Memorandum submitted by Margaret Bishop
(FL 47)
With particular reference to upper Thames valley
and Gloucestershire, and what steps public authorities should
take to alleviate flooding problems.
SUMMARY
This memorandum looks at factors causing flooding
and what steps should be taken to alleviate it with emphasis on
the containment and management of flood water in traditional flood
plains and water meadows. The Cotswold Water Park contains many
lakes suitable for this use and should be managed in future with
flood alleviation as a major objective. Recognition of the importance
of its role in flood containment, would benefit not just local
towns and villages but the whole of the Thames valley. Flooding
is a frequent regular occurrence in this area and includes rivers
and lakes, rain water run-off and sewage flooding. Local Councils
should be asked to carry out a full flooding survey and compile
information for use by appropriate public bodies. Often the most
cost-effective action would be to lower river banks in places
to allow floodwater to be contained where it does little harm.
The Environment Agency should be instructed to look for situations
where this least costly method could be utilised, and to oppose
any development proposals which would prevent it. Monsoon drains
should be built to carry rain water away rapidly, and drains and
ditches kept open. Housing or commercial development should not
take place until the amount of waste water that the proposals
will produce has been investigated and adequate provision made.
Agriculture should be managed to prevent excessive rain water
run-off, and subsidies could be paid for land to be used as water
meadows. The public should be educated to understand that heavy
rainfall and subsequent flooding may become frequent and regular
occurrences, and to practice water containment and management
as a matter of course.
1. General Causes
This is an area with a shallow ground-water
table, held near the surface. Two main factors are involved in
flooding.
2. How this rainfall is managed.
Because of climate change, excess rainwater
is expected to increase and flooding to occur more frequently.
The causes of heavy rainfall related to climate change are outside
the scope of this memorandum. The issues of water management are
very much matters for the Committee to consider. Heavier than
usual rainfall produces flood water which has to go somewhere
and will naturally flow into the lowest point available. Strategically
important areas such as power plants, water plants, hospitals
etc need protection by flood barriers and defences, but in principle,
we must realise the futility of flood defences which relieve one
place but divert the flow, passing the problem elsewhere, and
increasing difficulties further downstream. We must take steps
to contain floodwater at places where it does least harm, either
in traditional flood plains and water meadows or, if no flood
plain is available, then by creating designated areas where excess
water can be safely stored. These storage areas could possibly
also be a useful resource in times of drought.
2. Cotswold Water Park
Surrounding the upper Thames are large areas
of gravel beds which have been extensively extracted in the past
50 years. This has created the Cotswold Water Park, a 40 sq. mile
area with more lakes and water stretches than the Norfolk Broads.
These are managed primarily for tourism development with the rationale
that economic development from tourism will replace declining
agriculture. Traditionally these gravel areas provided settlement
beds and soakaway areas where excess floodwater could be accommodated,
but water containment is no longer an objective. At present a
consultation exercise is being carried out to determine the future
management of the Cotswold Water Park, and a report has recently
been produced. This report acknowledges that areas with shallow
groundwater held near the surface are often subject to flooding
when heavy rainfall occurs, and mentions the use of lakes as flood
alleviation mechanisms, but there has been no consideration of
this in the management proposals. The gravel beds have served
a vital function as the flood plain for the area for thousands
of years, and the current proposals for development are threatening
this. In view of the increased rainfall expected as a consequence
of climate change, it would seem desirable for as much floodwater
as possible to be retained in the upper Thames valley and Cotswold
Water Park to alleviate flooding in Oxford, Abingdon and towns
further down the Thames. It is imperative that in future the Cotswold
Water Park should be managed with much more recognition of the
importance of its role in flood containment, not just for local
towns and villages but for the whole of the Thames valley.
3. Recent Flooding
The Fairford/Lechlade area of the Eastern section
of the water park was severely affected by the floods of late
July 2007, but this is not an exceptional circumstance. Many houses
in the district have suffered repeated episodes of flooding, often
sewage flooding, and there have been 5 or 6 serious episodes since
the year 2000. In 2006, the water authority, Thames Water Utilities,
invested £3.3 million in a new pumping station at Moor Farm,
Fairford, but though the sewage capacity was greatly increased,
it cannot cope with excess rainwater and has not been sufficient
to stop severe flooding occurring.
In this area there are 3 major contributing
factors, flooding from rivers, rain water run-off and sewage flooding.
The relevant authorities are the Environment Agency, Gloucestershire
County Council and Cotswold District Council, but they will be
overwhelmed with work as most of Gloucestershire has been affected
by flooding to some degree. I suggest that local parish and Town
Councils should be asked to carry out a full survey of where the
flooding happened, where it came from, whether river, run-off
or sewage etc. and compile information to pass on to these bodies
and to Thames Water. This information could then be used to decide
where river banks will need strengthening, where additional drainage
is needed, and the emergency planners could work out where pumping
by the Fire brigade would be most effective. During the July 2007
flooding, it was found that pumping carried out by the Fire Brigade
relieved some areas but made conditions worse for others.
