5.1 This chapter examines the aims, need for and principles of reinstatement, and provides guidelines on treatment strategies and techniques. These guidelines are outline only and are not intended to be written directly into specifications. More detailed information on techniques can be obtained from Chapter Two (Literature Review) and from the references cited in that chapter.
5.2 Aims of reinstatement can be listed as follows:
- to create a stable, low erosion environment
- to create a visually unobtrusive site
- to create an area that is safe for people and animals
- to create as ecologically natural an end result as possible
5.3 Every aim is unlikely to have the same importance at every site, either because the desired condition is already present, or is not considered to be pertinent. Identification of the need for restoration is thus vital to the selection of aims and, hence, appropriate reinstatement strategies.
5.4 There are four main reasons why reinstatement might be necessary, namely, erosion control, reduction of visual impact, safety, and reduction of direct ecological and geomorphological impact (as distinct from indirect impacts due to erosion). Erosion control could be deemed to be obligatory, while the need for other measures may be more subjective depending on the location of a site. For example, should every pit be reinstated to the same visual standard regardless of its location and visibility in the landscape? These questions are explored below, along with consideration of the factors that should be considered during survey to identify need for reinstatement.
5.5 Areas of bare sand in the machair/dune system are vulnerable to wind erosion, the near vertical faces created during working being particularly so. Mather and Ritchie (1975?) state that "irrespective of the scale of the operation, extraction creates deflation surfaces and features with erosional characteristics". Harris and Ritchie (1989) point out the impact tracks of extraction vehicles have on the machair and dune surface.
5.6 If wind erosion becomes established it could spread beyond the boundaries of the pit and lead to blowout, resulting in large scale instability of the fixed dune zone and/or large quantities of loose sand being blown onto the adjacent machair. Clearly the geomorphological and ecological character of the system is significantly changed, particularly if the machair grassland is lost. Furthermore, drifting sand can block roads and adversely affect agricultural operations.
5.7 It is argued that natural erosion and blowouts are facets of the dune/machair system and should be left untreated, particularly because the machair is a dynamic habitat which requires a small input of fresh sand (Hansom and Combor 1995). However, sand extraction is not a natural phenomenon and, for this reason, the policy adopted by these guidelines is that treatment for erosion control should be carried out if necessary.
5.8 However, identifying this need is problematic. As discussed in Chapter Two, there is very limited reference to the impact of sand extraction in dune or machair systems and is by and large limited to that quoted in Section 5.5 above. Likewise, there is limited reference to the overall erosion problem created by quarrying in the study area, although Angus and Elliott (1992) state that all but one of over a thousand reseeding schemes in the Western Isles assisted by the IDP in the 1960s involved shell sand, extracted from both beach and machair. They reckon that surprisingly few major erosion problems seem to have arisen as a result, possibly because people were sufficiently aware of the worst problems that could arise. However, these "problems" and how they were avoided are not further explored for machair quarrying.
5.9 At a site specific level some pits are reported to be causing a large scale problem, such as active pits at Barvas in Lewis (Harris and Ritchie 1989), and the active pit at Horgabost surveyed for this study. A few others surveyed appear to be on the verge of large scale erosion problems. In all the cases listed, the reason for instability can be pinpointed (i.e. quarrying of mobile dunes at Barvas, exposed hillside location at Horgabost, and poor reinstatement techniques at the reinstated sites).
5.10 However, definitive geomorphological criteria for identification of the need for erosion control can only be formulated by surveying a range of both stable and unstable, unrestored pits. This was not carried out in this study survey, the objective of which was to consider reinstatement techniques and which therefore visited mainly restored pits.
5.11 Erosion risk is also determined by the relative exposure of the site, but, again, it is not possible in this study to provide definitive criteria to determine this risk. This is partly because of the limited usefulness of the survey in this respect, but also because the relationship between prevailing wind direction and topography can sometimes be a poor indication of erosion risk due to eddying and funnelling. A final consideration is that it may not be possible to predict the likelihood or impact of occasional but very destructive winds.
