Flood Risk in Worcester
A well known and much publicised characteristic of the River Severn is its dramatic rise and fall, and consequent spillage over the flood plain. At least once a year the river discharges onto the flood plain and on occasions adversely affects property. The land adjoining the river is an essential element in the capacity of the river to deal with flood flows. It provides areas over which the water may flow limiting the depth to which the water needs to rise and temporarily stores water, again limiting the flows and levels passing downstream. The City Council recognises the importance of preserving this function and, where possible, the need to restore its capacity where it has been eroded by past developments. The City Council also recognises that it is necessary to ensure that any redevelopment of the existing flood prone areas is carried out in such a way as to eliminate the damage caused by flooding. Further, it is recognised that there are ecological benefits to be gained from areas which are subject to flooding, e.g. attraction of certain species of bird and fauna.
In 1990 the then National Rivers Authority (now Environment Agency) and the City Council commissioned a major study of the flood plain of the River Severn in Worcester . The features of the modern flood plain were recorded and advanced computer modelling was used to predict the effects of flood events of varying intensity and known frequency e.g. 1 in 25 years. The cumulative impact of development in the flood plain and possible flood defences were also tested. The study led to the establishment and adoption of policies to control development within the flood plain and to minimise the flood risk.
The policies have been reviewed. Most recently this has been to consider whether they should be “saved” for future use when the Local Plan ceases to bevalid later in 2007 and in the light of the publication of PPS 25 “Development and Flood Risk” PPS25 gives weight to the susceptibility of land to flooding as a material planning consideration, it applies a precautionary principle to decision making so that risk is avoided where possible, recognises the role of flood plains as a natural form of flood defence together with their wider ecological and amenity value, and acknowledges that engineered flood reduction measures and defences may not always be the appropriate solution. The guidance introduces a risk assessment of proposals for development in or affecting a flood risk area. This is linked to a sequential approach that directs development away from high risk areas.
The policies for the flood plain are based on the principles of PPS25 including preserving and protecting the flood plain (areas of high flood risk with an annual probability of flooding of 1.0% or greater) function by not allowing development within areas of high flood risk and reducing the flooding of existing properties. The flood plain is divided into three zones, as shown on the Proposals Map, and the policies for each zone will be applied as follows:
Undeveloped Flood Plain ["Blue Zone"*] (corresponds to category 3c Table 1 in PPG25) ‑ areas where the basic flood plain function remains intact and there are no significant buildings. Open land uses, playing fields, park land or car parking will be permitted in appropriate locations, but no construction of buildings or other structures leading to the loss of flood plain or obstruction of flood plain flows will be permitted. Development, such as road crossings of the valley where there is no alternative, will be permitted provided compensatory works are carried out and no detriment is proven.
Developed Areas/Low Flood Risk ["Yellow Zone"*] (corresponds to category 3a Table 1 in PPG25) ‑ areas which are inundated by water in some flood events but whose function is primarily flood water storage, with no significant obstruction of flood water flows. The precedent of existing development is recognised, and opportunities for appropriate redevelopment are a possibility. Intensification of use by residential development will not be permitted as it places more people in “health and safety” risk during flood events. Where, in exceptional circumstances, residential development is considered, it must be demonstrated by means of a flood risk assessment that the objectives of this policy are achieved, including safe, dry pedestrian access. Other forms of development will only be permitted provided floor levels are raised 600mm above the 1 in 100 year flood level. The raising of surrounding land for car parks or other amenities will not normally be permitted but, where feasible, the raising of access roads will be allowed. The provision of compensatory flood storage volume will be required. In all instances an improvement in flood water flows in and around any site within such areas will be sought.
