|
|
|
|
This section describes a sample of five case studies of work recently carried out on the trunk road network, which illustrate a positive environmental approach in action. It is anticipated that new examples will be added as the Plan is implemented over the next few years.
1. A830 Polnish Bridge - Loch Nan Uamh Rock Architecture
2. A95 Allochy Bridge - Free Passage of Fish
3. Evan Water River Diversion
4. Logie Easter - Garrick Bridge Stumps
5. Otter Mitigation Measures - Skye Bridge
A830 Polnish Bridge - Loch Nan Uamh Rock Architecture
This case study illustrates how a diverse project team of engineers, ecologists and landscape architects can work together to produce a project which is successful in terms of function, appearance and contribution to biodiversity. The project also demonstrates the importance of the substrate in habitat creation and the construction of an environmentally successful scheme. As stated in CEL:LfN, "Diverse ground conditions are the foundation for diverse vegetation".
In accordance with the Fitting Roads policy, the Scottish Executive was determined that the latest improvement project on the 'Road to the Isles' should not only be fit for its purpose but also be fit for the environment and landscape.
Therefore the designers and contractors set out to create a road setting that integrated as much as possible with the surrounding landscape and allowed opportunities for regeneration and maturation within the local landscape. This was accomplished in a number of ways:
Rock architecture describes the technique used to create rock cuttings that are designed and shaped to meet specific needs. In this case the objective of the cutting design was not solely to allow the passage of traffic, but also to integrate with the surrounding landscape. A cutting was created with natural texture, colour and form, comprising bays and buttresses, cracks and crevices within the constraints of the pre-splitting construction technique.
With this rock foundation in place, the peat excavated from the road line was used to best effect. It was placed on berms; poured down the rock face to lodge in crevices; piled up in the bays and buttresses of the cutting; and laid into the rock trap ditch.
The verges and cuttings were then either hydroseeded or left to regenerate naturally from the peat or adjacent woodland. Trees and shrubs grown from seed collected in the area two years previously were planted in the flat verge area and amongst the rock slopes where required.
The project is now in its second year and is integrating and maturing well in its setting. Visual impact on the landscape has been minimised and it is clear that, in the short time since its completion, biodiversity within the road corridor is increasing.
A95 Allochy Bridge
This case study illustrates how even small maintenance projects can be designed and built so that adverse impacts on local biodiversity can be minimised, and that in some cases enhancements are possible. The study also demonstrates the practical application of environmental policy.
The original masonry bridge over the Allochy Burn was extended on one side using steel girders in the 1930s. Over the intervening period the girders became badly corroded and recently the bridge was demolished and replaced using a pre-cast concrete box construction.
The design and construction of this project had an impact on the local environment in two key areas:
These two impacts are discussed in more detail in the Scottish Executive environmental policy documents: Cost Effective Landscape: Learning from Nature and The Free Passage of Fish.
In accordance with these policies, a sketch design was pepared with the objective of mitigating these impacts. The design included:
This was a small and cost-effective piece of work, which has lessened the impact of the bridge considerably.
Evan Water River Diversion
Although this project was completed in 1995, before the publication of the Dumfries and Galloway BAP, the work illustrates how the objectives of the Scottish Executive and Dumfries and Galloway Biodiversity Partnership can be integrated and represents a good practice example for future collaboration. The A74 Evan Water Advance Diversion project is also a particularly good example of the application of stage 4 of the CEL:LfN procedure: Monitor Implementation.
The Dumfries and Galloway BAP contains key objectives with regard to watercourses; two of these are applicable to the work undertaken by the Scottish Executive on the Evan Water.
They are:
Following the environmental assessment process it was apparent that the Evan water was environmentally important in terms of its contribution to Scottish biodiversity, especially for invertebrates and birds; and its status and as a nursery area for Salmonid fish. It also made a significant contribution to the landscape character of the area.
Consequently, in 1994, a contract was let with the primary purpose of diverting the Evan Water in an ecologically sound manner. The project was designed in such a way as to minimise impacts on biodiversity, and was deliberately separated from the main road works contract. This approach was chosen to allow time for the river to settle down before the road works commenced, and also to allow the design and construction teams to concentrate solely on the river works without other distractions.
Eleven separate diversions were designed and constructed approximately two years in advance of the roadworks, each one around 250 to 500 m in length. Each was designed to protect and enhance river water quality, biodiversity and the structure of the river embankment.
A detailed survey of the river was carried out in accordance with the River Habitat Survey methodology, including an assessment of the character of the river and its banks and vegetation characteristics, pools, rapids, riffles and spawning grounds etc. A design was produced which comprised the following measures:
Channel Alignment
The diverted river was designed to copy the meandering pattern and width of the existing river where possible.
Channel cross section
The existing river provided the template as to the best cross section. Constrictions and widening were incorporated to create rapids and pools. Floodplains were also catered for.
Channel longitudinal section
The design of the longitudinal section allowed for shallow riffles, diversity of streambed texture, deeper pools, rapids and small waterfalls to match the existing river.
Landscape and ecology
Native trees and shrubs were planted along the banks to recreate the original riparian vegetation characteristics and to allow a suitable pattern of light and shade along the river course. Aquatic and marginal plants were placed in appropriate locations and an organic geotextile membrane pre-seeded with locally appropriate seed mixes was used to stabilise and revegetate riverbanks.
