Dredging abandoned, saving Marlow sacrificing Bisham

Dear Sir or Madam,

There has been no regular dredging of the Thames near Marlow since
1996.

Can you please confirm that this failure to dredge has not
increased the risk of flooding in Marlow and Bisham? It seems to be
basic physics that if an engineered watercourse is allowed to
become shallow, it will have less water-carrying capacity and will
over-top its banks with less volume flow. Can you please provide me
with the scientific justification for your response?

There is said to be a proposed system of bunds on the Marlow side
of the Thames to protect areas of Marlow built in the flood plain.
Can you please provide me with details of the proposed defence
system and confirm that these proposed defences will not exacerbate
the risk of flooding in Bisham? Can you please provide me with the
engineering justification for your response?

Thank you in anticipation.

Yours faithfully,

Mike Post

Dear Enquiries, Unit,

Thank you for your initial response. I look forward to hearing from
you.

Yours sincerely,

Mike Post

Dear Ms Edwards

Thank you very much for your very informative reply to my FOI
request regarding dredging of the Thames near Marlow and the Marlow
Flood Alleviation Scheme.

Whilst the information you have provided is very informative, you
have not responded to my request for confirmation that the failure
to dredge since 1996 has not increased the risk of flooding in
Marlow and Bisham. I also requested the scientific justification
for your response. There is anecdotal evidence that the reach of
the Thames immediately downstream of Marlow weir is considerably
shallower than in the past. It is obvious that a shallower river
can carry less volume flow of water before it floods. Can you
please confirm whether or not the Environment Agency has records of
the river bed level for this particular short reach of the Thames.

You may be aware that our MP, Theresa May, is to make a visit of
inspection later this month.

I note from the five-page Halcrow Dredging Summary, dated July
2009, that dredging has been undertaken near Marlow since the late
1940s “to maintain a navigable channel and to manage flood risk by
maintaining the channel flow capacity”. I further understand that
the Thames in Marlow has been designated, at least in draft, as a
‘heavily modified watercourse’. Perhaps you can please confirm that
this is the case?

With regard to the Marlow Flood Alleviation Scheme, it seems
intuitive that groundwater from the Marlow side of the river which
is pumped back into the river, rather than being allowed to
disperse in the floodplain on the Marlow side, must have an effect
on the level of water on the Bisham side of the river and a
consequential detrimental effect on properties in Bisham. I should
be grateful for the engineering justification (for which I asked in
my enquiry) for this not being the case. I should also be grateful
for information on the assumptions which have been fed into your
models, which I assume are digital rather than physical.

From a purely personal perspective, perhaps the most interesting
document is the Halcrow map, reference WNGLDC-913 “Flood Extent
After Marlow Flood Alleviation Scheme”, which clearly shows that
our family home, Meadow House, is above the 1 in 100 year river
flooding both before and after the flood alleviation scheme. I hope
that the CD of my photographs of the 2003 flood which I gave to the
Agency in 2003 were helpful in constructing this map.

Finally, I should also be grateful for your email address which was
transmitted in your reply as a series of ‘x’s and also the email
address of Doug Hill.

Thank you in anticipation.

Yours sincerely

Mike Post

Dear Edwards, Marie,

Can you please confirm that you have received and are addressing my
reply to you dated 10 September 2009. I am a little confused by the
system.

Many thanks in anticipation

Yours sincerely,

Mike Post

Dear Edwards, Marie,

Further to my FOI request of 14 August 2009 and my follow up dated
10 September 2009, I should be grateful if you would let me know
when I can expect a response.

Yours sincerely,

Mike Post

Dear Edwards, Marie,

Thank you for the reply. Perhaps you could try my google mail
account which has large capacity for attachments. The address is
[email address]

Regards

Yours sincerely,

Mike Post

Dear Edwards, Marie,

Can you please confirm that you have received my alternative email
address, [email address] ?

Many thanks.

Yours sincerely,

Mike Post

Dear Edwards, Marie,

Thank you for the update. The google mail account has huge
capacity.

Yours sincerely,

Mike Post

Dear Edwards, Marie,

Thank you for sending the information to my googlemail account
which I have now received. I shall study it before coming back to
you in due course. I shall also send an acknowledgement via email
to Doug Hill.

