proposed solar park development at cave farm, nr pitney, somerset ...

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____________________________________________________________________________________________ J-3999.7-FM Flood Risk Assessment & SUDS Design, Cave Farm, Nr Pitney, Somerset V2 ___________________________________________________________________________________________ 4.0 FLOODING MECHANISMS A number of possible flooding mechanisms have been considered at the site, and are discussed below. 4.1 Groundwater Flooding Investigation of ground water flooding has been undertaken within the South Somerset SFRA. Springs showing the emergence of ground water at the surface have been identified and are shown in Appendix D. Several springs are located north of the site near Bramwell, however, no springs are located within the region of the site. A large area to the north of the River Cary is low-lying (around 5m AOD) and requires significant land drainage in the form of rhynes, and ditches etc. The site is located between 35m AOD and 50m AOD, which suggests it should not suffer from similar ground water issues The SFRA does report on suspected ground water flooding events around Langport, however, this was recorded in 1954. Ground water as a source of flooding is particularly difficult to identify. Areas are typically assessed with respect to their geological properties and historic events , The SFRA continues with: “The available records appear to indicate emerging groundwater (i.e. in excess of the norm) in response to extreme rainfall. These appear to be localised and may in part relate to poor “land” drainage. None of the recorded occurrences appear to be widespread and do not therefore appear to be a reflection of regional rises in groundwater level.” Given that the development is non-residential, the site topography is high/steep relative to the surrounding area, and, that the solar panels are supported on frames which give limited resistance to the flow of water, ground water flooding will not be considered further within this report. 4.2 Overland Sheet Flow The site is set in a rural environment with fields surrounding the entire site. Due to the sites elevation relative to the surrounding topography, and the location of the nearby watercourses which can intercept overland flows, the risk of any significant overland flows being generated that can effect the site are considered to be small and will not be considered further within this report. Surface water runoff generated by the development of the site is considered further in section 6 of this report. 4.3 Fluvial (River) Flooding The EA’s Indicative Flood Map illustrates that the entire site is located within Fluvial Flood Zone 1. This implies the site has greater than a 1 in 1000 year chance of being affected by fluvial flooding. As discussed in Section 3.0, the closest watercourse/drainage ditch to the site has a very small catchment of less than 1km 2 and will therefore, have limited capacity to generate significant flows. As such the fluvial flooding will not be considered further within this report. P:\Job Files 3900-3999\J-3999-FM AEE Flood Risk Assessments\J-3999.7-FM Cave Farm\Report V2 4
____________________________________________________________________________________________ J-3999.7-FM Flood Risk Assessment & SUDS Design, Cave Farm, Nr Pitney, Somerset V2 ___________________________________________________________________________________________ 4.4 Tidal Flooding The site is well outside of any areas of tidal influence, located at a minimum elevation of around 35m AOD. Given the nature of the site, and surrounding topography, tidal flooding has not been considered further within this report. 4.5 Flooding as a Result of Development The proposed development will introduce impermeable area around the site to areas that were previously permeable. This could have the potential to increase the runoff rates across the site which could increase the flood risk to adjacent sites. Following further inspection of the development layout (shown in Appendix B) it can be seen that the proposed solar park infrastructure only introduces a small area of impermeable surfaces through the foundations of the solar panel arrays, inverters and the central control station. It is thought that rain falling on each solar panel table will runoff the panels and flow/infiltrate in the sheltered rain shadow area underneath the down-slope modules. All access and maintenance roads are proposed to be constructed from permeable methods and therefore, will not contribute to increased runoff rates from the site. This impermeable area totals 350m 2 , which is only around 0.3% of the total site area. Therefore, the drainage system need only contend with the volume of runoff from this area to ensure flood risk is not increased, the potential for a sustainable drainage system to be installed within the development will be outlined further in Section 5.0 of this report. P:\Job Files 3900-3999\J-3999-FM AEE Flood Risk Assessments\J-3999.7-FM Cave Farm\Report V2 5
Page 1 and 2: PROPOSED SOLAR PARK DEVELOPMENT AT
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Page 17: APPENDIX A SITE LOCATION PLAN
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Page 24 and 25: H2OK Systems Limited Page 1 Nanjerr
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