FLOOD DEFENCES ALONG THE R. MEDWAY AROUND

TONBRIDGE.

The ProblemThe 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.

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.

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.

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.

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

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

Promenade & Flood Wall

• This is the floodwall further along the river.

• Here it has been incorporated into a riverside walk & made a local attraction.

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.

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.

Flood Proof Building

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

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.

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.

SUMMARY

Tonbridge is defended against flooding in a variety of ways.

1. Engineering works (walls, barriers, gabions etc.)

2. Land use planning (zoning, washlands.)

3. Planning & preparedness (flood proofing.)

4. Defences are both upstream & in the town.

For a Video of the Defences Click Here