5.12 Because of these uncertainties, the strategy adopted by this report is that any pit with existing or potential wind scour features is at risk and warrants some form of reinstatement regardless of the relative shelter of the site. However, vulnerability to eroding winds should be assessed, albeit approximately, as it is an important factor in determining the appropriate reinstatement strategy. The guidelines below should then be considered as provisional only. They are based on a common sense approach, utilising field observations and the literature on dune and machair erosion.
5.13 Sites should be surveyed to determine if any of the following three main erosional features are present.
- steep unprofiled faces which suffer undercutting and slumping
- exposed fill which causes scouring
- deflation surfaces on pit floors, particularly in deep, narrow, steep sided pits aligned to the prevailing wind.
All three can be integrally linked.
5.14 Deflation surfaces on quarry floors may be more difficult to identify than the other two features. A deflation surface is formed when a sand is blown down to a solid plane, including for example bedrock, a shell or stone deposit, a remnant topsoil layer and the water table. A pit with a deflation surface but with active sand movement may be acting as a conduit to sand blowing inland from the coast, as is commonly seen in blowouts in the study area. Potential as well as existing erosion features should be identified, if possible, in recently worked out pits, as quarrying operations may have temporarily prevented erosion getting a hold. (For example, slopes could be very steep and unprofiled but not as yet show signs of undercutting). Slopes of more than 35o should be considered as potential erosion features. Any uncovered fill, whether re-exposed or merely uncapped, should be considered as an erosion risk.
5.15 The relative shelter, or perhaps more usefully, the exposure of the site to eroding winds should be assessed by considering the following:
- distance of the site from the sea
- nature of surrounding topography and location of pit within it
- alignment of pit with prevailing winds
- presence of blown sand on adjacent grassland
- other evidence of past erosion (e.g. photographic, anecdotal)
This assessment should be carried out on a site by site basis by field survey, considering features and situations peculiar to each pit. None of these criteria are foolproof on their own, particularly the first three for the reasons discussed in 5.11 above, and should therefore always be considered together.
5.16 Logically, the further a pit is from the sea and the more sheltered it is by surrounding landforms the less likely it is to suffer erosion. The least eroded pits visited during the study were located in relatively stable machair in the lee of dune ridges. The most eroded pits were located nearer the sea and/or in mobile dunes, or in relatively open machair. Funnelling could occur if a pit is aligned with the prevailing wind (assuming such a wind exists). The presence of significant amounts of blown sand on surrounding grassland is one of the most reliable signs of active erosion, although its absence has to be interpreted with care as very strong winds could deposit sand some distance from the pit. Aerial photographs may be useful in allowing some idea of past erosion activity and movement, for example, whether and how much eroded areas have spread. Local knowledge can prove to be useful particularly when analysis of prevailing wind direction and topography is confounded by local effects of eddying and funnelling as previously discussed. Many of the smaller pits are located in relatively sheltered areas, demonstrating an awareness of local conditions.
5.17 Assessment of visual impact is fairly subjective and depends on people's perceptions. However, on the basis of the survey, two main facets of unrestored pits were seen to result in a negative visual impact, namely, bare sand and associated erosion features, and features indicating artificiality and/or dereliction. (In the view of the report authors, the latter are usually more visually intrusive than the former). Assessment of visual impact should therefore include consideration of the following features:
- areas of bare sand
- landforms/ slope profiles
- capping materials
- derelict machinery
- dumped spoil or rubbish
- stands of undesirable vegetation, such as tall ruderals
5.18 As discussed in Chapter Three, visual impact also depends on the position of a site in the landscape, for example, pits with bare sand located adjacent to natural erosion features can be relatively unobtrusive. Likewise, pits with unnatural looking landforms can be unobtrusive if located away from roads or vantage points or are hidden by topography. Unless the line is taken that all pits should be restored to the same visual standard, obtrusiveness in the wider landscape will also need to be assessed.
