Portlock Road Drainage Improvements

Oceanit was contracted by the City and County of Honolulu, Department of Design & Construction to design a coastal structure that could reduce sedimentation from occurring within the outlet of the Portlock Storm Drainage Outfall. The site is located along Portlock Rock and Maunalua Bay in East Honolulu, on Oahu.

A condition existed where sediments would wash down from the watershed on land and collide with sediments being washed into the outfall from the sea by wave action.

This collision was causing blockages in the outfall and creating flooding issues around the outfall and Portlock Road. An older structure was implemented in the 1960s and improved in the mid-1980s, but has subsequently collapsed, creating additional blockages at the outfall pipe.

Oceanit’s design of the new structure approximately matches the footprint of the damaged structure that had previously served to mitigate sediment blockage.  The structure has an L-shaped design; the shore-parallel offshore arm dissipates wave energy, while the shore-perpendicular arm connected to an existing seawall disrupts wave induced longshore sediment transport.  Oceanit applied the equations and methods in the United States Army Corp of Engineers (USACE) Coastal Engineering Manual to design this coastal structure.

Oceanit prepared all applications, obtained approvals for all required permits (from Dept of Army, Dept of Health, City and County of Honolulu, DLNR (OCCL and SHPD) and Planning Dept).

In addition to the Plans, Specifications and Cost Estimates, Oceanit provided a Basis of Design, Coastal Assessment, Marine Terrestrial Report, an exemption for an Environmental Assessment, BMP and Water Quality Monitoring Plan. Post-design support services were also provided during bidding and construction.