SOUTH CAMBRIDGESHIRE DISTRICT COUNCIL. REPORT TO: Land Drainage Advisory Group 19 April 2007 Corporate Manager for Health and Environmental Services

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1 SOUTH CAMBRIDGESHIRE DISTRICT COUNCIL REPORT TO: Land Drainage Advisory Group 19 April 2007 AUTHOR/S: Corporate Manager for Health and Environmental Services Purpose Environment Agency Great Ouse Catchment Flood Management Plan 1. To agree a response to consultation by the Environment Agency on the Great Ouse Catchment Flood Management Plan. Background 2. The Great Ouse Catchment Flood Management Plan (CFMP) is a strategic policy document for catchment-wide flood risk management, looking 50 to 100 years ahead. The Great Ouse catchment covers an area of 8,587km². The River Great Ouse is the primary river system; it starts in Northamptonshire near Brackley and then passes through Buckingham, Newport Pagnell, Bedford, St Neots, St Ives and Earith before it crosses the Fens and flows into The Wash. The main tributaries include the rivers: Tove, Ouzel, Ivel, Cam, Lark, Wissey and the Little Ouse. The majority of the District of South Cambridgeshire is located within this catchment. 3. The plan examines how flood risk might change in the future, taking account of land use, development and climate change. It sets out the steps the Environment Agency will take to manage flood risk to address these changes. The Environment Agency has published the plan for consultation until 30 th March, and intends to finalise the plan in May Considerations 4. The CFMP identifies areas of flood risk, utilising the Environment Agency Flood Map, which indicates areas at risk of 1 in 100 or 1 in 1000 level flood events. The Agency estimate that under existing conditions, during a 1 in 100 event, 33,172 people, and 16,843 properties are at risk of flooding within the high impact areas of the catchment, causing an estimated total of 61,932,000 annual average property damages, as well as impacts on agriculture and environmental assets. 5. The CFMP then examines the impact of climate change, working on the basis of a 10% increase in peak river flows by It considers the impact of urban growth, and the resulting increase of impermeable areas in the region. It highlights the importance of Sustainable Urban Drainage Systems to manage flood risk from development. As a result of future changes in the catchment there will be an increase in peak river flows. Generally, an increase in peak flows will lead to an earlier onset of flooding, and for a given event the flood extent and flood depth will be larger. The Agency estimate that under future conditions 56,539 people, and 29,488 properties will be at risk of flooding within the high impact areas of the catchment.

2 6. Having established the extent of the risk, the role of this strategic plan is to develop a flood risk management strategy to address it. The Agency believes that a key opportunity for catchment wide sustainable flood risk management is to reduce flood risk in the Fens by storing water in the upper areas of the catchment. The CFMP identifies the extra volume of floodwater, as a result of climate change, that would reach the Fens from the five most important rivers. It then uses geographical analysis to determine the maximum amount of storage that would be possible within these rivers, taking account of constraints such as existing and planned development. 7. The CFMP proposes that the next stage in this process will be to carry out a Catchment wide hydrological study for the River Great Ouse and its tributaries. The study will identify additional flood storage areas to reduce flood risk at the catchment scale. These storage areas may be located within the District. 8. The CFMP divides the catchment into smaller areas, and develops appropriate policies for each of those areas. It then sets out an action plan, to detail how those policies will be implemented. The two areas of particular relevance to South Cambridgeshire are the Southern Rivers, and the Bedford Ouse. Catchment Wide Actions 9. The CFMP proposes a number of actions that should be implemented across the Great Ouse catchment. A number of these are directly relevant to development planning in the District: Liaise with planning authorities to make sure that brownfield sites within the floodplain are not automatically redeveloped. Identify opportunities to reduce runoff from land-use by future de-intensification. Encourage rigorous planning control to restrict new development in the floodplain. Promote the use of sustainable drainage systems where appropriate. The Southern Rivers 10. The main rivers in this unit are the River Cam, River Rhee, Bourn Brook, and the River Granta. The floodplain of this catchment is narrow and the rivers react quickly to heavy rainfall. There are a significant number of people and properties at risk from main river flooding. Within the 1 in 100 year flood extent there are 11,000 people at risk and 3,869,000 average annual damages. Current flood risk management measures include channel maintenance and flood warning. Flood defences help to protect Cambridge, Bassingbourn, Croyden and Wendy. The CFMP states that further action to reduce flood risk should be taken at the following locations: Great Chesterford, Sawston, Cambridge, Trumpington, Cottenham and Westwick 11. The catchment wide hydrological study will identify flood storage areas to reduce flood risk at the catchment scale. These storage areas may be located within this policy unit and would reduce flood risk at the places listed above. This may mean no other flood risk management measures would need to be taken. A River Cam and tributaries flood risk management study is to be prepared to investigate this, and what further actions need to be taken. This is identified as a medium priority, to take place between 2010 and The study will also consider actions which will attenuate/balance flood flows by creating washlands and balancing reservoirs or by restoring the natural floodplain. This study will also review the Bin Brook Flood Alleviation Scheme to assess whether it is appropriate within the context of strategic flood risk management.