5.19 A sensible policy to adopt may be that treatment to reduce visual impact of partially restored or old pits is undertaken only at obtrusive sites, but reinstatement at newly closed pits should ensure that no features of dereliction remain or are introduced. Whether or not the creation of natural looking landforms is recommended for every new site needs to be decided (although unnatural looking features will in many cases require erosion control treatment).
5.20 The need for reinstatement and,or remedial measures to reduce visual impact will in some cases have to be balanced against the potential impacts of carrying them out. This is particularly pertinent in the case of slope reprofiling. Regrading already vegetated pits will create, albeit temporarily, slope instability and could destroy existing ecological interest. Furthermore, the impact of artificial looking slopes is somewhat diminished once vegetation covered.
5.21 Sites should be surveyed to assess the presence of hazards that could endanger the public or grazing animals. The two main features in this respect are steep, unstable slopes and uncovered or re-exposed fill, including in the latter case, holes in the ground which have opened up with settlement.
5.22 It will need to be decided whether the same standard of restoration should apply to all sites. For example, safety may be less of a consideration away from recreational areas.
5.23 This refers to the direct damage possibly caused to nature conservation and geomorphological interest in the original siting of the quarry. Most pits to date in the study area are relatively small and their impact per se on ecology and geomorphology is likewise probably limited. However, this could change with increasing size of operations in which restoration of the original ecological and geomorphological systems (or something of similar value) may become more pertinent.
5.24 Ecological factors might also be an important consideration if reinstatement has been inappropriate or badly carried out. Vegetation typical of "disturbed" land, or "wasteground", growing on fertile imported capping will lower the naturalness and typicalness of the machair habitat. As well as survey to identify such species, the nature conservation value of the adjacent machair will also need to be considered if recommendations for remedial measures are to be limited to areas of high nature conservation value. (It is possible that all machair is considered to be of high enough value to warrant remedial treatment).
5.25 If the aim of creating as natural an end result as possible is to be achieved, the ecological impact of restoration techniques employed for other reasons should also be considered. Past restoration of many quarry, mine or industrial sites, particularly if fairly old, has sometimes not benefitted ecological interest and in some cases has damaged it. This is a strategy rather than a need that can be identified by field survey, and is further discussed below.
5.26 As discussed in Chapter Three, infilling is generally not a satisfactory method of restoration as erosion is reactivated if the fill becomes exposed, as it has at some of the survey sites. Furthermore, even if infilling has been carried out to a high standard, the threat of future re-exposure due to very destructive weather events or long term coastal erosion can never be discounted. Similarly, the poor long term success rate of many highly engineered sand dune restoration and coastal defence schemes indicate that this approach is also unsuitable for sand pit reinstatement.
5.27 Guidelines in this report are therefore based on the principle that reinstatement should achieve its aims through landforming and revegetation rather than infilling or highly engineered options. This will often result in a hollow of some sort remaining after restoration, but as found in the survey, these are often visually unobtrusive once vegetated, far less so than exposed fill and reactivated erosion.
5.28 It is recognised that at some pits landfill, rather than restoration, may be the primary aim of infilling and guidelines for restoration of such sites are therefore also given. The approach taken in this report, however, is that infilling is a secondary use of the pit and is not a reinstatement technique in itself.
5.29 Reinstatement guidelines are given on the assumption that pits are outwith the influence of significant wind blown sand or wave attack. However, it is recognised that these conditions could prevail in a very few cases, warranting brief consideration of this situation.
5.30 It is often the case that natural regeneration of worked out mines and quarries of any type produces the most ecologically interesting and visually acceptable end result (see SNH manual on use of manipulation of natural regeneration as a restoration technique (SNH 1995)). For example, the vegetation of a naturally recolonised sand pit will in most cases have a greater affinity to the adjacent machair than one that has been reseeded. This is an important consideration in a habitat which is generally of high nature conservation value.
