Ackers Weir by Sanctus
Shortlisted for Brownfield Awards Category 1 - Best Project Prepatory Work
Removing Ackers Weir, Birmingham
Remediation in an Active River Channel
An Industrial Legend
Sanctus were commissioned by the Wildlife Trust for Birmingham & the Black Country (WTB&BC) to remove Ackers Weir in Tyseley, South-East Birmingham. The currently 3-tiered, 2.6m high weir was first noted on site around 1852 and was used to form a body of water known as the Mill Leat which was used as a water supply for a former metal works located to the north-east of the weir. The river is known to have been used to wash and cool metal products as they were formed with the resulting effluent, along with run-off from other nearby historical industrial operations including the Birmingham Small Arms factory, a fireworks factory, railway and welding works, re-entering the water course.
The contaminated sediments contained within the water re-entering the river were known to have accumulated behind the weir. This accumulation of contaminated sediments has created a significant barrier to the removal of the weir due to the risk of mobilisation and downstream migration of the impacted sediment. Sampling of these sediments by others previously had identified a range of contaminants including heavy metals, polyaromatic hydrocarbons and petroleum hydrocarbons. Over time these sediments have started leaching metals out into the river, effecting the water quality downstream of the weir.
The metal works which survives to this day has changed its processes to no longer require a water supply from the River Cole. The associated Mill Leat has also continued to accumulate silt and desilting works, previously carried out by Birmingham City Council, were deemed to be too costly to carry out regularly due to the need to dispose of the impacted / contaminated sediments.
Weir Removal & Stage One Restoration Removal of the weir aligns with the Water Framework Directive and long term landscape vision of the River Cole Catchment to reconnect the river environment, creating habitat and improving opportunities for fish passage along the River Cole and surrounding catchment. Although the Mill Leat was no longer required to supply water, the removal of the weir had yet to be carried out due to the complex structure, high hydraulic jump and associated contamination. The lead partners (WTB&BC) had also been unable to find an organisation with the expertise and experience to manage such a complex project in its entirety, achieving weir removal and stage one restoration without negatively impacting the surrounding natural environment.
Sanctus were therefore approached directly by the WTB&BC and the Environment Agency as we possess the unique ability to deal with this incredibly challenging remediation and environmental engineering project.
Why Remove Ackers Weir?
Sanctus are committed to removing barriers to fish migration and improving sediment connectivity in natural river environments, seeking to restore natural processes and conditions wherever possible. At Ackers the heavily contaminated sediments, held in place by the weir structure provide a legacy risk and have the potential to continue to reduce water quality of the Cole and Mill Leat as well as hugely impacting the aquatic environment downstream.
Under the Water Framework Directive (WFD) Cycle 2 classification from 2019 the river ‘Failed’ the assessment based on its chemical composition indicating that the River Cole required remedial works to improve its water quality. A hydraulic head difference of circa 1.8m during times of mean flow was considered a major barrier to the movement of fish up and downstream. This was demonstrated by the rivers ecological classification under the WFD as ‘Poor’. Furthermore, surveys carried out previously have identified a significant difference in biodiversity between the river channel upstream and downstream of the weir demonstrating that the weir presents a defining barrier to the migration of species.
By retaining the weir in place, the cost of maintaining the structure and managing the risk associated with its misuse was considered by Birmingham City Council to be unsustainable and a significant social and economic risk for the local community. The removal works therefore align with the areas wider Environmental Enterprise Improvements scheme and the Tyseley Local Development plans.
Characterising the River
In order to fully understand the history of the site as well as the environmental setting of Ackers Weir, Sanctus produced a Phase 1 Desk study, assessing the records available from a range of regulatory bodies as well as a wide range of historic maps to facilitate the production of an accurate Conceptual Site Model (CSM). This enabled the weir to be contextualised within its environment and aided in the identification of potential risk elements that would need to be addressed prior to its removal.
Previous investigation works spanning a 2km stretch of the River Cole had produced some 6,324 environmental monitoring data points which had identified elevated Lead and Polyaromatic Hydrocarbons within sediments samples in and around the Weir. Sanctus undertook a thorough data gap filling exercised based on the conceptual model and carried out further sampling to ensure that the materials around the weir, both upstream and downstream were fully characterised using contemporary data.
A review of historic habitat records had also produced a further 217 data points for fish populations and habitats within the catchment which were used to understand how the presence of the weir had impacted biodiversity. This information was fed into the sites CSM to provide a full realised model of the site minimising the risk of identifying unexpected contaminants later on in the project and enabling Sanctus to provide cost certainty to the client, a fundamental requirement of ensuring the project remained viable.
