Mr & Mrs Clarke Proposed Development at The River House, Balderstone Flood Risk Assessment

Transcription

1 Proposed Development at The River House, Balderstone D2192-FRA-01 5 Nov 2015 PSA Design Ltd Consulting Engineers The Old Bank House 6 Berry Lane Longridge Preston PR3 3JA Tel Fax [email protected]

2 Document Control Sheet Job Date Issue Copy D /10/15 Original Originator G Sanderson. Checker..D Wallbank.... Approver D Wallbank.... PSA Design Ltd. All rights reserved. No part of this report may be copied or reproduced by any means without prior written permission from PSA Design. If you have received this report in error, please destroy all copies in your possession or control and notify PSA Design. This report has been prepared for the exclusive use of the commissioning party and unless otherwise agreed in writing by PSA Design, no other party may use, make use of or rely on contents of the report. No liability is accepted by PSA Design for any use of this report, other than for the purposes for which it was originally prepared and provided. Opinions and information provided in the report are on the basis of PSA Design using due skill, care and diligence in the preparation of the same and no explicit warranty is provided as to their accuracy. It should be noted that and it is expressly stated that no independent verification of any of the documents or information supplied to PSA Design has been made.

3 Contents 1.0 Introduction 2.0 Flood Zone & PPG Categorization Proposed Flood Precautions & Limitation Measures 5.0 Surface Water Run-off 6.0 Conclusions Figures & Drawings Figure 1 Locations map via Google Maps Figure 2 Environment Agency Flood Maps a) Surface water flooding maps b) Flooding from river/sea c) Flooding from reservoirs d) Flood map for planning Figure 3 United Utilities Service Map Existing Plans Proposed Plans D Existing Site Plan C Proposed Site Plan Holiday Let C Proposed Holiday Let Plans and Elevation

4 1. Introduction 1.1. PSA Design Ltd has been commissioned to prepare a (FRA) in support of a proposed development at The River House, Balderstone There are two separate applications being made on the site. The first seeks approval to extend the existing dwelling with a new single storey lean to extension. The second application seeks permission to construct a new single storey holiday let building in place of an existing portal frame storage building. This FRA has been prepared to cover both The River House is located on Balderstone Hall Lane, Balderstone, Blackburn, BB2 7LA. It lies within a rural settlement by the western bank of the River Ribble. The site locality is shown on Figure 1 attached The national grid reference for the site is E, N The existing and proposed development layout is shown on the drawings attached, prepared by Sunderland Peacock Architects The proposals to construct a new single story extension on to the existing property are shown on drawing B (Proposed Plans & Elevations). The proposals to replace the existing portal frame storage building with a holiday let cottage are shown on drawing C (Proposed Holiday Cottage Floor Plan & Elevations) Drawing D shows how the existing layout of the site. Drawing D shows how the new development integrates with the existing site. The proposed extension area on the existing building is relatively small and can therefore be classified as a minor development. The holiday let cottage replaces the existing out building, with no additional impermeable areas to the site. 2. Flood Zone & PPG Categorisation 2.1. Reference to the online Environment Agency flood mapping (included as Figure 2d) shows the site falling withinflood Zone 2. This means the land is assessed as having a 1 in 100 and 1 in 1

5 1000 annual probability of river flooding (1% - 0.1%) or between 1 in 200 and 1 in 1000 annual probability of sea flooding (0.5% - 0.1% in any year Under the requirements of Planning Practice Guidance (PPG) Flood Risk & Coastal Change, the Local Authority is required to apply a risk-based sequential test to new developments. This allows them to direct development to areas which are at the lowest probability of flooding With reference to Table 2 from PPG, a development consisting of Buildings used for dwelling houses or Sites used for holiday fall into the More Vulnerable category Therefore, in accordance with Table 3, PPG indicates that the development is appropriate Given that this is an extension to a property and also demolition/conversion of an existing building, it is considered that the sequential test is not relevant in this instance. Regardless, the sequential test is a planning issue that will be dealt with separately as part of the application Specific flood levels data has not been acquired at the time of writing this report. However, given the site lies in Flood Zone 2 it can be assumed that flood depths in this area will be relatively shallow. An extract of the EA flood map is included as Figure 2b, which highlights the proposed site on the edge of Flood Zone Reference to the online EA mapping (included in Figure 2a) shows the site is located outwith an area at risk of flooding from surface water Reference to Figure 2c shows the site lying within an area susceptible to flooding from Reservoirs. Online searches have not flagged up any instances of previous flood events at the site. Reservoirs in the UK have a good safety record with no incidents resulting in loss of life since The Environment Agency act as the enforcing authority for the Reservoir Act 1974 and this ensures that all reservoirs are inspected and supervised by an approved panel of engineers. It is therefore considered that the risk posed by flooding from reservoirs is very low The site is located outwith an area susceptible to ground water flooding as confirmed in the Ribble Valley SFRA 2

6 3.5. Review of the Ribble Valley SFRA showed no specific reference to the site or Balderstone as having flooding problems. 4. Proposed Flood Precautions & Limitation Measures 4.1. The proposed house extension floor levels should be set at or above the existing property floor levels. It is also recommended that the internal sockets be raised 900mm above ground level and the floor is of solid construction The proposed holiday floor levels should be set 300mm above existing ground levels. It is also recommended that flood resilient measures are integrated into the final design in accordance with Communities and Local Government document Improving the flood resilience of new buildings A flood warning and evacuation strategy should also be developed and agreed with the LPA prior to letting the holiday let. In its simplest form this will ensure that a formal strategy is applied and implemented on site and that the owners, residents and guests are aware of the risk, understand their responsibilities and are aware of the safest point of refuge. Flood depths are not considered to be of any significant depth regardless. 5. Surface Water Run-off 5.1. According to the United Utilities service plans, the existing surface water run-off is collected via a private system, as there is nothing highlighted on the water providers records. It is understood that this eventually outfalls into the River Ribble The comparison between the existing and proposed site is highlighted on Drawing D & D It can be seen that there will be no increase in surface water run-off as a direct result of the proposals. 3

7 5.4. All surface water run-off generated by the proposals will be clean roof water run-off There will therefore be no increase in flood risk related to surface water run-off from the site. 6. Conclusions 6.1. The development is for a proposed single storey extension and a new holiday let cottage built in place of an existing portal frame out building The site lies within Flood Zone 2 and in accordance with PPG is appropriate for such development Any flooding at the site is likely to be from river but there is no record of historical flooding at this location or highlighted in the Ribble Valley the SFRA 6.4. Finished floor levels of the lean to extension will be set at or above the existing property Finished floor levels of the holiday let will be set 300mm above existing ground levels Despite the low risk of flooding, the development will also incorporate a number of flood mitigation measures as outlined in Section 5 above. A flood evacuation plan, to the approval of the LPA, will also be established Surface water run-off will continue to drain to the existing infrastructure on site. There is no increase in impermeable areas as a result of the proposals. 4

8 Maps Figure 1 Locations map via Google Maps Figure 2 Environment Agency Flood Maps e) Surface water flooding maps f) Flooding from river/sea g) Flooding from reservoirs h) Flood map for planning Figure 3 United Utilities Service Map 5