RMB Chivenor Flood Defence Scheme. Non-Technical Summary FINAL. Version 3.0

Transcription

1 RMB Chivenor Flood Defence Scheme Non-Technical Summary FINAL Version 3.0

2 RMB CHIVENOR FLOOD DEFENCE SCHEME ENVIRONMENTAL STATEMENT CONTENTS 1 INTRODUCTION AND BACKGROUND II 2 THE PROPOSED PROJECT III 3 CONSIDERATION OF ALTERNATIVE OPTIONS III 4 METHODOLOGY V 5 POPULATION V 6 FLORA & FAUNA VI 7 SOILS AND GEOLOGY IX 8 WATER RESOURCES IX 9 AIR AND CLIMATE X 10 MATERIAL ASSETS X 11 LANDSCAPE AND VISUAL XI 12 CUMULATIVE AND INTERACTIVE XI 13 ENVIRONMENT COMMITMENTS AND IMPLEMENTATION XII 14 CONCLUSION XII FIGURES Figure 1 Figure 2 Figure 3 Location plan Proposed Scheme Nature Conservation Designations RMB Chivenor FDS NTS_v3_Final_ doc (I)

3 1 INTRODUCTION AND BACKGROUND 1.1 Introduction Defence Estates is an organisation of the Ministry of Defence and is responsible for the management of the MOD estate. The Defence Estate comprises some 240,000 hectares (ha) in the UK with over 4,000 sites, which includes the Royal Marine Barracks (RMB) Chivenor in North Devon. Debut Services Ltd (Debut) is Defence Estates Regional Prime Contractor responsible for providing estate management solutions in the South West of England. Black & Veatch Ltd (B&V) is an engineering and environmental consultancy and part of Debut s supply chain. B&V are responsible for the design of the proposed Flood Defence Scheme at RMB Chivenor. Due to the size of the proposed defences, an Environmental Impact Assessment (EIA) is required under the Town and Country Planning (Environmental Impact Assessment) (England and Wales) Regulations B&V have undertaken the EIA for the proposed flood defence works and prepared an Environmental Statement. This document is the Non-Technical Summary of the Environmental Statement. 1.2 Site Description Photo 1: Aerial view of RMB Chivenor RMB Chivenor is a former Royal Air Force (RAF) Airfield, which was taken over by the Royal Marines in 1985 and is currently occupied by 59 Independent Commando Squadron Royal Engineers; Commando Logistics Regiment Royal Marines; 22 Squadron RAF; and 624 Volunteer Glider Squadron Air Training Corps. The Base is located near Barnstaple, Devon on the northern bank of the Taw estuary close to the River Taw/Caen confluence as shown in Photo Need for the Project The existing flood defences are provided by a combination of natural ground, raised earth banks and flood walls, but a significant proportion are not owned or maintained by the MOD. A Tidal Flood Risk Assessment (FRA) was undertaken which considered extreme tidal levels and the extent of flood risk areas, taking into account the predicted effects of climate change. A substantial part of the Base is at risk of tidal flooding, and that the extent and severity will increase with time due to climate change. Tidal flooding has the potential to affect the use of the airfield, in addition to the use and integrity of the sewage treatment works, electricity supply, existing buildings, storage areas and other infrastructure. Furthermore, the inundation of some of these assets may result in water pollution. In the near future, the MOD proposes to undertake redevelopment at the Base, which would be compromised by future flood risk. On this basis, a flood defence scheme is essential. RMB Chivenor FDS NTS_v3_Final_ doc (II)

