Flood Risk Assessment
Total Page：16
File Type：pdf, Size：1020Kb
Flood Risk Assessment KDS0094_FRA Project – KDS0094_Altitude Cornwall – Snow Park & Associated Facilities East Crinnis Farm Par Cornwall PL24 2SD Foreword The Altitude Cornwall project aims to introduce new year-round facilities to Cornwall with the introduction of a snow park and associated parking and access which overlooks the popular Carylon Bay in Par. This Flood Risk Assessment (FRA) has been produced with reference to the .gov website - guidance for river maintenance, flooding, and coastal erosion. The Environment Agency have provided information about the type and levels of flooding susceptible in the area. At a local level, the Cornwall Local Flood Risk Management Strategy as well as the Par & St Blazey Community Flood Plan have been used in the production of this report. This report aims to provide a thorough assessment of the current flood risk to the area from different types of flooding. Any increased or potential risk caused as a result of Altitude Cornwall will be evaluated, inclusive of the measures introduced to mitigate flood risk. 1.0 Introduction 1.1 Site and context Altitude Cornwall will be accessed from Lamellyn Road located off Par Moor Road (A3082) in Par, PL24 2SQ and currently forms land owned by East Crinnis Farm & Holiday Park. Please refer to drawings - KDS0094_JB_001_PL24 2SD_M3_A_0001 & 0002 of the submitted documentation for the location & block plan. The site is approximately 56,899sqm and currently in agricultural use. It is fairly level along the northern boundary falling away in a steep slope from north down to south plateauing again to a valley bottom. A public right of way bounds the north and along the eastern boundary runs Lamellyn road. Par and St Blazey are situated on the south coast of Cornwall surrounded by steep hills to the west, north and east. The Pontsmill Valley feeds from the north and Treesmill from the east. Much of the heart of both Par and St Blazey consists of low-lying flat land with the Par River and Trefry Canal running through. Areas of Par and St Blazey are considered at risk of surface water, river and coastal flooding. The site falls under the St Austell and Par Rivers flood watch boundaries. The closest main river to the site is Sandy River, ID481, which runs to the south of the site on the far side of the main Par Moor road, approximately 138m away. A second river not classified as a main river, Bodelva Brook ID1732, also runs past the south of the site and again, south of Par Moor Road approximately 110m away. These two rivers pose the most likely flood risk to the site. 1.2 Site images View from north of site facing Carlyon Bay Proposed entry point on Lamellyn Road off Par Moor Road (A3082) 1.3 Site Visualisation Birdseye visual representation of the proposal from south east perspective 2.0 Assessing Flood Risk In assessing the flood risk for a particular proposal, it is important to assess the different types of flooding that may have relevance to the project. It is also important to note that the site for Altitude Cornwall is large and therefore different areas of the site may fall into different categories of flood risk or possibly be susceptible to different kinds of flooding. 2.1 Critical Drainage Area St Austell & St Blazey have well-known Critical Drainage Area’s (CDA), so it is important to locate Altitude Cornwall in relation to those. As displayed in the image below, the site is not within the CDA of St Austell or St Blazey, sited just east and south respectively of the two areas. CDA’s are areas that have critical drainage problems highlighted by the local planning authority and the Environment Agency. New development in these areas is acceptable with the expectation of incorporating measures to reduce flood risks. Altitude Cornwall have incorporated these measures as a sustainable scheme despite not being located with the local CDA’s. St Austell & St Blazey CDA’s in relation to Altitude Cornwall 2.2 Flood zones & extent of flooding The image below, provided by the environment agency, highlights a rough outline for the Altitude site and indicates the present flood risk as of February 2021. As can be seen above, much of the site (90.7%) falls into flood zone one which is considered to be land with less than 1 in 1,000 annual probability of river or sea flooding. A small and most southern portion of the site can be seen within flood zone 3 which increases the flood risk to 1 in 100 (>1%) annual probability of river flooding, or 1 in 200 (>0.5%) annual probability of flooding from the sea in any given year. Information provided from the flood warning information service on the government website can categorise and breakdown the flood risk