Dorset Stour Catchment Flood Management Plan Summary Report June 2012 Managing Flood Risk We Are the Environment Agency

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Dorset Stour 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.

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Environment Agency Manley House Kestrel Way Exeter EX2 7LQ Tel: 0870 8506506 Email: [email protected] www.environment-agency.gov.uk

I am pleased to introduce our summary of the Dorset Stour Catchment Flood Management Plan (CFMP). This CFMP gives an overview of the flood risk in the Dorset Stour catchment and sets out our preferred plan for sustainable flood risk management over the next 50 to 100 years.

The Dorset Stour CFMP is one of 77 CFMPs for England The Dorset Stour catchment has a history of flood risk. and Wales. Through the CFMPs, we have assessed Over the last 50 years engineering schemes have been inland flood risk across all of England and Wales for the implemented to reduce flood risk in the catchment. At first time. The CFMP considers all types of inland present 780 properties are at risk in the catchment in a flooding, from rivers, ground water, surface water and 1% event (taking into account flood defences). This is tidal flooding, but not flooding directly from the sea likely to increase to over 2,900 properties in the future. (coastal flooding), which is covered by Shoreline We cannot reduce flood risk on our own, we will Management Plans (SMPs). Our coverage of surface therefore work closely with all our partners to improve and ground water is however limited due to a lack of the co-ordination of flood risk activities and agree the available information. most effective way to manage flood risk in the future. The role of CFMPs is to establish flood risk management We have worked with others including: Dorset District policies which will deliver sustainable flood risk Councils, Natural England, Wessex Water and the management for the long term. This is essential if we National Farmers Union to develop this plan. are to make the right investment decisions for the This is a summary of the main CFMP document, if you future and to help prepare ourselves effectively for the need to see the full document an electronic version can impact of climate change. We will use CFMPs to help us be obtained by emailing target our limited resources where the risks are [email protected] greatest. or alternatively paper copies can be viewed at any of This CFMP identifies flood risk management policies to our offices in South West Region. assist all key decision makers in the catchment. It was 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 Richard Cresswell what has been achieved and consider where we may South West Regional Director need to review parts of the CFMP.

Environment Agency Dorset Stour 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 Bournemouth and Christchurch sub-area 12

2 St Leonards, Verwood and West Moors sub-area 14

3 Wimborne Minster, Corfe Mullen and Sturminster Marshall sub-area 16

4 Middle Stour, Tarrant, Winterborne and Allen sub-area 18

5 Blandford Forum sub-area 20

6 Hambledon Hills sub-area 21

7 Upper Stour and Blackmore Vale sub-area 22

8 Gillingham sub-area 24

9 Stourhead sub-area 25

Map of CFMP policies 26

2 Environment Agency Dorset Stour 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 Dorset Stour Catchment Flood Management Plan 3 Catchment overview

The Dorset Stour catchment is Towns within the catchment include sites. Important environmental sites located in the south west of England. Gillingham, Wincanton, Shaftesbury, in the catchment include Dorset It extends from the headwaters of the Sturminster Newton, Blandford Heaths (Ramsar, Site of Special River Stour at Stourhead flowing Forum, Verwood, Wimborne Minster Scientific Interest (SSSI), SPA, south east through Gillingham and and Corfe Mullen. Environmentally Sensitive Area) and Blandford Forum to Christchurch The Cranborne Chase and Wiltshire The landscape of the Dorset Stour Harbour where it enters the English Downs Area of Outstanding Natural catchment varies considerably with Channel. Beauty (AONB). Important the varying geology along the Stour’s environmental sites in the catchment Map 1 shows the location and extent course. This influences both the include two AONB, three SAC, one of the Dorset Stour CFMP area. It river’s characteristics and the causes Ramsar and SPA, 13 SSSI (including includes the Rivers Stour and its of flood risk across the catchment. the River Frome SSSI), two National tributaries including the rivers Crane, The upper catchment consists of Nature Reserves and 1,800 Allen, Tarrant, Winterbourne and impermeable clays of the Blackmore Scheduled Monuments. Lodden. The downstream limits of Vale resulting in shallow valleys with the CFMP area meets with the wide floodplains. The central band of upstream boundary of the Poole and permeable chalk on Cranborne Christchurch Bay Shoreline Chase results in steeper valleys and Management Plan (SMP) at narrow floodplains. The lower Christchurch. catchment has the semi-permeable The Poole and Christchurch Bay SMP sands, clays and gravels of the deals with coastal flood Dorset Heaths. management, while the CFMP Run-off and changes in water levels considers the risk from tidal flooding. are rapid in the many streams on the The overall catchment area is about clays. Water levels rise more slowly 1,240 square kilometres, and has a in the rivers across the chalk, the population of around 400,000. rivers being fed by groundwater. Almost three quarters of these Within the River Stour catchment people live in the Bournemouth, there are a number of sites Poole and Christchurch designated for their environmental conglomeration in the south of the importance including Special Areas catchment. Away from this urban of Conservation (SAC), Special conglomeration the catchment is Protection Areas (SPA) and Ramsar largely rural.

