Leatherhead Flood Group
Meeting on Thursday 20th March 2014
Presentation by Environment Agency
and Thames Water
at Leatherhead Leisure Centre at 19.30 – 21.30
Present (about 50 people):
Chaired by:
Tim Hall (Surrey County Councillor, Leatherhead and Fetcham East)
Councillors:
Bridget Lewis-Carr
MVDC Leatherhead
Raj Haque
MVDC, Fetcham West
Environment Agency:
Sarah Smith
Senior Team Leader for South West London and the Mole
Mark Douch
Flood and Coastal Risk Manager
Tim Norton
Flood Resilience Manager (Hydrologist)
plus others from the Environment Agency
Thames Water:
Claire Collard
Representatives from local businesses, including Mercure (owners of Burford Bridge Hotel),
Fusion Lifestyle (running Leatherhead Leisure Centre), CIB Communications (at
Leatherhead Fetcham Grove)
also Residents from Thorncroft Drive (Leatherhead), Wallis Mews (Leatherhead), Cannon
Grove (Fetcham) and Cannon Way (Fetcham), as well as near the Rye Brook
Summary
 The floods were caused by fluke rainfall, not Gatwick releasing water or the Lower Mole
closing sluice gates.
 The EA are bidding for funding for a modelling project for the Mole. Due to funding
restrictions they are leaving the task of clearing debris to the riverbank owners.
 The EA are requesting everyone to fill in questionnaires to compile a report of the flood
events.
 Residents could set up a Flood Action Group and work towards Community Resilience.
 Thames Water are working on the overwhelmed sewage system. Blocked gullies should be
reported to Surrey County Council.
 It is hoped to organise a meeting discussing Community Resilience, with a speaker from the
National Flood Forum.
Environment Agency Presentation
Mark Douch from the Environment Agency (EA) described the build-up to the floods, with
the 6th December 2013 tidal wave on the East Coast. The unusual weather pattern was caused
by a large temperature differential across North America affecting the course of the Jet
Stream, bringing a succession of low pressure systems causing a long spell of extreme
rainfall.
Between 13th December 2013 and 16th February 2014 the Thames Catchment received 409
mm of rainfall. 56% of annual average rainfall fell in those 66 days, i.e. over half the annual
total rainfall in about 2 months.
This rainfall was of an exceptional nature - the most recorded since records began in 1883.
1.
Fill in questionnaires
Sarah Smith asked businesses and residents to fill in EA questionnaires to help compile what
actually happened – where and when the water came and went, and to what depths,
particularly internally. Photos (less than 10Mb) can be sent to the EA address:
flooddata@environment-agency.gov.uk. An EA report on the River Mole is due in June
2014.
2.
Hydrologist Report
Tim Norton, an expert hydrologist, displayed hydrographs showing river levels and rainfall
for Dorking, Leatherhead and Downside Bridge, Cobham. The Mole Catchment Area was
saturated at the beginning of December:
On 21st/22nd Dec
On 23rd/24th Dec
The 5 day total was
22 mm of rain fell
50-75 mm of rain fell
107 mm (which equalled more than one month’s rain in 5 days)
which was over 400% of the expected average – a “Phenomenal” event.
At Leatherhead 52 mm fell in 18 hours, in places it was above 70 mm.
The 3 Flood Warning codes were explained:
Flood Alert
Flood Warning
Flooding is possible. Be prepared
Flooding is expected. Immediate action required
Severe Flood Warning
Severe flooding. Danger to life
At 8.09 on 24th December a Flood Warning was issued for Leatherhead, and at 14.10 a
Severe Flood Warning was issued.
Tim explained that the EA endeavour to issue flood warnings before the actual flood, but on
24th December they were so extremely busy that they did not manage to keep up with
everything.
3.
