«LONDONWEST MIDLANDS ENVIRONMENTAL STATEMENT Volume 2 | Community Forum Area report CFA7 | Colne Valley November 2013 ES 184.108.40.206 VOL LondonWest Midlands ...»
CFA Report – Colne Valley/No7 | Ecology
7.4.22 Approximately 5ha of grassland with scrub within the Mid Colne Valley SMI lies within land required for the realignment of the National Grid overhead power lines. As part of the precautionary assessment, it is assumed that this loss will result in a permanent adverse effect of the conservation status of the habitat that is significant at the district/b0rough level.
7.4.23 At the River Colne approximately 170m of the river will be modified in a location adjacent to the Long Pond resulting in the removal of riparian72 vegetation and changes to river hydromorphology. This will be a permanent impact, as part of the river banks will be reinforced to maintain the new channel shape. However, the modified section of river will be engineered to prevent any upstream or downstream hydrological changes (see Section 13 for more information). Piling for the construction of viaduct piers could also adversely affect water quality and quantity. These changes are unlikely to have a significant effect on the conservation status of the River Colne as vegetation will re-colonise after construction and the majority of the river will remain unaffected.
7.4.24 It is considered unlikely that any other effects on habitat receptors significant at more than the local/parish level will occur. This includes hedgerow habitat and standing water, as relatively small areas are being affected given the abundance in the
surrounding landscape. Effects significant at the local/parish level are listed, Volume 5:
The riparian area is the interface between a watercourse and land. It includes the bank profile and associated terrestrial and emergent vegetation.
remove the majority of foraging and nesting habitat for this species. It is unlikely that the birds will be able to maintain their existing range. The loss of a rare species from the area will result in a permanent adverse impact on conservation status that is significant at the county/metropolitan level.
7.4.28 Land required for construction of the Proposed Scheme will include a single population of coralroot. Among other factors, the conservation status of this species depends on ancient woodland soils. In Ranston Covert and Battlesford Wood, 1ha of ancient woodland habitat supporting coralroot will be removed. This will reduce the known population of this species to a single colony in the area leading to an increased risk of extinction. This will result in a permanent adverse effect on coralroot that will be significant at the county/metropolitan level.
7.4.29 The viaduct and overhead power line diversion will cross habitats known to be used by otters along the River Colne and at several of the lakes. It is not expected that there will be any fragmentation of otter movement routes, as extensive areas of open water, the Grand Union Canal and the majority of the River Colne will remain unaffected by the Proposed Scheme. As part of the precautionary assessment, it is assumed that a breeding holt may be present within land required for construction of the Proposed Scheme. Loss of an otter holt could result in an adverse effect on conservation status that would be significant at up to the county/metropolitan level.
7.4.30 The viaduct and overhead power line diversion will cross habitats that may be used by water vole. As part of the precautionary assessment, it is assumed that loss of these habitats could result in a permanent adverse effect on conservation status that is significant up to the county/metropolitan level.
7.4.31 If present, construction could remove habitat suitable for great crested newt from two
the realignment of the National Grid overhead power lines may remove ponds and ditches in the vicinity of Uxbridge Golf Course and Buckinghamshire Golf Course; and the proposed sustainable placement area will remove four ponds and surrounding grassland east of South Harefield.
7.4.32 The conservation status of great crested newt depends on the availability of breeding ponds, foraging habitat and features for hibernating in close proximity to each other.
The loss of possible breeding ponds and surrounding terrestrial habitat could reduce the viability of the breeding population or fragment a metapopulation, if present, resulting in reduced genetic diversity. These impacts could result in a permanent adverse effect on the conservation status of each population that would be significant at up to the county/metropolitan level.
7.4.33 If present, common reptile species could be affected in three locations:
the Colne valley viaduct satellite compounds may remove grassland with scrub in the vicinity of Moorhall Road;
CFA Report – Colne Valley/No7 | Ecology
the realignment of the National Grid overhead power lines may remove grassland with scrub within Uxbridge Golf Course; and temporary material stockpiling along woodland edge habitats between Harvil Road and Harefield No. 2 Lake may remove grassland with scrub.
7.4.34 Habitat loss may reduce foraging and sheltering opportunities below that which is required to maintain viable populations in both locations. These impacts could, therefore, result in a permanent adverse effect on the conservation status of reptiles that is significant at up to the county/metropolitan level at each location.
7.4.35 The removal or disturbance of habitat features that are utilised by bats during breeding, hibernation or migrating between roosts is considered to have the potential to result in adverse effects on the bat populations or assemblages during construction.