4 Environment Agency Dorset Stour Catchment Flood Management Plan Map 1. Location and extent of the Dorset Stour CFMP area

Legend

Stour CFMP Mere Urban areas Wincanton Salisbury Main rivers Railway Shaftesbury Motorway

Marnhull

Fordingbridge Sherborne Sturminster Newton Verwood Ringwood N Blandford Forum Wimborne Minster

Dorchester Wareham Bournemouth 0 3 6 9 12 Kilometres

➜ The Stour in flood at Wimborne Minster

Environment Agency Dorset Stour Catchment Flood Management Plan 5 Current and future flood risk

Overview of the current flood risk What is at risk?

Flood risk has two components: the Currently, the main sources of flood At present there are around 1,500 chance (probability) of a particular risk for people, property, people and 800 commercial and flood and the impact (or infrastructure and the land are: residential properties at risk in the consequence) that the flood would whole catchment from a 1% annual • river flooding from the River Cale have if it happened. The probability probability river flood taking into at Wincanton and River Stour in of a flood relates to the likelihood of account current flood defences. This Sturminster Newton and a flood of that size occurring within a means that 1% of the total Blandford Forum; one year period. It is expressed as a population living in the catchment percentage. For example, a 1% flood • tidal flooding up to Iford; are currently at risk from flooding. has a 1% chance or 0.01 probability It is difficult to assess the current of occurring in any one year, and a • surface water drainage flooding, impact of flooding to environmental 0.5% flood has a 0.5% chance or which has occurred in features. Designated sites at risk 0.005 probability of occurring in any Bournemouth. Rural areas have would not actually be damaged by one year. The flood risks quoted in the potential to be at risk from the inundation, and in some, the this report are those that take surface water flooding. ecosystem depends on flooding. account of flood defences already in • groundwater flooding which has place. occurred in Wimborne Minster 17 Scheduled Monuments are at risk of flooding, these being mostly This catchment has a long history of and Sixpenny Handley and on bridges. Again, the actual risk of flooding. The most significant event other watercourses such as those damage from flooding is limited. in recent years occurred in Iford and draining Cranborne Chase and Longham and other hamlets in the Winterborne. November 2002 when 80 properties were affected by river flooding after a period of heavy rainfall on a saturated catchment.

➜ Park homes at Iford were flooded by the River Stour in November 2002

6 Environment Agency Dorset Stour Catchment Flood Management Plan Map 2. Flood risk to property in a 1% annual probability river flood, taking into account current flood defences

Legend

Properties at 1% risk of flooding Mere 25 - 50

51 - 100

> 100

Stour CFMP Main rivers

N Sturminster Wimborne Marshal Minster Ferndown

Winterbourne Winterbourne Kingston Zelston

Bournemouth 0 4 8 12 16 Kilometres

Table 1. Locations of towns and villages with properties at risk in a 1% annual probability river flood taking into account flood defence.

Number of properties at risk Locations

> 100 Wimborne Minster, Bournemouth, Winterbourne Kingston

51 to 100 Sturminster Marshall, Mere

25 to 50 Winterbourne Zelston, Motcombe, Gillingham

Table 2. Critical infrastructure at risk:

1 electricity sub-station, 1 water treatment works, 1 km of main roads, and 0.8km of mainline railway

Environment Agency Dorset Stour Catchment Flood Management Plan 7 Where is the risk? How we currently manage the risk

More than 40% of the people and The catchment has a history of flood Activities that reduce the probability properties that are at risk within the risk, generally due to the high of flooding include: catchment from a 1% annual rainfall that can lead to extensive • maintaining and improving probability river flood are located in flooding of the river valleys, and existing flood defences and the Winterbornes. A further 2.5% are prolonged wet periods that can lead structures, including pumping located in Bournemouth. to groundwater flooding. stations; The distribution of properties at risk Over the last 25 years, engineering • maintaining river channels; from a 1% annual probability river schemes have been implemented to • maintenance of road drainage flood is illustrated in Map 2. Table 1 reduce flood risk in the catchment, and sewers; summarises where there is flood risk including: • working with local authorities to to more than 25 properties. We influence the location, layout and • building a flood relief channel in recognise that there is also a design of new and redeveloped conjunction with flood banks on potential risk from surface water and property and ensuring that only the River Lodden at Gillingham. groundwater flooding. However, appropriate development is This provides protection up to a further studies following on from the allowed on the floodplain through 1% annual probability river flood; CFMP are needed by us and our the application of Planning Policy • building flood banks and walls on partners to quantify this potential Statement 25 (PPS25). the Shreen Water at Gillingham, risk. on the Stour at Bournemouth and Activities that reduce the Christchurch, on the Stour at consequences of flooding include: Sturminster Marshall, on the River • understanding where flooding is Allen at Wimborne, and in likely by using flood risk mapping; conjunction with a pumping • providing flood forecasting and station on the Stour at Blandford warning services; Forum. These provide protection • promoting awareness of flooding up to a 1% annual probability so that organisations, river flood. communities and individuals are These measures have all reduced aware of the risk and are prepared flood risk. in case they need to take action in time of flood; In addition to these engineering • promoting resilience and schemes, other flood risk resistance measures for those management activities are carried properties already in the out in the catchment. These include floodplain. activities which help to reduce the probability of flooding and those that address the consequences of flooding.

