IMPACT OF ASH DIEBACK (CAD) ON EARTHWORKS STABILITY AND THIRD PARTY LIABILITIES
Request ID: FOI-1715-2122 Date published: 29 December 2021
You asked
FOI REQUEST – LONDON UNDERGROUND LIMITED - IMPACT OF CHALARA ASH DIEBACK (CAD) HYMENOSCYPHUS FRAXINEUS ON EARTHWORKS STABILITY AND THIRD PARTY LIABILITIES
Ref:
A. FOI Act 2000.
B. FOI Request TfL Ref: 1303-1213 dated 7 Nov 12.
C. FOI request TfL Ref: 0258-2021 - Vegetation Management: Why we do what we do – TfL undated document.
D. London Assembly Environment Committee report January 2012 - On the right lines? Vegetation Management on London’s Railway Embankments.
E. Network Rail Review of Earthworks Management - Professor Lord Robert Mair - February 2021.
1. This FOI request addresses London Underground Limited’s (LUL) engineering and vegetation management responses to the impact of Chalara Ash Dieback (CAD) Hymenoscyphus fraxineus on network earthworks and third party liability.
2. I have attempted to locate the information required from publicly available sources but cannot locate any information which relates specifically to the impact of CAD, with the exception of TfL’s response to the FOI Requests at References B and C. The former response indicated TfL had no ash trees which were then suffering from CAD and also that no count was made of the number of ash trees on LUL estate. The latter and more recent FOI response indicated that all trees are subject to a 3 monthly cycle of inspection and that diseased trees are felled or made safe as quickly as possible, although the criteria for each was not discussed in detail. The publicly available London Assembly Environment Committee report from January 2012 on railway embankment vegetation management, at Reference D, did not address the impact of CAD.
3. Clearly CAD is now a much more significant issue than it was in 2012. The significant report at Reference E in particular discusses the role of trees in earthwork stability but highlights the need for further work to quantify the effectiveness of managed vegetation and bioengineering for Network Rail earthwork slopes. The loss of large numbers of trees due to CAD must be a factor in addressing this issue.
4. The following information is requested:
a. Details LUL policy or management plans which specifically address assessment and risk mitigation for the impact of CAD on network earthwork stability and third party liability. Please make any plans available.
b. Reference C mentions a TfL Landscaping and Vegetation Standard most recently reviewed in 2017. Please make this standard available.
c. Details of any general LUL consultation with local authorities on the potential impact of CAD on infrastructure and third party liabilities. eg the potential for increased/reduced earthwork displacement or falling trees and their impact on adjacent property.
d. Details of any LUL planning for a managed approach to prioritise ash tree clearance and re-establishment of alternative trees. Please include the criteria for felling or making safe ash trees. Does LUL now monitor the number of ash trees present at lineside?
e. Details of any LUL plans to monitor long-term pore water pressure variation and earthwork displacement to assess and quantify the impact of significant tree removal due to CAD on high plasticity clay embankments. Are specific earthworks of concern monitored for stability and if so how are monitored earthworks selected?
f. Details of how vegetation management is organised across LUL network management zones. Which management area of LUL has responsibility for the management of vegetation on the Metropolitan Line at Northwood? How can they be contacted?
g. Please provide information on the date and results of the last assessment of the Metropolitan line infrastructure between Northwood and Moor Park with respect to:
i. Trees; their assessed state of health, maintenance, and any overhanging of adjacent properties.
ii. The stability of the earthworks and any indications of displacement of earthworks.
5. I appreciate the administrative burden of FOI requests but, as was highlighted at Reference D, public consultation on vegetation management on London’s railway embankments has not been strong in the past and it is notable that the information publicly available from TfL on this subject is considerably less than that from Network Rail.
We answered
TfL Ref: 1715- 2122
Thank you again for your request received by Transport for London (TfL) on 2 November 2021 asking for information about the impact of Ash dieback (CAD) on earthworks stability on the London Underground network.
Your request has been considered in accordance with the requirements of the Environmental Information Regulations and our information access policy. I can confirm that we hold some of the information you require. Your questions and our replies are as follows:
Details LUL policy or management plans which specifically address assessment and risk mitigation for the impact of CAD on network earthwork stability and third party liability. Please make any plans available. We do not have specific plans for CAD as our tree inspections take into account the state of each tree and any risk it may pose regardless of the cause for the poor tree health.
Reference C mentions a TfL Landscaping and Vegetation Standard most recently reviewed in 2017. Please make this standard available. Please see attached as requested.
Please note that in accordance with TfL’s obligations under the Data Protection legislation some personal data has been removed, as required by Regulation 13 of the Environmental Information Regulations. This is because disclosure of this personal data would be a breach of the legislation, specifically the first principle of the legislation, which requires all processing of personal data to be fair and lawful. It would not be fair to disclose this personal information when the individuals have no expectation it would be disclosed and TfL has not satisfied one of the conditions of Schedule 2 which would make the processing ‘fair’.
Details of any general LUL consultation with local authorities on the potential impact of CAD on infrastructure and third party liabilities. eg the potential for increased/reduced earthwork displacement or falling trees and their impact on adjacent property. We do not hold this information because we haven’t consulted with any local authorities on this issue.
Details of any LUL planning for a managed approach to prioritise ash tree clearance and re-establishment of alternative trees. Please include the criteria for felling or making safe ash trees. Does LUL now monitor the number of ash trees present at lineside? Ash trees are not on the preferred species list so self seeded saplings are removed during the course of routine vegetation management. Established trees are managed through the inspections as described in answer a. above.
Details of any LUL plans to monitor long-term pore water pressure variation and earthwork displacement to assess and quantify the impact of significant tree removal due to CAD on high plasticity clay embankments. Are specific earthworks of concern monitored for stability and if so how are monitored earthworks selected? As per our answer to point a, we do not have specific plans for CAD as our tree inspections take into account the state of each tree and any risk it may pose regardless of the cause for the poor tree health.
Details of how vegetation management is organised across LUL network management zones. Which management area of LUL has responsibility for the management of vegetation on the Metropolitan Line at Northwood? How can they be contacted? Ourvegetation is managed by our Track section within London Underground – the management is divided into three zones – North, East and West as per the attached diagram. The area you have asked about would come under the North area.Please contact our customer services on[email protected]orsee our website at https://tfl.gov.uk/help-and-contact/if you wish to make any comment orraise an issue.
Please provide information on the date and results of the last assessment of the Metropolitan line infrastructure between Northwood and Moor Park with respect to:
Trees; their assessed state of health, maintenance, and any overhanging of adjacent properties.
The stability of the earthworks and any indications of displacement of earthworks.
Between Northwood and Moor Park there is around 2,200 meters each track side so 4,400 meters in total which includes hundreds of trees. We don’t write a report on every single tree but we report by exception when we find an issue with a particular tree.
Please see attached a document which shows the issues found during the inspections for the past 12 months in the specific area you have identified. The inspection findings are raised as work orders and assigned to the various teams for rectification. The list shows the work orders raised from the inspections for the past 12 months.
If this is not the information you are looking for, or if you are unable to access it for any reason, please do not hesitate to contact me.
Please see the attached information sheet for details of your right to appeal as well as information on copyright and what to do if you would like to re-use any of the information we have disclosed. Yours sincerely Sara Thomas FOI Case Officer FOI Case Management Team General Counsel Transport for London
