Your Ref: Planning Application W/13/01789/OU
Our Ref: Drainage Objection 6/11/14 SDW
Emma Worley
Principal Planning Officer (South)
Wychavon District Council
Civic Centre
Queen Elizabeth Drive
Pershore
Worcestershire
WR10 1PT
Flax Willows
Fallon Lane
Bretforton
Evesham
Worcestershire
WR11 7GZ
6th November 2014
Dear Emma,
Planning Application W/13/01789/OU – Comments on drainage ditch proposal
Your letter of 24th October invites comments on additional documents relating to the above
application and a proposed drainage ditch. In fact Version 7 of the Flood Risk
Assessment (FRA) shows only very minor changes from the previously published version
of the FRA which has now been removed from the Web Site. The other ‘additional’
information comprises a drawing of the showing the ditch structure and a new ‘drainage
strategy’ drawing showing a ‘French Drain’ connecting the storage tanks to the drainage
ditch. My comments below relate to all the published information on the ditch proposal,
the indicative drainage strategy and the relevant context.
1. Quality of the revised FRA (Version 7) and credibility of its authors.
This is the seventh attempt of the authors to get this document right. This was and
still is a poor quality document riddled with errors and misleading statements. It
conveniently ignores important relevant information (e.g. the fact that WCC has
confirmed EA maps as being wrong) and the quality control is poor.
[For example: in V5 the Contents page is numbered incorrectly, para. 1.11 refers to Section 6 covering
Surface Water Management when it actually covers Foul Water; in the latest version (V7) on page 13
paras. 2.1.2 and 2.1.3 are incorrectly numbered; etc. etc. etc.]
The severe flooding of the site in 2007 is completely ignored and the equally severe
flooding of more than 50% of the site in 2012/13 is referred to in para. 4.2.7 as
‘localized ponding …to parts of the site’. Crucially the report does acknowledge that
‘the causes of the flooding are not known’, but the rest of the report conveniently
ignores the fact that the flooding mechanisms on this site are not fully understood.
Despite the well known facts that the site floods, with groundwater levels at zero, the
report initially stated a groundwater level of 1.7m (based on dry period measurements)
and suggested soakaways as a solution (see FRA para. 1.16.4). This is an example of
conveniently ignoring reality and proposing something now accepted as unworkable.
In the light of the above and the comments below:
i.
The competence and credibility of the organisation who have taken seven
attempts to get the FRA correct, and still failed, needs to be seriously questioned.
ii.
It makes it difficult to trust any data, information and conclusions in the report.
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2. Extension of the site into Flood Zone 3 requires Sequential Test and
Exception Test.
The addition of the drainage ditch land in the site means that the site now extends into
and includes land clearly rated as Flood Zone 3. In fact the drainage ditch changes
topology and breaches a natural barrier between the site and a natural watercourse
and land rated as at serious risk of flooding (Flood Zone 3). This requires proper
Sequential and Exception Test. If any further houses are needed in Bretforton, which
I strongly dispute, other land which is not subject to such regular flooding, and would
not require complex, risky water management solutions, is available. The very same
point is made towards the end of Tony Jones report (dated 14th May 2014) in which he
concludes the application should be refused because of the many residual risks
associated with the flooding of the site.
The applicant has failed to recognize the need for a Sequential and Exception Test.
3. Drainage strategy and increased flood risks from breaching natural
protection from Flood Zone 3 land
The revised Flood Risk Assessment (from the same organisation who got it wrong last
time) is still WRONG and deeply flawed.
The report admits (para. 4.2.7) that the causes of flooding on the site are not known but
subsequently completely ignores this fact in drawing up their drainage scheme.
Worcestershire County Council (WCC) have confirmed that the site regularly floods,
that current Environment Agency (EA) surface water flood maps are WRONG, but that
formal investigation of the causes of the flooding is not justified on resource grounds. It
is accepted that the flooding results from a combination of rising ground water (from the
aquifer running under the site) and surface water, but the precise mechanisms and
causes will remain unknown (see separate correspondence published on web site).
The so called drainage strategy seems to ignore the groundwater issues. It has
already been demonstrated (and is recorded in the FRA) that groundwater levels rise
to zero in flood conditions and this alone would swamp the storage tanks, which have
been grossly undersized anyway (see below).
Drainage Ditch would be ineffective and in fact add to the flooding risk
The FRA ignores the fact that the watercourse into which the drainage ditch is
supposed to discharge is in an area rated as Flood Zone 3 and will itself almost
certainly be flooded when needed. Rather than reduce risk to the proposed
development and surrounding property the drainage ditch significantly increases risk
because:
i.
Environment Agency data shows that the watercourse north of the site, which
is in Flood Zone 3, has flooded to over 39m even before worst case and
climate change factors are included. In effect the flooding is higher than the
site and Fallon Lane properties.
ii.
The drainage ditch would breach the natural barrier/dam of the higher land
along the hedgerow to the north of the site which protects the site from the
higher risk Flood Zone 3 land which emanates from the watercourse/brook.
iii.