8 Environment Agency Dorset Stour Catchment Flood Management Plan The impact of climate change and future flood risk

In the future, flooding will be annual probability flood. Flood risk Figure 2 shows the difference influenced by climate change, from rivers increases mainly in between current and future flood changes in land use (for example Bournemouth and Sturminster risks from a 1% annual probability urban development) and rural land Marshall. river flood at key locations in the management. In the Dorset Stour catchment. Following on from the The sensitivity testing undertaken catchment, climate change will have CFMP, organisations need to work has shown that increased run-of rates the greatest impact on flood risk. The together to investigate flood risk from and rising sea level as a result of following future scenario for climate other sources (e.g. surface water and climate change have a significant change was used in the CFMP: ground water flooding) in more detail. effect on flooding and flood damage • 20% increase in peak flow in all across the catchment. Changes in In general, it is unlikely that the watercourses. This will increase land use management also have impact of flooding on environmental the probability of large-scale flood significant impact on flooding. In the sites will change significantly in the events; lower catchment the high urban future. • a total sea level rise of 925 mm by density and accumulation of the year 2100. This will increase increased run-off upstream results in the risk of flooding at, the most notable increase in Bournemouth and Christchurch. damages. Elsewhere in the catchment the impact of changes in Using river models we estimate that land use management is significant by 2100, around 6,100 people and for local communities. 2,900 properties across the catchment may be at risk from a 1%

Figure 2. Current and future (2100) flood risk to property from a 1% annual probability river flood, taking into account current flood defences

2500

2000

1500

1000

500 Number of Properties at Flood Risk at Properties Number of 0 Sturminster Marshall Tarrant The Winterbournes Wimborne Minster Bournemouth

Current Future

Environment Agency Dorset Stour Catchment Flood Management Plan 9 Future direction for flood risk management

Approaches in each sub-area

We have divided the Dorset Stour catchment into nine distinct sub-areas which have similar physical characteristics, sources of flooding and level of risk. We have identified the most appropriate approach to managing flood risk for each of the sub-areas and allocated one of six generic flood risk management policies, shown in Table 3.

To select the most appropriate policy, the plan has considered how social, economic and environmental objectives are affected by flood risk management activities under each policy option.

Map 3. Dorset Stour sub-areas ➜ Gillingham, Dorset. June 1917 Legend

Bruton Dorset Stour CFMP Salisbury Mere Sub-area

1 Wincanton Bournemouth and Christchurch Gillingham (Policy 4) Broad Chalke 2 St Leonards, Verwood and West Moors (Policy 6) Shaftesbury 3 Wimborne Minster, Corfe Mullen R and Sturminster Marshall (Policy 3) Marnhull 4 Middle Stour, Tarrant, Sherborne Winterbourne and Allen (Policy 3) Sturminster Newton 5 Blandford Forum (Policy 3) 6 Hambledon Hills (Policy 3)

7 Upper Stour and Blackmore Vale Verwood (Policy 6) Ringwood Blandford Forum 8 Gillingham (Policy 3) N 9 Stourhead (Policy 3) West Moors

Wimborne Minster

Dorchester Wareham 0 4 8 12 16 Bournemouth Kilometres

10 Environment Agency Dorset Stour Catchment Flood Management Plan Table 3. Policy options Policy 1 Areas of little or no flood risk where we will continue to monitor and advise This policy will tend to be applied in those areas where there are very few properties at risk of flooding. It reflects a commitment to work with the natural flood processes as far as possible.

Policy 2 Areas of low to moderate flood risk where we can generally reduce existing flood risk management actions This policy will tend to be applied where the overall level of risk to people and property is low to moderate. It may no longer be value for money to focus on continuing current levels of maintenance of existing defences if we can use resources to reduce risk where there are more people at higher risk. We would therefore review the flood risk management actions being taken so that they are proportionate to the level of risk.

Policy 3 Areas of low to moderate flood risk where we are generally managing existing flood risk effectively This policy will tend to be applied where the risks are currently appropriately managed and where the risk of flooding is not expected to increase significantly in the future. However, we keep our approach under review, looking for improvements and responding to new challenges or information as they emerge. We may review our approach to managing flood defences and other flood risk management actions, to ensure that we are managing efficiently and taking the best approach to managing flood risk in the longer term.

