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Kinmel Bay Wastewater Treatment Works

Directly addressing one of the Strategic Responses within DCWW’s 2050 Plan – ‘Protecting our Critical Wastewater Supply Assets’

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To provide capacity to accommodate population growth from a major 1700-home strategic development at Bodelwyddan, Mott MacDonald Bentley (MMB) was tasked by DCWW with the design and construction of a new inlet works with screens, screening handling and grit removal.

This project involved a review of the existing site and use of DCWW’s R&V process to determine the best overall outcome: the construction of a new inlet works to cater for a peak 1250l/s incoming flow, with balancing capacity due to the pumped nature of flows arriving at the works and diurnal flow pattern. ​

Purpose

The existing inlet works regularly overtopped due to the volume and nature of the flows arriving at the works; the connection from the new Bodelwyddan development would only increase flows further. The new inlet works needed to  accommodate for this.

An existing network review also identified additional flows from some of the pumping stations, caused by ongoing O&M issues.

The new inlet works, and balancing tank will enable the works to screen and remove grit from all incoming flows and accurately pass forward the flow to treatment before spilling to storm.

Data analysis of incoming flow and rainfall allowed for a reduction in balancing tank volume, versus the DCWW specification. This reduction in volume resulted in significant TOTEX and carbon savings.

Approach – Hydraulic modelling to optimise design

We considered hydraulic modelling to optimise layout and ensure hydraulic performance of the new inlet works.

Consulting experts within the wider MM Group, we opted to commission a scale physical hydraulic model.

Initial testing of the model prompted several improvements to improve hydraulic performance.

Dye and particle test runs with DCWW and screen supplier, Huber, demonstrated the flow was evenly distributed across the screens in different scenarios, both upstream and downstream. This enabled Huber to issue their guarantee for the screens, despite the deviation from their usual minimum requirements.

During low flow simulation, the model showed areas of grit deposition, something that quickly dissipated during screen rotation and when flows increased. It was also observed that the grit trap may require a low-level baffle wall to encourage flow around the circumference (TBC during commissioning and may not be required due to conical nature of grit trap.

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Conclusion

The physical model helped understand the complex distribution of flows at the new 1250 l/s elevated works.

The model prompted several changes to improve hydraulic performance, including inclusion of baffle walls and channel fillets, reduction in channel length and relocation of grit trap. 

The changes in geometry of the physical model, from the initial model have streamlined the flow and eliminated areas where deposition of solids was previously seen.

Staggering the inlet screens kept the overall width of the inlet works to a minimum and allowed full access around each screen. Running the launder below the coping level provided two positive features: 1 - allowed for easier access to and around inlet screens for inspection and maintenance and 2 - kept screen length to a minimum

Want to learn more? Speak to Amelia Winslade @ MMB

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