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Colne Valley


2 - Overview

2.2.7 states that: the Proposed Scheme will continue on:

a viaduct approximately 3.4km long, starting approximately 190m west of Harvil Road and which will vary between 11m to 15m above the ground/water level. The viaduct will have a solid 1.4m high protection barrier adjacent to the tracks on each side. For the remainder of the western side of the viaduct there will be a 3m high noise fence barrier alongside the 1.4m high protection barrier.

This makes no mention of the overall height. Presumably the height quoted is to the track bed and to this must be added the noise barriers and overhead gantries meaning that the overall height will be substantially higher.

2.3.25 states that it will be necessary to install piled foundations within the Source Protection Zone1 and that ‘therefore a piling method will be chosen to mitigate contamination of ground water.’ This indicates the unnecessarily rushed timetable to prepare this Environmental Statement and is one of many examples throughout the entire document of missing detail and vague wording. The viaduct represents a major intrusion into the Colne Valley Park and its environment and it is unreasonable and unfair to expect people to comment - in this their last chance for public involvement - without important details being made available to them.

2.3.31 states that: Alternative routes for four PRoW will be required: a temporary alternative route for Bridleway DEN/3 to the south of its existing alignment via A412 Denham Way/North Orbital Road, DEN/P and Tilehouse Lane for a period of approximately three years and six months, adding an additional 1km. It will then be permanently diverted approximately 150m to the south, adding an additional 270m to allow provision for the future construction of the Heathrow spur without any impact to this PRoW; a temporary alternative route for Bridleway DEN/2, 500m to the south of its existing alignment along the boundary of Juniper Wood for a period of approximately five years and six months, adding an additional 1.2km. It will then be permanently reinstated along the original alignment; temporary closure of Bridleway CSP/44 for a period of approximately five years and six months. It will then be permanently reinstated along the original alignment; and temporary closure of Bridleway Rickmansworth 004 which currently runs east/west to the north of Tilehouse Lane for a period of five years and six months. It will then be permanently reinstated 250m to the south across the new Tilehouse Lane overbridge, adding an additional 400m.

The temporary stoppage of paths and lengthy diversions (if any diversion at all) will have a massive negative impact on the ability of people to use the network of footpaths and bridleways in the Park. Some of these paths that are being stopped up act as key links within the rights of way network and connect up many publicly accessible green spaces.

2.3.58 is a further example of lack of detail and explanation. This says that the compound for the Chiltern Tunnel South portal will be used to manufacture the concrete ring segments for the tunnel linings. This sounds a very significant operation, but there are no details about

what it entails. Just what are the environmental considerations and proposed mitigations for this enormous operation?

2.4.6 exemplifies further vagueness with respect to maintenance. We are told there will be routine preventative maintenance, including grinding and milling of rails (a very noisy practice) and ‘more periodic’ heavy maintenance as necessary. All this will take place ‘at night’. Again, there are no details of the frequency, duration and level of noise and lighting expected. Without such detail it is difficult, if not meaningless, to make worthwhile comment.


3 - Agriculture, forestry and soils

3.4.9 states that: During the construction phase, the total area of agricultural land used will be approximately 251.8ha as shown in Table 6. Of this total, 121.5ha will be restored and available for agricultural use following construction.

The assumption that agricultural land will be restored to pre-existing quality and will be handed back to the original owner does not take into account the impact the scheme will have on the future ability for the land to be farmed. Negative factors that do not appear to have been considered include:

The lack of continuity of farming activity

farmland is rarely as good once ‘restored’

the fields will be much smaller and divided by railway, access roads, balancing ponds, cuttings and embankments, new watercourses and therefore less practical and less economically viable for farming

These factors are more significant in the urban fringe of the Colne Valley because there are many more pressures on land (because of its proximity to London) than in more rural areas.

3.4.27 demonstrates further examples of vague and subjective assessments from which it is impossible to draw meaningful conclusions. Land requirement bringing ‘an impact of medium magnitude’, loss of forestry amounting to a ‘minor adverse’ effect. Not only are these unspecific but are entirely the opinion of the HS2 assessor who, inevitably, will seek to play down the impact.


5 - Community

5.4.2 tells us that access for walkers, cyclists and horse-rider through and around construction compounds will be maintained ‘where reasonably practicable’, without explanation of who will judge whether a course of action is reasonably practicable and what criteria he or she will use to make that judgement.