Policy 4 Areas of low, moderate or high flood risk where we are already managing the flood risk effectively but where we may need to take further actions to keep pace with climate change This policy will tend to be applied where the risks are currently deemed to be appropriately-managed, but where the risk of flooding is expected to significantly rise in the future. In this case we would need to do more in the future to contain what would otherwise be increasing risk. Taking further action to reduce risk will require further appraisal to assess whether there are socially and environmentally sustainable, technically viable and economically justified options.

Policy 5 Areas of moderate to high flood risk where we can generally take further action to reduce flood risk This policy will tend to be applied to those areas where the case for further action to reduce flood risk is most compelling, for example where there are many people at high risk, or where changes in the environment have already increased risk. Taking further action to reduce risk will require additional appraisal to assess whether there are socially and environmentally sustainable, technically viable and economically justified options.

Policy 6 Areas of low to moderate flood risk where we will take action with others to store water or manage run-off in locations that provide overall flood risk reduction or environmental benefits This policy will tend to be applied where there may be opportunities in some locations to reduce flood risk locally or more widely in a catchment by storing water or managing run-off. The policy has been applied to an area (where the potential to apply the policy exists), but would only be implemented in specific locations within the area, after more detailed appraisal and consultation.

Environment Agency Dorset Stour Catchment Flood Management Plan 11 Sub-area 1

Bournemouth and Christchurch

Our key partners are: works have been undertaken to The vision and reduce flood risk to properties, preferred policy Bournemouth Unitary Council businesses and infrastructure, notably on the left bank at Jumpers Policy Option 4 - we are already Poole Unitary Council Common and Iford. There is a managing the flood risk effectively residual risk of flooding to property Christchurch District Council but we may need to take further and considerable disruption to actions to keep pace with climate Highway Agency transport within the area. Surface change. water flooding is also of concern. Network Rail There are opportunities to reduce There is a history of flood incidents flooding in Bournemouth and Wessex Water in the areas of Iford Bridge, Christchurch by increasing storage Holdenhurst and Hurn Road. Major on the floodplain upstream. flood events were recorded in 1954 Bournemouth has a relatively high and 1979 impacting Holdenhurst, The issues in this likelihood of surface water flooding, Iford Bridge, Red Hill and Riverway sub-area which would need to be Recreation Park. 170 properties, investigated. primarily at Tucton, Iford and Wick, This sub-area covers the reach of are likely to be affected in a 1% the River Stour from downstream of annual probability flood event. Of the A338 road bridge to these 94% are residential Christchurch Harbour. It includes properties (including a Home Park), the urban areas of Bournemouth the remainder of which includes and the western part of shops, hotels and clubhouses. The Christchurch. future 1% annual probability flood This reach of the Stour is tidally event is expected to see the number influenced upstream to Iford Bridge of properties at risk increased to on normal tides and up to 2,100. Blackwater Bridge on Spring tides. Increases in flood levels as a result The natural floodplain is relatively of future change may cause wide and is important for providing overflowing or bypassing of existing flood storage. Where development defences. has encroached onto and constrains the floodplain, flood protection

12 Environment Agency Dorset Stour Catchment Flood Management Plan Proposed actions to implement the preferred policy

• Strengthen Development Control advice, including the use of SuDS, through Local Development Framework policies to ensure no increase in runoff from new developments and seek opportunities to reduce runoff, where possible.

• Develop Surface Water Management Plans for Bournemouth & Christchurch.

• Undertake a study of resilience of Iford, railway and Tuckton bridges under flood conditions and from extreme tides.

• Assess potential for improving current defences, to retain standard of protection in the future, as part of the System Asset Management Plan.

• Install monitoring equipment to quantify surface water flooding in urban areas.

• Increase coverage of Flood Warnings Direct service, in Bournemouth & Christchurch

• Improve and develop emergency response & Major Incident Plans.

Environment Agency Dorset Stour Catchment Flood Management Plan 13 Sub-area 2

St Leonards, Verwood, Moors and Dorset Heaths

Our key partners are: There are no major flood defences, This Policy is appropriate for this but an attenuation scheme in the sub-area for the following reasons: East Dorset District Council Moors Valley Country Park provides • The current risk of flooding is low some protection to areas despite the relatively high New Forest District Council downstream from minor flooding. number of people living there; Christchurch District Council Floods have been previously • The risk to caravan parks is Bournemouth Unitary Council recorded at Ferndown, West Moors, currently managed by owners’ St Leonards, Verwood and management plans. Poole Unitary Council Longham. Properties, transport and • Factors influencing change, land were affected. There is particularly urban development Natural England evidence that flooding has and land use management Forestry Commission restricted access to and within change will increase the level of Bournemouth Airport. Around 50 risk only slightly; Wessex Water properties may be at risk of flooding • This is a large rural sub-area with in a 1% annual probability flood opportunities to change how the National Farmers Union event. This will increase to around land is used and possibly change Dorset Wildlife Trust 90 properties in the future. flood storage to tackle rapid runoff due to soils, slope and the The sub-area is, on the whole, way the land is used; relatively permeable and flooding is • Factors influencing change in this mainly caused by groundwater. The issues in this sub-area are likely to affect Surface water flooding from sub-area isolated properties and villages, agricultural run-off is of concern. making large schemes unfeasible The sub-area is mainly a source for This sub-area covers two tributaries and of the Dorset Stour, the Moors and flooding further downstream. Crane Rivers. It includes the urban There are opportunities to reduce areas of Verwood, St Leonards, West the contribution that flood flows Moor and Ferndown, along with The vision and from the sub-area make to flooding many small villages and hamlets. downstream by improving or preferred policy creating wetland habitat. In the Moors River catchment there are mainly isolated properties and Policy Option 6 - we will take action temporary or seasonal with others to store water or accommodation, such as caravan manage run-off in locations that parks, that are at risk of flooding. provide overall flood risk reduction Flooding results from the capacity of or environmental benefits. local channels being exceeded and constrictions caused by road crossings.