Yours sincerely,

Mike Post

Dear Marie Edwards,

Thank you for the information on river surveys of the Marlow to
Cookham reach which has arrived by my googlemail account. I should
be grateful if you would try resending the information on the Flood
Risk Assessment since all the appendices were blank.

You will recall that I asked: “Can you please confirm that this
failure to dredge has not
increased the risk of flooding in Marlow and Bisham? It seems to be
basic physics that if an engineered watercourse is allowed to
become shallow, it will have less water-carrying capacity and will
over-top its banks with less volume flow. Can you please provide me
with the scientific justification for your response?

So that comparisons can be made, can you please provide me with
similar surveys which predate 1995? I am particularly interested in
the large area of river below Marlow weir which is white on the
survey maps which seems to indicate that approximately 58% of the
river adjacent to the property ‘Marlow Meadows’ may be silted up.

Yours faithfully,

Mike Post

Dear Edwards, Marie,

As requested on my google mail account, here is the message that I
sent via the whatdotheyknow website.

Dear Marie Edwards,

Thank you for the information on river surveys of the Marlow to
Cookham reach which has arrived by my googlemail account. I should
be grateful if you would try resending the information on the Flood
Risk Assessment since all the appendices were blank.

You will recall that I asked: “Can you please confirm that this
failure to dredge has not
increased the risk of flooding in Marlow and Bisham? It seems to be
basic physics that if an engineered watercourse is allowed to
become shallow, it will have less water-carrying capacity and will
over-top its banks with less volume flow. Can you please provide me
with the scientific justification for your response?

So that comparisons can be made, can you please provide me with
similar surveys which predate 1995? I am particularly interested in
the large area of river below Marlow weir which is white on the
survey maps which seems to indicate that approximately 58% of the
river adjacent to the property ‘Marlow Meadows’ may be silted up.

Yours sincerely,

Mike Post

Dear Edwards, Marie,

Please find below the email that I have just sent to Doug Hill.

Dear Doug

I have finally managed to find time to look at the dredging and
survey information that you kindly sent me about the Cookham Reach
from Marlow to Cookham on the Thames.

It is striking that between March 2003 and April 2008 an estimated
185,252 cubic metres of silt were scoured from the Reach. It is
also extremely striking that the overwhelmingly orange shade of the
river indicates that virtually the whole length of the Cookham
Reach river bed was between 0.25 metres and 0.5 metres higher in
March 2003 than it was in April 2008. In other words, the whole
length of the reach was predominantly between 0.25 metres and 0.5
metres shallower in 2003 than it was in 2008.

March 2003, the date of the 2003 survey, was shortly after the
flood in January that year which was devastating to several
properties in Quarry Wood Road, Bisham including the Compleat
Angler hotel. The whole of the Cookham Reach was approximately 0.25
metres to 0.5 metres shallower in early 2003 than it was in 2008.
It cannot but be suspected that the Environment Agency’s decision
to abandon routine dredging during the eighties and nineties
resulted in the whole length of Cookham Reach becoming shallower
than desirable. If it is shallower, the river will overflow its
banks more quickly, than when it is deeper, like a gutter with its
bottom full of rubbish. It appears that by early 2003 the
traditional capacity of the whole length of this Reach had been
substantially reduced.

Whilst it is reassuring to know that, thanks to self-scouring, the
river has (or had in 2008) substantially increased capacity since
the 2003 floods, it seems that there is prima facie evidence in the
two July 2008 ‘Cookham Reach Erosion and Deposition Charts’ that
the Environment Agency’s failure to take measures to maintain the
depth of the Cookham Reach up to 2003 may have exacerbated the
flooding along that stretch of the Thames in 2003.

We need to know the reason for the apparent self-scouring of the
river since 2003. We also need to receive reassurance from the
Environment Agency that the river will be regularly surveyed to
ensure that the bed-level does not rise again. If the Reach does
again become shallow, we would expect suitable, traditional,
good-housekeeping measures, such as dredging, to be undertaken, to
restore the capacity of the river to its pre-Environment Agency
state.

Thank you for your help. As you suggested, I shall send this email
to you and copy it onto the whatdotheyknow website.

Kind regards

Mike Post

Yours sincerely,

Mike Post

Dear Edwards, Marie,

Here, for the public record, is the exchange of emails between Doug
Hill and me.

