Client: Skanska/Dwr Cymru Welsh Water Duration: July-August 2017 Value: £69,000

To propose and install temporary works solution and carry out site investigation within the watercourse of the River Usk.


The current Prioress Mill Pumping station was evaluated as being inefficient and inadequate to keep up with current consumer demands, and presented an unacceptable risk to the security of supply to the reservoir it supplied. It was determined that a refurbishment of the existing station to meet the demands was not possible within the operational constraints of the station and as such a new RWPS facility was required.

In order to inform the design of the new RWPS, Site Investigation (SI) works needed to be carried out to determine the ground conditions. The proposed ground investigation works include up to nine boreholes and seven trial pits. Two of the boreholes are to be carried out within the River Usk SAC/SSSI watercourse.  The River Usk Special Area of Conservation (SAC)/Site of Special Scientific Interest (SSSI) borders the northern boundary of the proposed development site.  Kaymac were contracted to propose and install a suitable temporary works solution that would permit the undertaking of the 2 boreholes within the watercourse. 

Due to the site access restraints, any solution would have needed to be assembled and dismantled within the watercourse, with the use of an 80t mobile crane to lift and remove the required plant, materials and equipment.

Prior to the works commencing, Kaymac met with the local NRW representative to discuss the works and obtain the necessary Flood Risk Activity Permits and permissions.  Once received, the portable dam system was installed and electric pumps used to dewater the working area.  A small excavator was then lifted into the dewatered area to level and profile the river bed to permit the drill rig to be used to carry out the bore holes.  The 80t crane was used to lift and retrieve the required plant, materials and labour from the working area each day, with the de-watered working area preventing any suspended silts or potential environmental hazards resulting though the works from entering the watercourse.


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