Supply Chain - River Work - Erosion Protection

The Don Regulators comprise three regulator gates on the River Rother that are owned, operated, and maintained by the Environment Agency (EA). The purpose of the regulators is to reduce the risk of flooding to settlements within the River Don catchment by attenuating flows in the River Rother. JBA-Bentley has completed the design and installation of the first regulator gate. The detailed design of the second gate is currently being undertaken, while the third regulator is being modelled as part of the optioneering phase. In addition to the installation of the first regulator gate, a bespoke full-channel fish pass has been installed directly downstream to improve migratory fish passage.

The Meadowgate Regulator is located within the Rother Valley Country Park. The historic regulator consisted of a single fish belly bottom-hinged tilting gate, operated by a single electrically powered hydraulic ram.

In 2023, JBA-Bentley replaced the gate with a top-down vertical control gate, improving the resilience of the structure. Alongside the regulator gate, a new control building and EA Office have been constructed. Both buildings have green roofs and EV charging. The gate was commissioned in February 2024 and is ready to operate during a flood event.

The gate is operated to ensure a maximum of 60m3/s forward flow is always maintained. When flows exceed 60m3/s the new gate is lowered and water levels in the Rother rise and begin to spill into the washlands located within the Rother Valley Country Park, which can retain approximately 1.5 million m3.

The removal of the bottom tilting gate provided an opportunity to improve fish passage on the River Rother through the installation of a unique full-channel width fish pass. This fish pass is designed with 4-tonne reinforced concrete ‘fish tiles’ featuring varied-height upstands supplied by Craven Concrete Ltd.

The tiles were designed with the aid of computational fluid dynamics modelling to ensure they influenced the nature of the flow to allow for varied fish species to migrate upstream while also withstanding hydrodynamic forces during extreme events. The fish species focused on are coarse fish, European eels, brown trout, large migratory salmonids, and lamprey.

The 40m long stilling basin has been removed by building up the existing concrete channel bed and grading out the levels to create a uniform slope. The ‘fish tiles’ have been laid onto the regraded channel. This is the first fish pass of its kind in the world.

The fish pass installation required the full channel as a dry working area. To achieve this, an innovative syphon system, designed by Dutch water specialist Vanderkamp UK, was installed. The solution involved complex temporary works and contingency planning.

To form the upstream dam, the new regulator gate was dropped to bed level, allowing upstream water levels to build up. The gate was designed to operate this way; hence no further calculations were required. Four syphon intake pipes were installed upstream of the gate to divert up to 12m3/s of flow out of the channel for 115m, around the working area.

The syphons were primed using electric vacuum pumps which expelled all the air from the system to draw water through the pipes. By utilizing the existing gate and power supply, the syphons had a far lesser environmental impact than a typical cofferdam and over-pumping solution. The total embodied carbon associated with the syphon solution was 464 tons.

Due to the scale of the flows being diverted, the loads imposed on the riverbanks by the pipes when full were considerable. JBA-Bentley and Vanderkamp UK worked together to design a temporary support system involving ground-bearing improvements, steel and timber supports, and retaining structures. Checks were also carried out on the existing channel wall where the forces from the syphons acted upon it.

In addition to work to ensure the stability of the syphons, an energy dissipation system was designed and installed at the syphon outlets to combat scour, and a bubble curtain was installed upstream to deter fish from entering the syphons. The installation of the system was done via a temporary crane pad. Due to the nature of the site and its space constraints, this was a challenging design. JBAB worked closely with the landowner, Rother Valley Country Park, to balance the desire to allow continual access into the park with ensuring the crane was safe to carry out the required lifts. To achieve this, the crane had to be placed in close proximity to the riverbank. Slope stability modelling and bearing capacity calculations were undertaken to ensure the crane could be operated safely.

Recent storm events have recorded flows higher than the syphon capacity. To manage the risk of this occurring during the programmed works, a contingency plan was developed.

