A9 Dualling Programme Strategic Environmental Assessment Non-Technical Summary
12. Soil and Water
SEA Challenges/ Opportunities
A9 dualling presents a number of challenges and opportunities with respect to soil and water considerations.
Challenges for soil include delivering a safe, dualled route with appropriately sited junctions, lay-bys and SUDS whilst minimising overall land-take, soil sealing and construction or excavation in peat and wetland areas, as well as protecting designated geological sites and habitats.
Challenges for water include delivering infrastructure with improved drainage that maintains hydrological regimes for peat and wetland areas, avoids increasing flood risks along the entire route and delivers construction of watercourse crossings that minimises impacts on designated water and ecological features.
The summary baseline table highlights the areas covered by peat and wetland as a percentage of the full 200m online corridor and a percentage of the total feature area (i.e. where a specific area of peat/ wetland is crossed by the corridor, the percentage of that area in the corridor).
The percentages are only used to provide an indication of the scale, but not the significance of the features along the corridor.
Route wide, the area covered by hard standing, in terms of road surfacing for online dualling, could potentially be in the order of 2sqkm (this is an extreme estimate). To provide some context, London's Olympic Park is approximately 2.4sqkm.
Route wide, a 2sqkm linear development over varied topography and soils is assessed as having minor adverse impacts on regional soil resources.
As hard standing effectively sterilises the area underneath in terms of soil biodiversity, SEA considers that A9 dualling will present minor to moderate adverse effects at the local level, depending on the habitat or ecological value of local soils affected within each section.
|Feature Type||% corridor area||% feature area|
|Peaty soils (podzols/ gleys)||24%||5%|
|Main watercourses (rivers)||Tay, Spey, Tummel, Garry, Dulnain, Findhorn|
|Watercourse crossings||At least 300 in the 200m corridor|
|200 year indicative flood zone||At least 40 areas in 200m corridor 9% total corridor area|
|Site of Special Scientific Interest (SSSI)||4 geological & mixed sites|
|Geological Conservation Review (GCR) Sites||4 sites|
Soil losses to hard standing would be even greater under alternative or near offline routes that require full dual carriageway construction, rather than widening the existing route.
Detailed route alignment studies and environmental assessment should work to minimise the overall area of land take required for dualling, focusing particularly on avoiding and limiting effects on higher value soils such as peat and productive agricultural land.
Prime quality agricultural land is considered a finite resource, and general guidance would be to avoid losses wherever possible. GIS analysis shows that prime quality, arable land (Grade 2-3.1) is found in the 200m corridor in Sections A and F.
In Section F, this prime quality land is around an already dualled section and is unlikely to be affected. In Section A, dualling has the potential to result in some, but anticipated to be minimal, loss.
Slightly lower quality (not prime) Grade 3.2-4.2, mixed agricultural land is found bordering the A9 in all sections except Section D. There are likely to be minor losses in Sections A, B, C, E and F; however overall losses associated with boundary widening for online dualling are likely to be minimal at the route wide scale.
SEA considers that online dualling will result in minor adverse effects on prime quality land (Grade 2-3.1) in Section A, and minor adverse effects on mixed agricultural land (Grade 3.2-4.2) across all sections, other than Section D where no such land is identified.
At the route wide level, potential losses of productive agricultural land are considered to present a cumulative minor adverse effect as the overall scale of losses is expected to be low.
The key areas of peat and peaty soils that will be affected by A9 dualling are:
- Section C - Drumochter Pass;
- Section D - Glen Truim;
- Section E - just past the Crubenmore dual carriageway (relatively small area); and
- Section F - remaining length of the route north of Carrbridge.
SEA considers that online dualling presents the potential for major adverse effects in Sections C, D and F, and minor adverse effects in Section E.
Online dualling would be expected to present lower risks to peat soils than alternative or near offline routes as these would be more likely to affect previously undisturbed areas of peat.
The area through the Drumochter Pass will be particularly challenging given the constrained nature of the valley floor and, should dualling impact areas of active blanket bog, then a major adverse effect at the site level would be determined as it is a priority habitat.
Local level peat ecology, hydrology and geotechnical survey will be required to determine locally appropriate solutions which minimise the potential effects of drainage and desiccation, and inform suitable restoration and management plans.
No wetland feature areas were identified in Section A; however, there are areas of wetland to be considered in all other Sections of the route.
SEA considers that A9 dualling presents the risk of losses at local levels resulting in minor to major adverse effects, depending on the sensitivity and value of the wetland habitat affected.
Wetland areas will require detailed consideration during route alignment studies to avoid, where possible, or to minimise the footprint where avoidance is not possible. Route alignment studies may have to consider alternatives outwith the 200m corridor to avoid wetland sites (within the context of other constraints).
Local level ecology and hydrology survey should determine the feeding water source for groundwater dependent wetlands, to inform measures to maintain the integrity of hydrological regimes, and the residual cumulative effect is assessed as minor adverse.
Geological SSSI and GCR Sites
There are only three key sites around single carriageway sections; Drumochter Hills SSSI, the Slochd GCR, and the Glen Garry area which has both GCR and SSSI designations (A9 Cuttings and River Garry GCR and the Glen Garry SSSI).
Other sites were identified in the A9 corridor area; however, they are around already dualled sections and not considered further in the SEA.
In Section C, the Glen Garry SSSI is designated for structural and metamorphic Dalradian geology, preserving evidence of the shallow water environment in which they were deposited as sediments over 600 million years ago.
This site creates a specific tension between general SSSI requirements to avoid impacts wherever possible, and the fact that the A9 dissects the site, exposing some of the features.
