Transcript FLOOD DEFENCES ALONG THE R. MEDWAY AROUD …

FLOOD DEFENCES ALONG
THE R. MEDWAY AROUND
TONBRIDGE.
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.
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