The basis of the plan was developed from a bespoke JBA flow forecasting system, which forecasted the flow over a 2-day period. Using the data from the forecasting system, flow monitoring data provided by Vanderkamp UK, upstream gauge data, and the storage capacity of the washlands upstream of the gate, JBAB could make informed decisions on whether the gate needed to be raised to allow flow to pass forward.

This decision was made with the aid of hydraulic calculations and decision flow charts within the contingency plan, allowing for quick and effective decision-making, ensuring flood risk was not impacted upstream and the safety and well-being of the site team working in the channel was never put at risk.

The Canklow Regulator is the furthest downstream of the three Regulators, approximately 3.5km upstream from the confluence of the River Rother and the River Don at Rotherham.

The existing structure consists of a single electrically powered vertical lifting sluice gate operated by an electric wire rope hoist, comprising a drive motor gearbox assembly, cross shaft with integral rope drums, and support bearings.

To improve resilience and the operation and maintenance of the asset, JBA-Bentley is completing the detailed design and build of a new vertical regulator gate and associated MEICA and civils infrastructure.

The MEICA structure consists of a 20.3-ton vertical gate, mounted on a new steel bridge and working platform, which shall also house 13.5 tons of drive equipment for operating the gate.

Two 4kW motors, working in a duty/standby configuration, will provide drive to the gate via bevel and gearboxes, which turn a single driveshaft spanning the width of the gate. On this driveshaft, one at either end of the gate, are rack and pinion gear assemblies, which convert the rotation of the driveshaft to the vertical motion of the gate. The total gear ratio from motor to driveshaft is an approximate reduction of 4410:1, allowing relatively small motors to be specified.

To support the new gate structure over the next 50 years, a new anchor restraint system has been designed. A buried sheet-piled ‘dead-man’ wall will be installed with ten 36mm anchor rods, evenly spaced, connecting to a waling beam on the wet side of the existing channel wall. This will be mirrored on both riverbanks.

The new infrastructure replicates the existing system, which has been determined to be past its design life and insufficient in supporting the new gate.

The existing superstructure of the control houses will be demolished, the foundations will be retained and extended where required to support the new gate structure using cast-in bolt sets.

A new permanent crane pad will be constructed on the south bank for the construction, maintenance, and decommissioning of the gate. This will double as parking spaces for EA operatives when not being used by a crane.

The JBA-Bentley team worked collaborative to optimise the delivery. This meant that site constraints were identified, and the design was completed with buildability and safety as the focus. A key constraint on the scheme is the proximity of the Northern Power sub-station and overhead power lines. The design of the dead-man walls, crane pad, and steelwork platform was completed to ensure that the plant and temporary works required for construction and installation were outside of the powerline exclusion zones.

The Woodhouse Mill Regulator is situated between Canklow and Meadowgate. It uses a single electrically powered vertical lifting gate to retain water. This gate is operated by an electric wire rope hoist, which includes a central drive motor and gearbox assembly, half shafts, spur and pinion driven rope drums, and support bearings, all counterweight assisted.

JBA-Bentley is currently carrying out hydraulic modelling on behalf of the EA as part of the optioneering phase. The options include passive solutions, such as a baffle or orifice plate spanning the width of the channel to continue to utilize the upstream storage. Due to the size of the Don catchment, the modelling required three individual models to be run together:

Multiple return periods are being considered, resulting in hundreds of models runs. The modelling also uses a continuous simulation approach, which adds to the complexity of the model runs.

The upgrading of infrastructure of the Don Regulators will ensure continued flood risk benefits into the future for the Don Catchment and surrounding area with improved resilience and reliability of the new assets. Alongside the reduction in flood risk, the environment and biodiversity will improve in the River Rother as a result of the Meadowgate Fish Pass.

The River Blackwater is an Environment Agency (EA) designated main river and runs through the centre of Langford in Essex. The Blackwater intake, operated by Essex & Suffolk Water (ESW) provides raw water for transfer to Hanningfield Reservoir. A smaller abstraction, which feeds the Langford Water Treatment Works (WTW), takes place at the Langford Mill intake approximately 150m downstream.