14 Environment Agency Dorset Stour Catchment Flood Management Plan Proposed actions to implement the preferred policy

• Develop a Moors and Heaths Strategy to investigate locations for flood attenuation and wetland creation

• Set up working groups to explore and encourage Agri Environment and Woodland Scheme grants to help fund the change of land use and its management to increase water retention in the sub- catchment.

• Encourage and influence the uptake of Agri Environment Schemes to provide better land use practice with respect to rainfall run off.

• Develop a Surface Water Management Plan for Verwood, Ferndown and St Leonards.

• Continue to provide Flood Warnings Direct service, including installation of a rainfall and river flow monitoring equipment.

Environment Agency Dorset Stour Catchment Flood Management Plan 15 Sub-area 3

Wimborne Minster, Corfe Mullen and Sturminster Marshall

Our key partners are: Flood alleviation schemes were Proposed actions built in the early 1990s at to implement the East Dorset District Council Shapwick, Sturminster Marshall and Wimborne Minster to protect 162 preferred policy Poole Unitary Council properties up to the 1% annual probability flood event. However, • Continue to provide Development Wessex Water around 200 properties remain at Control advice, including the use risk in this event. The future 1% of SuDS, through Local annual probability flood event is Development Framework policies The issues in this expected to see the number of to ensure no increase in runoff sub-area properties at risk increase to 280. from new developments and seek opportunities to reduce runoff, This sub-area covers reaches of the where possible. • Develop Surface Water River Stour from Shapwick to The vision and Wimborne Minster. It includes the Management Plans for Wimborne urban areas of Wimborne Minster preferred policy Minster, Corfe Mullen and (located at the confluence of the Sturminster Marshall. Policy Option 3 - we are generally River Stour and Allen) Sturminster • Assess potential for improving managing existing flood risk Marshall (located at the confluence current defences, to retain effectively. of the Rivers Winterborne and Stour) standard of protection in the future, as part of the System and Corfe Mullen. This Policy is appropriate for this Asset Management Plan. sub-area for the following reasons: The floodplain of the Stour is • Continue to provide Flood extensive. Periods of high • The current level of flood risk is Warnings Direct service. groundwater levels maintain high low and it is not expected to • Continue practice and base flows on the chalk fed increase greatly in the future. development of emergency tributaries, which, together with • The current flood risk response & Major Incident Plans. heavy rain, can lead to rapid and management activities, carried • Continue with existing level of extreme responses from these out for the localised fluvial and maintenance, looking for watercourses. The coincidence of surface water and urban drainage efficiencies and improvements. tributary flood flows with the Stour flooding problems, are poses a risk of flooding at considered appropriate for the Sturminster Marshall and Wimborne level of risk. Minster. There are some problems associated with local surface water and agricultural flooding in and around the urban fringes of Wimborne.

