Monmouthshire County Council
Development Control Team
New Market Hall
Market Buildings
Priory Street
Monmouth
NP25 3XA
Ein cyf/Our ref: SE/2012/115315/02-L01
Eich cyf/Your ref: DC/2012/00250
Dyddiad/Date:
3 September 2012
FAO: Jo Draper
Annwyl Syr/Madam / Dear Sir/Madam
CHANGE OF USE FROM COMMERCIAL TO RESIDENTIAL AT MAYFIELD,
LLANBADOC, USK, NP15 1SY
Thank you for referring the above planning application, which we received on 27 April
2012. We received further information on 18 July 2012.
We have considered the information submitted in support of the above application i.e.
topographic survey dated 22 June 2012, and data request information provided by the
Environment Agency, dated 17 November 2011. A site specific Flood Consequences
Assessment (FCA) has not been produced for the proposed development. We have
therefore interrogated the information we hold, in order to better understand the risks
and consequences of flooding associated with the proposed development. Based on
this information we advise as follows:
The proposed development site lies entirely within Zone C1, as defined by the
Development Advice Map (DAM) referred to in Technical Advice Note 15: Development
and Flood Risk (TAN15). Our Flood Map information, which is updated on a quarterly
basis, confirms the site to be within the 1% (1 in 100 year) and 0.1% (1 in 1000 year)
annual probability fluvial flood outlines of the River Usk, which is a designated main
river. Our records show that the proposed site has also previously flooded from the
River Usk, during December 1979.
Since this time, flood defences have been constructed in the area. These defences
were built to provide protection against a 1 in 100 year flood. We consider that these
defences are of a good standard and they are inspected annually by the Environment
Agency.
The application proposes a change of use from commercial to residential development.
In flood risk terms, this represents an increase in the vulnerability of the use. Your
Authority should consider whether this is acceptable, we refer you to Section 6 of
TAN15 in this regard.
Asiantaeth yr Amgylchedd Cymru/Environment Agency Wales
Rivers House (St. Mellons Business Park) Fortran Road, St. Mellons, Cardiff, CF3 0EY.
Llinell gwasanaethau cwsmeriaid/Customer services line: 03708 506 506
www.environment-agency.gov.uk
Cont/d..
The topographic survey undertaken by Usk Land Survey indicates that the building
threshold level is 18.031 metres Above Ordnance Datum (AOD). We have assumed this
to be the finished floor level of the building.
The relevant threshold to consider in line with A1.14 and A1.17 of TAN15 is that the
proposed development should be free from flooding during the 1 in 100 year event
including an allowance for climate change for the lifetime of the development. Indicative
tolerable flood conditions for a 1 in 1000 year flood event are given in table A1.15 of
TAN15.
The building is predicted to be flood free during the (defended) 1 in 100 year (including
an allowance for climate change) flood event. Predicted (defended) flood depths to the
building in the 1 in 1000 year flood event are 1.01 metres, with predicted flow velocities
of 0.36 metres/second. The predicted flood depth and velocity is therefore greater than
the indicative tolerable conditions (600mm and 0.1m/s), as set out at A1.15 of TAN15.
It should be noted that the building threshold level of 18.031 metres AOD is generally 1
metre higher than the surrounding land, the risk (depth) to the area surrounding the
building and access routes to and from the property would be therefore be on average 1
metre higher than the depths given for the building.
The freeboard to the top of the flood defences, in the vicinity of the site, ranges from
300mm to 20mm . We recommend that freeboard should be 500mm on soft defences,
such as those in vicinity of site, to provide an adequate safety margin against possible
breach / overtopping scenarios.
Therefore, in view of the inadequate freeboard on the defences, we have considered
the information available concerning the flood risk posed to the site without the
presence of defences, which would give an indication of the potential flood depths that
would be experienced on site in the event of a breach of the flood defences.
Predicted (undefended) flood depths to the building during a 1 in 100 year (with no
allowance for climate change) flood event and a 1 in 1000 year flood event are 20mm
and 940mm respectively. With reference to A1.14 of TAN15, development should be
designed to be flood free during a 1 in 100 year flood event, including an allowance for
climate change. Paragraph A1.15 of TAN15 also advises indicative tolerable depths of
flooding during a 1 in 1000 year extreme flood event, based on the undefended flood
level this threshold would be exceeded by 340mm. We are unable to advise what the
predicted depths of flooding would be during a (undefended) 1 in 100 year (including an
allowance for climate change) flood event, as we do not hold this information.
It should be noted that it is likely that should a breach in the flood defences occur, the
speed of inundation and velocities would be likely to be far in excess of the tolerable
conditions advised within TAN15.
We acknowledge that the proposed development is for the change of use from a
commercial use to residential. Due to the scale and nature of the proposed
development we have no objection, however as outlined above the applicant should be
aware that the proposed development is at risk of flooding should a breach in the flood
defences occur.
As it is for your Authority to determine whether the risks and consequences of flooding
can be managed in accordance with TAN15, we recommend that you consider
consulting other professional advisors on the acceptability of the developer’s proposals,
on matters that we cannot advise you on such as emergency plans, procedures and
Cont/d..
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measures to address structural damage that may result from flooding. Please note, we
do not normally comment on or approve the adequacy of flood emergency response
and procedures accompanying development proposals, as we do not carry out these
roles during a flood. Our involvement during a flood emergency would be limited to
delivering flood warnings to occupants/users.
We recommend that the applicant signs up to our free Floodline Warnings Direct
service. The applicant can sign up to this service through our website or by calling
Floodline on 0845 988 1188 or Typetalk 0845 602 6340.
In areas at risk of flooding, we recommend that consideration be given to the
incorporation of flood resistance/resilience measures into the design and construction of
the development. These could include flood barriers on ground floor doors, windows
and access points, implementation of suitable flood proofing measures to the internal
fabric of the ground floor, and locating electrical sockets/components at a higher level
above possible flood levels.
We also note that a new 2 metre high close board fence is proposed as part of the
application. We recommend that any fencing erected on site should be of an open
nature, to allow the free passage of flood water should a flood event occur.
Should you have any further queries, please contact Claire McCorkindale on 02920
245147.
Yn gywir / Yours faithfully
Gemma Beynon
Swyddog Cynllunio/Planning Liaison Officer
Deialu uniongyrchol/Direct dial 029 20 245297
E-bost uniongyrchol/Direct e-mail gemma.beynon@environment-agency.gov.uk
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