South East Hampshire Catchment Flood Management Plan Summary Report December 2009 managing flood risk We are the Environment Agency. It’s our job to look after your environment and make it a better place – for you, and for future generations. Your environment is the air you breathe, the water you drink and the ground you walk on. Working with business, Government and society as a whole, we are making your environment cleaner and healthier. The Environment Agency. Out there, making your environment a better place. Published by: Environment Agency Guildbourne House Chatsworth Road Worthing, West Sussex BN11 1LD Tel: 08708 506 506 Email: [email protected] www.environment-agency.gov.uk © Environment Agency All rights reserved. This document may be reproduced with prior permission of the Environment Agency. Introduction I am pleased to introduce our summary of the South East Hampshire Catchment Flood Management Plan (CFMP). This CFMP gives an overview of the flood risk in the South East Hampshire catchment and sets out our preferred plan for sustainable flood risk management over the next 50 to 100 years. The South East Hampshire CFMP is one of 77 CFMPs for flooding and highway flooding of drainage systems. At England and Wales. Through the CFMPs, we have present over 2600 properties are at risk in the catchment assessed inland flood risk across all of England and in a 1% event (taking into account flood defences). Wales for the first time. The CFMP considers all types of This will increase to approximately 3500 properties in inland flooding, from rivers, groundwater, surface the future and these are concentrated in the settlements water and tidal flooding, but not flooding directly from of Portsmouth, Havant, Hambledon and Wallington. the sea (coastal flooding), which is covered by We cannot reduce flood risk on our own, we will Shoreline Management Plans (SMPs). Our coverage of therefore work closely with all our partners to improve surface and groundwater is however limited due to a the co-ordination of flood risk activities and agree the lack of available information. most effective way to management flood risk in the The role of CFMPs is to establish flood risk management future. The key partners we have worked with are policies which will deliver sustainable flood risk Portsmouth City Council, Havant Borough Council, management for the long term. This is essential if we Fareham Borough Council, East Hampshire AONB, East are to make the right investment decisions for the Hampshire District Council, Gosport Borough Council, future and to help prepare ourselves effectively for the Natural England, Hampshire County Council, Defra, impact of climate change. We will use CFMPs to help us Winchester City Council, Southern Water, Hampshire target our limited resources where the risks are greatest. Wildlife Trust. This CFMP identifies flood risk management policies to This is a summary of the main CFMP document, if you assist all key decision makers in the catchment. It was need to see the full document an electronic version produced through a wide consultation and appraisal can be obtained by emailing process, however it is only the first step towards an [email protected] or alternatively integrated approach to flood risk management. As we paper copies can be viewed at any of our offices in all work together to achieve our objectives, we must Southern Region. monitor and listen to each others progress, discuss what has been achieved and consider where we may need to review parts of the CFMP. The main source of flood risk is from river flooding and Toby Willison to a lesser extent surface water flooding, groundwater Regional Director, Southern Region Environment Agency South East Hampshire Catchment Flood Management Plan 3 Contents The purpose of a CFMP in managing flood risk 5 Catchment overview 6 Current and future flood risk 8 Future direction for flood risk management 11 Sub-areas 1 Portsmouth and Langstone Harbours 13 2 Hamble 15 3 Lower Hamble and Lower Meon 17 4 Wallington River 18 5 Havant and Denmead 19 6 Chalk Catchment 21 7 Old Wallington Town 23 Map of CFMP policies 24 4 Environment Agency South East Hampshire Catchment Flood Management Plan The purpose of a CFMP in managing flood risk CFMPs help us to understand the • IDBs, water companies and CFMPs aim to promote more scale and extent of flooding now other utilities to help plan their sustainable approaches to managing and in the future, and set policies activities in the wider context flood risk. The policies identified in for managing flood risk within the of the catchment; the CFMP will be delivered through a catchment. CFMPs should be used combination of different approaches. • Transportation planners; to inform planning and decision Together with our partners, we making by key stakeholders such as: • Land owners, farmers and will implement these approaches land managers that manage through a range of delivery plans, • The Environment Agency, who will and operate land for projects and