16 Environment Agency Dorset Stour Catchment Flood Management Plan ➜ Wimborne, Dorset. August 1896

Environment Agency Dorset Stour Catchment Flood Management Plan 17 Sub-area 4

Middle Stour, Tarrant, Winterborne and Allen

Our key partners are: High base flows from the chalk We estimate that around 360 maintain relatively constant flows in properties are at risk in a 1% annual North Dorset District Council the Winterborne. Periods of high probability flood. This number is groundwater, together with heavy expected to rise to around 370 in Purbeck District Council rain can lead to rapid and extreme the future 1% annual probability responses from the Winterborne with flood event. East Dorset District Council the onset of flooding in steeper areas The sub-area is mainly a source for Natural England close to the source and overflowing flood risk further downstream. of the channel elsewhere. Historic Forestry Commission settlements, isolated properties and National Farmers Union villages are entwined with the Winterborne and its tributaries. The The vision and villages of Winterborne Whitechurch, preferred policy Winterborne Kingston, Winterborne The issues in this Stickland and Winterborne Zelston Policy Option 3 - we are generally have a well documented history of sub-area managing existing flood risk flooding from 1979 onwards, mainly effectively. This sub-area covers the reach of caused by springs emerging, the the River Stour from Shillingstone to Winterborne overflowing and Policy 3 applies to this sub-area for Spetisbury, excluding the urban groundwater. the following reasons: area of Blandford Forum. It includes Transport routes including the A31, • This is a largely rural sub-area the groundwater fed chalk streams A354, A350 and A357 roads have with a number of small villages the Tarrant and Winterborne as well previously been affected by and isolated properties currently as the River Allen catchment. flooding, causing inconvenience at a limited risk of flooding; In this reach of the Stour flooding is and stress to the local communities • Flood risk in the future caused by generally confined to the floodplain, which are otherwise isolated. climate change does not increase which, on the whole, is narrow and significantly and we can manage The fact that groundwater flooding confined by topography. High base it satisfactorily by what we are lasts a long time makes many of the flows from chalk fed streams currently doing; effects of flooding, such as flood maintain a relatively constant flow • Changes in upstream sub-area recovery and stress, much worse. in the Tarrant, which, together with Upper Stour and Blackmore Vale Several incidents of surface water heavy rain, can lead to flooding could reduce flood risk further in flooding have been recorded in the happening rapidly. Flooding has the future. sub-area. been recorded in the past along the floodplains of both the Stour and Tarrant, including the small villages of Tarrant Monkton, Tarrant Hinton and Tarrant Keyneston and Tarrant Gunville.

18 Environment Agency Dorset Stour Catchment Flood Management Plan Proposed actions to implement the preferred policy

• Continue to provide Development Control advice, including the use of SuDS, through Local Development Framework policies to ensure no increase in runoff from new developments and seek opportunities to reduce runoff, where possible.

• Set up working groups to explore and encourage Agri-Environment and Woodland Scheme grants to help fund the change of land use and its management to increase water retention in the sub- catchment.

• Assess potential for improving current defences, to retain standard of protection in the future, as part of the System Asset Management Plan.

• Continue to provide Flood Warnings Direct service.

• Continue practice and development of emergency response plans.

• Continue with existing level of maintenance, looking for efficiencies and improvements.

• Install monitoring equipment to quantify rainfall and ground water flooding in sub-catchment.

Environment Agency Dorset Stour Catchment Flood Management Plan 19 Sub-area 5

Blandford Forum

Our key partners are: We estimate that six properties are Proposed actions at flood risk. In the future the risk is to implement the North Dorset District Council expected to increase only slightly, but with the number of properties at preferred policy Emergency Services risk remaining less than 10. • Continue to provide Development Control advice, including the use The issues in this The vision and of SuDS, through Local Development Framework policies sub-area preferred option to ensure no increase in runoff from new developments and seek This sub-area covers the urban area Policy Option 3 - we are generally opportunities to reduce runoff, of Blandford Forum, including the managing existing flood risk where possible. villages of Stourpaine and effectively. • Assess potential for improving Blandford St Mary. This policy applies to Blandford current defences, to retain In the middle catchment the Stour Forum for the following reasons: standard of protection in the cuts through the central chalk band, future, as part of the System • There is very little current flood which is intersected by intricate Asset Management Plan. risk despite the relatively high river valleys and winterbournes. • Continue to provide Flood number of people living here, due Flooding is generally confined to the Warnings Direct service. to the defences in Blandford floodplain, which, on the whole, is • Continue practice and Forum, and we cannot justify narrow and confined by topography. development of emergency large-scale improvements; The main urban area at risk from response & Major Incident Plans. • Flood risk in the future caused by flooding is Blandford Forum and a • Continue with existing level of climate change does not series of embankments are maintenance, looking for significantly increase and we can maintained for flood defence to the efficiencies and improvements. manage it satisfactorily by what south and west of the town. Flood we are currently doing; risk from Pimperne Brook is • A more sustainable option to the managed by pumping station to the pumping station at Pimperne Stour. Brook may be investigated Since defences were built in 1986 through this policy; and 1992, flooding affecting • Changes in upstream sub-area transport routes, land and buildings Upper Stour and Blackmore Vale has been recorded in 2000 and could reduce flood risk further in 2003 at Stourpaine and Durweston the future. as a result of the Stour overflowing channel and banks. Flooding has historically been recorded around the Blandford Bridge.

