Doran Consulting was engaged by Causeway Coast & Glens Borough Council for (i) the preliminary and detailed design, obtaining statutory approvals, procurement, Project Management and Supervision of the upgrade works to the North Pier revetment/breakwater structure; and (ii) Portrush Harbour maintenance dredging and mooring replacement. Doran Consulting also discharged Principal Designer duties for both Projects.
Dredging works were required within Portrush Harbour to re-establish sufficient water depth at low tide due to an accumulation of sand within the harbour. Doran Consulting undertook 3D modelling, using available bathymetric surveys, to determine the volume of material to be dredged; this being circa 22,500m3. Slope stability analysis was undertaken to determine suitable dredge pocket batter gradients and environmental grab sampling was specified, procured and analysed for inclusion in statutory approval applications.
The existing breakwater structure, located seaward of an existing stone pitched revetment, comprised 0.3t to 6.2t rock armour and exhibited signs of significant erosion with exposure of the existing revetment mass concrete toe beam identified during further investigations undertaken by Doran Consulting which included detailed condition assessment and dive survey. Voids were identified, and further investigated using GPR, within the revetment structure.
The detailed design of the revetment/breakwater upgrade Works comprised spectral wave modelling to establish the design inshore wave conditions at sections along the breakwater. The design of the rock armour considered a 1 in 100 year storm event and, with design wave heights in excess of 5m, 10-15t and 12-18t rock armour was required along the North Pier. A 140m x 3.4m high concrete toe beam was required to protect the existing revetment structure and concrete repairs required to the existing revetment and wave wall.
The rock armour incorporated in the Works was obtained from Aggregate Industries’ quarry located at Glensanda, Oban in Scotland. A total of 17,500t of 10-15t and 5,500t of 12-18t rock armour was delivered to site using a towed 900t capacity dumb barge. A 250t crane fitted with clamshell was used to off load the individual rock armour units which were subsequently placed using a 120t excavator.