The existing outfall at Kymin, Penarth had been subject to deteoriation and storm damage over the years and subsequently, it’s original brick egg construction had failed and blocked the outfall entirely with brick and other debris. Morgan Sindall Plc commissioned Kaymac to remove the debris so that the outfall could be recommissioned
The consented discharge point of the outfall lies at approxiamtely the low spring tide mark and as such, careful planning was required to ensure that Kaymac selected the optimum tide to visit and carry out the works. The Autumnal equinox was selected as it would offer the best opportunity to be able to undertake the works in a timely and efficient manner, working to the predicted lowest tides of the year. The predicted tide levels would only permit approximately 3 x 4 hour working windows to carry out the clearing works. Aside to clearing the blockage within the outfall, there were a number of isolated areas of damage to the existing concrete surround of the outfall that required repairs.
Upon mobilising, Kaymac carried out the works during suitable tides, chasing the receding tide for each shift. Once the sea level allowed, the discharge point of the outfall was located and an excavator used to clear the brick and debris at the outlet. A working area was then excavated and then dewatered using pumps to permit inspection. At this point, the pipeline was found to be 100% blocked.
As the blocked sedimentary material had been considered as potentially environmentally hazardous, Kaymac ensured that as the outfall was being cleared this material would be pumped to a jet vacuuation unit. As the position of the works was approximately 200m from the foreshore, a wheeled mobile unit had to be mobilised to the foreshore at each suitable tide.
The wheeled unit could not access the discharge point and as such, a tracked clearing unit was then taken down the beach which would pump the material approximately 200m back to the jet vacuuation unit.
Working through the allowable working windows, the outfall was entirely cleared back to the foreshore. A CCTV survey was then carried out from the upstream inlet point to confirm that the outfall was completely clear.
Whilst the clearing works were being undertaken, a secondary team were working on carrying out the concrete repairs to the existing outfall surround. These areas were again within the tidal zone and so the areas had to be cleaned, prepared, shutters installed and concrete poured within the working time permitted by the incoming tides. Concrete with an underwater additive was used to ensure that the fresh concrete would not ‘wash-out’. The works were completed ahead of programme and to within the alloted budget.