5.31 The problem with this approach in the study area is that the risk of wind erosion often necessitates intervention of some kind. Visual and safety considerations may also necessitate action (although these are not specific to coastal sand pits). In general, however, the lower the level of reinstatement input, the more ecologically "natural" will be the end result. Reinstatement aims should therefore be achieved using the lowest possible level of intervention.
5.32 Using landforming and revegetation as the basis for reinstatement is in itself a "low intervention" approach, but it is possible to determine the minimum level of necessary treatment within this approach. For example, sites with naturally established vegetation may not require anything more than some form of tidying up, while reseeding may not be necessary at every regraded site.
5.33 Four reinstatement strategies which roughly reflect increasing levels of intervention (in ecological terms) are recommended, as follows:-
Do nothing Remedial measures Landforming Revegetation
More than one of these strategies could be implemented at a site. The application and techniques involved in the use of these strategies are discussed below.
5.34 The "Do nothing" option could be applied in two situations; the first is the naturally revegetated pit and the second is where shelter permits natural colonisation of bare sand.
5.35 Unrestored pits which have naturally revegetated are often fairly unobtrusive and support a relatively natural plant community. In many cases it would be best to leave these untouched as they are likely to be stable and have some ecological interest. Even if their topography appears to be rather artificial, the ecological impact and instability created by regrading may possibly outweigh the visual benefits. It may be that remedial tidying up is all that is required to improve a pit's appearance, as discussed below. Regrading may only be necessary if parts of the pit appear to be eroding or present a safety hazard.
5.36 Judging when the shelter will permit natural colonisation is difficult. Natural regeneration can occur on eroded machair once conditions are right, such as a permanent deflation surface being reached. It was also observed to have occurred at some old pits. However, as previously discussed, it is not possible to definitively predict which sites are stable enough to allow the process to occur. Because of this, natural regeneration on bare sand can only be safely recommended for pit floors which are damp or wet, although there may be drier, very sheltered sites at which it is also possible.
5.37 Natural colonisation in this instance could result in the development of a dune slack type of community, adding interest and diversity to the habitat. Mather and Crofts (1972) report the occurrence of natural revegetation on deflated surfaces which have reached the water table at quarries in Sanna Bay. Some consideration should be given to the "ethics" of creating dune slack type habitat in areas in which it does not naturally occur. Although the resulting feature would not be "natural", it could be argued that it would add diversity to the overall dune/machair habitat in the area. Conversely, if other dune slack or marshy grassland communities are some distance away it may take some time for colonisation to occur and the resultant community might be relatively impoverished. However, it is still likely to be more interesting than that resulting from reseeding.
5.38 These include treatment to remove signs of dereliction or disturbance such as old machinery, piles of dumped rubbish or spoil, inappropriate capping materials and stands of undesirable species. They can be considered as cosmetic measures, carried out mainly for visual, ecological and safety reasons, and may sometimes be all that is required if no erosion features are present. They may also be necessary at poorly reinstated sites, the removal of inappropriate capping and undesirable species being exclusive to this situation. Some badly restored sites may require remedial regrading, which is dealt with in the next section under Landforming.
5.39 Inappropriate capping materials include imported non-machair top or subsoil and coverings which contain extraneous materials such as large stones and rubbish. Apart from being visually obtrusive, the dark humic topsoil which was seen at several sites, is likely to be too fertile for the habitat and therefore unlikely to support a machair plant community, even after reseeding. Whereas the visual impact will decrease after revegetation, the ecological impact will remain. Whether treatment is carried out may depend on the visibility of the site and the conservation value of the site's environs.
