651 - City and County of Honolulu Kaka‘ako Catch Basin Retrofits, South Street Bicycle Lane Permeable Pavement, and Sheridan Street/Kapi‘olani Boulevard Bioretention Area Case Studies

The City and County of Honolulu MS4 permit requires that 10% of all the City’s MS4 structures be retrofitted with permanent BMPs, with an emphasis on the implementation of low impact development (LID) practices. The following case studies will illustrate the procedures to design and permit stormwater structures with manufactured treatment devices and LID BMPs in a tropical urban environment. The Kaka‘ako Catch Basin Retrofits involves three levels of retrofits of 45 dilapidated existing concrete catch basins. Level 1 involves repairing the damaged face of the catch basin with durable concrete and automatic retractable screen. Level 2 involves the replacement of the top slab of the catch basin with a new concrete slab and an access hatch vice a manhole cover and an automatic retractable screen on the catch basin inlet. Level 3 involves the complete replacement of the catch basin with a tree filter box, planter box, or bioretention cell. Dry cast concrete was explored as a way to speed up the production of concrete structures and ensure consistent quality of the structures. The South Street Bicycle Lane Permeable Pavement project involves the replacement of existing asphalt pavement with four different permeable pavement/paver surfaces: porous asphalt, pervious concrete, and two different pavements. Green pavers vice painted pavers will be used. Bicyclists will be surveyed to evaluate the rideability for the different permeable surfaces. Electronic surveys, in-person intercepts surveys, and a bicycling event day coordinated with the Hawai‘i Bicycling League will be used to collect ridership data. The intersection of Sheridan Street and Kapi‘olani Boulevard is at a low point and floods. A bioretention cell will be constructed at this intersection to treat the stormwater that ponds and encourage infiltration. Because of lapsing construction funds, all three projects were placed on a fast-track design and permitting process. In addition, the potential for impacting nā iwi (or Native Hawaiian artifacts) needed to be addressed.