Summary
Sanctus were appointed by Sheffield City Council to improve impacted sediment built up in Forge Dam Pond and renaturalise the Porter Brook. This would reduce the rate of future silt deposition and with it the long-term maintenance liabilities whilst restoring the amenity value of Forge Dam to the local community and protecting the water course downstream.
Pre-Commencement Works & Regulatory Liaison
Sanctus carried out extensive regulatory liaison with several departments within Sheffield City Council, Environment Agency, nearby landowners, stakeholders and volunteers to obtain the necessary permits/permissions and buy in. The scope of work included:
- Site set-up including installation of full silt mitigation measures comprising silt curtains, sediment and bubble curtains, fish rescue, continual monitoring, natural filtration methods and water treatment, monitored by our dedicated Environmental Mitigation Champion;
- Rigorous environmental cleaning stations and procedures for decontamination, disinfection, boot, wheel and personal monitoring systems, administered and overseen by our dedicated Biosecurity Champion,
- Dedicated ecologists for watching brief role to identify/observe for at risk species, including identifying a rare colony of previously undiscovered white claw crayfish.
- Removal, milling and re-use of site won alder trees and preparation for the reuse and creation of the innovative river training wall with sustainable hazel fascines;
- Set up of telemetric variable flow-rate pumps and pipework to facilitate the over pumping of water from the Porter Brook de-watering the silt that has built up within the pond;
- Removal, improvement and re-use of silts existing vegetation for creation of offsite wetland forming the improved Beighton Marsh Nature reserve in Sheffield. With Selection of sympathetic plant specimens for replanting around Forge Dam at the end of the project;
- In order to protect the existing fish species, present within the pond Sanctus were required to carry out a fish rescue exercise, removing the fish living in the pond, with the specimens being recorded and visually checked for signs of harm or disease before being relocated. With stop net exclusions erected and checked frequently up and downstream.
Cause and Solution
The sedimentation of the Forge Dam Pond occurs during flashy flows from sediment laden head waters from the peak district enter the pond, spread out and rapidly lose the energy required to transport sediment, causing the sediments to fall out of suspension. Sanctus’ solution to this problem was to build a semi-porous training wall along the southern bank of the pond connecting point, where the Porter Brook enters the pond, to the weir crest, where the water exits the pond, reforming the Porter Brook providing a naturalistic bed improving formerly buried riffle pool structures.
The wall was sympathetically designed using green-engineering solutions by Sanctus’s award-winning team to renaturalise the Porter Brook enhancing amenity for the Forge Dam Area and improved on the expected gabion wall structure. The wall using site won vegetation reduced sediment entering the pond and allowed equilibrium flow into the main body of the pond ensuring oxygenation and preventing stagnation, with designated fish passage sections.
Material Management and Habitat Creation
Using materials within a few metres of where they grew meant fewer materials were imported using natural materials to form the wall enabling the structure to be populated by a range of invertebrates.
Over 5,000m3 of sediment was moved to provide a range of water depths throughout the pond offering a range of aquatic habitats. Approximately 1,700m3 was reused on site above the water line as part of the site reprofiling works to form soft banks in place of the pre-existing vertical concrete face. The remaining material was used to enhance another nature reserve in Sheffield creating new wetland habitats with a developed seedbank, enhancing the local environment whilst reducing vehicle movements.
Due the industrial legacy, sediment treatment/improvement was accomplished by carrying out an initial drawdown of water levels in the pond to the level of sediment, followed by the excavation of sumps into the sediment to the required depth and pumping out of the water as it drained out of the sediments naturally under gravity. This passive dewatering approach meant that the drying out of the sediment did not require any bulky equipment/expensive additives whilst allowing bioremediation to improve soil health.
Sanctus were able to keep the local park open with temporary bridle way diversions, and active footpath management, providing an alternative bridlepath, footpath and access improvements improved access ensuring free public access to the site during works. With designated viewing areas and information boards to inform visitors of the work, program and benefits.
Sanctus made it a priority that the charity group that had raised most of the funds for the project ‘The Friends of the Porter Valley (FoPV)’ group was regularly updated on the progress of the works. This included presenting the scheme design progress and vision at their Annual General Meeting and Sheffield City Council. This was exceptionally well received and gave them absolute confidence that their funds they had worked hard to raise were being well spent. Sanctus engaged with local colleges and students to provide project data locally to enhance educational resource. Sanctus engaged in video interviews, press interviews and vlogging to assist the council in its delivery and publication.
Sanctus engaged FoPV in the replanting of the reprofiled pond margins enabling them to take ownership of the project at its final stages and providing a sense that their efforts had led to a hugely successful outcome whilst ensuring buy-in from frequent site users.
Successful Completion
Completion of the Forge Dam restoration released an enhanced area of local historic significance improving the river, protecting historic infrastructure while improving on wide range of biodiversity, providing opportunities for the reintroduction of species that were historically present. Through Sanctus’ philosophy to work sensitively within the environment, the works were completed without major disruption to the local flora and fauna and involved the local community. These works will help deliver and preserve environmental, ecological, and social value throughout the Porter Brook Valley for many years to come. The scheme was highly commended in the Brownfield Briefing Awards for the Best Community Engagement as well as Wining Best Remediation of a Smaller Site a true reflection on Sanctus’ commitment to environmental betterment.