5.40 Treatment could include complete removal by scraping, or if the site is rather exposed and prone to wind blow, partial removal and incorporation of the capping into the sand surface. Stands of undesirable species such as tall ruderals usually result from the importation of fertile capping, the complete or partial removal of which will get rid of the plants. If complete removal is not possible, scraping to leave at the maximum 3cm depth, followed, if possible, by incorporation into the top 5cm of the sand surface, should discourage growth of vigorous species while providing some nutrients for growth of the desired turf species.
5.41 Safety factors, as well as visual and ecological ones, would have to be considered when deciding whether the treatment to remove extraneous material in the capping layer should be carried out. If removal by hand is too difficult, the whole layer may again have to be scraped off.
5.42 Sand extraction usually results in steep, unstable slopes, necessitating regrading at the majority of sites to create stable surfaces and reduce sand blow. Any site where existing or potential erosion features have been identified should be treated. Contouring can also be used to create natural looking topography, although the extent to which this needs to be carried out may depend on the visibility of the site. This strategy is appropriate for newly worked out pits, and should be incorporated into the extraction operation of any future pits. Landforming may also be appropriate to poorly reinstated pits which require remedial regrading.
5.43 To prevent progressive erosion of the adjacent machair, slopes should be graded to a maximum of 35o with an 's' shaped profile, and with no sharp breaks of slope left in place, as shown below.
This operation may require cutting back the turf at the top of the slope. In most cases it can be carried out by JCB at the top and bottom of the slope, but in difficult situations, turf cutting and upper slope grading may have to be carried out by hand. The turf should be saved for use in revegetation. Straight edges and uniform slopes should be avoided.
5.44 The newly graded upper slope should be protected, if possible, from further undercutting by brashings laid on the surface. If these are unavailable, and the site is exposed, an alternative, more long term, approach will probably need to be employed. This involves pegging in rolled-up geotextile material under the steep upper face at the point of undercutting and allowing the sand to fall into the roll. Erosion will naturally grade back the upper face, but the geotextile will prevent undercutting, resulting in a smooth slope profile. Seaweed placed in the geotextile prior to under pegging will encourage plant growth.
5.45 Slopes in already reinstated pits may require remedial regrading if erosion is still active. In some cases only the upper faces may require reprofiling, leaving intact vegetation on lower, stable faces if at all possible.
5.46 Regrading may also be necessary to decrease the potential wind tunnel effect in deep, steep sided, linear shaped pits. This may necessitate quite significant landforming to make the pit more rectangular shaped and shallower, and to reduce slope angles of the sides. In this case sand removed from the widened sides is used as infill (infilling in this case being acceptable). However, the resultant increase in area of the pit could be impractical if adjacent land use mitigates against this. In this situation, infilling with some other fill material to raise the floor level and reduce the gullying effect may be the only option available, although not generally recommended. Further information on this technique is given in Section 5.54 to 5.58.
5.47 Pits which have been breached from the mobile dune zone or the beach are highly susceptible to blowout and regrading alone is unlikely to suffice as a restoration measure. Their treatment is considered in Sections 5.51 to 5.53.
5.48 In many cases, revegetation, usually in the form of reseeding, is carried out after regrading to stabilise the sand surface. The problem with reseeding sand dunes or machair is that it rarely produces a plant community that is totally, or even partially, similar to the original or surrounding communities. However, as discussed above, allowing natural colonisation of bare sand to occur is risky except on wet surfaces or in very sheltered sites. A compromise would be to allow natural regeneration, whilst stabilising the sand surface with a mulch which would also supply nutrients and increase water holding capacity of the sand. It may also be worthwhile planting marram in conjunction with a mulch. Although this will eventually die back because of the lack of fresh sand, it will fulfill a stabilising role during the crucial colonisation period.
