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Flooding mitigation at Rose Gardens
The application for the construction of small commercial units to provide small business opportunity and provide employment in wales.
Accordingly, NRW allow 75 years for applications of less vulnerable usage. There is differing opinions regarding the life span of a building though where it has been established for dwelling being 100 years
[see APP/A6835/A/12/2169673]
Information is available from BCIS Construction, BS 7543 also gives guidance on the durability, design life and predicted service life of buildings, constructed assets and their parts.
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Extracted from BS 7543
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As you can see from the above chart an industrial building would have a medium design life of 30 years should the building reach 50 years, then we would be below the NRW 75 years recommendation, this would meet the requirements of TAN 15.
The site lies on the edge of the flood map approximately safe refuge would be minutes away and with the application being less vulnerable and early warning being in place there is no danger to life as the topographical levels rase to 33m some 110m from the site.
In relation to flooding elsewhere we would not increase the existing site levels, in addition as the units are commercial/industrial there would be not requirement for heating hence the buildings would not be are tight this would provide leakage for any floor waters preventing a volume of water being forced elsewhere
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FLOODING ADDENDUM POINTS
In relation to point ‘iii’ of the FRA, the site comprises an existing garden and has not previously been
developed. As such, the development site does not meet the definition of previously developed land.
A recent High Court decision has held the definition of “previously developed land” A recent High Court decision has held that the definition of “previously developed land” (also known as Brownfield land) within the National Planning Policy Framework (NPPF) excludes private residential gardens in “built-up” areas only, but not private residential gardens elsewhere.
The Attached FRA in support of the application states the levels are worst case there the minimum ground floor level meets TAN15 and the of the new properties will have voids below to ensure that flood storage as per recommended in the Former Police Station, Prestatyn planning appeal mentioned below
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The NRW ‘Historic Flood Map’, included in Appendix C, shows no records of historical flooding at or near to the site. The PFRA contains no records of fluvial flooding at or near to the site.
As shown on the LiDAR extract (Appendix B), Gutter Fawr is situated at or below 4m AOD and is below site levels (site levels are typically above 4.5m AOD). Any potential flooding from Gutter Fawr would likely be conveyed to and stored within lower lying land north-east of the site, where levels generally vary from 4.1m AOD – 4.3m AOD.
- It can be concluded that the risk of fluvial flooding to the site is low.
Tidal flooding could occur from overtopping of the defences during an extreme tidal event. Flooding could also occur from a breach of the flood defences. The NRW ‘Historic Flood Map’ (Appendix C) shows no record of historical tidal flooding affecting the site.
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The site is defended by the Talacre Embankment which has a crest level of 6.46m AOD. A comparison of extreme sea levels and flood defences shows that no overtopping of the Talacre Embankment is estimated during all present-day events up to and including the 0.5% AEP event. Minimal overtopping (40mm) is estimated during the present day 0.1% AEP event.
The ‘Defended Scenario Flood Extents Outer Dee and Talacre’ map (taken from the ‘Tidal Dee Flood Mapping – JBA December 2012), included in Appendix C, shows that the site is flood free during all defended events up to and including the 0.5% AEP event with climate change up to the year 2086.
Undefended Event
There is no modelled breach information available for the River Dee in this location. Therefore, an assessment of a tidal breach has been made through comparison of undefended tidal flood levels and site levels. This is considered as a ‘worst case’ approach.
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The NRW ‘Flood Risk from Surface Water’ map (Appendix C) shows that the site is at very low risk of surface water flooding, meaning it has a less than 0.1% annual probability of flooding.
The PFRA contains no records of surface water flooding at the site. It can be concluded that the risk of surface water flooding is low.
The Dŵr Cymru Welsh Water (DCWW) sewer records show that there is a 300mm public foul sewer adjacent to the north-eastern boundary of the site flowing south-east.
Any potential flooding arising from the 300mm public foul sewer adjacent to the north-eastern boundary of the site would be intercepted by Gutter Fawr and would not affect the site.
The PFRA contains no records of sewer flooding at or near to the site. It can be concluded that the risk of sewer flooding is low.
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There are no records of groundwater flooding at or near to the site. The PFRA does not indicate groundwater flooding as a concern within Flintshire. It can therefore be concluded that the risk of groundwater flooding is low.
Summary of Potential Flooding
It can be concluded that tidal flooding is the main potential source of flood risk at this site. Potential significant flood depths are estimated at the site when accounting for a defence breach (undefended event) and climate change allowance.
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Should the Planning Authority be minded permitting the development we will implement the following The developer will install flood resilience and resistance measures to minimise the consequences of a flood event.
The following flood resilience and resistance measures should be installed to minimise the impact of flooding:
Keeping finished floor levels as per existing site in order to prevent flooding elsewhere
Use robust construction materials (engineering bricks);
Raise electronic control units and sockets as high as practical;
A Roberts’s dipArch [tech] Cert Construction Law [dist]
A Roberts
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