As a result of the above the ditch would allow flood water from the watercourse
to flow into and across the site and Fallon Lane and to reach properties in
Fallon Lane. [Clearly shown by analysis of topological data].
iv.
When the ditch needs to discharge exceedence flows this will not be possible
because the watercourse will almost certainly have flooded.
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Thus, the net result of the ditch would be to be to increase the risk of flooding
on the site, Fallon Lane and properties on Fallon Lane.
Storage Tanks are grossly undersized and will become irrelevant in flood conditions
The FRA almost completely ignores the groundwater issues. The tanks have been
sized to deal with surface run-off only and any contribution from rising groundwater
from the aquifer under the site has been ignored. Additionally as pointed out above
water will flow onto the site through the breach in the natural barrier to the north of the
site created by the proposed drainage ditch.
A simple calculation of the amount of water which would have to be dealt with can be
made from previous instances of flooding at the site. Making conservative assumptions:
Site area:
25,000 sq m
More than half the site has flooded on previous occasions but let us assume 50%, so
Flooded area:
12,500 sq m
Assuming a conservative 0.2 m average flood depth gives:
Water Volume:
2,500 cubic m
Ignore worst case storm conditions but add 30% for climate change:
Adjusted water volume: 3,250 cubic m or 3,250,000 litres
The tanks have been sized at just 830 cubic m, grossly inadequate. It is easy to see
how the tanks would be rapidly overwhelmed by a combination of groundwater and
surface water run-off. Then add the fluvial flood water flowing into the site from the
brook as noted above and the tanks become irrelevant in terms of site drainage. A
Qbar rate far in excess of the quoted 8.3 l/s would be required.
A Drainage Strategy with no credibility – the triple whammy flood risk
Severn Trent has no statutory obligation to accept groundwater into public sewers.
The FRA conveniently ignores rising groundwater as a contributor to filling the tanks.
Wormald Burrows would therefore appear to have misled Severn Trent in what
they have been asked to do.
Add to all of the above the fact that the detailed interaction between the three types of
flooding on the site (fluvial from the brook, pluvial from rainfall and groundwater from
the underground aquifer) is uncertain and not understood, and we have a drainage
strategy without any credibility.
A further factor of uncertainty which has not been considered is the impact of the
Crest Nicholson (CN) development at the rear of Fallon Lane on groundwater flow
under the current site. In all probability groundwater flow will be impeded.
In storm conditions we could therefore be facing increased flood risk from the
triple whammy of storm level rainfall, of rising groundwater (partially blocked by
the CN development) and of water from the flooded watercourse pouring into
the site through the natural barrier breached by the drainage ditch.
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4. Maintenance of the ‘ditch’ and associated infrastructure.
Assuming for one moment that the proposed drainage ditch were of some value in a
drainage strategy, it is unrealistic to expect that the ditch and associated complex
infrastructure would be maintained effectively to 100% for 100% if the time, in
perpetuity. It is not clear who would carry this responsibility but presumably residents
on the completed development would pay for it and control the maintenance
arrangements. This would mean other residents in Bretforton (say in Fallon Lane)
would be dependant on these residents for managing their flood risk, without any
control or means of redress.
This is totally unacceptable.
5. Increased Flood Risk for Fallon Lane properties which will be trapped in
a ‘flood valley’ by this development.
The FRA confirms that land levels on the site will be raised to 39m. This level is
above some sections of Fallon Lane and certainly higher than parts of Fallon Lane
properties. The CN development at the rear of Fallon Lane has also raised land
levels above 39m and thus Fallon Lane and its properties would end up in a valley.
Furthermore as pointed out above the proposed drainage ditch will open up a path for
floodwater from the brook to the north to flow into the site and thus onto and across
Fallon Lane.
The inevitable conclusion is that this development would increase flood risk for
Fallon Lane properties.
WDC has been asked for a categorical assurance that, if approved, this development
would not increase flood risk for any properties in any circumstances whatsoever.
They have declined to give such an assurance.
The Flood and Water Management Act 2010 requires authorities to avoid development on
land subject to flood risks and on no account approve development which could increase
flood risks for existing residents/property. In the light of the above, there cannot be any
certainty that the proposed drainage strategy will work, or that there will not be an increase
in flood risks.
WCC have confirmed that the EA surface water flood maps for this site are wrong, that this
site regularly floods and that the true causes and mechanisms of the flooding will not be
investigated.
I am not aware that the applicant (Kler Group) has taken any notice whatsoever of these
facts or acknowledged the accepted inaccuracy of the EA maps. In simple terms, if the
causes of the flooding are not known it is not possible to design a system to deal with it
with any confidence at all. On these grounds alone there should not be any
development on this site.
Please draw attention to all the points in this letter to member of the Planning Committee
when this application comes before them.
Please post this letter on the web site.
Kind regards,
Stuart Ward.
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