5.4.4 warns that residents of Swakeleys Road will suffer from ‘significant effects on air quality and noise’ during construction which will have a ‘major adverse effect’ on their quality of life. Other residential areas nearby will suffer the same fate. No attempt seems to have been made to look for alternative arrangements for construction and no mitigation measures are suggested.

5.4.5 The Chiltern Society supports the views of Hillingdon Outdoor Activity Centre (HOAC) and its supporters fighting to save the centre which provides outdoor education for all but with priority given to young people and those who are disadvantaged or disabled. It would not be able to operate during construction and it must be doubtful if it would survive thereafter. The Colne Valley viaduct passes right over the centre and across the middle of the lake. Apart from the visible impact on the centre, the presence of such a large structure will inevitably affect the wind patterns impacting upon the sailing activities. As stated in the ES, there are no other centres providing similar services in neighbouring local authority areas. Its loss would be a massive blow for all those that currently use the facilities. The Society feels the Government has an obligation to the hundreds of its users, young and old, to save the centre and/or give it greater protection or assist with a suitable relocation.

5.4.16 states that: The construction works are predicted to result in a change in amenity for users of Denham Waterski Club through a combination of effects. The in-combination effects are significant noise effects at the club house and significant visual effects associated with views south, west and north from the club of the construction activity. The clubhouse is used for instruction and tuition, as well as being the focus for events and therefore changes to this environment are considered to affect the club. The effects are likely to coincide for a period of approximately one and a half years. The combination of these effects is considered to result in a moderate adverse effect and is therefore significant.

The impact on Denham Water Ski club will be huge as it is unlikely that they would be able to operate during the construction phase. In the longer term, the site would be changed forever. The loss of trees would remove the barrier to the North Orbital Road and expose users to traffic noise and wind. This would be in addition to the noise of the trains and potential vibration due to the viaduct’s close proximity to the Clubhouse as well as the visual aspect.

The Proposed Scheme would change the current woodland character of the site permanently, There would be a major financial effect on the club, both short and long term through the loss of goodwill during the construction phase and it must be doubtful that the Club could survive.

5.4.18 states that: it is ‘considered’ that the Colne Valley Regional Park is large enough to absorb the construction of HS2 and retain its function. This is a serious misinterpretation. Regular users of the park already see a park under stress, affected by noise and pollution from the M40/M25/A40. The park retains its popularity, attracting thousands of visitors, mainly from nearby London boroughs, and has to be creative in coping with such numbers while retaining a countryside feel. HS2 will impose a new, intolerable strain on the park. Currently, the park remains a significant outdoor barrier between the Metropolis and the Chilterns AONB. In our opinion, HS2, particularly in the construction period, will erode that barrier to the extent that the Park's effectiveness as a major outdoor recreational area is will be seriously undermined.


7 - Ecology

7.3.2 lists the considerable number of locations where HS2 ecology consultants were not permitted access to conduct a Phase 1 habitat survey and 7.3.12 lists areas of woodland, including ancient woodland, many of which are described as habitats of principal importance. Ecological studies in sensitive areas such as this usually take many months to complete, assuming that full access is granted. The only conclusion we can draw from this section therefore, is that the assumptions are at best inadequate and at worse incorrect.

7.4.4. concedes that there will be a loss of breeding bird habitat which will result in a decline for a number of breeding birds of various species in the Mid Colne-Valley SSSI and the combined effects of woodland and wetland loss will result in what is described as a

permanent adverse impact’ on the integrity of the SSSI, which in turn is described as ‘significant’ at a national level.

7.4.13 notes that: more than half of the Denham Country Park Nature Reserve is required for construction of the proposed scheme. Other nature reserves in the area will also be impacted. Sections 7.4.25 to 7.4.34 contain a depressing list of bird habitat and other wildlife and plant life that will be adversely affected, including the risk of extinction of the coralroot when its main woodland habitats - the ancient woodlands of Ranston Covert and Battlesford Wood are removed. Britain cannot afford to keep eroding increasing rare and precious habitats. A report by the RSPB in 2012 stated that a fifth of British birds had disappeared in the last 50 years, primarily because of the loss of habitat. If this disastrous proposed route is to be accepted the Government must insist that these habitats be protected.


9 - Landscape and visual assessment

The landscape character areas (LCAs) within CFA 7 are not of the special quality in the Chilterns AONB but do, in combination, create a significant green lung between the edge of London and the AONB. They are well used by walkers, cyclists and horse riders and provide areas of tranquillity even though they are crossed by busy roads and existing rail lines.

