Stormwater Management For The Improved Resiliency Of Highways During Extreme Events In Steep Watershed Regions: A Modeling Case Study In Waimanalo, Hawaii

Abstract

Extreme weather events, such as short-duration, high-intensity rainfall, can lead to natural hazards and cause damage to urban infrastructure. It is predicted that the occurrences of extreme weather events will tend to increase due to global climate change. Therefore, there is a need to engineer stormwater best management practices (BMPs) to prevent damage from extreme weather-related hazards like floods to public and private property in urban areas and areas undergoing urbanization, as urban areas are especially vulnerable to climate change. To prepare for extreme weather events and prevent damage from them, this study investigates how extreme storms in steep, urbanized watersheds contribute to flood damage, as well as how municipalities can mitigate these problems. To achieve these objectives, we create a watershed-scale, hydrologic model of overland flow to conduct a case study of the storm event that caused major damages in 2018 in Waimanalo, Hawaii. Using the results of this model in conjunction with a field survey and past community input, we assess the potential flooding risk at thirteen observation points (OPs) in a mixed urban-agricultural watershed to determine BMP recommendations for mitigating damages from future storms. Each OP has unique resultant model data that lead to respective BMP recommendations. Our analysis evinces the need for maintenance of existing, degraded stormwater infrastructure and the implementation of BMPs that provide high peak rate control and can be retrofitted to the local environment, such as pervious pavement, grassy swales, and infiltration berms.