Cambridge House, Henry Street, Bath BA1 1UR

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1 Flood Risk Assessment Cambridge House, Henry Street, Bath BA1 1UR For Full Planning application to BANES Council June 2011 Introduction This report is prepared as requested by B&NES to accompany the planning application. Information has been sought from the Environment Agency and from flood information produced for the adjacent Southgate retail development. This building received a planning consent to build 13 hotel apartments to both wings of the office last year. This report was also submitted at this time (10/1270/FUL). Building Description Cambridge House is an existing modern building in the centre of Bath within the Bath Conservation Area and World Heritage site. The building is arranged over two wings (North and South) which were built at different times, probably between 1950 and The building is generally 5 storeys with a plant and stair enclosure on the roofs of both blocks. The ground floor is occupied by retail units with 4 storeys of offices above. There is also a basement to the North Wing which accommodates a car park for the offices and a plant and service area. Aerial view of Cambridge House (outlined in red)

2 Proposed Development The proposal is to join the two office wings across the external lightwell with a corridor. The offices are presently split by a 2.5 metre slot through the centre to form a deep lightwell. The proposals will allow for an enlarged floor plate to create a more useable and flexible office Proposed floor plan and elevation of link corridor

3 Ground floor main entrance and alternative cores and building levels Floor Risks The flood risk within this section of the city are summarised below: 1. High flows in the River Avon from several days of heavy rainfall in the upstream catchment: The characteristics of this flood mechanism are that there would be one or two days warning of possible flood conditions and probably 12 hours warning of flood risk in Bath generally. Flood water is likely to overflow the embankment near The Ambury, travel eastwards into Dorchester Street some way south of the proposed development. 2. Thunderstorms/Flash flooding: a heavy rainstorm over Bath could overwhelm the old combined sewer causing surface water runoff to flow along roads. The bank of the River Avon is higher than the general levels 165 metres south west of the site so ponding will occur but this is 1.7 metres below the approximate site level. Summary of levels -Flood level for 1in100 annual probability river flood m AOD -Flood level for 1in100 annual probability river flood including an allowance for climate change prediction m AOD - Level which may be reached in thunderstorm flooding -19.7m AOD Design average ground level of site (20.1m + 0.6m) Level of entrance door to proposal Level of alternative means of escape door Finished floor level of lowest habitable room m AOD m AOD m AOD m AOD Management of Surface Water The present building has a flat roof. The proposed extension generally has a flat roof also with a small area of pitched roof around the perimeter. Therefore the amount and rate of water to be put into the drainage system will remain the same as existing. Flood Resilience and Resistance The Site as stated by the Environment Agency is predominantly in Flood zone 1 with the south west corner within flood zone 2. Both the exits from the proposal are within the flood zone 1 area or on the perimeter, therefore the flood zone assessment relates to zone 1.

4 The EA stated that they rate this site as a Moderate Flood Risk Area. EA site centred map showing River Flood zone (zone 2 light blue) Level 2 SFRA Map for Bath showing Surface Water Flooding

5 Summary of Potential flood risks - The alternative exit for the site sits within River Flood Zone 1. - A large area of Bath has a high risk level for surface water runoff. The site is within a high risk area for surface water flooding. There is not any published data within the Banes SFRA regarding the frequency and severity of surface water flooding. The site sits higher than the area where water would pond so it is expected that any such floods would be a short term hazard in the area. In discussion with Sam Capel the EA Development and Flood Risk Engineer for the region stated that I would advise that you complete your Flood Risk Assessment (FRA) using the information above [EA site centred flood map] and stating that the development proposals are for the extension to the roof area, thereby posing no additional flood risk to the development. This can be completed either as a separate statement or as an addition at the end of your Design and Access Statement. There are two exits from the building the main entrance at a level of 22.2m and the alternative fire exit at 21.06m. the alternative exit is on the very edge of flood zone 2 and the main exit is above the flood zone. The area of the city north of the site is on a gentle slope up therefore leaving the site in this direction will be towards safety and the area does not form a dry island. Report produced by James Pearce Architects June 2011