We believe that there is a confused methodology for assessing visual impacts, as well as misleading photomontages taken from selective viewpoints.

9.5.4 to 9.5.29 describes the range of disruption to the landscape and the tranquility that HS2 consultants believe will occur in the Harefield Farmland Valley Slopes LCA; the Colne River Valley LCA; the Colne Valley LCA; and the Maple Cross Slopes South LCA. They are mainly assessed as ‘moderate’ and ‘medium’ adverse effect, with on ‘major’ adverse effect on the landscape in the Colne River Valley LCA. We believe this to be a gross underestimation.


12 - Traffic and transport

Traffic and transport is a very complex part of the ES. As with the rest of the report, there are constant references to other publications some of which were not to hand and others had parts missing or contained very misleading information. This led to much wasted time and effort trying to find the required information. Other aspects of concern regarding Traffic and Transport are covered in our response to Volume 5 Technical Appendices Transport Assessment.

There is no doubt that construction traffic will add considerably to the levels of traffic on Motorways and main roads as well as local roads throughout the area. There could be up to 980 HGV two way trips and up to 580 car/LGV two way trips per day. In addition there will be 102 Car/LGV and 9 HGV two way trips from CFAs 8,9/10 and 460 HGV from CFA6 which will impact on this area. As has already been pointed out, further analysis is impossible because of the errors in the report. There can be no doubt however that the impact for the users of the A412/North Orbital Road will be major adverse and extremely significant for those who are just trying to go about their normal everyday business. Many will be affected by the delays and others will be out of pocket through having to find an alternative route. Yet another hidden cost of HS2!



Traffic congestion is already a major imposition in this part of South Buckinghamshire. The stretch of the M25 between the M4 and the M40 is the busiest road in Britain, carrying an average 196,000 vehicles a day (source Roadsuk.com).

When the M25 suffers its regular gridlock, some motorists leave the motorway to seek alternative routes via local roads, thus adding to local congestion.

The imposition of such a vast amount of additional construction traffic, outlined above, over many years will place an unsustainable load on the local road network. In our view:

It will mean increased congestion on motorways, A roads, B roads and local roads over a wide area. It will lead to longer journeys for emergency vehicles, public transport and school transport as well as private cars.

It will lead to greater risks, particularly involving vehicles travelling to Heathrow to catch flights, and it will increase air pollution in the immediate area.

It will mean increased delays for business traffic and those travelling to work, bringing incalculable costs to industry

In addition, the assumption (12.4.5) that HS2 workers starting work at 8am and leaving at 6pm and therefore "arriving before the morning peak hour and leaving after the evening peak hour" is woefully inaccurate (see our detailed response on rush hours in CFA 10). The morning peak period in this part of South Bucks runs between 7.30am and 9.30 am and the evening peak builds up from 4.00pm with school traffic until 6.30pm as any local motorist will confirm.

In our view the traffic calculations in the ES are weak and do not take into account the current conditions. That together with the quite obviously incorrect data makes it imperative that detailed and comprehensive traffic study must be made before the Second Reading.

(See Vol.5 TR 001-000 Table 7-3)


13 - Water resources and flood risk assessment

Draft ES 13.5.12 states that: “site compounds for … the south portal of the Chiltern Tunnel are both located in areas classified by the BGS as having a ‘very high’ susceptibility to groundwater flooding”.

This potential risk has disappeared from the final Environmental Statement, although it is noted that 225 workers, rising to a maximum of 310 workers per day, could be on site at this compound location, which will be active and therefore at risk of flooding for up to eight years.

13.2.6 states that: the tunnelling methodology is yet to be decided and it is ‘assumed’ that it will be a closed system and that the tunnel lining will be constructed such that leakage will be kept to a minimum. Given that it is admitted elsewhere in this document (section 13.3.5) that groundwater flow through the chalk is largely through ‘fissure’ (joints and fractures), it seems a gross omission that only a desk based (section 13.3.15) assessment has been made of the density of such joints and fractures in this area and that there is no borehole data to support this. A more detailed study is recommended in order to allow for the tunnel design to be drawn up with procedures in place to mitigate calculated ground water flow along known fracture and joint systems rather than being based on assumptions.

It is widely recognised that this section of the proposed route is through the Seaford Chalk Formation, noted throughout for its regular distribution of flint bands, many of these being semi-continuous tabular flints. No detailed borehole logs exist along this part of the proposed route as yet, which would indicate the precise location of such flint bands and yet these flint levels are known from other chalk tunnelling projects to be points of major ground water flow. This characteristic of the chalk of this section to be tunnelled is not considered anywhere in the Environmental Statement.

