River Dargle Flood Defence Scheme

OCSC were appointed by Bray Town Council to prepare proposals for a flood defence scheme for the River Dargle at Bray, Co. Wicklow.  The process commenced with a hydrological study of the catchment to determine design critical flood flows and computational modelling to identify and quantify flood risk levels along the length of the River Dargle.  An options study conducted by OCSC assessed a broad range of alternative solutions and identified the preferred option.  OCSC prepared a design that was assessed using physical modelling at a scale of 1:100.  OCSC led the team that brought the project through the planning permission process, which included preparation of an Environmental Impact Assessment.

OCSC were then appointed by SIAC Civil Engineering Contractors to provide detailed design services in the Design-Build contract to deliver the flood defence scheme.  The scheme comprised flood defences and channel improvements for 3.1km of the River Dargle.  The flood defences include 2km of structural walls (contiguous piles, sheet piles and reinforced concrete) and 2km of embankments.  Almost one kilometre of new sewerage was required to divert existing sewers affected by the works.  Membrane non-return valves were fitted to all outfall pipes and culverts.

A critical element of the works was provision of a new culvert to augment flow capacity of the existing Bray Bridge on Main Street (R761 Regional Road).  The culvert is 7.4m wide, 4.0m high, 6m deep and located immediately behind the abutment of the existing stone arch bridge.  The culvert was designed to allow for construction without impacting the existing bridge whilst maintaining traffic on Main Street to pass with minimal interruption.

The completed scheme provides Bray Town with protection from the 100-year return period fluvial flood and the 200-year return period tidal flood.