Marlow Flood Alleviation Scheme Environmental Statement Non-Technical Summary Final WNGLDC Environment Agency Title
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Non-Technical Summary i. Introduction and background Introduction The Environment Agency (generally referred to in this non-technical summary as we or us ) has prepared an Environmental Statement (ES) to document the statutory Environmental Impact Assessment (EIA) process and report the likely environmental effects associated with a proposed flood alleviation scheme for Marlow, Buckinghamshire Marlow Flood Alleviation Scheme 1. The Non-Technical Summary forms a summary of the key issues raised in the Environmental Statement and is used/available as a standalone document. This Non-Technical Summary includes nine illustrations, which are identical to the figures from the ES. They have not been re-numbered; hence their numbering is not sequential. The scheme will comprise the construction of flood defences (flood walls and flood bunds), groundwater pumping wells, improvements to surface water drainage, local ground raising and compensatory flood storage areas in various locations in and around Marlow. The study area (see Figure 1.1) encompasses residential areas near Gossmore Lane and Pound Lane and fields near Lower Pound Lane, all within Marlow. The study area is low-lying and has been subject to river and groundwater flooding on a number of occasions, most recently in January 2003. The study area is administered by Buckinghamshire County Council and Wycombe District Council. The proposed flood alleviation works require planning permission and fall under the Town and Country Planning (Environmental Impact Assessment) (England and Wales) Regulations 1999 (under Schedule 2 of the Regulations). The ES will accompany the planning application to Wycombe District Council. The proposed scheme will be undertaken in accordance with development plan policies and appropriate mitigation has been provided where necessary. Flood Management Options Options we considered during the development of the scheme to manage the river and groundwater flooding included do nothing (no intervention to reduce the flood risk), do minimum (providing emergency measures and flood warning only) and various options to improve the standard of flood protection and reduce the risk of river and groundwater flooding. We also considered alternative alignments of flood defences and alternative locations of compensatory flood storage areas. The scheme is not intended to address short-term flooding from rainwater runoff. The proposed scheme will provide protection to 287 properties in the Pound Lane and Gossmore Lane areas of Marlow against flood events with a one per cent annual 1 Both the Gossmore Lane area (previously referred to as Firview Close Flood Alleviation Study ) and Pound Lane area were initially identified and progressed as separate flood alleviation schemes. However, due to the need to provide a combined flood storage area at Lower Pound Lane, and additional benefits associated with combining the two sites, both projects have been combined into a single integrated flood alleviation scheme for Marlow.
probability of flooding (i.e. a 1 in 100 chance of flooding in any one year). Figures 2.3 and 2.4 show the areas which will benefit from the scheme. Description of the scheme The scheme involves construction works in three areas (see Figures 3.1 to 3.3), which are listed upstream to downstream, as follows: - Lower Pound Lane area Approximately 11ha of compensatory flood storage area will be excavated on the northern edge of Lower Pound Lane. This area will be landscaped to provide new wildlife areas comprising scrapes and meadow grassland. Pound Lane area A continuous flood-wall at the rear of residential properties in Pound Lane formed of reinforced concrete with cladding of brick or material of similar appearance. The wall will be approximately 260m long and have a maximum height above local ground level of 1.5m and an average height of approximately 1.2m. A bund approximately 0.5m high at Marlow Sports Club to provide a flood defence. Eight groundwater pumping wells. Approximately 1.3ha of compensatory flood storage area for flood storage will be excavated in a field at Marlow Sports Club. This will provide a proportion of the storage required, with the majority provided at Lower Pound Lane. This is proposed to compensate for the loss of storage within the floodplain as a result of the construction of the flood defences. The provision of a central level area (approximately 65m x 100m) in the same field as the bund and flood storage area will provide Marlow Sports Club with an opportunity to create a formal recreation area, at some point in the future (subject to gaining the necessary consents). A 1.5m wide path, utilising the base of the flood-wall, will be retained at the rear of the properties in Pound Lane to enable annual inspections and maintenance. In order to prevent the public from accessing the woodland area at the rear of properties in Trout Close a gate will be located along the route of the access path at the location of the existing chain-link fence. The fence and gate will be 1.2m high. The earthworks at Pound Lane will re-use approximately 500m 3 of material excavated from the compensatory storage area to avoid excessive transportation and landfill capacity impacts associated with disposing of material at a licensed tip. A further 4,200m 3 will be transferred from the Pound Lane area to the Gossmore Lane area for use in the flood defences there. Gossmore Lane area Three flood-gates at Millbank An earthwork bund, approximately 1.4m high and 110m long, across the northern side of Pergola Field. A flap-valve added to the outfall connecting a road gulley near 37 Mill Road to the river. A brick-clad reinforced concrete wall, approximately 1.5m high, around and within two gardens. This connects the bunds in Pergola Field and the playing field. A flood bund with a sheet pile core within the playing field, behind the houses of Gossmore Close.