However, the point at which such impacts are considered likely to result in a significant adverse effect on the conservation status of the population concerned will differ dependent on the status of the species concerned.
7.4.36 Habitat used by an assemblage of 11 species of bat will be affected where the viaduct will be constructed in the Mid Colne Valley SSSI. Three known common and soprano pipistrelle roosts will be lost when the trees supporting the bat boxes are removed.
The bat species recorded roosting in this area use several roosts within their range and readily use new or alternative roosts. With an abundance of alternative roosting opportunities within the surrounding woodland and farmland, the loss of these roosts is unlikely to significantly affect the bat assemblage.
7.4.37 The mosaic of woodland, wet woodland, flowing water and open water that will be lost is an optimal foraging resource and the River Colne is an important commuting feature. The loss of these habitats may result in the temporary disturbance of the bat assemblage, however, it is likely that all component species will disperse to, and forage within the abundant surrounding woodland and open water and are likely to use the nearby canal or lake edge as an alternative north-south commuting route.
Therefore, it is unlikely that these impacts will have an adverse effect on the conservation status of the bat assemblage. For the same reasons, there is no expected adverse effect on the bat assemblage that is likely to be present in land south of Moorhall Road. Several Daubenton’s bat roosts will be removed when woodland is cleared, although no maternity or hibernation roosts will be lost. Daubenton’s bats will use several roosts within their range and will readily use new or alternative roosts.
The Colne Valley viaduct laydown satellite compound will be within 20m of a Myotis sp. roost in a building, which may be a Daubenton’s bat maternity colony. The compound will not, however, restrict the likely flight lines from the roost to the adjacent open water or woodland. The roost, which is within 30m of the A412 Denham Way/North Orbital Road, is also already subject to noise and vibration disturbance from passing traffic. The Daubenton’s bat population associated with the River Colne may be affected by clearance of vegetation in this area. However, there is an abundance of optimum habitat (open and flowing water that is bounded by woodland) within the wider landscape and alternative commuting routes along the nearby canal and lake edges. Therefore, it is unlikely that these impacts will result in an adverse effect on the conservation status of Daubenton’s bat.
Wetland habitat will be a swamp and/or marshy grassland depending on local hydrological and soil conditions.
CFA Report – Colne Valley/No7 | Ecology Habitat reinstatement under the viaduct – after construction, woodland and scrub habitats will be allowed to re-colonise and/or they will be replanted in the land required for construction of the Proposed Scheme with the exclusion of areas that are directly beneath the viaduct or in the service road.
7.4.42 Opportunities for habitat creation are also possible within the green space between the M25 motorway, the A412 Denham Way/North Orbital Road and Chalfont Lane.
Grassland, open water and scattered trees are likely to be created as part of the restoration of the construction area.
7.4.43 A number of other habitat areas will be created primarily for the purposes of flood compensation and landscape screening or compensation. It is likely that these measures will indirectly provide ecological benefits, such as foraging and nesting opportunities for birds.
7.4.44 As part of the precautionary assessment, it has been assumed that all land identified as being required for the realignment of the National Grid overhead power lines will be cleared of vegetation. Some of this land will be required for construction and during the detailed design stage opportunities to retain parts of this area will be considered.
7.4.45 The loss of woodland breeding bird habitat from the Mid Colne Valley SSSI will be compensated for by habitat creation in Tilehouse Lane and Battlesford Wood woodland creation areas as described previously. This new woodland will take at least 30 years to be of comparable value for most bird species, although it will be beneficial as a foraging resource sooner. The provision of nesting features will be provided in accordance with the principles of mitigation (Volume 5: Appendix CT-001-000/2).
7.4.46 To compensate for the loss of approximately 0.75ha wetland habitat used by breeding birds in the Mid Colne Valley SSSI and Mid Colne Valley SMI, about 4.5ha of new wetland habitat will be created within three of the ecological mitigation areas, as described previously.
7.4.47 In addition to the compensation for the loss of habitats from within the SSSI, compensatory habitats for additional loss of grassland, scrub and woodland within the Mid Colne Valley SMI will be created at the Harvil Road woodland creation area; the National Grid feeder station wet-grassland area; and the Ickenham auto-transformer feeder station woodland/grassland creation area.
