Modeling Cost Effectiveness of Green Infrastructure at Stormwater Runoff Critical Points in Maunalua Bay Watershed, Oʻahu

Abstract

Like many urbanized areas, the watersheds surrounding Maunalua Bay are highly developed with impervious surfaces and channelized waterways. This can cause issues with stormwater. Stormwater is water that flows over impermeable surfaces (roads, roofs, etc.) after heavy rain events. Stormwater can pick up pollutants as is flows down slope, negatively impacting the health of water bodies. It can also cause flood events impacting infrastructure and lives Green Infrastructure (G.I.) techniques can be implemented to improve conventional infrastructure and stormwater management. Green infrastructure is an approach to stormwater management that tries to mimic the natural water cycle. Most green infrastructure traps and treats water from a storm event and then slowly releases it back into the environment allowing for more control on the quantity of water being released. We created a map that identifies areas in Maunalua that have the highest potential for stormwater mitigation via G.I. Using existing maps on land cover, slope , soil permeability and storm drain density, we created a model that ranks each map attribute in terms of stormwater risk. This map can assist regional stakeholders in prioritizing and evaluating the costs and benefits of adopting G.I. techniques.Our model identified two stormwater "hotspots" within the Kamilo Iki watershed. One "hotspot" validated the model with existing green infrastructure already present. The other "hotspot" lacked green infrastructure. Using the EPA stormwater calculator we identified the most cost effective green infrastructure for a residential neighborhood.