Expert assessment of the sediment samples demonstrated that, following bioremediation works to reduce the concentrations of organic compounds, sediments would be suitable for reuse in and around the river to create new flood plain habitat. The material will be reprofiled to create a range of habitats including hibernaculum’s which will be populated by a range of flora and fauna thereby increasing the biodiversity of the area further improving the rivers WFD classification.
Leachate analysis was also carried out to assess how the presence of the sediments within the river were impacting the water quality. This analysis demonstrated that the leachate being produced contained concentrations of contaminants in exceedance of the Environmental Quality Standards (EQS) for freshwater bodies confirming that the sediments in the vicinity of the weir had the potential to have a detrimental effect on the water quality downstream. Water samples recovered from both upstream and downstream of the weir demonstrated that the leachate released from the sediments was potentially having a detrimental effect on the water quality with the highest concentrations of contaminants being identified at the weir and
downstream of the weir.
As the riverbed will require reprofiling upstream of the weir following its removal Sanctus commissioned a detailed hydraulic model of the river including a physical survey of the river channel both upstream, and downstream of the weir. This identified the extent of sediment removal required to achieve a natural profile following the weir removal works and prevent the mobilisation of large volumes of sediment in a short period should the river be allowed to reach sediment equilibrium on its own, determining that 440m3 of sediment would need to be removed.
The hydraulic model carried out extended 1.5km upstream of the weir and was used to detail how the flow of the river would change and become naturalised throughout the landscape following the removal of the weir. This independent modelling demonstrated that the removal of the weir would be beneficial with respect to the risk of flooding by actually reducing the flood risk downstream, prior to Sanctus’ involvement this was a previously unanticipated benefit of the removal of the weir and something which was celebrated by all involved.
Throughout the preparatory works Sanctus remained in close contact with the regulators and the client ensuring that at all stages of the project all parties were involved and invested with the reality of weir removal and the proposed methodology from achieving environmental improvement.
In order to secure approval for the removal of the weir the regulators first needed reassurance that this would not lead to sediment mobilisation of contaminants including sediment downstream. This was achieved through the design of a Site-Specific Working Plan (SSWP) detailing how the works would be carried out and the controls that would be implemented throughout the project that would prevent the migration of contaminants and sediment offsite. Additionally, the SSWP detailed the processes to be carried out on the extracted sediments to make then physically and chemically suitable for reuse and how they were to be placed on the reuse area which would remove the risk of them migrating back to the river following their placement. This was based on Sanctus’ previous experience of working in and around aquatic environments. This detailed planning and design supported extensive consultation and communication such that all parties supported the weir removal in the way Sanctus recommended. This meant that when it came to the application of the permits required for the removal of Ackers Weir there were no unexpected queries to be received from either the Environment Agency nor from the client or Birmingham City Council.
Achieving Project Viability
As the available funding for project was limited, Sanctus designed a scheme which retained the sediments within the bounds of the site. Following a walkover of the area Sanctus were able to identify a parcel of land approximately 35m downstream of the weir which was deemed suitable to receive the sediments. In order to facilitate the reuse of the materials on site Sanctus compiled a Materials Management Plan (MMP) which was submitted to CL:AIRE for approval prior to the works commencing. By declaring the MMP the sediments removed from the river would not automatically be classified as waste and could be reused on site. By facilitating the reuse of the sediments on site Sanctus was able to create a significant cost saving improving the economic feasibility of the project as well as significantly reducing the carbon footprint of the project by minimising the number of vehicles moving to and from site.
In parallel to the MMP Sanctus compiled a Remediation Strategy further detailing the works that were to be carried out and how the materials due to be removed from the river channel were to be assessed to confirm suitability for reuse. This was also submitted to the regulators for approval as part of the preparatory works.
Achieving a fully approved and commercially viable proposal for the removal of Ackers Weirs solved a generation legacy problem which continues to pollute the natural aquatic environment every day. This was achieved through the extensive review of the available historic information and completion of supplementary information gathered to fully characterise the site resulting in a robust conceptual site model. Sanctus were then able to demonstrate how the removal of Ackers weir would be of environmental and ecological benefit for the wider environment justifying to all parties the multiple environmental and socio-economic benefits.
By fully understanding the site and its environmental context Sanctus were able to develop a plan for the removal of the weir which would be cost effective to the client while achieving all of the goals and minimising the risk posed by the works to the wider environment.
By creating such a robust model and through engaging with the regulators throughout the preparatory works Sanctus were able to obtain the required permits with unusual ease. This means that the site works themselves will proceed quickly and effectively with Sanctus hitting the ground running minimising both the time on site and the effect of the physical works on the water body once funding is formally approved in 2022 ready for works to commence on June 16th.