Upper Ogden Reservoir

Overview

Located near Barley, Lancashire, this reservoir supplies over 54,000 United Utilities (UU) customers with sustainable, gravity-fed water. Originally constructed in 1906, the dam has been operational for over a century. A spillway was added in 1991 to manage excess water flows, but over time, the downstream gabion wall, designed for environmental and aesthetic considerations began to fail due to prolonged exposure to extreme storm flows.

To prevent potential erosion of the dam, a regulatory action required the design and construction of a robust long-term solution that would ensure the safe passage of water beyond the toe of the dam. The project was also driven by lessons learned from the near failure of the Toddbrook Dam in 2019. Mason Clark Associates, in collaboration with Stonbury and United Utilities, delivered a resilient new spillway wall and erosion protection measures while minimising environmental impact in this sensitive South Pennine SSSI.

Challenges and Solutions

The spillway repairs project presented several complex engineering and environmental challenges, all of which were carefully addressed through collaboration and innovative design:

• Extreme water flows and erosion risks: the spillway’s design needed to withstand high-energy water flows while minimising future erosion. We optimised the thickness, shape, and concrete mix of the new wall, incorporating a carefully designed base slab and plunge pool to dissipate energy from weiring water, reducing downstream impact.
• Difficult site access and environmental constraints: the reservoir is located within a remote and sensitive SSSI, requiring strict environmental controls. Construction was scheduled during the summer months to avoid extreme weather, while a temporary cofferdam with a relief pipe was installed to maintain a dry working area without disrupting compensation flows to the watercourse.
• Maintaining public access and community relations: the works were situated near popular walking trails, requiring careful coordination with the local community. Stonbury and UU engaged proactively with the Parish Council to manage traffic flows and minimise disruption.

MCA's Contribution

We played a pivotal role in the project, providing expert design and engineering services to ensure the long-term resilience of the spillway. Our key contributions included:

• Structural and hydraulic engineering: we designed a high-strength concrete wall and optimised the base slab shape to enhance water flow dynamics, minimising future erosion.
• Project coordination and stakeholder engagement: we collaborated closely with United Utilities, Stonbury and the local community to maintain site safety, manage logistical challenges and ensure regulatory compliance.

Results

The project successfully restored the spillway’s structural integrity while removing the risk of erosion to the dam and riverbed below. Despite extreme weather delays, the works were delivered within the agreed budget and regulatory timeframe.

• All stone material was reused and repurposed, eliminating waste removal from the site and reducing the project’s carbon footprint.
• An eco-welfare cabin was used to reduce energy consumption, and plant machinery operated on hydrotreated vegetable oil (HVO) fuel, cutting greenhouse gas emissions by up to 90%.
• The new spillway solution is designed to protect the dam for another 100 years, ensuring safe and sustainable water supply for United Utilities customers.

We used our expertise in hydraulic infrastructure, structural engineering and sustainable construction, delivering safety-critical upgrades while balancing environmental and community considerations.