13.3.23 states that Gravel deposits form a shallow aquifer across the valley floor and the lakes occur where these gravels have been excavated. Groundwater levels in the gravels mirror those in the lakes. Any potential wide scale changes to the groundwater levels and quality in the gravels may therefore impact surface water quality and levels and vice versa.

Exactly what does ‘may’ mean in this context and what are the implications?

13.3.24 states that: vertical groundwater flow is generally restricted by a layer of weathered Chalk at the surface of the Chalk and some thin layers of finer material in the superficial deposits. However, the lower permeability layers are not consistent across the valley either in thickness or presence. Therefore in places the Chalk aquifer is vulnerable to contamination from the gravels and lakes due to the potential hydraulic continuity that is present.

Exactly what are the implications of this statement?

13.4.4 states that: the detailed design of the realignments will be completed in consultation with the Environment Agency to meet their objectives with respect to hydraulic capacity, flood risk, ecology and hydromorphology. Where reasonably practicable, the permanent channel realignments will be constructed in advance of other activities associated with the viaduct construction.

The term will be is not good enough in the context of a final ES. Where reasonably practicable, is not specific enough. Will it happen or won’t it and on what criteria is the term based?

13.4.5 states that: drainage, including that from access roads and hard standings, will discharge, where reasonably practicable, to sustainable drainage systems (SuDS) balancing ponds, prior to subsequent discharge to watercourses or if necessary to sewer.

Again the statement that this will only happen if reasonably practicable is not good enough. We need to know that it will happen regardless of whether or not it is reasonably practicable.

13.4.22 states that: specific monitoring to determine the potential impact to PWS (Affinity Water) and private abstractions will be undertaken. The monitoring schedule (to be agreed with the Environment Agency and in consultation with Affinity Water) will include monitoring before, during and after construction until the groundwater quality has stabilised within acceptable limits. The monitoring data will be assessed and used to define appropriate mitigation, should it be required.

Local authorities must be involved in such discussion.

13.4.30 states that: the Proposed Scheme includes 35 pier footings to be constructed within different sections of the Mid Colne Valley lakes including Savay Lake and, within the SSSI at Long Pond. A temporary jetty will be provided along the route and coffer dams will be constructed around each pier footing. These structures will not affect the hydrology of the lakes since the overall surface areas affected by the Proposed Scheme are small in relation to the area of each lake. The potential impacts on water quality in some individual lakes could lead to a risk of a significant adverse effect.

The use of the word ‘could’ is unsatisfactory when used in connection with a potentially significant adverse effect.

13.4.31 states that: tunnelling, piling and retaining wall construction could have the potential to impact on groundwater quality due to the migration of fluids or suspended bedrock particles giving rise to raised turbidity. At the scale of the classified Mid Chilterns Chalk groundwater body any turbid groundwater will be attenuated within the Chalk and diluted in regional flow and the overall impact on the groundwater body as a whole is deemed to be negligible which for this high value receptor would be a neutral effect and therefore not significant.

In common with many themes, the basis on which HS2 remove the ‘significance’ of an issue is not robustly demonstrated. These remain real risks to the local water resources and environment.

13.4.32 states that: the impact of any change in groundwater quality in the wider groundwater body on surface water and water dependent habitats will be negligible. Surface water features and associated water dependent habitats in the area are of high value leading to a neutral effect.

What does ‘negligible’ mean in this context.

13.4.33 states that: although effects on wider water body receptors are considered to be neutral, if fissures connect the working area of the Proposed Scheme directly to very high value receptors such as PWS, the impact of even low levels of turbidity could cause the closure of a source due to the high quality required to be met for potable use. This risk is especially the case where the Colne Valley viaduct piers are sited within the areas designated SPZ1 TH177 and SPZ1 TH174 and where the SPZ1 TH027 will be intercepted by the retaining walls for the Tilehouse Lane cutting. If a PWS was forced to shut down this would be a major impact and will therefore result in a significant adverse effect.

The use of the word ‘if’ (twice) in connection with a potentially major impact resulting in a significant adverse effect is much to vague.

13.4.34 states that: in addition, there is potential to impact groundwater quality at high value receptors such as PWS in this study area that may result from construction of the Proposed Scheme in the neighbouring CFA8, such as the Chiltern tunnel. This is because the direction of groundwater flow is from west to east and south-east from CFA8 into this area. As such, there is a risk that there could be an adverse effect on the PWS in this study area resulting from tunnelling activities in CFA8.

