Powys County Council planning policy for sustainable drainage reports, flood risk assessments and contaminated land risk assessment are driven by environmental conditions and the local authority policy.
Guidance for architects, and developers on flood risk, drainage and phase 1 contaminated land reports is summarised below with links to the key summary documents.
The Council’s guidance follows a risk-based framework, in line with the Model Procedures for the Management of Land Contamination CLR 11(Defra & Environment Agency 2004) document.
Stage 1 – Risk Assessment
Phase 1: Preliminary Risk Assessment (Desk Study)
Risk assessment is an iterative process, which should be carried out within a tiered framework. Hence it may become necessary to revise assumptions made in the early stages of the assessment as more information becomes available about the site.
The purpose of the preliminary risk assessment is to develop an outline conceptual model and establish whether or not there are any potentially unacceptable risks to human health, ecosystems, property or controlled waters, arising from potential contamination at the site. The main activity at this stage is the collection of information required to identify all possible pollutant linkages at the site and prepare the outline conceptual model. This stage is often referred to as the ‘desk study’, although a site walkover survey may also be undertaken to verify data and obtain additional information such as anecdotal evidence from employees etc.
Planning policy and advice in Wales requires a precautionary approach to be adopted when considering the development of land. This is particularly important where the end uses being considered are sensitive to contamination, e.g. housing, schools, hospitals and children’s play areas.
A preliminary risk assessment is the minimum submission required for a planning application for redevelopment on a brownfield site where land contamination may be present. The preliminary risk assessment may include some site investigation or monitoring data collected to help outline the need or otherwise of a quantitative risk assessment.
The LPA will need to have enough information to be confident that the site can be reasonably remediated before planning permission is granted. Pre-planning discussions with the LPA is considered good practice and encouraged in order to provide advice to applicants on the minimum requirements for each site, which will be specific to the conceptual model.
Please see the developers guide below for details of the further risk assessment stages.
Powys usually require a Site walkover survey as part of the Desk Study, though it would be worth confirming this with the Contaminated Land Officer and an environmental consultancy such as GeoSmart, depending on the Site.
Powys County Council
The Powys LDP area has a varied topography of upland plateau, rolling ridges and hills with sharply incised valleys that lead down to narrow twisting valley floors, which follow the rivers Severn, Vyrnwy, Tanant, Wye, Usk, Irfon, Ithon, Dyfi, Teme, Tawe and the Lugg along with other smaller watercourses.
The topography of the plan area has meant that historically a large number of settlements and main transport routes are located in valleys at important river crossings; as a result of this a number of settlements are constrained by flood risk. Whilst the flooding of rivers and coastal waters is a natural process which plays an important role in shaping the environment it is difficult to predict and the consequences can be very significant. Flooding can place lives at risk, cause considerable personal trauma and result in extensive damage to property, whilst also causing severe disruption to communications and the economy.
Site developers should establish if the site is within an area of flood risk. If a development site has been identified as being in an area at risk from flooding (Zone C, possibly Zone B) is of low vulnerability and meets the justification tests outlined above, a flood consequence assessment (FCA) will need to be undertaken. Where the site is within an area of flood risk, checks should be made to ensure the development proposal complies with TAN 15 and LDP Policy DM6. Proposals for highly vulnerable development (as defined in TAN 15) in areas at high risk from flooding will not be feasible as the planning application is likely to be refused.
There may be instances where the development proposal is within an area of flood risk but is considered acceptable by the guidance in TAN 15. This would only be after a Flood Consequences Assessment (FCA) has been prepared (in accordance with the guidance in TAN 15) and considered acceptable. It would be beneficial for the FCA to include a conceptual drainage design strategy. This can assist in the selection and design of SuDS components for the site and can be used to demonstrate no increased flood risk elsewhere.
Development proposals in areas at high or medium risk of surface water flooding (identified in the Wales Flood Map) will also need to undertake an FCA, particularly to ensure the development does not increase flood risk elsewhere.
The main rivers that flow through Powys include the Severn, Vyrnwy, Tanant, Wye, Usk, Irfon, Ithon, Dyfi, Tawe and the Lugg. In some areas fluvial flooding from these sources is the main source of flood risk; this includes the settlements of Llanidloes, Newtown, Meifod and Builth Wells.
Surface water flooding is exacerbated in some areas, such as Hay-on-Wye (Brecon Beacons National Park), where flooding occurs due to a combination of high river levels within the River Wye and large flows in the Dulas Brook. Similar events occur at Llandrinio, Derwenlas, and Knighton In the case of Llandrinio, the Sarn Wen Brook outfalls into the River Vyrnwy. At Derwenlas, the problems relate to high tidal cycles in the Afon Dyfi where surface water flooding is exacerbated due to high water levels in the local watercourses within the village.
Powys County Council
All new Welsh developments are now required to include Sustainable Drainage Systems which comply with National Statutory SuDS Standards. Part of this process includes sign off by relevant SuDS Approval Bodies (SABs) to the Local Authority in which a planning submission for development is made. GeoSmart have produced a blog post on the Welsh SuDS regulations here.
Powys County Council
There is no local information on historic groundwater flooding, which suggests that the risk of groundwater flooding in Powys is low.
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