5.49 Recommended mulches are peat, seaweed or machair topsoil, but only the latter if it can be taken from a site that is anyway to be dug up. Topsoil can be used as a top dressing of about 5cm depth, or if the sand is very unstable, a layer of about 10cm depth could be applied and used as a capping. Non-machair topsoil should be avoided if possible and should not be used in areas of high nature conservation value. Unlike peat and seaweed, topsoil is naturally incorporated only very slowly into the surface beneath. If it is anything but a few cm thick, it will act as a capping, with plants growing in this layer only, rather than into the sand. For this reason, non-machair topsoil will probably result in the ingress of undesirable species.
5.50 If the only mulch available is non machair soil, it should be applied at no more than 2 to 3cm depth and should be incorporated into the sand surface. Subsoil would be preferable as this will be less fertile than topsoil and is less likely to contain undesirable species.
5.51 This technique of "aided" regeneration could be tried in regraded pits which have a low erosion risk. It is has already been successfully undertaken, albeit inadvertently, during trials at Oldshorebeag in Sutherland. Here, areas which had been mulched with peat but where seed did not take were stable enough to allow natural colonisation in the cracks around the peat "plates". A sand binder should not be used where either natural or aided regeneration is planned as this will prevent seed coming into contact with the sand or mulch. A combination of natural and,or aided colonisation and reseeding may be possible at some pits.
5.52 One of the drawbacks to both natural and aided regeneration is the length of time it may take to produce complete vegetation cover, which may not be politically acceptable or find favour with some members of the general public. For this reason, these techniques may not be suitable in sites that are near to roads, settlements or recreation areas. However, the appearance of a mulched site is probably little different from machair prepared for cultivation or left newly fallow.
5.53 Exposed sites, or those where sand blow is obviously occurring should be seeded. A mulch should always be applied, preferably either peat or seaweed. If seeding onto bare sand without a mulch, a sand binder should always be used. As discussed in Chapter Two, the efficacy of a sand binder used with mulch is not clear in the literature, the indications being that a mulch on its own can often be more effective. This point will need determining in the field by the use of trials, as discussed below.
5.54 A seed mix suitable for use on machair should be used, which could either be the CCS recommended mix (see CCS Information Sheet 5.2.2 (1987) Reseeding of Dune Pastures), or that given in Appendix Two. Where a site is located in a particularly ecologically sensitive area, such as an SSSI, the use of a green hay crop, used as a seed inoculum, should be considered. However, trials will be needed to establish the efficacy of this technique, as discussed below. Where vegetation of the surrounding dunes or machair includes marram, this species should be included in the seed mix at low densities. Where there is considerable local sand movement within a pit, all reseeding should be carried out at the same time to prevent sand blow onto seeded areas. If this is not possible, perhaps due to phased restoration, marram grass planting will have to be considered as an option for the early phases.
5.55 Areas up to one hectare in size should be hand seeded. On larger areas where the ground is sufficiently level for tracked or four wheel drive vehicles, either cross-sowing in drills using a Cambridge roller, harrowing in, or ideally, direct drilling, could be tried. Hydroseeding should only be carried out on large sites or steep slopes where machinery or trampling during hand seeding would create too much instability.
5.56 As discussed in Chapter Two there appears to be some confusion regarding the use of chemical fertilizer, with CCS (1987) maintaining that fertilizer should be applied before and after seeding. In contrast BTCV (1986) note that its use should always be restricted to a minimum necessary to maintain the typical flora for the site and that it might not even be necessary with the use of some organic mulches. This is supported by the long time practice of machair cultivation using only seaweed as an organic fertilizer, a practice which although has declined, is promoted by the Integrated Development Programme (IDP) and ESA schemes. A sensible policy, therefore, may be that fertilizer should not be used with natural regeneration, but should be considered in aided regeneration and reseeding, particularly at exposed sites. Growth should be monitored and further fertilizer applied if necessary.
5.57 Contouring and revegetation may not be enough to restore the occasional pit located in mobile dune zone or those affected by breaching from the beach or mobile dunes.