of the Altitude site from different types of flooding, such as: • Flood risk from surface water – very low risk. This means that each year this site has a 0.1% chance of flooding. • Rivers and the sea – very low risk. This means the chance of flooding in this way is less than 0.1% each year. Contextually, the ‘very low risk’ classifications on the previous page refer to the main site and much of East Crinnis Farm at post code PL24 2SD. This needs to be broken down further. Below we can see that due to the large size of the site, the southern portion of the land falls within the slightly higher risk category of flood zone 3 whilst the rest of the site is within flood zone 1. Site visualisation with approximate location of flood zones. 2.3 Flood zones & extent of flooding - Rivers and sea Site entrance The proposed site entrance falls within a medium risk category for flooding from rivers or the sea. A medium risk increases the chance of flooding each year up to between 1% & 3.3%. Although categorised as medium risk it seems appropriate to mention that no ‘vulnerable development’ will be within this section of the flood zone. This site is over 110m away from the rivers that pose the risk and is at an elevated level. A flood realistically reaching the site would have to be an enormous body of water. 2.4 Flood zones & extent of flooding - Surface water Demonstrated below, the extent of flooding from surface water is even less than that of the above rivers and sea. Again, the vast majority of the site presents very low risk with just a very small parcel of land at the proposed entrance that falls into the higher low-risk category. In this instance, low risk of surface water means the chance of flooding is between 0.1% & 1% each year. In this low-risk scenario of surface water flooding, the flood warning information service indicate estimated flood depths to the south of the site would be below 300mm. 2.5 Groundwater No instructive site investigations have been undertaken at the site but due to the topography and height relative to sea level, ground water flooding is envisaged to be of low risk. 2.6 Sewers South West Water utility mapping has been requested and viewed in the preparation of the planning application and this report. The utility asset plans can be found as supplementary documentation included within the planning application. The Altitude site does not currently have access to SWW sewers nor are there any within the vicinity to cause concern of flooding from overflow. It is therefore considered a low flood risk. 2.7 Highways Flooding from highways has been investigated and the risk has been identified as being low risk. The site sits at a higher elevation than Par Moor Road so any excess water will follow the natural flow away from the site. The topography of the land means the site rises in elevation above Lamellyn Road with larges hedges bordering the site will keep any highway water on Lamellyn Road (north & east of the site) and divert it either north away from the site or south, toward the sea if travelling on the east border. The flooding sources and flood risk are summarised in the table below: Source of flooding Altitude Cornwall Site Risk Rating Fluvial (river) & coastal (sea) Varies across site – very low to medium Reservoirs Low Surface Water Varies across site – very low to low Ground water Low Sewers Low Highways Low 3.0 Planning application & flood risk The Altitude Cornwall planning application and associated works are largely confined to flood zone 1 and pose minimal flood risk. However, a small portion of the site does fall into flood zone 3. In refence to the Birdseye visualisation earlier in this report and the submitted site plan, drawing number KDS0094_JB_001_PL24 2SD_M3_A_0004, the at-risk structures of the proposal are limited to the entrance and roadway, open green space, wetland and a small portion of the overflow car park. Definition of development in terms of flood risk - Under the flood risk vulnerability classification information gathered from the government website, it describes ‘buildings used for leisure’ as less vulnerable. The part of the development in flood zone 3 is classified as water-based recreation / open amenity space. The table below indicates acceptable development types within each flood zone. Flood Essential Highly More Less Water zone infrastructure vulnerable vulnerable vulnerable compatible 1 YES YES YES YES YES 2 EXCEPTION YES TEST YES YES YES REQUIRED 3a EXCEPTION EXCEPTION TEST NO TEST YES YES REQUIRED REQUIRED 3b EXCEPTION TEST NO NO NO YES REQUIRED The site is located across flood zone 1 and 3. Most of the development is located within flood zone 1 which is low risk and classifies all uses of land as appropriate.