13.4.36 states that: the source protected by SPZ TH171 is much closer to and directly down gradient of the Proposed Scheme (Chiltern tunnel) in CFA8 than TH027 and TH177. As a result of this proximity the risk of turbid water entering this abstraction point is greater than for those protected by SPZ TH027 and TH177 and hence would result in a major impact that would be a significant effect.

The admission that there is a risk to the public water supply should not be dismissed so lightly. What exactly is the scale of this risk?

13.4.37 states that: a temporary jetty will be constructed across the River Colne and floodplain for construction of the viaduct. The deck and supporting structure of the jetty will be designed to take account of the potential for increased flood risk through measures to be incorporated within a site-specific flood risk management plan, as described in ‘Other mitigation’. There remains the potential for the jetty to obstruct some flood flows temporarily during the construction works resulting in moderate impacts on flood risk to very high value receptors with a resulting large and significant adverse effect.

The phrase there remains the potential in connection with an impact with significant adverse effect is just not specific enough. What is the likelihood of this flood risk taking place?

13.4.43 states that: the foundation piling is likely to disrupt groundwater flow. If significant flow horizons within the Chalk are obstructed this could lead to a reduction in flow to PWS abstractions that are particularly close to the route. The source protected by TH177 is located approximately 25m north-east of the route. It is predicted that the drawdown of groundwater levels at the source is likely to increase or there could be a reduction in yield by the same proportion. This potential additional drawdown or decline in yield could give rise to a major impact on the operation of this very high value receptor, particularly during times of drought. This would then be a very large and significant effect.

The use of vague terms such as likely, it is predicted, could be and could give rise is again totally unacceptable in connection with a major impact with a very large and significant effect. It is not satisfactory to risk such receptors without additional planning. Once impacted it is almost impossible to implement corrective actions.

13.4.48 states that: in respect of PWS, HS2 Ltd will agree a management strategy with the Environment Agency in consultation with Affinity Water that will cover timing of any physical mitigation, the scale and nature of monitoring and the thresholds at which actions are invoked (in terms of both quality and flow) the nature of other intervention measures and the responsibilities for ensuring agreed actions occur.

We were promised full and final details in the ES and so, at this stage, surely the phrase will agree should be have agreed.

13.4.49 states that: the private abstraction at Tilehouse Lane may be used for drinking water and further mitigation is likely to comprise the provision of an alternative water supply or other appropriate compensation for loss of the borehole.

Yet again a specific commitment is required instead of a vague is likely.

13.4.53 states that: tunnelling and other construction below the water table has the potential to impact on groundwater quality. If fissures connect the working area of the Proposed Scheme directly to the Affinity Water groundwater abstraction which is protected by SPZ TH171, the impact of low levels of turbidity will be major due to the high quality required to be met for potable use, resulting in a large and significant temporary adverse effect during the construction works.

Again, vague terms such as has the potential and if are just got good enough in connection with a major impact resulting in a large and significant temporary adverse effect is just not acceptable.

13.4.54 states that: piling for the viaduct piers could disturb the groundwater flow regime to the Affinity Water groundwater abstraction protected by source protections zones referenced as TH177. Flow horizons to the abstraction are likely to be penetrated and obstructed and as a result there could be a permanent reduction in yield at the source, resulting in a very large and significant effect which could occur during construction works.

Non-specific terms such as could disturb, are likely and could be are not acceptable when used in connection with an impact leading to a very large and significant effect.

13.4.55 states that: until a management strategy is agreed with the Environment Agency in consultation with Affinity Water, one potentially significant temporary residual effect and one potentially permanent adverse effect on the Affinity Water groundwater abstractions remain.

At this stage it is unacceptable that a management strategy has still to be agreed when it was promised that the ES would be a final document containing all relevant information.

13.4.56 states that: until design of the temporary jetty is complete and the site specific flood risk management plan is agreed with the Environment Agency, a potentially significant temporary residual effect on the risk of fluvial flooding remains. During construction works flood conveyance capacity will be reduced by the presence of a temporary jetty across the River Colne resulting in a moderate impact on very high value receptors and a large and significant effect.

It defies belief that at this late stage, a design for the temporary jetty is still not complete.



The above statements identify a number of risks to the PWS. As the Colne Valley catchment supplies 22% of London’s water supply, the mitigation methods to be used for each risk should be clearly identified.