«LONDONWEST MIDLANDS ENVIRONMENTAL STATEMENT Volume 2 | Community Forum Area report CFA7 | Colne Valley November 2013 ES 220.127.116.11 VOL LondonWest Midlands ...»
7.3.22 Korda Lake, Harefield Moor Lake, Long Pond, Broadwater Lake and Tilehouse Lake South have poor plant diversity and support invertebrate communities associated with high nutrient levels. These lakes do not qualify as a habitat of principal importance and are of local/parish value.
7.3.23 Other lakes were not accessible for survey, they are likely to have a similar water chemistry and substrate to the lakes that were surveyed and are therefore considered to be of up to local/parish value.
7.3.24 There are 11 ponds (identified using aerial photography and OS maps) in or adjacent to land required for construction of the Proposed Scheme. Field surveys of a pond east of the M25 and another in Ranston Covert and Battlesford Wood found that they supported common aquatic plants and/or were heavily shaded by surrounding woodland and dried annually. They were not considered sufficiently species-diverse to qualify for a detailed pond survey and do not qualify as a habitat of principal importance. The surveyed ponds are of local/parish value.
Eaton M.A. et al. (2009) Birds of Conservation Concern 3: the population status of birds in the United Kingdom, Channel Islands and the Isle of Man. British Birds 102, pp296–341 Assessed against Hertfordshire data as the majority of the SSSI is in this county – Hertfordshire Bird Club (undated) Hertfordshire Bird Atlas, available online http://www.hertsatlas.org.uk/ (accessed 2nd October 2013)
Ferguson, D. (2012) The Birds of Buckinghamshire. Buckinghamshire Bird Club. Buckinghamshire White, G.J and Harris, A.J. (2008) The wetland resource of the Colne Valley: an assessment of its importance to nature conservation, with special reference to waterbirds. Natural England, Herts. and Middx. Wildlife Trust and Environment Agency Stockers Lake which is 3km away is the other lake considered by White and Harris (2008) to be of high importance to birds in the River Colne valley. It will not be affected by the Proposed Scheme.
A tetrad is a 2km x 2km grid square.
Bat Conservation Trust (2012) The state of the UK’s bats: National Bat Monitoring Programme Population Trends 2012. BCT. London Wray, S., Wells, D., Long, E. and Mitchell-Jones, T. (2010) Valuing bats in ecological impact assessment. In Practice: December issue. CIEEM Potential bat roost – sites or features that may be used by bats to roost (for example mature trees or old buildings). Potential roosts are graded as being of low, moderate or high potential to support bats depending on the likely suitability of the feature concerned.
Nationally scarce = invertebrates which are recorded in 16-100 hectads (10km squares) but not included in one of the Red List Categories.
https://jupiter.erm.com/owa/redir.aspx?C=mqEyxnYYE0OJUc6sa-ZeOQgQvBFFmdAIjkctQ0T0slyQrxntBAfSNmfT8TBNfdXDgBitdtQRn4.&URL=https%3a%2f%2fecl.webhop.net%2fowa%2f%3fae%3dPreFormAction%26a%3dForward%26t%3dIPM.Note%26id%3dRgAAAAC 6bFclJ7tvQJ0vtxCsVN2RBwCwITyiUUhKTrvHymapjdcFAAAARZKcAACwITyiUUhKTrvHymapjdcFAAADDRiCAAAJ%26pspid%3d_1381399913462_64111 1363%23_ftn1 Colin Plant Associates (2006) Invertebrates and Ecological Assessment. Unpublished Report to the Institute of Ecology and Environmental Management JNCC (2011). Taxon designations spreadsheet. Available online at:. http://jncc.defra.gov.uk/page-3408 (accessed 19th September 2013) James, T.J. (2009) Flora of Hertfordshire. Hertfordshire Natural History Society. Norwich No Hertfordshire criteria were available for the significance of otter populations, therefore, Buckinghamshire criteria were used (part of this area is in Buckinghamshire): BMERC and TVERC (2009) Criteria for the Selection of Local Wildlife Sites in Berkshire, Buckinghamshire and Oxfordshire.
BMERC and TVERC A set of local populations within some larger area, where typically migration from one local population to at least some other patches is possible.
Wildlife and Countryside Act 1981 (1981 Chapter 69) Available online at: http://www.legislation.gov.uk/ukpga/1981/69 (accessed September 2013).
Tracking Mammals Partnership (2009) UK Mammals Update 2009. JNCC, Peterborough CFA Report – Colne Valley/No7 | Ecology Effects arising during construction 7.4 Avoidance and mitigation measures 7.4.1 The following measures have been included as part of the design of the Proposed
Scheme and avoid or reduce impacts to features of ecological value:
the viaduct will be built using a temporary construction jetty to limit permanent loss of standing water habitat;
the design span of the viaduct prevents the need for a pier in the Grand Union Canal. This reduces the loss of standing water and will allow continued movement of species along the canal;
the location of the proposed construction compound north of Moorhall Road reduces loss of woodland from the SSSI;
Old Shire Lane will be retained within the Proposed Scheme boundary to protect two important hedgerows;
the design of the Colne Valley viaduct ensures the River Colne will be diverted to flow between two viaduct piers avoiding the need for a long river diversion and associated loss of river habitat and ancient woodland; and modification of the river channel will be undertaken so as not to affect downstream flow characteristics or the frequency, duration or depth of flooding (as described in Section 13).