5.58 Where breaching is from the mobile zone, erosional processes in the pit will be similar to those in a blow out situation. In this, sand will be blown into the pit from the beach or mobile dunes and erosion of the sides and probably the landward end of the pit will occur. Reinstatement in this case must follow that undertaken on blowouts, using sand trapping techniques. This should involve marram planting and the use of sand fences, which has been found to be relatively successful in the study area (Angus and Elliot 1992, Hansom and Combor 1995). The use of geotextile matting in association with polythene bag sections or "pillows" appears to have been less successful and is therefore not recommended. Details on sand trapping can be obtained from the CCS Information sheets and the BTCV Sand Dunes Handbook, as referenced in Chapter Two.
5.59 Where breaching has resulted in wave attack on the seaward side of the pit, sand trapping may have to take the form of sand fence boxes which have been found to be successful on wave washed dunes (see BTCV Handbook). However, if there is not sufficient wind blown sand to build up inside the boxes, some other form of barrier may have to be constructed. Solid barriers in general have a low success rate for preventing dune erosion, but gabions dug into the foredunes and covered with sand and gravel to provide a shallow gradient have worked well at the West Geirnish Coast on South Uist (Angus and Elliot 1992). The barrier at Horgabost, which is probably constructed from solid fill material, appears to have worked well to date because of the very sheltered nature of the back beach which it adjoins. However, it is unlikely to be successful in a high energy wave environment, illustrating the great importance of adopting a site specific approach to this particular problem.
5.60 Following from this latter point, the whole question of reinstatement of breached pits should be examined. Natural blowouts are considered by some to be part of the dynamic process of dune and machair evolution and which should only be treated if property or safety are threatened. Breaching of pits sited close to the sea will in many cases be due to the natural process of coastal erosion. Attempting to repair or prevent the breach may be futile in the long term and it may even be worth considering flooding as a reinstatement option, creating a lagoon type habitat, for such pits. The threat of breaching has implications for infilled pits, in which the fill will become re-exposed without constant intervention. Removal of fill from such sites might be a more pragmatic approach to adopt. Clearly, infilling of sites close to the coast should be avoided in the first place, even if the coast is currently accreting.
5.61 Infilling pits with inert material is not regarded as a restoration technique, but as a use of the pit which requires a particular method of reinstatement.
5.62 The greatest problem with infilling is the re-exposure of the fill that often occurs, either due to poor filling technique, inadequate covering, settlement, or animal burrowing, or a combination of all four. In addition. there is the added risk at many sites near to the shore of re-exposure by marine erosion. Exposed fill initiates wind scouring and, along with settlement holes, poses a safety hazard, as well as being visually unattractive.
5.63 Where pits are to be filled, it is recommended that the sides are first graded. This will decrease the pit's volume, but will lessen the effects of wind scouring if re-exposure were to occur. The vertical sides of some of the re-exposed pits seen during survey were greatly exacerbating erosion.
5.64 Fill material should be properly compressed to minimise settlement. This is relatively easy with spoil, but material such as scrap iron and rubble are more difficult to treat. Scrap metal such as old cars should be well crushed, possibly by trafficking with heavy machinery, as seen at some sites, and each layer of fill should be covered with spoil to "plug" the holes. Large boulders should not be included in fill material as these cannot be compressed and create void spaces which are difficult to fill.
5.65 The top layer of covering should be at least 30cm in thickness and should be finally capped with a minimum of 20cm of sand or sandy subsoil (the latter being less likely to contain undesirable species than topsoil). The filled surface should be flush with the adjacent original land surface. This should then be mulched and seeded as described above. Machine seeding may not be possible if there is a risk of mixing the sand capping with the lower spoil cover layers.