The general position that partial or full removal of any rock outcrop would present adverse impacts on the site's qualifying features is accepted; however, dualling may equally open up other features of geological interest, and there may be opportunities for enhancement in the area, via lay by positioning and providing safe pedestrian subway access to both sides of the road.
SEA recommends discussion and agreement with SNH, on a preferred approach to this particular SSSI site, to inform strategic design guidance. Should the decision be that no construction takes place within the site boundary, route alignment studies will have to consider alternative alignments outwith the 200m corridor in this area.
The Drumochter Hills Mixed SSSI is designated for fluvial (river) geomorphology. This is one of the many issues facing dualling through the Drumochter Hills site.
SEA recommends discussion and agreement with SNH, on a preferred approach to this particular SSSI site, to inform strategic design guidance. It is likely that this issue could be discussed under the workshop previously recommended to inform a strategic Appropriate Assessment for the Drumochter Hills SAC/ SPA designations.
SEA considers that A9 dualling presents potentially mixed effects, with risks of adverse impacts and opportunities for local enhancement.
Potential enhancement benefits could be realised around Glen Garry and Slochd; however, early agreement is required with SNH on the preferred approach to provide strategic guidance.
The main rivers along the A9 corridor include the Tay, Tummel and Garry to the south of the Drumochter Pass, and the Spey, Findhorn and Dulnain to the north of Drumochter.
Each has numerous tributaries, and GIS analysis indicates that there are at least 300 instances where the 200m wide online corridor crosses a watercourse, although around 75 are at already dualled sections.
The analysis showed that the number of crossings required in each A9 Section, typically doubles between 15m and 100m from the current route.
SEA considers that, in all cases, online dualling will minimise the number of watercourse crossings, culverts and engineering works.
SEA considers that A9 dualling presents potentially minor to moderate adverse effects at the local/ site level, depending on the sensitivity of the local watercourse, habitat and species.
Due to the number of crossings and culverts required, moderate adverse effects are anticipated, cumulatively, at the route wide scale.
Effective design advice from river geomorphology and ecology specialists, and consultation with SNH and SEPA, will minimise local and cumulative risks, and the residual cumulative effect is assessed as minor adverse.
Drainage and SUDS
Upgraded sections of the A9 will be designed and constructed to meet current drainage standards, including SUDS provisions.
Incorporating SUDS along the length of the newly dualled sections will help ensure effective retention and settlement of surface water runoff before discharge, with a likely reduction in pollutant levels in the discharge.
Considered cumulatively over the 129km to be dualled, SEA assesses this as a potentially significant improvement over current conditions, especially over the long term.
Given that the A9 is a rural trunk road, there is a need to incorporate high quality, landscape driven design when considering any large, visible SUDS features such as retention ponds/ detention basins.
SEA considers that this approach will be more likely to minimise the visual effect of SUDS features and deliver greater potential for secondary benefits in terms of ecological enhancement and habitat creation.
SEA also considers that the improvement of drainage provisions along the route will provide additional/ enhanced opportunities for mobile species to cross the road, thereby reducing the potential barrier effects of a widened road.
In areas where later design stage surveys identify mobile species activity, or around areas designated for relevant species such as otter, then enhancement measures should be incorporated into drainage designs including larger pipes/ culverts and mammal ledges. Such requirements should be defined by ecology specialists.
SEA considers that the improvement of A9 drainage, with incorporation of SUDS, will present:
- Minor local benefits, aggregating up to a moderate regional benefit, with respect to long term improvements to discharge water quality
- Minor local benefits, potentially aggregating up to a moderate regional benefit, with respect to provision of crossing opportunities, habitat connectivity, limiting barrier effects and potential habitat creation for biodiversity
- Mixed effects in terms of landscape and visual issues, where sympathetic design of individual SUDS features could be an enhancement/ present minimal issues locally, but where a large number of SUDS features could have a noticeable effect on regional character.
A route-wide A9 dualling Strategic Flood Risk Assessment (SFRA) is underway and will continue through the SEA Environmental Report public consultation period.
The route crosses some of the largest rivers in Scotland, including the three main river catchments of the Tay, Spey and Findhorn. It also crosses areas with known flood history and it is recognised that 'medium to high' flood risk areas are unlikely to be completely avoided under the dualling programme.
The SFRA will carefully consider A9 dualling in areas sensitive to flooding; primarily to avoid increasing flood risk and areas of flood hazard.
Preliminary SFRA Scoping considered that A9 flooding from groundwater, coastal, sewer and infrastructure failure is unlikely. The SFRA will focus on flooding from rivers and surface water.
Initial review has identified that the key risks associated with dualling include:
- New or widened embankments within the functional floodplain, potentially resulting in reduction of flood storage and increase in flood level;
- New watercourse crossings potentially limiting flow conveyance and resulting in flow backup, increase in flood level and wider flooding.
Preliminary consultation with SEPA agreed the following:
- Dualling will be designed in consideration of the 1 in 200 year return period flood event;
- Consideration to be given to flood risk during construction phases, including temporary works and storage of materials outwith the functional floodplain;
- Alignment options that locate SUDS features within the functional floodplain will be required to demonstrate there is no change in flood risk, and no impact to water quality.
SEA considers that A9 dualling could potentially present major adverse effects at the local and route wide scales. However, SFRA followed by more detailed Flood Risk Assessment where required at the local level, will work to ensure that A9 dualling results in no net increase in flood risk.
Therefore SEA determines that A9 dualling will have no significant effect on flooding risks.
SFRA findings and recommendations will be incorporated into the SEA Post Adoption Statement and finalised monitoring framework.