7.4.48 Loss of breeding bird habitat from the Mid Colne Valley SMI will be compensated for by habitat creation measures already outlined above including the Tilehouse Lane woodland creation area; wetland creation areas at Harefield No. 2 Lake and Harefield Moor Lake; the Harvil Road woodland creation area; the National Grid feeder station wet-grassland area and Broadwater Lake. The new bird islands within Broadwater Lake will provide replacement nesting habitat for terns, gulls and waterfowl should small numbers be disturbed from the south-west corner of Broadwater Lake, Korda Lake and Harefield Moor Lake.
7.4.49 Measures outlined above to compensate for the loss of habitat from the Mid Colne Valley SSSI will also compensate for impacts on Tilehouse Gravel Pits BNS. The sites overlap and thus the habitat affected is the same.
CFA Report – Colne Valley/No7 | Ecology 7.4.50 Measures outlined above to compensate for the loss of habitat from the Mid Colne Valley SMI will also compensate for impacts on Denham Country Park LNR and Fray’s Valley LNR. The sites overlap and thus the habitat affected is the same.
7.4.51 The loss of woodland from Dew’s Dell SBI will be compensated for by the Harvil Road woodland creation area, as well as the nearby landscape planting.
7.4.52 At the River Colne east of Denham BNS, if areas of habitat are temporarily lost, vegetation will quickly re-colonise or be planted after construction in accordance with the principles of mitigation (Volume 5: Appendix CT-001-000/2). If required, the reinstatement of the river habitat will be completed in consultation with the Environment Agency to seek to meet their objectives.
7.4.53 Following the successful implementation of these measures in accordance with the principles of mitigation (Volume 5: Appendix CT-001-000/2) and the maturation of the habitats, the effects relating to loss of habitat and the breeding bird assemblage within these designated sites is likely to be reduced to a level below that which is significant.
7.4.54 To compensate for the loss of up to approximately 30ha of woodland, of which 24ha is semi-natural broadleaved woodland and 1.0ha is ancient semi-natural woodland, a total of 19.5ha of lowland mixed deciduous woodland will be created in the Tilehouse Lane, Battlesford Wood and Harvil Road woodland creation areas. In addition, significant areas of woodland and scrub will be created as part of the landscaping.
There are also likely to be scattered areas of tree planting within the environment open space area, between the M25 motorway, the A412 Denham Way/North Orbital Road and Chalfont Lane.
7.4.55 Ancient woodland is irreplaceable. However, the loss of woodland will be compensated for through a range of measures. Ancient woodland soil with its associated seed bank and associated species (including coralroot) will be translocated to the Tilehouse Lane woodland creation area. This will increase the connectivity between Juniper Wood, Little Halings Wood and Great Halings Wood, which are all ancient woodlands. Other measures such as planting native tree and shrub species of local provenance and translocation of coppice stools and dead wood will be used as appropriate.
7.4.56 Compensation for the possible loss of up to 5ha of unimproved grassland is described within the mitigation for the Mid Colne Valley SMI as the site includes all grassland that will be affected.If an otter holt were to be lost to the south of Moorhall Road, it will be replaced in one of the wetland compensation areas that was previously described and in accordance with the principles of mitigation (Volume 5: Appendix CT-001-000/2) and will therefore be sufficient to maintain the favourable conservation status of otter in the Colne Valley.
7.4.57 If water vole are present to the south of Moorhall Road, they will be moved to the wetland creation areas previously described, before construction starts. These areas will be designed in accordance with the principles of mitigation (Volume 5: Appendix CT-001-000/2) to provide alternative habitats, in advance of construction. New habitat will be sufficient to maintain the conservation status of water vole in the Colne Valley.
CFA Report – Colne Valley/No7 | Ecology
7.4.58 Compensatory habitat to address the possible impacts on great crested newt population at Uxbridge Golf Course, Buckinghamshire Golf Course and farmland east of South Harefield will be provided within the National Grid feeder station wet grassland area and the Harvil Road woodland creation area. The habitat creation will be in accordance with the principles of mitigation (Volume 5: Appendix CT-001-000/2).
This will include the provision of ponds, terrestrial habitat and hibernation habitat sufficient to maintain the favourable conservation status of the populations affected.
7.4.59 Compensatory habitat to address the impacts on possible reptile populations from Harvil Road and Harefield No. 2 Lake, habitat adjacent to Moorhall Road, grassland within the Mid Colne Valley SMI and Uxbridge Golf Course will be created in the National Grid feeder station wet grassland creation area and the Tilehouse Lane woodland creation area. The habitat creation will be in accordance with the principles of mitigation (Volume 5: Appendix CT-001-000/2). This will include the provision of rough grassland, open water and habitat features for breeding and hibernating sufficient to maintain the conservation status of the populations affected.