5.66 In many cases it could be difficult to specify a definitive strategy or technique for a site, particularly in relation to digging versus under-pegging for slope grading, seeding versus natural regeneration, and to the use of fertilizer, mulches and sand binders, as discussed in some detail at the end of Chapter Four. The ideal would be to set up field trials one or two years prior to restoration to establish the best practicable options (A.Scott, pers. comm. 1996). However, this may not be possible in many cases and a different approach may have to be adopted. This could be one which utilised several different strategies and/or techniques within the restoration scheme. For example, some areas could be seeded, while other areas could be naturally regenerated, or some areas could be mulched with and without a sand binder. The site would have to be monitored as part of the aftercare scheme, and remedial measures carried out where treatment had been unsuccessful, using the strategy/ technique(s) shown to have worked.
5.67 As discussed in Chapter Two, fencing to keep out grazing stock and rabbits will be crucial at most sites until vegetation is well established. However, fences can themselves cause problems, attracting rubbing animals and causing sand build up. Long, straight stretches of fenceline should therefore be avoided. In many cases, some additional form of rabbit control, such as trapping, shooting and gassing, may be needed at large sites.
5.68 Once reinstatement is complete, the site should be monitored until it can be confirmed that revegetation has been successful and that there are no potential or developing areas of erosion. This could take anything up to five years. Remedial measures will be necessary if erosion features start to appear, or seeding does not take, or natural regeneration is not proceeding at a sufficient rate, or grazing is causing significant damage. These measures might include regrading, reseeding, repeat fertilizer or mulch applications, rabbit control and fence maintenance respectively.
FIG. FIVE SUMMARY OF REINSTATEMENT PROCEDURE
Erosion Control
Visual improvement
1. ASSESS NEED FOR RESTORATION
Safety
Ecological improvement
existing revegetation
2. DECIDE STRATEGY )
FOR ) depends on site stability & shelter
REINSTATEMENT )
visual impact
3. TREATMENT
(Combination of treatments possible within a site)
Do nothing Cosmetic Landforming Revegetation remedial
measures
Existing nat. To remedy To stabilise pit To stabilise sand
regen. poor slopes surface
acceptable/ reinstatement
site v.
sheltered
permits
nat.regen.
Remove dumped Cut back undercut Mulch to speed up objects, hand upper face & nat. regen. if
pick stones etc grade slope to site v.sheltered
max. 35o
or
Remove underpeg undercut Mulch, seed &
inappropriate face with fertilise rel.
capping & geotextile roll exposed sites
species
Widen linear pits Possibly add
sand binder in
v.exposed sites
Revegetate if necessary
Stock and rabbit control necessary
(fencing and other measures)
4. AFTERCARE AND MONITORING
Remedial grading/seeding/fertilizer/mulch/rabbit control if necessary
5.69 Perhaps the best way of avoiding erosion problems would be by siting pits in low erosion risk areas. Similarly, ecological and visual impact can be minimised by expedient siting. Advance planning to identify sites in which geomorphological, visual and ecological impacts would be minimised is therefore highly recommended.
5.70 However, whereas methods for establishing ecological and visual sensitivity are reasonably well established, geomorphological sensitivity is less often considered. The development of guidelines on dune and machair sensitivity and a site location strategy might therefore be sensible, particularly if larger scale operations are likely in the future. An example of such a scheme can be seen in the dune-type classification system used as baseline information in the sand mining permit decision making process for Michigan's inland sand dunes (Buckler 1986).
5.71 This chapter clearly shows that there is rarely any one definitive way to carry out reinstatement. Every site has to be considered individually, and specifications drawn up only after careful consideration of the geomorphological, visual and ecological character of each site and its environs, as well as the safety factors peculiar to each pit. Careful field study is therefore an essential precursor to any reinstatement plan, as is the need for a flexible approach whilst carrying out operations because of the still very experimental nature of many of the practices. For the same reasons, and because of the unpredictability of the dune and machair environment, the restorer also has to be prepared to carry out post-treatment remedial work, the need for which can only be determined up by regular monitoring. However, planning to integrate some aspects of reinstatement within the operational phase of the pit will greatly reduce the time and effort put in to post operational restoration.