7.4.2 The assessment also assumes implementation of the measures set out within the draft CoCP (CT-003-000), which includes translocation of protected species where appropriate.
Assessment of impacts and effects Designated sites 7.4.3 The Proposed Scheme crosses the west side of the Mid Colne Valley SSSI on a viaduct between Moorhall Road and the A412 Denham Way/North Orbital Road. Approximately 19ha (14%) of the SSSI lies within the land required for the construction of the Proposed Scheme; 5.4ha is open water (6% of the open water is the SSSI); 2.9ha is running water (50% of the length of the River Colne within the SSSI); approximately 10ha is woodland (33% of the total area of woodland within the SSSI), and 0.75ha is swamp vegetation (20% of the total area of swamp within the SSSI).
7.4.4 There will be loss of breeding bird habitat and disturbance of breeding birds in the Mid Colne Valley SSSI. Loss of habitat will lead to a reduction of suitable nesting sites and therefore, over the five year construction period, a reduction in the abundance of birds within the SSSI, such as BoCC – red or amber list species such as song thrush, bullfinch and reed bunting, and also reed warbler, sedge warbler and garden warbler. Breeding birds using woodland and wetland in the SSSI will also be disturbed during construction by an increase in noise, vibration, light, and the increased presence of people and movement within land required for construction of the Proposed Scheme.
The viaduct will be parallel to the retained blocks of Ranston Covert and Battlesford
CFA Report – Colne Valley/No7 | Ecology
Wood for about 750m and thus a large area of woodland used by breeding birds will be subject to disturbance. Within the SSSI, habitat loss and disturbance will cause an overall decline in the numbers of breeding birds for a range of species.
7.4.5 Wintering water birds in the Mid Colne Valley SSSI will be disturbed by the same factors as the breeding bird assemblage and for the same length of time. However, the diversity and abundance of its wintering bird assemblage is likely to remain
the main areas affected in the SSSI (Korda Lake, Harefield Moor Lake, the east of Tilehouse Lake South and Long Pond) support relatively low numbers of water birds and there are no species exclusively associated with these lakes.
Broadwater Lake is by far the most important location for wintering birds in the SSSI (based on field data and desk study information) and is outside the land required for the construction of the Proposed Scheme;
the south-western corner of Broadwater Lake is less than 100m from the viaduct construction site and will be disturbed. However, Broadwater Lake is of sufficient size to retain the bird assemblage if one location is subject to disturbance and, for most species, this particular location is not critical to their use of the lake;
wintering birds, which are displaced from the south-western corner will find alternative roosting and foraging areas. There is already a refuge area in Broadwater Lake to protect birds from disturbance from recreational activities such as sailing and this will remain undisturbed;
construction hours will be during daylight and thus bird night roosts and feeding areas are likely to remain undisturbed;
lakes outside the SSSI (e.g. Troy Lake, Pynesfield Lake and Lynsters Lake) will be unaffected and there will be no impacts on wintering bird populations using them; and after construction standing water in Korda Lake, Harefield Moor Lake, Harefield No. 2 Lake and Savay Lake will be available again for wintering birds to use.
7.4.6 The combined effects of woodland and wetland loss and decrease in numbers of breeding birds will result in a permanent adverse impact on the integrity of the Mid Colne Valley SSSI that will be significant at the national level.
7.4.7 No significant effects are expected on the integrity of Fray’s Farm Meadows SSSI.
Construction traffic is expected to increase NOx concentrations and nutrient nitrogen deposition on a small part of the SSSI as its southern extent is close to the A40.
However, most of its southern boundary is set back from the roadside and any changes in air quality will be for the duration of the construction period only.
Therefore there will be no long-term build up in deposition or a measurable change in the plant species-richness or abundance. The change in air quality will be small in comparison with background concentrations and any such change will have a negligible effect on the SSSI.
CFA Report – Colne Valley/No7 | Ecology 7.4.8 The Colne Valley viaduct will be constructed across the Mid Colne Valley SMI. The following assessment considers impacts on each of the SMI’s designated features.
Among other factors, the extent of species-rich grassland and wet woodland habitat, and the species-richness and abundance of its breeding bird assemblage are important to its integrity.