Raising the level of the football pitch at the playing field with a low bund around it to provide flood defence. A concrete wall in the A404 drainage ditch alongside the playing field, with a flap valve to allow normal drainage out to the river while preventing flood water backing up the ditch. Part of the access track leading to the car park will be raised to complete the flood defences. Raising the road at the north end of Gossmore Lane to create a ramp approximately 30m long and 70cm high. Eight groundwater pumping wells (to pump groundwater when rising groundwater levels threaten to cause flooding). Construction accesses Gossmore Lane area The main entrance is located at the eastern end of the football pitches at Gossmore Lane adjacent to the The Pines residential dwelling. The second entrance will be where Mill Road meets Gossmore Lane adjacent to a dwelling known as Furleigh Cottage. Pound Lane area Access will be directly from Pound Lane and into the Marlow Sports Club car park. Lower Pound Lane area Access to the site will be from Lower Pound Lane, through a field and over a stream; this is necessary because the bridge carrying Lower Pound Lane over the stream is too weak for heavy vehicles. We have designed (and subsequently modified) the scheme to minimise social and environmental impacts and provide environmental enhancements. Consultation Effective stakeholder consultation and public engagement was central to the development of the Marlow Flood Alleviation Scheme in order to arrive at a scheme that is acceptable to as many parties as possible and to engage those parties in the process. During the development of the scheme, we consulted affected landowners and local residents, statutory consultees (Natural England and English Heritage), other key organisations (such as Wycombe District Council and Buckinghamshire County Council) and our internal environmental and flood-protection specialists. A public exhibition was held in Marlow on 8 July 2009 to present the preferred solution for flood risk management and to provide an opportunity for comment and discussion on the proposals. Comments received at all stages in consultation have been taken into account in the finalisation of the scheme, leading to the preparation of the ES. ii. The Existing Environment, Impacts and Mitigation Figures 16.1 to 16.3 show the environmental features, constraints and opportunities associated with the proposed scheme. Human Beings The proposed scheme will have a major benefit by reducing the risk of river and groundwater flooding to 287 properties. However, the proposed works lie adjacent to residential properties on the southern edge of Pound Lane, Bream Close and Trout Close, the northern edge of Lower Pound Lane and the southern edge of
Gossmore Lane. During construction, there will be increased traffic flows on the local road network, visual intrusion and elevated levels of dust and noise which will cause disruption for residents, the majority of whom will ultimately benefit from improved flood protection. Some properties (Millbank apartments and two houses) will also experience temporary disruption due to work in their gardens. With the exception of two nights of work described below, all works will be timetabled to reduce the potential for disturbance and be carried out during normal working hours, 7am to 7pm weekdays and 7am to 1pm Saturdays, with the noisiest activities not starting before 8am or finishing after 5pm. Strict safety standards will be in place to protect members of the public and the construction workers themselves. Information will be made available to local residents and the public in relation to the nature, timing and duration of particular construction activities. We will continue to consult occupants and owners of affected properties over the construction programme. In addition, we will agree vehicle routes and timings, and parking restrictions with Buckinghamshire County Council in order to minimise the risk of disruption on the local road network. It is inevitable that the level and nature of noise generated by construction activities will be greater than the pre-existing background noise levels and is therefore likely to cause disturbance and disruption to local residents. Disruption due to construction is however generally a localised phenomenon and temporary in nature. Noise predictions indicate that noise levels have the potential to disturb residents during the construction works. Affected areas include those properties around Millbank, Gossmore Close, Gossmore Lane, Grayling Close, Trout Close and Pound Crescent. The River Thames lies immediately south of Gossmore Lane area and the Thames Path National Trail (public footpath) follows the river through Marlow. Recreational users will be affected by construction works during the temporary closure of Pergola Field and the land used as a playing field and associated football pitch. The Thames Path will be temporarily diverted. However, on completion of the scheme, part of the Thames path will be improved through resurfacing (see Environmental Enhancements) and a circular walk suitable for wheelchair access will be created. Ground raising will also improve the football pitches leaving them flatter, less stony and less prone to flooding. Local road raising at the top of Gossmore Lane adjacent to the railway is likely to increase journey times for vehicle users and result in some traffic congestion. Prior to the road raising works, affected residents and the Rugby Club will be notified of the construction programme. The exact timing of the works will depend on Network Rail s requirements, as a small part of the scheme is on railway land. Two nights of construction work are needed so that localised raising of Gossmore Lane can be carried out without needing to close the railway. There will be no other night-time working. The excavated material (4200m 3 ) to be transferred from the Pound Lane area to the Gossmore Lane area for use in the flood defences equates to approximately 30 HGV movements per day each way over a four-week period. The HGV movements will be restricted to between 9am and 3pm (or 4pm during school holidays) to avoid rush hour and school run times. Land Use There will be temporary localised closure of amenity land adjacent to Marlow Sports Club at Pound Lane and further temporary losses of two areas of public open space. Additional land will be required for site compounds, storage