Lower Mole Scheme
Sarah Smith explained that the Lower Mole Scheme starts at Cobham, towards Esher, 10
miles from Leatherhead, which is about a 15 metre drop in height. There was no back-up
effect from the Lower Mole Scheme – it did not have an impact on Leatherhead.
4.
Gatwick
Sarah Smith continued: the water released by Gatwick Airport from their balancing ponds
constituted less than 5% of the volume of the River Mole at Gatwick. By the time it reached
Leatherhead, with contributions of water from the tributaries and the heights of Box Hill and
Ranmore, it constituted less than 1% of the volume of water flow. When the River Mole is
high, it is difficult to discharge water into the river, due to the minimal difference in water
levels. Gatwick did nothing different from their normal procedures. They did not empty
their balancing ponds directly into the Mole. All EA’s investigations show there was no
obvious mass discharge into the Mole. It was controlled and held back.
Gatwick contributed £4m to the Upper Mole Scheme.
Ed and Linda Tippelt have visited Gatwick and toured the balancing pond system; their report
is available online:
http://cannongrovefetcham.wordpress.com/gatwick/
Ed clarified the figures: the highest flow at Gatwick was 20 cubic metres per sec (m3/s).
Gatwick released water at 1.9 m3/s, i.e. less than 10%. Leatherhead flow at 6.15 am was 100
m3/s and peaked at 150-160 m3/s (the measuring equipment was under water and failed,
therefore this is an estimate based on other figures). Therefore the Gatwick contribution of
1.9 m3/s was far less than 1% of the 150-160 m3/s. Gatwick cannot discharge directly. The
run-off water is directed to a cleaning plant 3 km away – they have 2 Archimedes Screws
lifting water into settling ponds where sediment settles and surface oil is removed. Once the
water has reached the required quality it can be pumped into the Mole. There are no sluice
gates involved in releasing water.
Nik Cookson understood the pumps at Gatwick failed, but it was suggested these were pumps
at the North Terminal where there were power cuts on 24th December, causing major
disruption. See the McMillan report released on 26th February 2014 at:
https://www.gatwickairport.com/PublicationFiles/business_and_community/all_public_publi
cations/2014/McMillan_report_Feb14.pdf
Sarah added that a lot of Gatwick’s flooding was from surface water from the extreme
rainfall. They pumped water around the site to protect critical infrastructure. EA staff were
on site.
Gatwick representatives did not attend the meeting, but they are willing to offer a site visit for
those interested in seeing how they deal with run-off water. Tim Hall is investigating this
possibility.
5.
Fast Water Disappearance
Someone asked why the water disappeared so quickly. Tim said there is no bathplug on the
river to let the water go when we want it to go. There is no gate to release. Heavy rainfall
caused the rise in water and the delay, as this flowed downstream and accumulated,
contributed to it flowing downstream very quickly. Even while it was still raining the effect
of that rainfall would come downstream hours, maybe days, later.
Tim said there are two ways of measuring the river level: either referring to the sea level or
local river bed level. The peak of the River Mole on 24th December was at 14.00 with 3.6
metres above river bed level. The peak of the rainfall was several hours earlier.
There were further questions about the fast disappearance of the river. The tide/wave began
at Wallis Mews, near Leatherhead Bridge at 8.30 am, by 9.45 am it was 18 inches deep, peak
between 12.00 and 14.00 at 27 inches deep, remaining high until 17.00, still full flow (c. 1824 inches deep) at midnight, but completely disappeared by 4.30 am on 25th December.
Steve Cannon from the Leisure Centre had never seen it go down so fast. Nick Bullen from
Swanworth Farm in Mickleham said it does disappear very quickly.
Mark explained that the speed of dissipation is different for every flood and depends on
ground conditions. More rainfall means 100% run-off. Tarmac and concrete have the same
effect as saturated ground – they cannot absorb any more.
6.
EA website
Linda Tippelt asked about the EA website, which appears to be for the benefit of the EA and
not for the public. We need information which is: easy to understand, accurate, kept up-todate, and user-friendly. She asked for copies of the Powerpoint presentation.