actions. use the plan to guide decisions agriculture, conservation on investment in further plans, The relationship between the CFMP, and amenity purposes; projects or actions; delivery plans, strategies, projects • The public and businesses to and actions is shown in figure 1. • Regional planning bodies and enhance their understanding local authorities who can use the of flood risk and how it will plan to inform spatial planning be managed. activities and emergency planning; Figure 1. The relationship between CFMPs, delivery plans, projects and actions. Policy planning • CFMPs and Shoreline Management Plans. • Action plans define requirement for delivery plans, projects and actions. Policy delivery plans (see note) Projects and actions • Influence spatial planning to reduce risk • Make sure our spending delivers the best and restore floodplains. possible outcomes. • Prepare for and manage floods • Focus on risk based targets, for example (including local flood warning plans). numbers of households at risk. • Managing assets. • Water level management plans. • Land management and habitat creation. Note: Some plans may not be led by us – we may • Surface water management plans. identify the need and encourage their development. Environment Agency South East Hampshire Catchment Flood Management Plan 5 Catchment overview The area of the South East Here it is mainly rural, with the tertiary deposits, such as more Hampshire CFMP has a population population generally dispersed impermeable clays. The River Meon of approximately 460,000 covers across small towns and villages. The flows over chalk for approximately 500 square kilometres and is catchment drains into a number of half of its length. Tributaries of the drained by the River Hamble, River designated sites of national and other large sub-catchments also Meon, Wallington River, River Alver, international importance for nature flow over chalk but are ephemeral West Brook and Hermitage and conservation, such as the Solent (short-lasting) streams that only Lavant Streams. It is a mixture of and Southampton Special appear when groundwater levels are rural and urban areas with three Protection Area/Ramsar site or the higher. The underlying geology has quarters of the land used as Solent Maritime Special Area of a significant impact on the agricultural. Conservation. It also contains hydrology of the area. Rainfall on important wetland sites such as the chalk areas tends to soak into the The main urban areas are located at Titchfield Haven Site of Special ground, recharging groundwater Havant, Waterlooville, Portsmouth, Scientific Interest. stores rather than rapidly entering Fareham, Gosport, and Hedge End. the river system as run-off. The catchment also includes the The northern part of the catchment South Downs Area of Outstanding lies on chalk while the southern Natural Beauty (AONB) to the north. part of the catchment consists of ➜ Warren Dam, reducing flood risk to residents of Leigh Park, Havant. 6 Environment Agency South East Hampshire Catchment Flood Management Plan Map 1. Overview map of South East Hampshire catchment. ‘The underlying geology is significant as chalky areas tend to soak up rainfall, recharging ground water stores rather than rapidly entering the river system as run-off.’ Environment Agency South East Hampshire Catchment Flood Management Plan 7 Current and future flood risk Overview of the current flood risk Where is the risk? Flood risk is the combination of the The most significant flooding of The main sources of flooding in the probability of flooding and its impact, recent times within the South East South East Hampshire CFMP area are that is, the chance of it happening Hampshire catchment occurred in from groundwater and surface water and the damage that occurs if it does 2000/01. During this time, prolonged although there is also a risk from happen. In the South East Hampshire heavy rain fell over a number of river flooding (fluvial flooding) catchment the CFMP has considered months throughout late autumn and which can be made worse by tidal flooding from rivers, surface water and winter. The high groundwater levels conditions. The map on page 10 sewage flooding from the drainage from all this water was considered to illustrates the consequences of a system, as well as groundwater be the most significant cause of the 1% annual probability event (1 in flooding. There are approximately widespread flooding. While places 100 year) occurring within the CFMP 3,500 properties in the catchment such as Hambledon or Wallington area. The areas with the highest that have a 1% chance of flooding in were badly affected by the flooding, concentration of properties at risk any one year from rivers or the distribution of incidents in the from river flooding are tabulated groundwater. We have assessed historic record tends to show relatively on page 9. flood risk across the CFMP area using small numbers of properties broad-scale computer modelling, flooding in a large number of places.