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5 2 THE PROPOSED PROJECT The proposed scheme is shown in Figure 2 and involves the construction of a new flood defence along a line around the main built up part of RMB Chivenor, together with isolated flood defences around a number of critical assets located around the airfield perimeter. These include a sewage treatment works and electricity sub-stations. The majority of the airfield area itself will not be further protected, therefore allowing this area to flood in response to climate change. The flood defences will generally be comprised of earth embankments and it is proposed to obtain all the material required for the embankments from borrow ditches and borrow pits on site, as well as using suitable existing material already stockpiled on site. Following construction, the borrow pits will appear as shallow grassed depressions approximately 1.5m deep. The proposed flood defences take into account sea level rise over the scheme s 25 year design life (i.e. to 2034). At that point the flood defences will need to be raised again if the standard of protection is to be maintained, taking into account sea level rise after The defences will therefore be designed in such a way that they can be raised in the future. 3 CONSIDERATION OF ALTERNATIVE OPTIONS Six options were initially considered to provide flood defences. An appraisal of the operational, physical, economic and environmental impacts and risks associated with each option was undertaken. This process enabled some options to be eliminated from further study and the remaining options to be taken forward for more detailed assessment, development and costing. The options appraisal included the following options: 1. Doing Nothing 2. Just maintaining the existing flood defences, and constructing improved standalone flood defences for new developments at the Base as required (Do Minimum Option) 3. Raising the existing flood defences along the edge of the Taw-Torridge Estuary and along the River Caen to protect the whole of the Base 4. Raising the flood defences around the MOD site boundary, to protect the whole of the Base (Outer Option) 5. Raising the flood defences along the edge of the Taw-Torridge Estuary, and constructing a tidal barrage across the River Caen, to protect the whole of the Base 6. Constructing new flood defences across the Base, to protect the main built-up area but not the airfield (Inner Option) Following the options appraisal, Option 6 (Inner option) was selected as the preferred option. Option 6 is the most cost effective solution and follows a managed adaptive approach recommended by government guidance on flood risk, whereby the changes in flood risk can be tracked and managed through multiple interventions over time. This enables a flexible approach to be followed which ensures best value for money. (III)

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7 4 METHODLOGY The EIA process normally begins with the screening process where a decision is made on whether any development requires a statutory Environmental Statement (ES). A determination was received from North Devon District Council that an ES would be required in support of the application. A process called scoping of impacts, which encompasses the identification of potentially relevant environmental issues, was then carried out. The scoping process identified that the environmental impacts of flood defence project would mainly occur construction phase and identified a number of specific issues to be considered within the Environmental Impact Assessment (EIA), including foraging habitat for birds. The collection of existing environmental information (known as baseline) used a combination of field surveys (e.g. ecological surveys) and desk studies. A 2km study area was established at the start of the EIA for desk-study information. For field surveys, a more immediate area was used, according to the environmental feature(s) being surveyed. The assessment of impacts culminates in the evaluation of the significance of the impact. The significance of the impact is the product of the sensitivity of the receptor and the magnitude of the change arising to the environment. The assessment of impact significance was classed as: Major; Moderate; Minor; or none. Where the assessment determined that there would be potentially significant impacts, mitigation measures were identified to avoid, reduce, compensate and remediate adverse impacts, or enhance potentially beneficial impacts. Where possible, these measures will be fed back into the design process, and any residual impacts were identified. The mitigation measures will be considered in the Project Environmental Management Plan, which will be passed to the Contractor and personnel responsible for operational management. 5 POPULATION 5.1 Baseline Conditions The principal settlements in proximity to the RMB Chivenor are Braunton 1km north and Barnstaple 8km east. Photo 2: Water resource centre at RMB Chivenor RMB Chivenor is a key strategic defence site and important for both the national and local economy. It estimated that RMB Chivenor generated 3.7% of the local GDP, supporting about 1,260 jobs and creating economic spending of about 0.75 million on purchases from local firms. RMB Chivenor also has a wide variety of sporting and recreational facilities on the base. (V)

8 5.2 Impact Assessment Due to the isolated nature of the site construction activities will be left to the flood plain and will therefore be of a minimal disturbance to the local community. There will be no direct disruption to any public rights of way. Traffic disruption will be kept to a minimum, as material for the embankments will come from the borrow pits and ditches so will not have to be transported to the site. Recreational activities on the base will not be affected. The proposed development has the potential to provide several temporary benefits during construction to the community and local economy such as increased demand for, and use of, local industrial and accommodation services. Once completed and in operation the proposed development will offer an improved standard of flood protection for the personnel living at RMB Chivenor and will enable the continuing use and future development of the Base. 5.3 Mitigation 5.4 The best form of mitigation remains the effective completion of the proposed development and rapid restoration of land to its previous condition. 6 FLORA AND FAUNA 6.1 Baseline Conditions Ecological surveys identified that the majority of the site is grassland of low ecological value (e.g. the airfield). However, habitats to the west of the site are of particular value for birds, including golden plover. Areas of seminatural habitats on site, including higher value grassland, open water and some scrub, are also suitable for reptiles such as the common lizard and grass snake, in addition to amphibians such as toad and palmate newts. Figure 3 shows nature conservation designations in the study area. On the Photo 3: Habitats on existing defence embankments Southern and Western Boundaries of RMB Chivenor is the nationally designated Taw- Torridge Estuary Site of Special Scientific Interest (SSSI). The nearest internationally designated site for nature conservation is Braunton Burrows Special Area of Conservation (SAC) which is 1.5km from the site. 6.2 Impact Assessment The Flood Defence Scheme avoids the majority of semi-natural habitats present on site and areas of concern for protected species. The proposed development footprint does not directly affect any of the designated areas of nature conservation. The construction phase of the defence offers a minor risk to some species, in particular to reptiles and birds, from habitat loss and disturbance. (VI)

