Overview
Cura Terrae were appointed through the Mining Remediation Authority’s hydrometry framework to upgrade the existing measurement structure at the outlet of the Chell Heath Mine Water Treatment Scheme (MWTS), near Stoke, and provide accurate time-series measurement of the discharged flows to prove compliance with their permit. The scheme at Chell Heath, is a passive gravity-fed scheme which provides treatment to the mine water via a series of reed beds.
The Client
The Mining Remediation Authority, formerly the Coal Authority, is an executive non-departmental public body, sponsored by the Department for Energy Security and Net Zero.
The organisation manages the effects of past coal mining. It deals with mine water pollution and other mining legacy issues.
It also owns, on behalf of the country, the majority of the coal in Britain. They provide services to other government departments and agencies, local governments and commercial partners, and contribute to the delivery of the UK Government’s Industrial Strategy and the environmental, social and economic priorities of the UK, Scottish and Welsh Governments.
Challenge
The existing V-Notch thin plate weir, located within a small channel downstream of the last reed bed of the site had completely failed. Attempts to repair this had been made by the maintenance contractor but these only lasted a short period. A more permanent long-term solution was required. The site is open to the public, and it is thought that the location may be at risk of vandalism
The requirement included the design, supply, and installation of a new primary device, flow monitoring, and data-logging equipment in line with relevant standards for flow monitoring (i.e. BS ISO 1438:2017 or BS ISO 4359:2013+A1:2017 and allowing for the relaxations permitted by the MCERTS standard).
The site had an existing 90o V-Notch weir that was being bypassed during high flows. In addition, one bank had failed, allowing low flows around the weir plate. The channel bed is uneven and soft, and overgrown with vegetation along the majority of its length.
Flow through the vegetation varied depending on the density of the vegetation and is somewhat skewed by the channel bed profile. Two photos of the existing arrangement are shown below.
Previous monitoring has been restricted to manual level measurements at the weir taken between 2015 and 2024 and converted to flow using theoretical ratings for a 90˚ V-notch. This data has been provided to our teams by the Mining Remediation Authority.
The Mining Remediation Authority reported that, “Given the way in which the manual readings have been taken, it is likely that they represent an underestimate of the flow. Also, manual readings are likely to have missed the extremes, especially peak high flows”.
The Solution
A new flow measurement structure was required, and after an initial survey and optioneering, it was determined that a flume was best suited. A detailed design was carried out which determined that a 100mm throated trapezoidal flume with 215mm wide approach channel extending 3.25m upstream was required.
During the Design Report stage, many aspects were taken into consideration from practical issues such as access, existing channel details, upstream lagoon overflow weir levels, other incoming flows to the area (from drainage pipes) and potential vandalism, through to technical issues such as mobile network signal availability and strength, and solar panel suitability. In addition, a number of potential primary structures were considered such as differing types of thin plate weirs and different shaped flumes, all to allow for the anticipated flows (min 4.4l/s, mean 8.83l/s and max 90l/s), available upstream head, conformance with the required standards and methods and ease of installation.
The work also included management of the existing flows by over-pumping and the regrading of the approach to the flume, to stop the bypassing of the existing weir during high flows.
Client Benefits
- Assurance that discharged flows were within stipulated limits
- Removal of an old and failing flow measurement primary structure and confidence in the design of the measurement structure upgrade
- Confidence in the measured flows due to the installation of a new bespoke designed primary flow structure that allows for the range of flows being experienced on the site.
- Confidence in the flow measurement accuracy due to the installation of a new reliable flowmeter and telemetry system.
- Confidence in the knowledge that peak flows will also be captured due to the continuous monitoring and improved primary structure design.
- A near real time view of the flows remotely via the telemetry system, particularly during storm or alarm conditions.
- The ability to build a reliable history of flows that can be used in any future development of the Chell Heath MWTS or be provided to regulatory parties.
- An inclined gauge board was also included for visual confirmation of flow depths.
Client Testimonial
Cura Terrae were appointed to our Hydrometry framework and have successfully delivered several flow measurement installations. The sites at Minto, Kames and Chell Heath presented unique challenges due to existing infrastructure, but their team worked closely with us to develop practical, innovative solutions that met our requirements and were delivered to a high standard.
Rob Burton BSc (Hons) MCIWEM CWEM Senior Hydrologist
