Information and Advisory Note Number 41                                                Back to menu

Restoration and management of mineral extraction sites in Quaternary landforms and deposits

1. Introduction

1.1 This Note applies to the restoration and management of mineral extraction sites where there is recognised scientific interest in surface deposits mainly produced by glaciers and their meltwaters during the Quaternary Ice Age. It includes both large-scale, commercial quarries and small pits operated on an informal basis, as well as disused quarries, pits and railway cuttings where surface deposits are, or have been, exposed.

1.2 Existing excavations in unconsolidated sediments such as sand and gravel deposits often constitute an important resource for scientific research and education. Sections in such deposits can reveal the sedimentary structure of landforms in areas where there are no natural exposures as well as illustrate important sediment sequences. This information and advisory note sets out the considerations and requirements for the incorporation of this interest in landscape restoration schemes. Only the earth science interest of such sites is addressed. Additional conservation interests, including biological and landscape considerations, may also need to be evaluated as part of the overall response to a particular situation and advice sought from other branches of RASD, Policy Directorate and Regional Advisory Services. Advice on the restoration of active process sites such as sand dunes will be covered separately.

2. Description of activity

Mineral extraction, usually in the form of sand and gravel quarrying in glacial deposits, can in some circumstances have positive benefits, albeit often at the expense of destroying all or part of the interest, particularly in the case of large-scale commercial operations (see Information and Advisory Note No. 40, 'Mineral extraction in Quaternary landforms and deposits'). Excavations may reveal more of the internal structure and sedimentary architecture of Quaternary deposits, expose new sequences previously undiscovered or provide exposures in areas where there are no natural sections away from rivers and the coast (Figure 1). Where these new sections have significant scientific interest, the question arises whether they can be conserved when working ceases and how this can best be achieved as part of restoration planning. In other cases, pits and quarries (both commercial and small scale) may have been disused for some time, and in the absence of active management, the sections may have become degraded or overgrown.

 

Figure 1. Quarrying may provide information on the sedimentary structure and origins of surface deposits, although at a loss of the landforms. Restoration proposals for such sites should consider the Earth science interest and the feasibility of incorporating conservation sections as part of the overall design.

2.1 Hard rock quarries and open cast mining may also involve the stripping of superficial deposits, revealing new exposures, and the same general guidelines as outlined below apply.

3. Nature of impacts

3.1 The main ways in which exposure is lost and access impeded are as follows:

• landfill
• grading of slopes
• vegetation growth on faces
• flooding of quarry floors
• fly-tipping of waste materials either over the top of the face or against the base of the section
• building developments on the quarry floor
• tree planting on degraded faces
• landscaping for recreation purposes.

However, with appropriate management planning, the long-term conservation of key sections can usually be accommodated around most forms of after use, providing that there are no significant practical problems, for example associated with drainage or slope instability (see below)

4. Management options and guidelines

4.1 Objectives

Two requirements may be identified for restoration and management of quarries and pits when working ceases These will normally be specified for individual sites in the Site Documentation Reports/Site Management Briefs produced by the Earth Science Branch. These are:

• Access to sections should be maintained both for purposes of study and machine cleaning. Providing that access is maintained, then after uses such as landfill, building development or woodland development can usually be accommodated around the conservation area through appropriate technical or planning design. A particular feature of sections in soft sediments is that any faces will progressively deteriorate through slumping and vegetation colonisation. However, it is not always essential, or indeed desirable, to keep sections continuously open
• Where sections are not kept open, the option to undertake future cleaning must be maintained, for example to allow access for specific scientific meetings or research projects. After such events, the sections may be backfilled (see Clava example below).

4.2 New planning applications

If key interests can be identified at the time of the planning application, the case should be argued for a conservation section to be established as part of the restoration plans (See Information and Advisory Note No. 40). Preferably this should be identified at the periphery of the area to be worked, bearing in mind the guidelines in section 4.3 below The greatest chance of success is if this condition can be built into the planning process at as early a stage as possible.

4.3 Existing working quarries

Where developments have existing planning consent and conditions, and new interest is discovered during working, then negotiations should be opened as early as possible After restoration conditions are approved, it is usually difficult and costly to achieve alterations The following guidelines are recommended.

4 31 Negotiate a permanent conservation section, or sections if the interest is dispersed. Particular questions to consider are:

• is the site conservable. will it flood or will sections collapse?
• is the key interest located in a conservable position within the site?
• is future site clearing feasible to demonstrate the key interest?
• can the interest be adequately represented in a limited area of section or in a series of small sections?
• is there an alternative section elsewhere or could one be excavated in a more practical location?

4 3.2 If the practical problems are insurmountable, or costs too high, then efforts should be made (a) to ensure that the site to be lost is fully documented; (b) to locate an alternative section if that is possible.