3 12. Elsewhere within this policy unit the risk of flooding is indicated as being small and sustainable, and the plan proposes continuing with current flood risk is appropriate. It also states that it may be suitable to reduce flood risk management actions at certain locations. Bedford Ouse 13. The main river in this policy unit is the Great Ouse. Tributaries include the rivers, Twins, Tove, Ouzel, Ivel, Alconbury Brook,and Kym. There are a significant number of people and properties at risk from main river flooding. Within the 1 per cent AEP (1 in 100 year) flood extent there are 67,000 people at risk and 34,031,000 annual average damages. Current flood risk management includes flood warning and channel maintenance in smaller villages and towns throughout the unit. Flood defences help to protect Bedford, Towcester, Milton Keynes, St Neots, Kempston, Thornborough, Shefford, and Huntingdon. The CFMP has identified that further action to reduce flood risk should be taken at Swavesey. 14. The catchment wide hydrological study will identify flood storage areas to reduce flood risk at the catchment scale. These storage areas may be located within this policy unit and would reduce flood risk at the places listed above. This may mean no other flood risk management measures would need to be taken. A Bedford Ouse flood risk management study is proposed to investigate this, and what further actions need to be taken, in the following locations: Godmanchester, Holywell, Huntingdon, Needingworth, Eaton Socon, Swavesy, Wyton, Offord Darcy, Offord Cluny, Lower Shelton, Stewartby, Brackley, Olney, Wilden, Bromham and Kempston. This is identified as a high priority, to take place between 2009 and Elsewhere within this policy unit the risk of flooding is indicated as being small and sustainable, and the plan proposes continuing with current flood risk is appropriate. It also states that it may be suitable to reduce flood risk management actions at certain locations. Implications 16. Financial Legal Staffing Risk Management Equal Opportunities Consultations 17. Effect on Corporate Objectives 18. Quality, Accessible Services Village Life Sustainability Partnership The CFMP addresses the impact of climate change on flooding, and the steps needed to achieve sustainable development. The Council continues to work in partnership with the Environment Agency on flooding issues.

4 Conclusions/Summary 19. The development of Catchment Wide Flood Management Plans represents a key step forward towards taking a strategic approach to managing flood risk. It is also an opportunity to highlight that the Council wish to be consulted on the more detailed plans that will follow, in particular the flood risk management studies that will address areas within the District. Recommendations 20. That the Members of the Land Drainage Advisory Group advise the Planning and Environmental Health Portfolio Holders to pass the following comments on the consultation draft plan to the Environment Agency: General The Council welcomes the proposals for managing flood risk at the catchment level. The Council wishes to continue to be involved in development of the plan, and preparation of the flood risk management strategies proposed for the sub areas. As a result of the substantial development proposed for the Cambridge area, it is vital that the most up-to-date guidance is available on flood risk, and that the Catchment Plan and resulting studies fully take account of this growth. In particular, the following locations will be critical: a. New settlement of 10,000 homes at Northstowe b. Major Developments on the edge of Cambridge (East, North, North West, South) c. Proposed sports lakes at Milton d. Route of the Cambridge Guided Bus and A14 widening proposals It is noted that the proposed study in the Swavesey and Fen Drayton areas (Policy Unit 4) has been designated High Priority. Due to the size and importance of the above developments, it is requested that the Agency considers increasing the priority rating for the River Cam and tributaries study (Policy Unit 3) from Medium to High and that the timescale is brought forward. The new town of Northstowe appears to be located on the junction of the Fens, Bedford Ouse and Southern Rivers policy units. Figures 3.26 and 3.27 do not give the required level of detail. Would it be possible to include the new town within one policy unit? Site Specific Fig. 1.3 Table 2.6 The Council regards the LDF as being of primary importance in the Cambridge Sub-Region and not secondary as indicated in the figure The Council is of the view that Cottenham Lode should be included as a relatively important sub-catchment as mentioned on p38 under the heading Ely Ouse.

5 S document The Council supports the comments on surface water quality outlined in the S3.2.2 Is it possible to include the proposed new town of Northstowe/Cottenham Lode on the Flood Zone Mapping? S3.2.4 Please add a subsection to include historical flooding that has occurred in Oakington, Longstanton, Rampton, Histon and Impington. Table 3.7 Table 4.8 Table 5.3 Infrastructure at risk please include award drain culvert at Histon on B1049 (Cottenham Lode tributary) It is unclear whether the village of Longstanton is included in the Section on Bar Hill to Westwick. Is it possible to investigate the agricultural land to the N.W. of Cambridge as a suitable storage area for the tributaries of the Cottenham Lode? Background Papers: the following background papers were used in the preparation of this report: Great Ouse Catchment Flood Management Plan available on the Council s website: A 24-page summary is also available to view on the Environment Agency website: Contact Officers: Jonathan Dixon (Principal Planning Policy Officer) Telephone: (01954) and Patrick C Matthews (Drainage Manager) Telephone (01954)