areas and working areas. Following reinstatement of all private and public areas and extensive landscaping, the residual adverse impacts will be only minor in nature or not significant. The works will also necessitate the permanent loss of: approximately 1000m 2 of scrubland and woodland for the construction of a flood-wall, groundwater pumping wells and a permanent footpath at Pound Lane and reduced agricultural productivity in approximately 27ha of agricultural land in the footprint of a proposed storage area at Lower Pound Lane. Also, approximately 6000 m 2 of public open space will be affected: it will be raised and will slope, but will still be available for public use. The impacts on agriculture will be mitigated by retaining agricultural use of the fields and by compensating landowners for the loss of productivity. Landscape and Visual Amenity The study area lies within the London Metropolitan Green Belt and an Area of Attractive Landscape, and falls within the Chilterns countryside character area. The proposed working areas lie within a flat low-lying landscape, typical of the wide floodplain of the River Thames. The greatest impact on the existing landscape character will be from the felling of an estimated 28 trees in the footprint of the proposed flood-wall at the rear of Pound Lane (although overall only a small area of the woodland will be affected by the proposals) and 16 trees in Pergola Field (plus the trees and shrubs in a hedge bordering Pergola Field). Replacement tree planting with native trees will be undertaken, however the replacement trees will not be in the existing woodland area, since there will be no room to re-plant them; they will be planted in an adjacent part of the Pound Lane site. The construction of the proposed scheme (notably the flood wall, earthworks and compensatory storage areas) will result in a change of views for residents and recreational users. The impact on these receptors will vary (from slight adverse for some receptors to substantial adverse for other receptors) dependent on the location, existing view and establishment of vegetation on completion of the scheme. Cultural Heritage, Archaeology and Material Assets No sites of already-known archaeological interest will be affected by the footprint of the proposed works although the Thames Valley, just upstream of Marlow is considered to have high archaeological potential. The proposed works will disturb buried archaeological remains in the footprint of the proposed works in excavated areas but may protect archaeological remains in areas where it is proposed to deposit fill material. We are working in consultation with the County Archaeologist and our internal archaeological officer to refine an archaeological mitigation strategy. Flora and Fauna The proposed scheme will be located in an area that includes public open space and woodland, and will involve the felling of an estimated 90 trees. As the works have the potential for disturbance to and loss of habitats (notably woodland and scrubland) and species during the construction works, mitigation measures will be implemented. These will include felling trees and clearing vegetation outside of the bird-breeding season and at times chosen to minimise risk to bats, avoiding the root zones of adjacent trees, minimising the footprint of the works and selecting access routes as far as possible to avoid flora and fauna Some habitat can be created as part of the scheme including the creation of meadow grassland in the proposed compensatory area at Lower Pound Lane. In addition, the proposals include planting of 200 trees to partially compensate for the trees being
felled. Replanting includes all areas of the scheme except the woodland, where tree planting is not considered appropriate since natural regeneration will occur. Plans showing measures to protect affected trees have been prepared and will be adhered to in order to minimise the number off trees affected by the scheme. Air and Climate Appropriate working methodologies will be used to minimise dust generated by the construction works. Loaded vehicles will be sheeted and a mobile road cleaning vehicle will be available. Water The release of soil / sediment into water courses and the accidental spillage of materials during construction of the proposed scheme have the potential to result in the deterioration of water quality in ditches and areas of stagnant standing water within the study area. However, following standard practices to minimise the risk of pollution, a pollution event is highly unlikely and the overall impact on water is negligible. Following completion of the scheme, and in addition to a reduced risk of river and groundwater flooding to 287 properties, there will be an intermittent benefit to water quality due to reduced flooding of highways and sewers. Soil, Geology and Hydrogeology No impacts on geological features or the groundwater regime are anticipated as a result of constructing the proposed scheme. Natural Resources and Sustainability The scheme will, where possible incorporate environmentally sustainable techniques and materials, and we will ensure that emissions are minimised and resources are disposed of in a sustainable manner. A Site Waste Management Plan will consider reduction, re-use and recycling of soils (in particular material excavated from the compensatory storage areas). We have prepared an Environmental Action Plan (EAP) to ensure that the mitigation measures identified by the EIA will be addressed during the implementation phase of the project. During the construction works, to the site supervisor will ensure that the actions identified in the EAP to protect the environment are implemented. iii. Environmental Enhancements The scheme provides major benefits by reducing the level of flood risk posed to human assets in the hinterland of the defences. The proposed scheme will also provide some environmental enhancements, which are discussed in greater detail in the ES, and are summarised below: Hard surfacing of the Thames Path National Trail between Millbank and the A404, and the construction of a new gravel surface path, resulting in the creation of a circular route for recreational users, which also provides wheelchair access. New timber benches (including some on new areas of hardstanding that provide wheelchair access) at Pergola Field in the Gossmore Lane area to replace existing deteriorating benches and picnic tables. These will have an enhanced view of the river compared to the existing benches. The existing memorial bench by the path in the middle of Pergola Field will be replaced close to its current position following completion of the scheme. The flood compensatory storage area at Lower Pound Lane will be managed to increase its habitat value. Some areas outside the floodplain will be
managed as meadow and excavated areas will be managed as wet meadow with scrapes. The scrapes will be ponds with shallow-sloping edges, designed to dry out from time to time in summer while containing water for a significant proportion of the year. These will provide suitable habitat for amphibians by discouraging colonisation by fish.