4.3.3 Where a permanent conservation site is established, a section may only require to be opened or cleaned for a specific research project or scientific meeting It is important that access for machine cleaning be maintained. It is also important that the site boundary should be drawn to include a reserve of deposit to allow for the removal of material and some recession of the face.

4.3.4 Future management of the site requires consideration. This may include requirements for fencing, warning notices, monitoring or interpretation.

4.4 Disused quarries and pits

4.4.1 The main objective is to maintain access to the key sediments for further study. Depending on the particular interest of the site, its level of use and the physical constraints of the site, the level of management will vary. Generally, cleaning will not be undertaken on a regular basis. In most cases, access may only be required occasionally for field meetings or research projects, and it will be acceptable to allow the sections to degrade between these events. It may even be appropriate to backfill excavated sections where these are likely to be unsafe or at the request of a landowner. Some sites with a high level of usage may require to be cleaned frequently to remove slumped material and vegetation; this will only be practicable for low faces with a good reserve of deposit. The most effective conservation may be achieved by ensuring that the sites can be re-excavated. The Site Documentation Reports/Site Management Briefs will contain detailed recommendations for individual sites. The critical factor is to ensure that access is maintained in the long term for machine excavation or cleaning.

4.4.2 Other general management requirements will usually include maintaining the site in a tidy condition and the removal of any tipped material or dense overgrowth.

4.4.3 PDOs should be used where appropriate to prevent (a) casual tipping of waste materials over or against sections; (b) tree planting in crucial areas; and (c) infilling of pits.

4.4.4 Intermittent further extraction may be permitted if it opens up the sections, but will depend on the scale and extent of the proposed work (See Information and Advisory Note No. 40).

4.5 Practical considerations and engineering design

4.5.1 The practicality of establishing conservation sections needs to be evaluated according to conditions on the ground (e.g.
height and stability of sections, groundwater levels, risk of pollution from leachate from landfill), location of the interest within the site, and future ownership and management.

4.5.2 Generally, conservation sections are most appropriate to show a vertical sequence of deposits which can be demonstrated in a relatively small section or in a series of small sections, as in a slot or trench that can be excavated either by hand or machine, for example to show a vertical succession of glacial and interglacial deposits or a fossiliferous horizon.

4.5.3 Where landfill is the proposed after use of a quarry, the overall design of the site may include the creation of a 'conservation void' to allow access to a conservation section (Figure 2). This will require a detailed engineering appraisal and design.

Figure 2 Schematic example of a conservation void left at the margins of a landfill site (from NCC, 1990).

4.5.4 Guidance for the design of conservation sections in a range of geological situations is given in the Appendices to Earth Science Conservation in Great Britain. A Strategy (NCC, 1990) and in the reports by Sir Alexander Gibb and Partners (1988) and M.J. Carter Associates (1989). Examples of their application in England are given by Bennett (1994) and Glasser and Lewis (1994).

4.5.5 The practicality of maintaining sections in disused quarries and pits will usually depend on the following constraints.

• Can the interest can be localised to a particular discrete section or sections? Usually it is not possible to preserve sections to show large scale sedimentary structures, for example in sand and gravel deposits. The best that can be achieved for such sites is to ensure that they are logged and documented during working.
• What is the stability of the deposits? Low sections are usually practical. High sections in superficial deposits are not practical, but stepped or graded sections can be designed where there is a reserve of deposits (see sources cited in section 4.5.4).
• Sites where the key deposits lie below the water table are not suitable for conservation.
• In some cases there may be major practical problems in maintaining a conservation section, for example where a quarry has been worked to the limits of the planning consent. In such a situation, it would be difficult to engineer a stepped face.
• Other practical issues that need to be addressed include the ownership of the conservation site, liability, safety, fencing requirements and access arrangements.

5. Afteruse

5.1 Landfill

Landfill usually presents the most difficult problems in reconciling after use and conservation. The principal constraints are the costs involved in loss of fill space (conservation void) and engineering design. By way of guidance, various practical considerations and design techniques are suggested in the sources listed in section 4.5.4, but professional advice will be required on engineering geology, hydrology and legal and planning issues. Consideration also needs to be given to detailed management requirements, including access and fencing, for example.

5.2 Land restoration

Restoration may be for agriculture or recreation purposes. This will usually involve the grading or buttressing of former faces. The earth science conservation requirements should be integrated into the plans for restoration and future management of the area to ensure that sections remain accessible for maintenance and cleaning where necessary. Consideration needs to be given to detailed management requirements, including access and fencing. Where woodland planting is proposed, this should be planned around the earth science interests.

5.3 Developments on quarry floors

Generally, development on the floors of disused quarries and pits can be accommodated providing that access is maintained to the sections for machine cleaning. The NCC Strategy Appendices recommend a minimum gap of 5m between the edge of a development and the base of a face. However, the precise width of gap should be assessed in relation to the local circumstances of face height and stability. An appropriate management plan should be implemented for the site, incorporating issues such as access and maintenance of fencing.

