A487 Machynlleth Bridge Improvement Scheme
Hydroseeding, erosion control and ecological planting for a sensitive highway corridor in Mid Wales.
The Challenge
Transport for Wales' A487 Machynlleth Bridge Improvement Scheme required the revegetation of 1 km of new highway earthworks in an environmentally sensitive corridor. A nearby SSSI and the presence of protected species meant that all seed and plant material had to be locally sourced, with no room for error on ecological compliance.
The site presented a demanding mix of steep embankments and low-lying wetland areas, each requiring a different seeding approach and careful environmental management. No fertiliser could be used due to the proximity of sensitive watercourses.
The programme was tight. Earthworks were being completed in phases, leaving newly exposed soils vulnerable to erosion and wash-off with every passing week. The client needed a specialist who could mobilise repeatedly at short notice, apply the right method to each area, and establish vegetation before rain and runoff caused damage.
Standard landscaping contractors could not meet the local provenance seed specification, navigate the environmental constraints, or provide the hydraulic application and specialist equipment needed for the steep slopes on this scheme.
Key Site Constraints
- Adjacent SSSI requiring zero-impact ecological management
- Protected species on site with strict compliance requirements
- Local provenance seed specification with no off-the-shelf alternatives
- No fertiliser permitted near sensitive watercourses
- Phased earthworks programme with ongoing erosion exposure risk
- Mixed terrain: steep embankments and low-lying wetland areas
What CDTS Delivered
Phased Hydroseeding and Conventional Seeding Across 20+ Mobilisations
Rather than a single mobilisation, CDTS North & West adopted a phased seeding strategy across more than 20 separate visits totalling approximately 40 days on site. Each visit targeted newly exposed soils as earthworks progressed, keeping the window of unprotected ground to an absolute minimum and reducing erosion risk throughout the programme.
Locally Sourced Seed Mixes Tailored to Each Zone
Multiple native wildflower mixes and low-maintenance amenity grass mixes were specified and applied depending on location, soil conditions, and ecological requirements. Seed application rates ranged from 4 g/m² to 30 g/m² depending on the mix and area being treated. All seed was locally sourced to meet the scheme's provenance requirements.
Right-Sized Equipment for a Sensitive Site
A 3,500-litre hydroseeder was deployed, deliberately chosen as the right-sized machine for the site, avoiding the ground disturbance associated with larger units. An Aebi mountain tractor was used for low ground pressure mowing of steep banks, protecting newly established vegetation and fragile soils.
Groweb Hydroseeding Mulch
Groweb hydroseeding mulch was applied to protect seed and retain moisture during establishment, supporting germination without the use of fertiliser or chemical soil amendments.
Native Hedging and Woodland Planting
In addition to seeding, CDTS carried out native hedgerow and woodland planting along fence boundaries and across various woodland plots on the embankments, delivering the full ecological planting specification on a single contract.
Environmental and Safety Controls
Environmental management was built into the programme from the outset. The phased approach itself was the primary control, establishing vegetation as quickly as possible to minimise exposed soil and reduce the risk of silt runoff into nearby watercourses. All works were carried out under full traffic management.
The Results
By seeding in multiple stages timed to follow the earthworks programme, CDTS kept exposed soil to a minimum throughout the scheme, the single most effective measure for preventing erosion and protecting the adjacent SSSI.
No erosion or wash-off events occurred on any of the seeded areas, with the only water-related incidents being natural flood plain flooding unrelated to the works.
Germination and vegetation cover varied by mix and time of year, as expected on a scheme of this duration and complexity. The phased approach ensured that each area received the right mix at the right time of year to give vegetation the best chance of establishing.
CDTS has been retained for three years of ongoing maintenance, providing continuity of care across the full establishment period.
Project at a Glance
| Scheme Length | 1 km |
|---|---|
| Services Delivered | Hydroseeding, conventional seeding, wildflower seeding, erosion control, native planting, ongoing maintenance |
| Mobilisations | 20+ visits over the project programme |
| Days on Site | Approximately 40 |
| Equipment | 3,500L hydroseeder, Aebi mountain tractor |
| Mulch Product | Groweb hydroseeding mulch |
| Fertiliser | None — excluded due to watercourse sensitivity |
| Maintenance | 3-year maintenance contract |
| Erosion Events | Zero (excluding natural flood plain flooding) |
Why This Project Matters
The Machynlleth Bridge scheme demonstrates CDTS North & West's ability to deliver the full scope of ecological seeding and planting services on a single contract for a Tier 1 civil engineering contractor.
From hydroseeding steep embankments to establishing native wildflower areas and planting woodland, every element was managed under one appointment, reducing the client's coordination burden and ensuring consistent environmental compliance across the site.
Key Takeaways for Procurement
- Single-source appointment covering hydroseeding, conventional seeding, wildflower establishment, native planting and ongoing maintenance
- Phased delivery aligned to the earthworks programme, minimising erosion risk throughout
- Zero erosion events on any seeded area across the full project duration
- Ecological compliance with locally sourced seed, no fertiliser, and sensitive management adjacent to a SSSI
- 3-year maintenance retention providing continuity of care through the full establishment period
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