CEFAS23-08 Contract Extension for BEEMS ABR Maintenance & Monitoring at the Hinkley Point C Frontage

The Supplier will undertake ad hoc Artificial Bunded Reservoir (ABR) maintenance and monitoring at the Hinkley Point C frontage.

The ABR design was proposed by Cefas as a method to compensate for the water that was diverted away from unique and protected intertidal algal mats by damage caused by a walking jack-up barge, which interrupted the drainage network when it transited across the rocky foreshore while being used to construct a large aggregates jetty.

The ABRs comprise of bunded walls strategically placed to form reservoirs that are filled on the rising tide and slowly release seawater when subsequently exposed by the ebbing tide. In total, there are four distinct ABR schemes on the Hinkley Point foreshore that comprise between one and seven individual reservoirs. Water exits through an orifice plate/outlet pipe installed in each of the bunds/cut channels that divide reservoirs. The size of these has been optimised to access as much water as possible over the low tide period. Occasional testing work is still conducted to ensure/improve the ongoing performance of these systems.

Telemetric depth gauges are also installed in each reservoir to monitor the performance of each system. These automatically send data to Cefas but require occasional removal/installation for/following maintenance.

The Supplier will be required to visit the site on an ad hoc basis to:

(1) Clear reservoirs and the orifice plates. Reservoir clearing will be conducted by hand by carefully handling manageable sediment (mainly cobbles/boulders) and moving them to a nearby area of shore platform outside the reservoir. A shovel will be used to move finer gravelly material. The area around the orifice plate may also be cleared of finer material with a metal/wooden rod.

(2) Conduct flow gauging work. The discharge rate through each of the reservoir outlets is gauged by weighing the water collected within a plastic sack over a timed period. This is conducted by a team of at least two fieldworkers; one tasked with filling the bag from the outlet and the other with timing the filling process with a stopwatch. The weight of the bag is subsequently measured with a set of hanging scales suspended from a 2m long bar held at either end by two fieldworkers. This task will be conducted in accordance with the manual handling guidelines.

(3) Remove/install telemetric depth gauges. The modular holster which houses the depth gauge simply requires a hex key to affix/remove devices, of which there are four. These will need to be returned to Cefas for maintenance/repair.