Although all efforts were made to ensure a thorough and sound design prior to starting the construction work, a very 'hands-on' flexible and sensitive approach was adopted in this contract. A landscape clerk of works was employed throughout the whole job and regular meetings were held between client, contractor and designers (engineer, landscape architect, ecologist), and representatives from the River Purification Board, SNH and the Solway Fisheries Board. The results of this approach were very positive and included:
The project was completed in spring 1996, and by December of that year nature had begun to recolonise and weather the diversions. The outcome of the scheme will be monitored over the years following the completion of the M6 motorway and the success of the scheme can then be gauged in technical terms. What is very apparent is the speed and ease with which nature has recolonised the affected reaches owing in part to the creation of appropriate conditions on the banks and bed of the river.
Further guidance on best practice in river diversion work is contained in the River Restoration Manual within the SEPA Natural Heritage Handbook.
Logie Easter - Garrick Bridge Stumps
This case study is a good illustration of the wise use of resources resulting in best value and biodiversity benefits.
Tree stumps are generally classified as waste materials, and removed for disposal at a landfill site. This is unnecessary and a waste of money, time and resources. It is also a lost opportunity in terms of maintaining biodiversity, as stumps provide a valuable habitat for wildlife, particulary invertebrates, while they rot down.
On this small improvement project, an alternative use was found for some of the excavated tree stumps and they were laid in the verge to create a minor landmark feature and to increase the biodiversity value of the verge. Woodcocks have been observed probing for food around the stumps and it is likely that additional wildlife will find this new feature in the verge a great opportunity.
Otter Mitigation Measures: The Skye Agreement
Draft 26 April 1999
The disturbance of wildlife was a serious consideration during the design and construction of the Skye Bridge. Mitigation measures were provided to reduce the effect on the otter population. A post construction study is now underway to assess the effectiveness of the mitigation measures. In April 1999 a workshop was held to get a broad view of the preliminary findings. The following points were agreed:
Contract certification
Future construction contracts shall include wildlife mitigation measures, design, implementation and maintenance check certificates. These certificates shall be signed by the wildlife professional responsible for the scheme.
Objective: To improve design construction and maintenance value for money.
Provision of multi-use wildlife mitigation measures
After giving due consideration to the specific mitigation needs of individual species, further consideration shall be given to the needs of other species and habitat fragmentation in the wider road corridor with a positive aim of providing multi-purpose mitigation measures.
Objective: To comply with aims of the TRBAP and make more efficient use of all mitigation measures.
Wildlife crossing opportunities
All underpasses and overstructures shall be designed and located so as to maximise the opportunity for wildlife crossing whilst not impairing the function of the structure. The provision of vegetated margins shall be considered and all opportunities shall be taken for locating the structures as close as practicable to likely wildlife crossing points.
Objective: To comply with aims of the TRBAP and make more efficient use of all structures, culverts, agricultural and pedestrian underpasses and bridges.
Dimensions of wildlife tunnels
The professionals responsible for the design of badger and otter underpasses shall recommend the size of pipe or other form of pass. Their recommendations shall be supported by well reasoned argument on the form and value for money of the tunnel.
The DMRB suggests that both otter and badger underpasses shall be pipes with a minimum diameter of 600mm. Recent research suggests that length and diameter should be related.
Objective: To ensure that tunnels are both ecologically functional and cost-effective especially in design and build forms of contract.
Mitigation measure management
Road managers responsible for wildlife mitigation measures shall be given information and training about wildlife needs. Discussions shall be arranged to encourage and further mutual knowledge and interest by all concerned.
Mitigation measures shall be inspected regularly and remedial actions that are required defined in Landscape Action Plans.
At defined intervals performance shall be assessed by a specialist and where necessary recommendations for change made.
Objective: To improve the management and value for money of mitigation measures but also to improve their future design and construction.
The need for temporary or permanent measures
Professional consideration shall be given to assess whether expensive mitigation measures shall be provided where experts agree that population fragmentation will only be affected in the short term and then not seriously. Temporary measures shall be considered in such circumstances.
Objective: To avoid construction of un-necessary measures and provide alternative approaches in political or emotive situations likely to demand over elaborate provision.
Provision of artificial otter holts
Artificial holts shall only be constructed in exceptional situations. Where they are considered necessary by an appropriately experienced wildlife professional, they shall be constructed of natural materials and need not necessarily be below ground.
Objective: To improve the value for money and efficiency of mitigation measures.
Permit to use
In new build situations, the issue of the permit to use certificate shall be conditional on mitigation measures being complete or other measures in place to protect wildlife from increased danger.
Objective: To provide enhanced protection to Scottish wildlife.
The appearance of wildlife mitigation measures
The wildlife professional, engineers and a landscape architect shall work together on the design of wildlife mitigation measures so that impacts on landscape character are minimised.
Objective: To ensure the appearance of all structures is considered in the design and management process.
Commitment to biodiversity action
The Trunk Road Biodiversity Action Plan should set down a clear strategy for the implementation of biodiversity recommendations so that actions are not wish lists.
Objective: To put Scottish Executive Policy into practice.
Public information
Consideration shall be given to the provision of public information, through literature or signage (e.g. in lay bys), on wildlife mitigation and biodiversity aims on the trunk road network.
Objective: To raise public awareness on the need for biodiversity protection and its value for money.
Badger fencing
Mike Harris, NE badger group, and John Ralston, SNH, to provide recommended fencing specification. Provided May 1999.
Objective: To ensure that effective fencing is installed to maximise the use of wildlife crossings and reduce road casualties.
|
|
|