Hi Doug

Thank you for your letter.

With regard to meeting up, Jean Garon, who lives on the Cookham
Reach just below Marlow weir is abroad at the moment. Perhaps when
she returns, and the weather is more clement, we could arrange to
meet. As a layman I am struggling with the concept that the river
bed can be higher but the river is not shallower for the same water
level.

Regards

Mike Post

Dear Mr Post

Dredging on the Thames

Thank you for your email dated 8 December 2009.

I recognise your concerns with regards to the difference in bed
levels from March 2003 and April 2008, however, from the survey
information available the river does not appear to have got any
shallower between 1999 and 2003. This shows that the end of the
dredging programme in the mid 1990’s did not lead to a rise in
river bed levels prior to the flooding in 2003. Our surveys from
2003 to 2008 show that the river has naturally self-scoured and has
lowered it’s bed level compared to 1999 and 2003.

The recorded changes in bed volume and levels depends on the timing
of the surveys in relation to periods of high and low river flow.
Net changes in bed volumes of up to around 100,000 m3 have been
recorded between surveys in some sub-reaches. The recorded annual
average net volume changes are typically in the range 10,000 m3 to
20,000 m3 per year in each sub-reach although larger transient
variations may be masked for the longer survey intervals.

At present we are carrying out yearly hydrographic surveys on Old
Windsor, Bell Weir and Penton Hook reaches, the 3 reaches for which
we have more frequent historical data. We will be comparing bed
level data with flow measurements to try to understand their
connection better.

We shall continue to monitor all reaches frequently using
hydrographic data in order to consider the need to dredge. We plan
to survey the Marlow to Cookham reach again in 2012/13. It is
important that any dredging strategy is well-informed, and takes
into account the natural sedimentation and scouring regime of the
river, as well as the costs and practicality of dredging and the
disposal of the waste.

If you would like to any further information please contact Doug
Hill, Thames, Wey and Loddon Asset System Management Team, Flood
Risk Management on 01276 454513 or by e-mail [email address].

Yours sincerely

Doug Hill
Team Leader - Asset System Management
Thames, Wey and Loddon

-----Original Message-----
From: Hill, Doug [mailto:[email address]]
Sent: 18 January 2010 12:03
To: Mike Post
Cc: Attfield, Kerry
Subject: RE: Marlow Bisham FOI

Mike,

Sorry for the delay in getting this response to you. I would still
like to meet up to go through the report and any issues in a bit
more detail and am happy to come over to Bisham. I'd prefer it if
we kept numbers to a minimum so that the conversation can be a bit
more focused. If you could let me know your availability I can set
some time aside.

Many thanks
Doug

Doug Hill
Team Leader - Asset Systems Management
Thames Region - South East Area
01276 454513

From: Mike Post [mailto:[email address]]
Sent: 29 December 2009 10:20
To: Hill, Doug
Cc: Edwards, Marie; Attfield, Kerry; Croucher, Graham
Subject: RE: Marlow Bisham FOI
Dear Doug

Thank you for the email. Can I respond fully some time later in
January. I think that some of the Quarry Wood Road residents may
wish to be involved and I will be away until mid-January.

Compliments of the season.

Regards

Mike Post

-----Original Message-----
From: Hill, Doug [mailto:[email address]]
Sent: 09 December 2009 09:39
To: Mike Post
Cc: Edwards, Marie; Attfield, Kerry; Croucher, Graham
Subject: RE: Marlow Bisham FOI

Mike,

Thanks for the email, I'll make sure it gets registered here as a
FOI request and managed appropriately. I'll get a response to you
as soon as possible but it may be worth us sitting down and
discussing the issue face to face. I can then produce a response
that can be put on the web site. I would also like to see the sand
bar that has built up near to the Lock Island.

Thanks,
Doug

Doug Hill
Team Leader - Asset System Management
Thames Region - South East Area
01276 454513

Yours sincerely,

Mike Post

Dear Edwards, Marie,

The whole purpose of this website is that the exchanges should be
public - there are other riparian owners interested. I should
therefore be grateful if you would up load any future emails from
the EA on to this site.

Thank you in anticipation.

Yours sincerely,

Mike Post