due to
• Clay geology
• Mixed land use - farmland, parkland, urban etc.
• The last major flood was in Sept. 1968 when 97mm
  of rain fell in 16hrs, this caused the river to
  exceed its bankfull capacity by 2.5 times.
• The flood did much damage to the town centre
  caused 1.5 million of damage
• In October 2000 Tonbridge was mainly unaffected
  by the worst flooding in the surrounding area for
  200 years.

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Leigh Flood Barrier

• Constructed in 1970, after the 1968 flood.
• Constructed 4km upstream from Tonbridge at a cost
  of 3.6 million.
• This is an in-line storage scheme is designed
  to store over 5.5m million M3 of water in a huge
  temporary lake.

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Leigh Flood Barrier 2

• The water is held back behind huge embankments
  then is released when the flood danger has
  passed.
• The temporary lake floods low grade farmland
  protects the higher value urban area of Tonbridge.

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Leigh Flood Barrier 3

• Downstream of the barrier the river has been
  artificially straightened.
• This allows the rapid release of water from the
  barrier when the flood risk is over.
• This straightening has cut of the Shallows
  meander.

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Flood Wall

• Most of the way through the town there is a 1 m
  high wall.
• This holds back water protects the town.
• This wall was rebuilt after the floods of Oct
  2000, when the wall protected the town from major
  flooding

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Gabion Boxes

• Below the flood wall on the outside of the
  meanders are these gabion boxes.
• These wire boxes are full of stones are
  designed to protect the river bank from erosion.
• Note the landscaping on top of the boxes

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Promenade Flood Wall

• This is the floodwall further along the river.
• Here it has been incorporated into a riverside
  walk made a local attraction.

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Revetments

• Here the river banks are protected by revetments.
• These prevent scouring erosion of the banks
  around the bridge.
• Note again the landscaping the riverside
  promenade.

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Flood Proof Buildings

• Many of the office blocks built by the river are
  flood proofed.
• The import land use in these buildings starts on
  the first floor.
• The ground floor is a car park, which can be
  emptied at time of flood.

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Flood Proof Building

• This is a flood proofed shed, built on stilts!

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Washlands

• In the town, by the river, are the Castle
  grounds.
• These are natural flat areas which the river
  floods during times of high flow.
• By flooding this area the urban areas are saved
  from the flood water.

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Land Use Zoning

• The area by the river is not built up.
• This area is left with permeable surfaces to aid
  infiltration.
• If this area is flooded then little damage will
  be done.

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SUMMARY

• Tonbridge is defended against flooding in a
  variety of ways.
• Engineering works (walls, barriers, gabions etc.)
• Land use planning (zoning, washlands.)
• Planning preparedness (flood proofing.)
• Defences are both upstream in the town.
• For a Video of the Defences Click Here