20 Environment Agency Dorset Stour Catchment Flood Management Plan Sub-area 6

Hambledon Hills

Our key partners are: and drainage networks will increase Proposed actions in the future due to more frequent to implement the North Dorset District Council and heavy rain caused by climate change. preferred policy Wessex Water There is a low to medium chance of • Continue to provide Development Natural England surface water flooding on the lower Control advice, including the use areas close to the Stour floodplain Forestry Commission of SuDS, through Local and a higher chance of flooding on Development Framework policies National Farmers Union the hills of Cranborne Chase. to ensure no increase in runoff Several instances of surface water from new developments and seek flooding from undersized drainage opportunities to reduce runoff, The issues in this networks in the villages of Iwerne where possible. Minster and Fontmell Magna and • Set up working groups to explore sub-area field run-off in Compton Abbas have and encourage Agri-Environment been recorded in the last 10 years. and Woodland Scheme grants to This sub-area covers an area of the There is a medium chance of help fund the change of land use CFMP with particularly high-grade groundwater flooding, and there are and its management to increase agricultural land and includes the records of flooding from springs at water retention in the sub- Stour from Child Okeford to Compton Abbas and Fontmell catchment. Shillingstone. Other watercourses Magna in 1979 and 1996. • Develop Surface Water include Collyer’s Brook and the Management Plans or seek We believe that no properties are at River Iwerne. property resilience grants for risk of flooding in the 1% annual Shillingstone. Historical flood records show that probability flood event, and it is • Continue to provide Flood flooding has occurred in the last 25 expected this will remain the case, Warnings Direct service, years at Bedchester, Compton in the future 1% event. Abbas and Fontmell Magna due to including installation of a rainfall springs and the overflowing of and river flow monitoring Collyer’s Brook. Flooding has also The vision and equipment. been recorded at Iwerne Minster preferred option • Continue practice and and Shroton on the Iwerne River. On development of emergency the smaller tributary of Cookwell Policy Option 3 - we are generally response plans. Brook, flooding in the last 10 years managing existing flood risk • Continue with existing level of has been caused by ditches and effectively. maintenance, looking for drains overflowing. efficiencies and improvements. This policy applies to the sub-area The A350 road in Iwerne Minster for the following reasons: and the A357 road in Shillingstone have recently been closed because • Flood risk is currently low. of flooding, restricting access from • We do not expect flood risk in the these villages to Blandford Forum. future caused by climate change to increase significantly and we It is likely that the risk of flooding can manage it satisfactorily using from overflowing of watercourses existing resources.

Environment Agency Dorset Stour Catchment Flood Management Plan 21 Sub-area 7

Upper Stour and Blackmore Vale

Our key partners are: and floodplain in contrast to the The vision and wider flood extent on the upper preferred policy North Dorset District Council Stour. Flows tend to remain largely within channel, or tend to spill onto Policy Option 6 - we will take action South Somerset District Council established and recognised areas of with others to store water or floodplain. At the confluence of the West Dorset District Council manage run-off in locations that Stour and Manston Brook, provide overall flood risk reduction Wessex Water Sturminster Newton suffers from or environmental benefit. flooding. Smaller communities National Farmers Union along the Stour valley, downstream This policy applies to this sub-area Natural England of the Stour-Cale confluence have for the following reasons: been liable to flooding in the past. Forestry Commission There is a well documented history • This is a large rural sub-area with of flooding throughout the sub-area opportunities for changing how most of it away from the two major the land is used and possible rivers – the Stour and the Cale. flood attenuation through The issues in this improving/maintaining sub-area There is relatively limited chance of connectivity between channel groundwater flooding in the and floodplain in line with This sub-area covers the rural areas majority of this sub-area. We need environmental objectives. This of the upper Stour and Cale to understand more the occurrence will help reduce peak flows and catchments and the Blackmore of surface water flooding. potentially benefit other sub- Vale. It includes the town of areas downstream; Tarrant, Water from this sub-area is a main Shaftesbury and Wincanton, and Winterbourne and Allen, source of flood risk for areas the villages of Sturminster Newton Blandford Forum, Hambledon downstream. and Stalbridge, along with many Hills and Gillingham; isolated villages and hamlets. Currently there are approximately • Factors influencing change in this 25 properties at risk of flooding in sub-area are likely to affect This sub-area is a seasonally the 1% annual probability flood isolated properties and villages, waterlogged catchment, which event. This is expected to increase where large schemes are responds rapidly to rainfall and, to 35 properties for the future 1% unfeasible. because of this, has a dense annual probability flood event. network of streams and tributaries. The topography of the Cale catchment determines the relatively narrow character of the river valley

22 Environment Agency Dorset Stour Catchment Flood Management Plan Proposed actions to implement the preferred policy

• Develop a Blackmore Vale & Upper Stour Strategy to investigate locations for flood attenuation and wetland creation

• Set up working groups to explore and encourage Agri-Environment and Woodland Scheme grants to help fund the change of land use and its management to increase water retention in the sub-catchment.

• Encourage and influence the uptake of Agri‐environment schemes to provide better land use practice with respect to rainfall run‐off.

• Develop a Surface Water Management Plan for Wincanton, and Sturminster Newton.

• Continue to provide Flood Warnings Direct service.