Tim agreed that the online river levels were not clear enough. It is difficult to show the
actual river levels as live; the historic data on recent highest levels is only updated annually.
The Leatherhead measuring station was under water, therefore not possible to get an accurate
reading.
The gauging station positioned downstream from Leatherhead, on the south side between the
two rail bridges, near Mill Lane. It was suggested that another one was needed at Young
Street, upstream from Leatherhead and Thorncroft, partway between the Dorking and
Leatherhead stations, but apparently it would be too costly.
7.
EA Measures
Since it would be 3-5 years before any major projects could be built, Councillor Raj Haque
asked what can be done to prevent severe flooding in the short term?
Tim said the EA is speeding up the process of issuing of Flood Warnings.
Sarah said the bidding for the funding for the Middle Mole Strategic Options Review is being
accelerated from the years 2015/16 to 2014/15 (i.e. Horley – Cobham, including
Leatherhead).
They are improving their flood forecasting methods.
They support community resilience and flood action groups.
The proposed modelling of the River Mole will run scenarios of different types of flooding
and water flows. They have to be careful that they don’t increase flood risk either upstream
or downstream. They have to protect the most people for the limited money available. There
are many stages to the process. They have to build a business case, do a cost-benefit analysis,
get planning permission, finalise and eventually construct the scheme.
There are some temporary measures available. Flood barriers do not protect against ground
water and foul drain water. Later in January more rain fell on saturated ground causing
further floods (on 17th 40-50 mm and 31st 35 mm).
The EA takes isolated rain gauge measurements from particular locations, but cannot
measure the whole area. Every rainfall event is different. It depends on the quantity and
intensity of rainfall, and the ground saturation. If water tables are already high then there is
more chance of run off.
Nik Cookson asked about obstructions in the river – fallen trees and debris. Thorncroft
residents have been waiting 15 months for the Council to repair the eroding riverbank and
access road. Sarah replied that the Government’s reduction in revenue money for clearing,
etc, imposed constraints on what the EA could do. Dredging and dragging often flushed
water through very quickly causing problems downstream.
Mark pointed out that the EA work under “permissive” power – they can only spend money if
it is available, but the ultimate responsibility for any river lies with the landowner (up to the
riverbed centre) who has a duty to allow water to pass through and to keep the watercourse
clear. The EA could serve notice on the landowner to clear the river. The EA monitors
whether “riparian responsibilities” are carried out on Main Rivers. (See the EA’s leaflet
“Living on the Edge” at http://cdn.environment-agency.gov.uk/LIT_7114_c70612.pdf). The
river Mole and Rye Brook are classed as Main Rivers.
Nik had heard the EA were prioritising wildlife above infrastructure.
The EA is now being directed to spend more money on new schemes and less on
maintenance. Wildlife reserves are built to create compensating land for flood defences built
over previous wildlife habitations.
8.
Infrastructure affected
Jackie Cookson mentioned that local businesses were thinking of moving out of the Mole
Valley, as a result of the flooding threat. Tim Hall added that the water supply was
threatened with the Leatherhead pumping station under water, reduced fire brigade capability
with their station flooded, and dodgy power supply with local electricity sub-stations
inundated. He described the situation as “very serious”, implying that there was a good case
for future investment.
Sarah responded that the EA try to reduce risk of flooding to property, homes and businesses.
They look at economic damage and include that in their appraisal to help them build a more
accurate business case. They look at how much central government money can be applied for
and where else the money can be sourced. A larger number of properties are eligible for
more money from government, a smaller number need to get the funding from elsewhere.
In the Mole Catchment between 300-400 properties were flooded. It was difficult to get a
precise figure. Tim Hall said it was about 120 residential properties in Leatherhead. The EA
has written to all affected business and household properties in Leatherhead. They need to
hear from flooded premises to compile an accurate picture. Photos would be very useful and
any less than 10Mb can be sent to the EA address: flooddata@environment-agency.gov.uk.
