Flood Consequences Assessment for a Replacement Dwelling at Melvilla Fourth Avenue Talacre Flintshire

Flood Consequences Assessment for a Replacement Dwelling At Melvilla Fourth Avenue Talacre Flintshire Revisions are shown in Red Text The proposed development 1. The site is within the village of Talacre, Flintshire 2. The proposal is for the construction of one single replacement detached dwelling with no bedrooms on the ground floor. The site is mainly utilised at present as a garden. 3. The site is within Zone C1 as defined by the Development Advice Map (DAM) which accompanies TAN15. Zone C1 is described as an area of the floodplain which is developed and served by significant infrastructure including flood defences. This is based on the Environment Agency’s Extreme Flood Outline of 0.1% (1 in 1000) probability of occurrence within any one year. Siting within this Zone requires a Flood Consequences Assessment to be carried out to assist the Planning Authority in establishing if the consequences of flooding in respect of the development are acceptable. 4. Existing Ordnance Survey Mapping indicates that the road level in the vicinity of the site (Main Street) is 4.80m AOD. Topographical survey levels within the site indicate existing levels varying from 4.80m to 4.90 AOD. Source and mechanism of flooding 5. The river Dee at its nearest point to the site is some 250m to the North, the river being tidal at this location in its lower estuarine form. 6. Surface water runoff from Main Street is unlikely to affect the site, as the proposed site levels will be higher than that of Main Street. There are existing sewers within the site, however raising of the site levels should reduce the probability of flooding affecting the site due to failure of these sewers. 7. The nearest still water levels for the river Dee as provided by Environment Agency Wales are:- 0.5% (1 in 200) 6.27m AOD approx In accordance with the advice in TAN15 an allowance for climate change over 100 years is to be added. This is based on the figures in Table 1 taken from the Flood and Coastal Defence Appraisal Guidance FCDPAG3 Economic Appraisal Supplementary Note to Operating Authorities – Climate Change Impacts October 2006 (DEFRA). 0.5% annual probability tide level = 6.08m AOD 0.1% annual probability tide level = 6.57m AOD 0.5% annual probability tide level include for 100 years climate change = 7.23m AOD 8. The defences to the north are a natural dune system which stretch from Barkby Beach near Gronant to Point of Ayr. approximately 250m to the East lie defences of man-mad earth embankment, these stretch along estuary from Point of Ayr southwards. Talacre Embankment has a crest of 6.46m AOD Depths of flooding 9. It is proposed that the general site levels be raised such that they are approx. 5.00m AOD. Where we would with an internal finished floor ground floor level of 340mm above the existing dwelling showing a betterment in accordance with TAN 15 and replacement dwellings 10. The submitted additional plan Melvilla Site Sections demonstrates that the Finished Floor Levels (FFL) are set at a greater height than the existing FFL and is considered a betterment 11. Thus, the site would flood under the 0.5% scenario required for a residential property with an allowance for climate change of 100 years. 12. As a result of the proposals the site would flood, including access to the site under the 0.5% probability event. In the light of the relatively good predictability of tide levels and weather warnings for conditions leading to tidal surge it is considered that the probable degree of flood warning available is more than adequate for the depths and probability of flooding likely to occur on the access to the site. Effects on other properties 13. The proportion of the site, which is a loose surfaced, impermeable area is unlikely to change significantly. Should the site be replaced with tarmac a condition contained in permission could be included to allow only Suds hence minimising the runoff generated by the proposal. Flood resistant/reduction measures 14. As the proposal is for a replacement dwelling then there is be an opportunity to consider the inclusion of flood resistant/reduction measures. However, as the proposed property’s ground floor level is above the 0.5% flood level with an allowance for climate change then this may not be justified. The construction is of brick and block including new PVCu doors and window, these allow a complete seal around the perimeter owing to the shootbolt locking system which pills the doors/window tight into the weather seals. The floor will be of concrete and wrapped in DPM minimising water rising through the floor, there will be no Air Brick designed into the construction as these would not be necessary owing to the construction Floor Warning Measures 15. The NRW floor warning direct services cover this area. Site owners would register to receive floor warning so as measures can be taken prior to fluvial or a tidal event Safe refuge would be at first floor level should that be necessary Summary and conclusion The site is within Zone C1 as defined by the DAM accompanying TAN15. The proposal is for a single detached replacement dwelling. Ground levels at approx. 5.000m AOD. Finished floor of the replacement dwelling will be set at 5.540 AOD. Betterment 340mm above the existing dwelling. Early flood warning for the site would be in place via registration with NRW floor warnings. Wednesday, 19 August 2020 .

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