4. River and lake flooding
The Environment Agency is responsible for management
of this type of flooding and should receive appropriate instruction,
technically qualified personnel, and funding to ensure that this
can be adequately carried out. It should be appreciated that often
the most cost-effective action would be to lower river banks in
places to allow floodwater to be contained where it does least
harm. Flood water has to go somewhere and will naturally flow
into the lowest point. If there is a lake, water meadow or flood
plain available at the lowest point with room for millions of
gallons of floodwater and no houses, no people, or domestic problems,
it should be utilised as a first choice solution. The Environment
Agency should be instructed to look for situations where this
least costly method could be utilised, and to oppose any development
proposals which would prevent it.
5. Rain Water Run-off
In countries where flash flooding from heavy
rainfall frequently occurs, it is customary to build monsoon drains
which rapidly carry it away. This system could easily be utilised
in this area, where there are many lakes which could accept surplus
rainwater, or in coastal areas where the drains could run off
into the sea. Again this is a relatively low-cost measure and
the Environment Agency should actively seek situations where it
could be applied. If this is not possible, drains, ditches and
culverts should be opened up and additional capacity provided
to relieve black spots where water collects, and if possible to
channel it away from roads and houses. There will need to be special
provision to deflect excess rainwater from strategically important
areas using both defensive floodwalls and drains or ditches to
divert the flow.
6. Sewage flooding
Thames Water area has many old towns with a
dual system, where rain water is not separated but allowed to
run into the sewer system and be pumped away. This is only adequate
for normal flows and where the system has ample capacity. In many
cases, housing development and the increased use of showers, washing
machines, dishwashers etc, means that there is little spare capacity
and certainly not enough to contain large volumes of excess rain
water, which comes up out of the drains in low-lying areas. In
these cases, flooding in times of heavy rainfall is inevitable,
and this is particularly distressing where the floodwater is combined
with sewage. The solution is to build new systems where sewage
and rainwater are kept completely apart, or to increase the pumping
capacity to deal with many times the normal flow. Both these are
expensive and would require millions of £s of investment,
so are unlikely to happen in the short term, but pressure should
be put on water authorities to use some of their excess profits
to prevent sewage flooding which is not acceptable. In the meantime,
any methods to divert rain water and prevent it entering the sewers
should be employed such as monsoon drains, ditches and culverts
as in 5.
7. Housing development
Post-war housing and commercial development
has proceeded with very little attention to water management.
This together with the increased personal and domestic use of
water has produced a huge increase in waste water, often without
the investment in water systems needed to contain it. Building
development has taken place in low-lying areas, often utilising
thick concrete slab foundations which keep the development dry
but create impermeable areas whose run-off increases flood risk
for others. Planning consent forms do enquire where waste water
will go, but usually 3 words "into existing sewers"
or "into soakaways" is regarded as sufficient. This
must change. I suggest that in future, in the same way that appropriate
energy efficiency calculations must be produced as a condition
of planning consent, water calculations should be called for.
These would take into account the number of bathrooms, toilets,
kitchen appliances etc, work out the probable waste water production
and give details of how and where this would be accommodated.
If additional provision needed to be made, this would have to
be organised before development could proceed, and the cost of
the necessary investment would be partly paid by the developer.
The futile argument about the desirability of building on flood
plains would be ended. In circumstances where this could go ahead
with proper provision at reasonable cost then the development
would proceed, if not then the development would not take place.
I suggest also that just as building is not allowed in front of
the building line, there should be limits on building at a height
above the ground level of surrounding buildings. In many countries,
houses in flood-prone areas are built with low level storage and
garages, or wet basements with laundry room and wet activity areas,
or on stilts. Ingenious design solutions could be found which
would enable houses to be built without decreasing the water holding
capacity at ground level which increases the probability of neighbouring
houses being flooded.
8. Agriculture
Traditionally the period after harvest with
short day-length when crops are not growing was used for hedging
and ditching activities. These have declined in recent years and,
to protect wild life, farmers have been discouraged or prevented
from digging out ditches. Farmers should be encouraged to keep
all ditches running freely, and be required to prevent excessive
rain water run-off onto neighbouring property. At present, subsidies
are paid for set-aside agricultural land, and no attention is
paid to water management. Farmers could be encouraged by subsidies
to harvest water and allow fields to be used as water meadows,
an old agricultural practice which was considered in suitable
areas to re-vitalise the land and produce earlier grass for stock
feeding.
9. Public Information
The Environment Agency produces good information
leaflets about what to do when flooding is expected, or after
a flood, but these are not widely known. Press releases could
disseminate this information more widely. The public should be
encouraged to be sparing in their use of water in times of flood,
just as in times of drought, since this minimises the waste water
entering the system, and therefore the total amount which has
to be accommodated. Motorists should be warned not to go past
"road closed" signs, not to enter flood water unless
they know the depth is manageable (abandoned cars block the road
for larger vehicles), and to proceed very slowly so as to minimise
the waves and splashing onto other vehicles and property.
We must learn to accept that heavy rainfall
and subsequent flooding may be frequent and regular occurrences,
and practice water containment and management as a matter of course.
There will be need for some high technology, high cost solutions,
but a great deal can be achieved by common sense and traditional
methods.
M Bishop (Mrs)
August 2007
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