Calderdale's structural engineer report

Dear Mr Meihuish

Re: Inspection/Report on retaining wall & trees on land adjacent to Windsor View, Hebden Bridge

Thank you for your letter dated 22 June 2004. Enclosed with your letter were the following:

1. Order no. PL DC 002872.

2. Tree Preservation Order C1245 2004P relating to Mill Pond adjacent to Windsor View, Hebden Bridge. This consists of an A3 sheet including the location plan and an A4 sheet listing numbers of trees within the group G1.

3. HM Land Registry Sheet with a proposed compromise TPO area marked on.

4. Letter dated 10 June 2004 from Kennedy Design limited, attached to which were representations in response to TPO C1245 2004P consisting of four pages and the appendix Health & Safety Review.

5. Health & Safety Review for Green Tops Ltd prepared by Solutions by Design, consisting of three double sided A4 sheets with an additional Appendix 1 showing protected trees in the area, Appendix 2 showing Tree Preservation Order, Appendix 3 showing another Tree Preservation Order, Appendix 2 of Kennedy Design Ltd's submission consisting of Peter Lodge Consulting Structural Engineer's letter report dated 08 March 2004, Peter Lodge Consulting Structural Engineer's letter dated 10 June 2004 and a letter from A Binns & Co, Professional Tree Care, dated 30 April 2004.

6. Also enclosed was an Arboriculturist's report dated 10 March 2004.

The above list has been provided in order that you are aware of the documentation I have had for consideration.

Having read through the documentation, I visited the site on Thursday 15 July 2004. At the time of my walkover inspection, it was raining.

Walkover Survey

The walkover survey of the woodland area revealed many of the features described in the various documentations. The main concern from a structural point of view is the trees growing from the various retaining structures, walls and old masonry structures. Trees growing in such locations cause damage to the structures. Damage is mainly due to the structural roots of the trees which expand causing damage to the stone structures. There were locations, particularly along Windsor View and to the dam structure to the back of Spring Grove, where the trees have grown to such a height that they are causing moment (rotation) forces on the walls - I would strongly recommend that these be removed before further damage is caused to these vulnerable structures. When these trees have been removed, the root system should be poisoned in order that the trees do not continue to grow.

New trees are likely to take hold in this area on a regular basis. It is important as far as the structures are concerned that these are annually maintained and that there is working space to operate. On walking around the site, my initial requirement was that the trees are kept away from these structures and I believe that a suitable distance, purely from the walkround inspection of the trees present would be approximately 3 metres. On inspecting the temporary Tree Preservation Order, the area that the TPO covers does appear to account for such a space away from the structures. No dimensions are given on the plan; however, using a scale rule the dimensions would, appear to be approximately 7.5 m from Windsor View and 5 m from the top face of the dam structure at the rear of Spring Grove. I am of the opinion, therefore, that the area that the TPO covers is acceptable from a structural point of view.

In Kennedy Design Ltd's letter of 10 June 2004, there is mention of a compromise area. I believe this is the area shown on the HM Land Registry A3 Sheet The compromise solution does address my structural considerations on the location of the trees but extends the boundary somewhat further. From a structural point of view, I have no objections to the compromise proposal, though from the Council's TRO point of view the area covered is somewhat reduced.

Arborlculturlst's Report

Much of the report concerns the description and species of trees, life expectancy and condition. These are all items that I do not feel qualified to comment upon. The report also addresses the activity of tree roots and trees on the structures, particularly Goat Willows growing from the top and sides of various embankments. I believe that the TPO Order currently temporarily enforced does not restrict the land owner from removing the problem trees.

Representations to TPO

In the second paragraph of this document it states that the "new provision TPO is however still not satisfactory and needs refinement since it seeks to retain trees that are far too close to the fragile structures on the site". I do not believe that this is the case; as stated above, I believe the scale dimensions on the TPO ensure that there are no trees on the structures.

With regard to the third paragraph and the working space, I would comment that the temporary TPO does allow sufficient space for inspection; however, as far as the repair is concerned, this would depend upon the scheme of any major repairs and would be best dealt with at such time as those repairs are necessary.

This section also reproduces comments on the working space for the felling operation covered in the other documents.

Peter Lodge Consulting Structural Engineer's letter dated 8 March 2004

Much of this letter concentrates on the damage that trees can cause to structures. I believe the Council are fully aware of this problem and generally agree with the comments made in the letter. However, the letter's final paragraph and accompanying sheet cite the NHBC Chapter 4.2 as being the appropriate distance of the trees from the wall. I believe this is an inappropriate use of the NHBC Standard. Chapter 4.2 of the NHBC Standards is titled Building near Trees "this chapter gives guidance on meeting the technical requirements and recommendations for building near trees. particularly on shrinkable soils". From the description so far given, it would appear that the soils are not shrinkable soils, therefore this Standard does not apply. The potential spread of the roots for moisture i.e. the fibrous roots being the ones that take up the moisture, is governed by the site conditions, soil type and availability of water. Roots will take the easiest course to obtain moisture. It has already been documented elsewhere in the reports that the ground towards the centre of the dam is waterlogged. It would therefore show that there would be ample water available, to supply the trees. I am of the opinion, therefore, that the modified TPO takes ample consideration of the potential of root spread. The distances quoted in the engineer's report of 17 m and 30 m are not appropriate on this site.

Peter Lodge's letter dated 10 June 2004

We have no further comments to make on this letter.

A Binns letter dated 30 April 2004

Mr Binns discusses briefly the possible difficulties in working on this site. I am of the opinion that the most appropriate method of dealing with the trees on this site would be for the careful hand felling of the trees using appropriate ropes and winches. I do not feel that it would be appropriate to use large machinery on this site as no information has been gained to show that the ground within the dam is capable of sustaining large loads of this machinery. The dam structure itself may not be capable of sustaining the additional loads placed on it by machinery. Access on to the site would have to be formed and this would also involve additional earthworks which would put additional pressures on the dam structures. The majority of the area to be cleared is made up of small trees and I would suggest the most appropriate way forward would be the clearing of all the small trees beyond the TPO area before tackling the larger trees using appropriate techniques after first developing a method statement.

Health & Safety Review prepared by Solutions by Design dated 10 June 2004

This report highlights the health and safety issues surrounding first of all the existing structures, for which the Council have acknowledged the need to remove trees to prevent further damage and to gain access to the structures. The modified TPO takes this into consideration. The report also relies on the consulting engineer's misinterpretation of Chapter 4.2. I believe that this has influenced point A under 'Conclusion Spring Grove dam wall' which says that all trees in the area shaded blue should be removed. It is also quite clearly highlighted in this report that the felling operations will have to be given particular care. However, the risk assessment does not address the potential problem of fetching heavy machinery on to the site given the unknown condition of the ground, existing dam structure and the effects of the additional earthworks.

Conclusion

We have been asked to comment on the modified Tree Preservation Order for the site with regards to the structural implications of the trees on the adjacent structures. Having read all the documents listed above and made a site visit, I am satisfied that the modified TPO adequately provides sufficient areas of the site outside the TPO for the inspection of the structures and to remove those trees that may have an influence on the structures. It is quite clear that the significant old structures surrounding this site are in need of repair and will also require continual inspections. I would also suggest that the areas of influence should be kept clear of trees in the future in order to mitigate the deterioration of the existing structures.

Yours sincerely

John A. Wood