5.4 Informal activities

Appropriate PDOs should be applied to cover activities such as fly tipping, tipping of farm wastes, etc, and recreational activities such as motor cycle scrambling etc on the defined conservation area.

6. Sources of further advice: relevant authorities and organisations

A number of authorities and organisations have responsibilities or interests in the working, conservation and management of sand and gravel workings. The bodies listed below may be able to give further information and advice as well as details of local representatives or contacts in your area.

SCOTTISH NATURAL HERITAGE
Research and Advisory Services Directorate
2 Anderson Place
EDINBURGH EH6 SNP
Tel. 0131-447 4784

• The Earth Science Branch (ESB) has responsibility for providing advice and information on the earth science interest and management of Quaternary landforms and deposits. Site Documentation Reports/Site Management Briefs produced by ESB for GCR sites provide basic information on the interest of individual sites and explain the key management objectives.
• The Landscape and Restoration Branch has similar responsibilities for providing advice on landscape issues.
  Policy Directorate 12 Hope Terrace Edinburgh EH9 2AS Tel: 0131-4474784
• provides advice and information on policy, planning and countryside conservation issues

Land Management and Advisory Services in Regional Headquarters will be able to advise on planning and landscape issues

QUATERNARY RESEARCH ASSOCIATION (QRA)
Current Secretary: Dr P Coxon, Department of Geography, Museum Building, Trinity College, Dublin (Tel: 010 353 1 6081213) -Professional association for individuals and organisations with interests in Quaternary science. Members, located throughout the whole of Britain, may be able to provide advice and information on the scientific interests and use of particular areas for research and teaching purposes. (Note that post of Secretary changes every 4 years. ESB will be able to advise on the current incumbent).

BRITISH GEOMORPHOLOG1CAL RESEARCH GROUP (BGRG)
Secretary: Professor I. Foster, School of Natural and Environmental Sciences (Geography), Coventry University, Priory Street, Coventry CV15FB. (Tel: 01203 838404) - Professional association for individuals and organisations with interests in geomorphology. Members, located throughout the whole of Britain, may be able to provide advice and information on the scientific interests and use of particular areas for research and teaching purposes. (Note that post of Secretary changes every 3 years. ESB will be able to advise on the current incumbent).

THE GEOLOGISTS' ASSOCIATION
General Secretary, Burlington House, Piccadilly, London W1V9AG (Tel: 0171-434 9298). An association for individuals interested in geology. Members may be able to provide advice and information on the scientific interests and use of particular areas for research and teaching purposes.

SAND AND GRAVEL ASSOCIATION (SAGA)
1 Bramber Court, 2 Bramber Road, London W14 9PB (Tel: 0171-3818770) - Trade association for the sand and gravel industry. SAGA operates a Restoration Guarantee Fund and makes annual awards for site restoration schemes.

7. Case studies

7.1 Dalroy and Clava Landforms SSSI

7.1.1 Clava is a famous site for a succession of glacial deposits, including shelly clays transported from the floor of the Moray Firth by the last ice sheet. The interest was first described last century when the deposits were worked for clay in a small pit. The pit has long been disused and the original faces are slumped and completely overgrown. Although nearby streambank exposures show part of the sequence, these could not be related to the original type section in the claypit. The significance of the site is such, however, that it merited designation on the basis of the original site descriptions.

7.1.2 In 1990, a section was excavated by mechanical digger in the original claypit, with the owner's permission, for a field meeting of the Quaternary Research Association (Figure 3). This not only allowed correlation with the exposures along the stream, but provided important new information on the origin of the deposits. The section was left open for several days after the meeting to allow other interested groups to examine the evidence. It was then largely backfilled, both for safety reasons and because it would not have been possible to stabilise a permanent face.

7.1.3 This example illustrates the approach that can be applied where there are practical difficulties in maintaining an open section. A similar approach has been adopted for a section that forms part of the interest at Ardersier SSSI.

Figure 3. Re-excavation of the shelly day at Clava, Inverness-shire. This example shows the importance of maintaining access for future site investigations where it is impractical to keep a section permanently open.

7.2 Kirkhill SSSI

7.2.1 Kirkhill is one of the most important Quaternary sites in Scotland providing the longest sequence of terrestrial deposits that document multiple cold and warm stages during the ice age. The interest of the site was first discovered in a section in the superficial deposits above the face of a disused rock quarry. There was a valid planning consent to infill the quarry completely with rubbish and to reinstate the land to agriculture. Although determined approaches were made to Banff and Buchan District Council, who were both the owners of the site and the planning authority, it proved impossible to amend the planning consent and to negotiate the establishment of a permanent conservation section at the site. Access was allowed, however, for the existing sections to be properly recorded before burial took place.