The River Blackwater splits into two channels at Langford Weir. The main River Blackwater flows westwards over the weir to a pond and continues to its confluence point with the River Chelmer, at Beeleigh, just north of Maldon Golf Club. Flows around the Langford Mill intake are conveyed in an eastern Blackwater channel to Beeleigh. The site is in a designated Conservation Area.

A summary of the works undertaken is as follows.

Prior to Stonbury’s involvement in the programme, Stantec UK undertook the detailed design of the structure for ESW. A design was selected to suit both the asset geography and the species likely to use the pass. The pass design featured two specialised channels: one with multi-sized eel tiles and the other with Larinier fish baffles, featuring a resting pool halfway along the fish side. The tiles in both channels of the gravity-fed system were engineered to optimise water flow and facilitate easy passage for aquatic species.

A project site environmental assessment sought to register and mitigate site-specific environmental impacts such as noise, land and watercourse pollution, waste materials and damage to local ecology. Identified environmental risks were controlled through measures detailed in risk assessments and method statements.

A preliminary ecological appraisal was undertaken during the pre-construction phase to determine the presence of dedicated nature conservation sites and protected species in proximity to the site. During assessment, the toxic plant hemlock water dropwort was identified, and specific H&S protocol was put in place to protect workers.

The Client worked closely with the EA during the flood risk activity permit (FRAP) application and continued a close dialogue throughout the project. This included a collaborative visit by several EA staff to view project progress and discuss potential improvements and initiatives.

As the site is in a conservation area which has a high potential for archaeology, the programme methodology included special measures to avoid breaking ground unless it was essential. Therefore, to install a safe access route to the working area, timber bog mats were laid to create a firm access road without excavating the ground.

Suppliers with a specialist machine were mobilised for the removal of two large tree stumps that were obstructing the location of the new pass.

While the working area was being dried, the team began excavating for the new fish pass. Initial excavations were supervised by the Client’s archaeologist, as stipulated in the planning conditions for excavation works. To avoid the necessity for the archaeologist to attend over several separate days, the site team carried out all excavations under one watching brief and backfilled before re-excavating while building the pass.

Bespoke steel supports were built and formwork was erected. A new concrete river wall was formed at the top of the pass to integrate with the existing structure. Formwork was then filled with concrete to create the main pass structure which included both fish and eel channels, a resting pool part-way up the fish pass, and cut-outs for stop logs and the new camera monitoring system.

After casting the concrete pass structure, the team installed an engineered wall on the river side of the structure and gabion baskets on the pond side to support the bank and backfilled behind the baskets with clean stone. The lower gabion on the southern side (nearest the bank) was placed to prevent pooling in what would otherwise be a ‘dead end’ for the fish and eels looking for a way into the pass. The banks and ground around the structure were then reinstated with the previously excavated material.

To complete the pass, the team lined the inside of the channels with bespoke Larinier fish baffles and tiles suitable for eels and elver. On the eel side, GRP mesh flooring was affixed on top of the channel. A handrail was installed around the structure to allow safe access for operatives to maintain the pass and remove debris, and a debris deflector was installed at the head of the eel pass to reduce debris entering the system.

The project posed two main challenges. First were the restrictions caused by the small working area constricted by two water courses and proximity to several protected trees. As there was only one access route to the working area, excavations and sheet pile installations had to be completed in stages, using an excavator with a Movax attachment, working backwards along the single access route.

Second, persistent heavy rain led to multiple major flood events which breached the Portadam and forced the team to reset the site and reinstate the working area before recommencing work. This was successfully managed by monitoring river and rainfall data to identify opportunities to reset and pump the area dry.

Video: Langford Weir Fish Pass - Courtesy of Stonbury Ltd

Addressing Stonbury’s and ESW’s commitment to deliver low-carbon, environmentally restorative infrastructure, each element of the project was completed using the most sustainable method practically available.

These included:

The team’s dedicated persistence achieved delivery despite the site constraints and setbacks due to unprecedented wet weather. The project will help facilitate the successful migration of fish and eels, re-connecting previously isolated populations and enhancing breeding opportunities. These benefits are highly likely to result in a significant increase in biodiversity.