9 Reinstatement of grassland on the flood defence embankments will maintain habitat across the site and is likely to be used by reptiles and birds. Additional habitat will be created within the borrow ditches behind the embankments. 6.3 Mitigation In order to avoid the risk of disturbance to nesting birds, all scrub clearance within the working areas will be undertaken outside of the nesting bird season (March August inclusive). Grassland in affected areas suitable for reptiles will be cut prior to construction, in order to encourage them to move away. An ecologist will be present to inspect affected areas immediately prior to construction start. Where habitats are to be disturbed or lost they will be replaced with habitat of equal or greater ecological value as described above. The habitats created within the borrow ditches will effectively offset any loss or disturbance to biodiversity features on site. Future flooding will also increase saline tolerant species on the airfield, however the site would not be flooded on a tidal cycle, estuarine habitats (such as saltmarsh and mudflat) would not develop. (VII)

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11 7 SOILS AND GEOLOGY 7.1 Baseline The Base is covered by a relatively thick topsoil layer, overlying alluvium (fertile soil deposited by rivers) in the form of stiff gravely and cobbley clay, over gravels. A Phase One Land Quality Assessment (LQA) established the overall site condition by identifying any potential sources of contamination and by providing an appraisal of environmental risks. 7.2 Impact Assessment Construction impacts on soils may comprise compaction by heavy machinery damaging the structure of soil, degradation from ineffective storage and handling, causing mixing of soil layers and wind and water erosion of stored and exposed organic soils, silts and/or crushed rock. Possibly contaminated sites have been identified and avoided by the scheme. The base as a whole is considered to be suitable for its current use without the need for extensive remediation. 7.3 Mitigation Appropriate soil protection and management measures will be implemented during construction. Following construction, the soil will be promptly restored and land reseeded. The selection of the alignment of the proposed flood defence has been chosen to reduce the risk of disturbing potentially contaminated soils. A Phase Two LQA involving soil and groundwater testing is proposed for the next stage of the project, to assess the presence (or absence) and extent of contamination in the areas identified. This will be discussed with the Environment Agency. 8 WATER RESOURCES AND QUALITY 8.1 Baseline Conditions Photo 4: Drainage outlet into Taw Estuary. The proposed flood defence scheme falls within the River Taw-Torridge and River Caen catchments. In 2000, the water quality of the Estuary was designated as Good under the Environment Agency s Estuary Classification Scheme. The base overlies what is classified as a minor aquifer and the groundwater in the area is classified as low vulnerability, due to the underlying geology. The Base currently has three consents to discharge water and there are a total of six groundwater abstraction licences in operation within 1km of Base. Much of the Base is at risk from tidal flooding. (IX)

12 8.2 Impact Assessment One of the main risks to surface waters during construction is over-ground run-off which may contain sediments and other pollutants. However, the majority of the works are separated from the estuary by grassland, and the estuary will naturally already contain some suspended solids. The excavations will not be deep enough to directly affect the minor aquifer. Overall the flood defence scheme will reduce the flood risk to the important built up areas of the Base and the proposed infiltration basins and ditches will provide enough capacity for any current and future additional surface water drainage from the Base during periods of heavy rainfall. 8.3 Mitigation Measures The contractor will be required to adopt best practise during construction to prevent pollution from sediment or accidental spillage. These may include measures such as use of sediment traps, procedures for storing potentially polluting substances. These measures will minimise risk of pollution to groundwater or surface waters. 9 AIR AND CLIMATE 9.1 Baseline Conditions The only existing emissions to air at RMB Chivenor are minor emissions from aircraft, armoured vehicles and other combustion sources. The site is within a semi-rural setting and its open nature consequently means that the prevailing winds are likely to disperse any emissions. 9.2 Impact Assessment Inevitably, dust will be produced during dry weather conditions; however it is likely that the majority of dust will be deposited in the area immediately surrounding the source (up to about 200 metres away). There are no sensitive receptors such as residential areas within 200 metres of the proposed development area and the surrounding area is predominantly grassland. Increased vehicle and plant movements during construction will emit minor exhaust gases but the open environment means that these emissions will mix and disperse and be of no significance. After construction, the scheme will have no effect on air quality. 9.3 Mitigation All plant and equipment will comply with the relevant legislation and standards relating to air emissions. Dust suppression measures will be used, where required, to keep dust to a minimum. 10 MATERIAL ASSETS 10.1 Baseline Conditions An archaeological desk study has identified several sites of known archaeological or heritage value at within the airfield and surrounding area. The site is within the floodplain of the Taw Estuary and there may also be unknown archaeological remains within the site. These are likely to be of local to regional importance. (X)