9.
Community Plan
The local community can help themselves by registering for Flood Warnings (Floodline 0845
988 1188), each household is recommended to make their own personal Flood Plan (see:
http://www.environment-agency.gov.uk/homeandleisure/floods/114720.aspx), and every
Community should make their Flood Plan.
Property should be restored in a resilient manner (see http://www.environmentagency.gov.uk/homeandleisure/floods/31644.aspx and
http://nationalfloodforum.org.uk/property-level-protection-community-tool/ ), using
recommended protection products.
Residents could consider setting up a Flood Action Group with Flood Wardens.
Riverbank owners need to consider their “riparian responsibilities” (See the EA’s leaflet
“Living on the Edge” at http://cdn.environment-agency.gov.uk/LIT_7114_c70612.pdf).
With regard to ground water flooding, homes and cellars are still being pumped out three
months on. Regarding Government guidance, the EA are planning a scheme.
Sarah highlighted the fact that for every household who claim the “Repair and Renew”
government grant, that amount comes out of the central grant, therefore for a major
community-wide scheme, such as the Middle Mole Options, the amount of grant remaining is
correspondingly reduced. Each “Repaired and Renewed” home is then taken out of the
equation, therefore the Middle Mole scheme would be deemed to protect fewer homes, i.e.
have less clout in gaining funding.
NB – It was pointed out that the insurance premium for the new houses in Cannon Way had
risen to 2 ½ times normal level.
Thames Water
Claire Collard from Thames Water gave a brief presentation, given the fact that it was 21.04.
1.
Sewage Flooding
Sutton & East Surrey Water provide the fresh water to the Leatherhead area, and Thames
Water deal with the waste water. Flood water overwhelms the sewage network, which is not
designed to cope with those unprecedented levels of water. This winter there were flooding
issues in areas where there had never been any problems before.
There are 2,600 pumping stations and 900 of them were overwhelmed with huge volumes of
water, but only 4 stations actually failed.
Thames Water had been working really hard 24 hours day and night to keep the network
working. They work together with the Environment Agency and local councils to keep the
system flowing.
There are 15 million Thames Water waste water customers, and 70,000 of them were affected
by sewer flooding. They deployed tankers but with the volumes of water it was nigh on
impossible, it was as if they were trying to pump out the river.
Thames Water needs information on where the failures occurred to build up a survey in order
get funding.
They are checking their sewers to remove any debris and blockages.
Tim Hall said Cannon Way had 2 or 3 instances of sewer flooding, and there was a Fetcham
Residents Association the following week.
2.
Rye Brook
Residents near Rye Brook had received a letter from Thames Water not accepting
responsibility for the sewage flooding in their house. They could not use their toilets in their
home on 24th and 25th December. Claire said that is a complex situation, and they are holding
a special meeting in April to look into that.
3.
Blocked gullies
Residents asked re blocked gullies. Thames Water are responsible for the drain pipework
underground – the actual sewers.
Tim Hall said the road grills (drain entrances/street drainhole covers/highway gullies) were
the responsibility of Surrey County Council, and asked that people report any blocked street
drains on the SCC website.
https://www.surreycc.gov.uk/roads-and-transport/road-maintenance-and-cleaning/problemson-roads-and-highways/report-a-defect-part-ii?defectid=237083
There had been problems with the contractor employed to clear the drains, but now SCC were
using a different company.
Blockages are exacerbated by builders filling up pipes or cutting them, as in Gatesden Road
and Cleeve Road.
The only proper drain maps date from 1990. Some sites are not even on the map.
4.
Flood Forum
Tim is working to set up a formal Flood Forum with representatives from the Council(s) and
the public. He hopes to invite a speaker (maybe from the National Flood Forum) to talk
about Community Resilience.
The meeting ended at 21.20.