Environment Agency Dorset Stour Catchment Flood Management Plan 23 Sub-area 8

Gillingham

Our key partners are: several properties were affected in Proposed actions the centre of the town and the Bay to implement the North Dorset District Council Road bridge was closed. Flooding also occurs near the railway preferred policy Emergency Services crossing. • Continue to provide Development Our broad scale modelling of the Control advice, including the use Stour and Shreen Water through The issues in this of SuDS, through Local Gillingham indicates approximately Development Framework policies sub-area 15 properties may be at risk in a 1% to ensure no increase in runoff annual probability flood event. We from new developments and seek This sub-area covers the town of do not expect flood risk to increase opportunities to reduce runoff, Gillingham, located at the substantially in the future. The where possible. confluence of the Stour, Lodden, future 1% annual probability flood and Shreen Water. event is expected to see the number • Assess potential for improving of properties at risk increase to 17. current defences, to retain Gillingham is located on the standard of protection in the confluence of three steep fast future, as part of the System responding watercourses draining Asset Management Plan. large agricultural catchments. The vision and Flooding has been experienced preferred policy • Continue to provide Flood many times in the past. Incapacity Warnings Direct service. of channels and road and rail Policy Option 3 - we are generally • Continue practice and crossings can lead to channels managing existing flood risk development of emergency being exceeded, properties flooding effectively. response & Major Incident Plans. and minor disruption to road transport. Soil erosion and build up This policy applies to Gillingham as • Continue with existing level of of sediment is a major problem in flood risk in the future caused by maintenance, looking for the upper catchment. Farming and climate change does not increase efficiencies and improvements. land use practices are thought to significantly and we can manage it have a significant impact on rainfall satisfactorily by what we are run-off rates and soil erosion. Major currently doing or through more flooding was recorded in 1979, sustainable measures. 1982 and 2000 due to high levels in the Stour and Lodden. In 2000

24 Environment Agency Dorset Stour Catchment Flood Management Plan Sub-area 9

Stourhead

Our key partners are: There is an estimated medium to Proposed actions high risk of surface and ground to implement the Wiltshire Unitary Authority water flooding in the Stourhead sub-area. We estimate that there is preferred policy South Somerset District Council less than 15 properties at risk from flooding in a 1% annual probability • Continue to provide Development National Farmers Union flood event. We expect there to be Control advice, including the use Natural England no increase in the number of of SuDS, through Local properties at risk in the future 1% Development Framework policies Forestry Commission annual probability flood event. The to ensure no increase in runoff from new developments and seek National Trust risk of dam break occurring associated with the lakes will be opportunities to reduce runoff, minimal with the current level of where possible. maintenance being continued in the • Set up working groups to explore The issues in this future. and encourage Agri‐Environment sub-area and Woodland Scheme grants to help fund the change of land use and its management to increase This sub-area covers the Cranborne The vision and Chase and West Wiltshire Downs water retention in the Area of Outstanding Natural Beauty preferred policy subcatchment. (AONB) and includes the villages of • Continue practice and Stourton, Penselwood and part of Policy Option 3 - we are generally development of emergency Zeals. managing existing flood risk response plans. effectively. • Continue with existing level of Stourhead includes the portion of maintenance, looking for This policy applies to the sub-unit the North Dorset Limestone Ridge efficiencies and improvements. for the following reasons: within the CFMP area, the source for • Ensure undertaker is managing both the River Stour and Shreen • Current flood risk is low; reservoir correctly. Water and a designated AONB. • There is no evidence to support Rainfall, which soaks into the that the impact of climate change permeable chalk and greensands could increase the frequency of underlying the Limestone Ridge, breaching of lakes associated appears as springs at Stourton and with the source of the Stour; Great Bottom, collecting in a series • The sub-area has particularly of lakes at Stourhead, and at the significant heritage. base of a depression as Shreen Water. Less than five floods have been recorded in the area in the last 90 years. Most recorded incidents relate to the breaching of lakes following heavy rain at Stourton and Gasper, resulting in inundation of buildings, land and transport routes.

Environment Agency Dorset Stour Catchment Flood Management Plan 25 Map of CFMP policies

Map of the policies in the Dorset Stour catchment Legend

Stour CFMP Main rivers Bruton 9 Mere Urban areas

8 Salisbury Preferred approach Wincanton Policy 1 Shaftesbury Broad Chalke Policy 2 Policy 3 Sherborne Marnhull Policy 4 7 Fordingbridge 6 Policy 5 Sturminster 4 Policy 6 Newton Verwood Ringwood Blandford 5 2 Forum N West Moors Wimborne Minster 4 3

Dorchester 1 Wareham Bournemouth

0 3 6 9 12 Kilometres

The sub-areas

1 Bournemouth and Christchurch 2 St Leonards, Verwood, Moors and Dorset Heaths 3 Wimborne Minster, Corfe Mullen and Sturminster Marshall 4 Middle Stour, Tarrant, Winterborne and Allen 5 Blandford Forum 6 Hambledon Hills 7 Upper Stour and Blackmore Vale 8 Gillingham 9 Stourhead

26 Environment Agency Dorset Stour Catchment Flood Management Plan Environment Agency Dorset Stour Catchment Flood Management Plan 27 Would you like to find out more about us, or about your environment?

Then call us on 08708 506 506* (Mon-Fri 8-6) email [email protected] or visit our website www.environment-agency.gov.uk incident hotline 0800 80 70 60 (24hrs) floodline 0845 988 1188

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