13 10.2 Impact Assessment There are no Scheduled Monuments, Listed Buildings or designated conservation areas located within 250m of the Base boundary. The direct impact on cultural heritage will be associated with groundworks from excavation of borrow pits, borrow ditches and diversion of services Mitigation An archaeological watching brief will be maintained during the excavation of the borrow pits and borrow ditches and will be agreed with Devon County Council prior to construction. A contingency will be made for the recording of any unforeseen discoveries. 11 LANDSCAPE AND VISUAL AMENITY 11.1 Baseline Conditions The Base is located on the banks of the Taw Estuary consisting of low-lying level flood plain. A landscape assessment of the Base describes it as largely undeveloped with contains runways, perimeter tracks and extensive grassland providing an open airfield character. Any change in the topography of the Base is unnoticeable either within the confines of the Base or from outside. Furthermore, although RMB Chivenor is a low-lying site surrounded by hills that provide clear vantage points, a number of limiting factors such as an abundance of hedgerows mean that views to the Base are often masked making it less noticeable. Photo 5: View of RMB Chivenor buildings from outside security fencing 11.2 Impact Assessment The main changes to landscape and views during the construction phase will arise from the clearance and reinstatement of all vegetation and excavation work. The full visual effect will be apparent from very few properties due to the isolated nature of the site. After reinstatement the borrow pits and ditches will be landscaped. The flood defence will also provide some low level screening from the operational runway area Mitigation Mitigation measures include the adoption of good construction practices including full site reinstatement; and integration with the current landscape management plan. These measures will ensure that any adverse effects are kept to a minimum and environmental enhancement opportunities are maximised. (XI)

14 12 CUMULATIVE EFFECTS 12.1 Cumulative Effects A cumulative impact assessment was undertaken in the Environmental Statement. Other proposed projects in the area which could potentially add, neutralise or interact with the impacts from the flood defence were identified and described. The projects identified where construction activities would overlap with the flood defence scheme on site were the construction of additional barracks accommodation and a mechanised transport workshop facility. Although there is some increased disturbance from multiple construction projects, these are all within the context of operations at the Base. It is anticipated that the combined impacts to the local economy during construction of these projects will be beneficial in utilising local resources and services. The proposed upgrade to the sewage treatment facility (STW) will lower the risk of pollution during inundation of the STW during flood events from the overflow of foul water pipes. This risk will also decrease in combination with the direct protection by a flood embankment to prevent inundation from flood waters. 13 ENVIRONMENT COMMITMENTS AND IMPLEMENTATION A Project Environmental Management Plan for the construction contractor to implement the mitigation identified in the Environmental Statement will be developed. The plan will be regularly updated, and will include, amongst others, a description of environmental constraints and measures to mitigate environmental impacts. Any issues that remain unresolved during the preparation of the Environmental Statement, or that arise as a result of further surveys and consultations with statutory and non-statutory bodies, will be carried forward into the detailed design phase. 14 CONCLUSION The Environmental Statement is a comprehensive record of the Environmental Impact Assessment of the proposed flood defence scheme at RMB Chivneor. The Environmental Statement has not identified any significant impacts that cannot be reduced by controls on construction techniques. These mitigation measures will be carried through into construction with a Project Environmental Management Plan and consultation with statutory authorities will continue through the life of the project. Assistance and advice will continue to be sought from experts to supplement, where necessary, the mitigation measures already proposed. It is thus considered that on completion of the reinstatement activities, there will be no long-term adverse impacts resulting from this development. There are, however, long term benefits for both humans and the environment. (XII)