Drainage Failure and Associated Urban Impacts Under Combined Sea-Level Rise and Precipitation Scenarios

Abstract

Existing sea-level rise tools for coastal urban areas may overlook precipitation impacts on municipal infrastructure. In tidally-influenced coastal zones, high water levels can hinder stormwater systems, leading to drainage failure, corrosion, and backflow of contaminated water. Waikīkī, the tourism hub of Honolulu, faces growing risks of flooding and infrastructure damage due to rising sea levels. Using the PCSWMM modeling software, this study simulates drainage failure under present and projected sea levels combined with precipitation. Findings reveal that a 5-year precipitation event at present sea level floods more inlets than three feet of sea-level rise while a 10-year event floods three times more inlets than four feet of sea-level rise. By 2050, a 5-year event could cause flooding severe enough to disrupt transportation and contaminate stormwater inlets across 70% of Waikīkī. When accounting for precipitation, 100% of outfalls will fail and 85% of the drainage system will be full by 2040. Results indicate 22–50% more flooded inlets during precipitation events than passive models at present sea level. Salinity and water level data from storm drains show that coastal infrastructure faces severe corrosion risks, potentially worsening drainage failure. Findings support the need for adaptive stormwater management to address compounding flood risks.