7.2.2 In view of the unique importance of the deposits, an alternative conservation strategy was developed. Since the deposits infilled a bedrock channel which appeared to continue beyond the quarry and beneath the adjacent ground surface, a detailed survey using geotechnical methods and auguring was conducted in this area. The results indeed proved that this was the case and the adjacent field where the sequence was adjudged to be best represented was selected as the GCR site and subsequently notified as an SSSI. Thus a key interest is effectively protected and can be accessed by drilling or by mechanical excavation as required. Because of the outstanding importance of this interest and the limited reserve of known deposit, this would not be done on a routine basis, but only for a major scientific reinvestigation.

7.2.3 This example emphasises the need for early contact with owners and planning authorities, preferably before restoration conditions are agreed, if permanent conservation sections are to be established. Fortunately in this case an alternative strategy was possible.

7.3 Littlemill Fluvioglacial Landforms SSSI

7.3.1 Littlemill is notified for a suite of esker landforms, sand and gravel ridges formed by glacial meltwaters at the end of the last ice age. At the time of notification, there was a valid planning consent for a sand and gravel quarry on part of the esker formation (see Information and Advisory Note No. 40). When working ceased, consideration was given as to whether a conservation section could be established (Figure 4).


Figure 4. Section in sand and gravel deposits at Littlemill Quarry, Inverness-shire, where it was impractical to maintain a conservation section because of the height of the face and instability of the deposits.

However, assessment showed that this was not possible on several grounds:

• the interest was in large scale sedimentary structures and bedding that could not easily be represented in a small representative section;
• the deposits were in unconsolidated sands and gravels and any large faces would quickly degrade;
• since the final face was worked back to the limit of planning consent and required to be buttressed to avoid collapse back into adjacent land, it would not have been possible to either excavate a stepped face or to carry out future cleaning;
• the final face was too high to maintain in a single section in safety.

7.3.2 This example illustrates the circumstances when it may not be possible to establish a conservation section. It is important in such cases that a permanent record of the exposures is made before the sections are graded.

8. Further reading

Bennett, M. 1994. The management of Quaternary SSSI in England, with specific reference to disused pits and quarries. In: Stevens, C, Gordon, J.E., Green, CP. and Macklin, M.G. (Eds), Conserving Our Landscape: Evolving Landforms and Ice-Age Heritage. Proceedings of the Crewe Conference. Peterborough, 36-40.

Bridgland, D. R. 1994a. The conservation of Quaternary geology in relation to the sand and gravel extraction industry. In: O'Halloran, D.,Green, C, Harley, M. and Knill, J. (Eds), London, Geological Society, 87-91.

Bridgland, D.R. 1994b. The conservation of quarry sections and other man-made exposures of Quaternary deposits. In: Stevens, C. Gordon, J.E.. Green, CP. and  Macklin, M.G. (Eds), Conserving Our  Landscape; Evolving Landforms and Ice-Age  Heritage. Proceedings of the Crewe Conference, Peterborough, 75-81

Carter, M.J. Associates 1989. An Investigation of Design Criteria for the Safe Angle of Repose for Landfill Schemes Involving Domestic, Industrial and Commercial Wastes. Commissioned Research Report to NCC, Peterborough.

Gibb, Sir A. & Partners 1988. Factors Affecting the Conservation of Geological Features in Quarries and Pits. Nature Conservancy Council, CSD Report 846. Peterborough.

Glasser, N.F. and Lewis, S.G. 1994. A report on recent excavation and conservation at Wolston Gravel Pit SSSI, Warwickshire. Quaternary Newsletter, No. 74,1-9.

Gordon, J.E. and Campbell, S. 1992. Conservation of glacial deposits in Great Britain: a framework for assessment and protection of sites of special scientific interest. Geomorphology, 6,89-97.

Gray, J.M. 1994. The Blakeney Esker, Norfolk: conservation and restoration, n: Stevens, C, Gordon, J.E., Green, CP. and Macklin, M.G. (Eds), Conserving Our Landscape: Evolving Landforms and Ice-Age Heritage. Proceedings of the Crewe Conference. Peterborough, 82-86.

Nature Conservancy Council 1990. Earth Science Conservation in Great Britain. A Strategy. Appendices. A Handbook of Earth Science Conservation Techniques. Peterborough, Nature Conservancy Council.

Scottish Office 1994. Land for Mineral Working. National Planning Policy Guideline NPPG4. Edinburgh, Scottish Office Environment Department.

Earth Science Site Documentation Reports/Site Management Briefs provide fundamental information on the interest of individual sites and explain the key management objectives.

9. Author

John E Gordon
Earth Science Branch
Research and Advisory Services Directorate
Scottish Natural Heritage
2 Anderson Place
Edinburgh EH6 5NP
Tel: 0131-4474784
 

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