Developed Areas/High Flood Risk ["Red Zone"*] (corresponds to category 3b Table 1 in PPG25) ‑ areas which are in strategic locations at "pinch points" in the flood plain and where existing development obstructs and inhibits flood flows. Development in this zone is at high risk or because of the past raising of land levels the existing development exacerbates flooding elsewhere in the flood plain. No development will be permitted which would prejudice the return of those areas to open land use. Existing areas of land and buildings will be permitted to remain at their present level of activity and scale but no development [either material change of use or other development] will be permitted which will consolidate or extend the lifetime of existing buildings, structures or works which already affect flood storage capacity and/or flood flows. Change of use of existing buildings to residential uses or uses which put life at risk will not be permitted. The long term aim is to return these areas to open flood plain. It is acknowledged that this process may take a considerable time and that in the meantime businesses and other activities within those areas should not be unduly restricted. The City Council's policy is therefore directed towards the clear indication that land use change will be sought when development opportunities occur and that there should be no intensification of existing uses. There will be a degree of flexibility in the operation of that policy to take into account the location and function of existing buildings and the ability to achieve improvement of flood flows in any proposals. In exceptional circumstances, redevelopment will be considered where they incorporate features which substantially restore the original function of the flood plain.
[* In the document "Policy for the Control of Development Within the Flood Plain of the River Severn" the zones are coloured].
It is of equal importance to protect areas at risk from flooding along other watercourses within the city. However, it is considered that if the 8m access strip is maintained along both banks of all watercourses, then the need for a red zone is not required beyond that strip. Within this strip the red zone policy would apply. Outside this strip, guidance received from the EA confirms that, in the case of Barbourne Brook, Duck Brook, Laugherne Brook, the use of “yellow” and “blue” zones is applicable, and the appropriate boundaries derived from the EA are shown on the proposals map.
The boundaries of the flood plains on these watercourses are derived from national based information from the Institute of Hydrology , modified by local conditions. The extent of the flood plain shown is indicative of the area at risk, and development proposals within, or on the edge of, the flood plains of these watercourses will be assessed on an individual basis. For developments that may have a significant impact on the watercourse, any planning application should be accompanied by a flood risk assessment including an appropriate modelled flood study.
PPS 25 advises that flood risk assessments are required when development is proposed in areas of flood risk. In Worcester , these areas are principally those referred to in Policies NE21, NE22, and NE23 as shown on the Proposals Map . Flood risk assessments may, however, also be required for other sites including those affecting the flood plains or watercourses, where known drainage or flash flooding problems exist, and for developments resulting in significant surface water run-off. The applicant for planning permission is responsible for producing the assessment. It should be provide prior to the submission of any planning application, and where it is not provided or is inadequate it may be considered as a reason for refusal of the application.
Advise on the contents of a flood risk assessment will be provided by the Environment Agency. All planning applications for sites in the flood risk areas identified in this plan will generally be expected to be accompanied by a flood risk assessment and the EA will provide advice on the identification of sites in other locations.
It is vital that foul sewage, contaminated surface water and trade effluent are disposed of in the most environmentally effective way, and in the City there is no reason why this should not be to the existing water reclamation works. Any lack of capacity should be addressed in a phased manner which should accompany development ‑ not by means of privately operated treatment plants. In circumstances where development cannot be achieved without detriment to water quality or the ecology, planning permission will be refused. It must be borne in mind that streams and wetlands can be recharged by ground water, and any contamination can lead to a long term deterioration in the quality of the receiving watercourse/wetland.
Water Resources Act 1991 imposes a duty on the EA not only to further the conservation of landscape, flora, fauna and geological features but also to take measures to enhance it so far as any of its functions are concerned. The EA is also under a duty to promote recreation and to have regard to the conservation of historic and archaeological features. Development can severely threaten these interests. The City Council recognises the importance of the natural watercourse system, wetland areas and ponds as valuable wildlife habitats, which, in addition to being of significant amenity and landscape value, should be protected and enhanced.
It is necessary that water resources are available for public water supply, and it is important that providing water for new development does not have a detrimental impact on existing users, nature conservation or recreation.