Conclusion
A greater emphasis on the optimisation of water-based restoration design is appropriate given the long-term effects of restoration compared with the relatively short operational life of a quarry and the proven potential for schemes to make a major beneficial contribution to the surrounding area. Conclusions on the overall project objectives are presented below.
Review of water-based restoration options and methodologies
This report attempts to provide the necessary technical background information and best practice guidance to inform experts from the range of disciplines involved in water based quarry restoration. It is evident that close co-operation between the associated professionals is necessary and requires a significant level of knowledge of the other subject areas involved. A lack of understanding of the combined hydrological, ecological, engineering and landscape issues can lead to unrealistic expectations for a restoration, and it is therefore desirable to set targets which are both ecologically and hydrologically meaningful and practical in terms of cost and engineering requirements. Information available in the literature, which includes several ALSF funded MIRO projects, has been consolidated and referenced if further detail is required.
The physical and practical constraints on a restoration scheme
A wide range of potential restoration end uses exist and the practical constraints on a selection have been examined and are presented within the report. What can be achieved at a given site is dictated to a large extent by the depth of the excavation and the watertable, the volumes and properties of fill material, water quality and influent/effluent volumes to the site. For this project a proforma datasheet has been developed to formalise site-specific data collection, produce a site water balance and allow comparison between sites. Water quality varied between different sources with consequences for proposed afteruse, in particular habitat creation.
The interaction of the site over time with the surrounding water environment is a key constraint on the long-term viability of a restoration and requires long-term monitoring data to incorporate extremes in recharge. Data from the study area indicates maximum and minimum levels of recharge and regional water levels (since records began) have been approached within the last 5 years and climate change predictions indicate this trend for greater temporal variability is likely to increase. Off-site data sources covering a sufficient time period and unaffected by quarry dewatering would be an aid in restoration design. A central database accessed via the MPA would be one solution to any potential data gap.
For wetland restoration designing ‘complexity’ into a scheme is essential in order to maximise the area of low-lying ground and areas of pond/ditch/shoreline and shallow water. In some cases mineral is being sterilised to provide restoration material for habitat creation consequently leading to a greater requirement for land elsewhere. Maximum extraction would utilise all the available mineral resource but limit the potential for habitat creation unless additional fill material can be sourced. Greater areas of wetland may be encouraged at the expense of returning land to often low grade agricultural usage.
The research indicates that many of the sites may be developed for a wide range of afteruses and the goals of the mineral operator, landowner and regional strategic guidance are the primary criteria to prioritise water-based restoration objectives. Rather than working up from the site-specific detail to suggest a use, it is perhaps better to consider, at least in brief, a range of potential end uses to inform the Mineral Planning Authority and other stakeholders of the available options, and then select and refine the most appropriate schemes based on the site detail.
The potential success of different restoration strategies
It is apparent that a measurement of the success of a restoration is very subjective and may include maximising mineral extracted and minimising land disturbed or increased benefit to the landowner; nature conservation; local residents and the wider community. In general the case study findings indicate that water-based quarry restoration has been generally successful although different stakeholders may argue that more may be done for their particular interest and the balancing of these differing priorities is divided between the MPA and the minerals operator.
Input from the end site user or restoration manager is considered a major benefit to achieving an optimum restoration design. A degree of flexibility is required in any restoration design and this can be managed successfully by regular consultation. A water management plan for the restoration, updated to incorporate changes in design and new data, would increase the chances of optimising the restoration. The plan would include the hydrological requirements of the target restoration and the methodology to achieve these, including contingency plans for variations from the anticipated water environment. The water control methodology and infrastructure put in place will have significant implications for the subsequent site use. Agri-environment funding may not be available where habitat creation is a requirement of planning consent but it may be relevant where third parties take on future management and are required to deliver and maintain habitat based on water level control.
In terms of success in delivering increased biodiversity it is important to distinguish between targeted habitat creation, where the aim is to contribute to the conservation of priority habitats within the wider landscape, and the ‘default option’, common to many restored aggregate sites, whereby deep lakes are fringed by landscaped overburden bunds supporting a mixture of woodland and grassland. These post-extraction ‘parkland lake’ landscapes may indeed support a good variety of wildlife and provide appealing amenity areas but they make a less specific contribution to the conservation of biodiversity. Quarry restoration has the potential to make a major contribution to the creation of fen and other wetland habitats, in particular those requiring a low nutrient input.
The research has highlighted a range of site afteruses many of which have good potential for implementation in the study area. The case study sites have been, or will be, returned to agriculture, nature conservation or potentially amenity use. These conventional options may be seen as having lower complexity and risk associated with them than other schemes. In addition the area available for restoration is a limiting factor.
Indications of the research project are that bigger is generally better, rather than the field-by-field approach currently in operation. Large areas allow greater potential for strategic planning, larger (more viable) habitat creation and major works such as flood alleviation schemes. However, negative public perception of large areas demarcated for extraction may lead to problems in obtaining planning permission and multiple land ownership makes matters complex.
Research input to the planning process
In order to employ planning strategy on a regional (landscape) scale, a method of meeting large-scale objectives is required. A primary concern of an operator is to extract mineral and guidance from the MPA is perhaps required to provide a range of potential end uses for sites in various locations that would be acceptable and encouraged. Data collected during the course of this research could be incorporated within a GIS-based system that may present a suitable platform for developing regional strategic policy. However as a result of the localised variability in geology and hydrology identified within this study considerable difficulty exists in transferring from the regional to the site-specific level.
Significant technical (ecological/hydrological) input is required at a regional scale to provide guidance for restoration, which is otherwise beyond the scope of a site-specific restoration design. The resources to provide this may lie with the Mineral Planning Authority and to some extent with the Environment Agency, Water Companies and Conservation bodies. Regular meetings with stakeholders to discuss technical issues, such as the steering group meetings held for this project, help to catalyse discussion and inform the planning process.
Integration between the Mineral Planning Authorities regional spatial strategy and the River Basin Management Plan co-ordinated by the Environment Agency may be a key step in guiding the design of water-based quarry restoration to address local issues such as low flows, scarce water resources, flooding, landscape setting and ecological diversity.