Frome and Piddle Catchment Flood Management Plan Summary Report June 2012 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 Manley House Kestrel Way Exeter EX2 7LQ Tel: 0870 8506506 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. June 2012 Introduction I am pleased to introduce our summary of the Frome and Piddle Catchment Flood Management Plan (CFMP). This CFMP gives an overview of the flood risk in the Frome and Piddle catchment and sets out our preferred plan for sustainable flood risk management over the next 50 to 100 years. The Frome and Piddle CFMP is one of 77 CFMPs for The Frome and Piddle catchment has a history of flood England and Wales. Through the CFMPs, we have risk. Over the last 40 years engineering schemes have assessed inland flood risk across all of England and been implemented to reduce flood risk in the Wales for the first time. The CFMP considers all types of catchment. At present 1,160 properties are at risk in inland flooding, from rivers, ground water, surface the catchment in a 1% event (taking into account flood water and tidal flooding, but not flooding directly from defences). This is likely to increase to over 1,490 the sea (coastal flooding), which is covered by properties in the future. Shoreline Management Plans (SMPs). Our coverage of We cannot reduce flood risk on our own, we will surface and ground water is however limited due to a therefore work closely with all our partners to improve lack of available information. the co-ordination of flood risk activities and agree the The role of CFMPs is to establish flood risk management most effective way to manage flood risk in the future. policies which will deliver sustainable flood risk We have worked with others including: Poole Borough management for the long term. This is essential if we Council; Dorset County Council, and Natural England are to make the right investment decisions for the and the National Farmers Union to develop this plan. future and to help prepare ourselves effectively for the This is a summary of the main CFMP document, if you impact of climate change. We will use CFMPs to help us need to see the full document an electronic version can target our limited resources where the risks are be obtained by emailing greatest. [email protected] This CFMP identifies flood risk management policies to or alternatively paper copies can be viewed at any of assist all key decision makers in the catchment. It was our offices in South West Region. produced through a wide consultation and appraisal process; however it is only the first step towards an integrated approach to Flood Risk Management. As we all work together to achieve our objectives, we must monitor and listen to each others progress, discuss what has been achieved and consider where we may Richard Cresswell need to review parts of the CFMP. South West Regional Director Environment Agency Frome and Piddle Catchment Flood Management Plan 1 Contents The purpose of a CFMP in managing flood risk 3 Catchment overview 4 Current and future flood risk 6 Future direction for flood risk management. 10 Sub-areas 1 Headwaters sub-area 12 2 The Chalklands sub-area 14 3 Dorchester sub-area 16 4 River Frome Corridor sub-area 17 5 Wareham Forest sub-area 18 6 Poole sub-area 19 7 Coastline sub-area 20 8 Swanage sub-area 21 9 Wareham sub-area 22 Map of CFMP policies 23 2 Environment Agency Frome and Piddle Catchment Flood Management Plan The purpose of a CFMP in managing flood risk CFMPs help us to understand the • Internal Drainage Boards (IDB), CFMPs aim to promote more scale and extent of flooding now and water companies and other sustainable approaches to in the future, and set policies for utilities to help plan their managing flood risk. The policies managing flood risk within the activities in the wider context of identified in the CFMP will be catchment. CFMPs should be used to the catchment; delivered through a combination of inform planning and decision different approaches. Together with • transportation planners; making by key stakeholders such as: our partners, we will implement • land owners, farmers and land these approaches through a range • the Environment Agency, who will managers that manage and of delivery plans, projects and use the plan to guide decisions operate land for agriculture, actions. on investment in further plans, conservation and amenity projects or actions; The relationship between the CFMP, purposes; delivery plans, strategies, projects • Regional Assemblies and local • the public and businesses to and actions is shown in Figure 1. authorities who can use the plan enhance their understanding of to inform spatial planning flood risk and how it will be activities and emergency managed. 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 and • Make sure our spending delivers the best restore floodplains. possible outcomes. • Prepare for and manage floods (including local • Focus on risk based targets, for example numbers Flood Warning plans). 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 identify the • Surface water management plans. need and encourage their development. Environment Agency Frome and Piddle Catchment Flood Management Plan 3 Catchment overview The catchment of the rivers in the with clay and alluvial deposits at the the surface through springs and Frome and Piddle CFMP are located lower end. The rivers Frome and fissures. This may cause in the south west of England. They Piddle discharge into Poole Harbour groundwater flooding locally in the drain from the North Dorset Downs, at sea level just downstream of upper area, in the middle area where flowing through Dorset to outfall into Wareham. The steep slopes at the low topography meets the chalk and Poole Harbour. Map 1 shows the top of the catchment lead to fast run- at fault and fold lines in the lower location and extent of the Frome and off responses to rainfall events. As area. It may also increase flooding Piddle CFMP area. It includes the gradients slacken and valleys across the whole catchment by rivers Frome and Piddle and their broaden through the catchment, increasing the baseflow of tributaries, and shorter rivers there is a more gradual response to watercourses. draining to Poole Harbour and run-off. The upper area of the The Frome and Piddle CFMP area is Swanage. catchment is underlain by chalk situated within the Dorset Area of geology up to 300m thick, which The downstream limit of the CFMP Outstanding Natural Beauty (AONB) readily absorbs rainfall and transmits area meets with the upstream and falls within seven of Natural it to the groundwater supplies, which boundary of the Poole and England’s Landscape Character in turn support spring and river Christchurch Bay Shoreline areas. Almost half of the CFMP area flows. This chalk aquifer is used for Management Plan (SMP) boundary at is within the Dorset Downs and public water supply. The middle and Holmebridge on the Frome, and at Cranbourne Chase Character Area. lower areas of the catchment are Wareham on the Piddle. The Poole This is a rolling chalk landscape with overlain by up to 100m of mixed and Christchurch Bay SMP deals with dramatic scarps and steep sided geology including clays that, in coastal flood management, while the valleys, supporting rich and diverse contrast to the chalk, do not readily CFMP considers the risk from tidal grassland habitats and it includes absorb water allowing it to remain on flooding. prehistoric features. Another third of the surface before discharging into the CFMP area is in the Dorset The overall catchment area is about the rivers. The large low-lying Heaths Character Area, an open and 900 square kilometres, and has a wetland areas around Poole Harbour, broad landscape with a variety of population of around 170,000. the site of important habitats, heathland, farmland, woodland and Except for the urban conglomeration provide attenuation locally. scrub. of Poole, it is a rural catchment, with The underlying geology of a urban areas making up only two per Important environmental sites in the catchment also influences cent of the total. The other main catchment include six Special Areas groundwater flows and in this urban areas include Dorchester, of Conservation (SAC), Poole Harbour catchment the groundwater flow Wareham and Swanage. and Dorset Heathlands Ramsar and regime is relatively complex. The Special Protection Area (SPA), 57 The Frome and Piddle catchment is water under the ground and water in Sites of Special Scientific Interest characterised in the upper reaches of rivers and streams interact and (SSSI) (including the River Frome the North Dorset Downs by open flooding can be caused by either SSSI), six National Nature Reserves chalk downland with steep scarp source or a combination of both. and 900 Scheduled Monuments.