7.4.9 Construction will reduce the extent of habitats for which the SMI is designated.
Approximately 25ha (8%) of terrestrial habitat in the SMI is in land required for construction of the Proposed Scheme. Of this approximately 4ha will be permanently lost during construction of the Colne Valley viaduct across Savay Lake and Harefield No. 2 Lake (2ha of semi-natural broadleaved woodland and 2ha of scrub and wetland habitat). A further approximately 15ha will be lost during the realignment of the National Grid overhead power lines (10ha of semi-natural broadleaved woodland from Widows Cruise Covert and Flagmoor Covert and 5ha of grassland with scrub). In addition, approximately 6ha of woodland and small areas of swamp vegetation will be lost where the SMI overlaps the SSSI (this has already described for the Mid Colne Valley SSSI). The vegetation clearance will result in a reduction of habitat available for breeding birds. In addition, there will be disturbance during construction.
7.4.10 The combined effect of woodland, wetland and grassland loss and disturbance of the breeding bird assemblage will result in a permanent adverse effect on the integrity of the SMI that will be significant at the county/metropolitan level.
7.4.11 Approximately 2.9ha (11%) of Tilehouse Gravel Pits BNS is within land required for construction of the Proposed Scheme, the majority of which is semi-natural broadleaved woodland. There will be disturbance to birds using the BNS during construction. These impacts will result in a permanent effect on the integrity of the site that is significant at the county/metropolitan level.
7.4.12 About 0.9ha (19%) of the River Colne east of Denham BNS is within land required for construction of the Proposed Scheme where National Grid overhead power lines will be realigned. This will result in a permanent adverse effect on the integrity of site that is significant at the county/metropolitan level.
7.4.13 Denham Country Park LNR will also be affected during construction. Approximately 10ha (52%) of this site is within land required for construction of the Proposed Scheme where National Grid overhead power lines will be realigned. This extent of habitat loss is a high proportion of the LNR and it will result in a permanent adverse effect on site integrity that is significant at the district/borough level.
7.4.14 In the Fray’s Valley LNR, approximately 4.2ha (6% of the LNR) of woodland and grassland will be removed where National Grid power lines will be realigned. The extent of habitat loss is relatively small in relation to the site’s size, however, as part of the precautionary assessment, it is assumed that the woodland and grassland lost is a habitat of principal importance. Vegetation clearance could therefore result in an adverse effect on site integrity that is significant at the district/borough level.
7.4.15 Dew’s Dell SBI lies partly within land required for the construction of the Proposed Scheme. Construction will result in the loss of approximately 1ha (11%) of the site,
CFA Report – Colne Valley/No7 | Ecology
which will result in a permanent adverse effect on the integrity of site that is significant at the district/borough level.
7.4.16 Denham Quarry Park LNR; London’s Canals SMI; the Colne Valley Gravel Pits Hertfordshire LWS; Harefield Hall and The Lodge SBI are all partly within land required for construction of the Proposed Scheme. The extent of habitat loss within these areas will be proportionally small and no significant effects on their integrity are expected.
7.4.17 It is considered unlikely that significant effects on site integrity will occur at the following designated sites: Ruislip Woods SSSI; Denham Lock Wood SSSI; Northmoor Hill Wood LNR; Northmoor Hill Wood and Wyatt’s Covert LWS; Breakspear House Woods SBI; Great Halings Wood LWS and Juniper Wood BNS.
Habitats 7.4.18 Construction of the viaduct in the western part of the Mid Colne Valley SSSI will result in the clearance of approximately 1.0ha of ancient woodland from Ranston Covert and Battlesford Wood. As an important component of the landscape in this area the extent of this irreplaceable habitat is important to its conservation status. Therefore the loss will result in a permanent adverse effect on its conservation status that will be significant at the county/metropolitan level.
7.4.19 In this area, there is approximately 30ha of broadleaved woodland within land required for the construction of the Proposed Scheme. This includes approximately 24ha of semi-natural broadleaved woodland and approximately 6ha of plantation
broadleaved woodland. The habitat losses relevant to the assessment comprise:
approximately 10ha in the Mid Colne Valley SSSI, including areas of ash woodland and alder woodland, which are described in the baseline. This includes Ranston Covert and Battlesford Wood, 1.0ha of which is ancient seminatural woodland;
approximately 2ha woodland around Savay Lake and Harefield No. 2 Lake, within the Mid Colne Valley SMI;
approximately 10ha in the area where National Grid overhead power lines will be realigned, including parts of Widows Cruise Covert and Flagmoor Covert, within the Mid Colne Valley SMI; and approximately 2ha distributed in a number of locations including the southern edge of Dew’s Dell SBI.
7.4.20 As extent is important to the conservation status of this habitat, these losses will result in permanent adverse effects that are significant at the county/metropolitan level for woodlands in the SSSI, SMI and at the district/borough level for other areas of woodland.
7.4.21 No significant impacts are expected on the ancient woodland within Pinnocks Wood as the electricity cables that will pass through this site will be tunnelled underground.
The depth of the utilities will be sufficient to avoid adverse effects on tree roots and will thus maintain the conservation status of the wood.