title: Development of a model to simulate groundwater inundation induced by sea-level rise and high tides in Honolulu, Hawaii.
abstract: Many of the world's largest cities face risk of sea-level rise (SLR) induced flooding owing to their limited elevations and proximities to the coastline. Within this century, global mean sea level is expected to reach magnitudes that will exceed the ground elevation of some built infrastructure. The concurrent rise of coastal groundwater will produce additional sources of inundation resulting from narrowing and loss of the vertical unsaturated subsurface space. This has implications for the dense network of buried and low-lying infrastructure that exists across urban coastal zones. Here, we describe a modeling approach that simulates narrowing of the unsaturated space and groundwater inundation (GWI) generated by SLR-induced lifting of coastal groundwater. The methodology combines terrain modeling, groundwater monitoring, estimation of tidal influence, and numerical groundwater-flow modeling to simulate future flood scenarios considering user-specified tide stages and magnitudes of SLR. We illustrate the value of the methodology by applying it to the heavily urbanized and low-lying Waikiki area of Honolulu, Hawaii. Results indicate that SLR of nearly 1 m generates GWI across 23% of the 13 km2study area, threatening $5 billion of taxable real estate and 48 km of roadway. Analysis of current conditions reveals that 86% of 259 active cesspool sites in the study area are likely inundated. This suggests that cesspool effluent is currently entering coastal groundwater, which not only leads to degradation of coastal environments, but also presents a future threat to public health as GWI would introduce effluent at the ground surface.
authors.affiliation: University of Hawai'i at Mānoa, School of Ocean and Earth Science and Technology, Department of Geology and Geophysics, POST Building, Suite 701, 1680 East-West Road, Honolulu, HI 96822, USA. Electronic address: skey@hawaii.edu.
authors.forename: Shellie
authors.initials: S
authors.lastname: Habel
authors.affiliation: University of Hawai'i at Mānoa, School of Ocean and Earth Science and Technology, Department of Geology and Geophysics, POST Building, Suite 701, 1680 East-West Road, Honolulu, HI 96822, USA.
authors.forename: Charles H
authors.initials: CH
authors.lastname: Fletcher
authors.affiliation: University of Hawai'i at Mānoa, Water Resources Research Center, 2540 Dole St., Holmes Hall 283, Honolulu, HI 96822, USA.
authors.forename: Kolja
authors.initials: K
authors.lastname: Rotzoll
authors.affiliation: University of Hawai'i at Mānoa, School of Ocean and Earth Science and Technology, Department of Geology and Geophysics, POST Building, Suite 701, 1680 East-West Road, Honolulu, HI 96822, USA; University of Hawai'i at Mānoa, Water Resources Research Center, 2540 Dole St., Holmes Hall 283, Honolulu, HI 96822, USA.
authors.forename: Aly I
authors.initials: AI
authors.lastname: El-Kadi
mesh_terms: D055868:Floods; D005544:Forecasting; D060587:Groundwater; D006254:Hawaii; D006801:Humans; D008962:Models, Theoretical
keywords: Groundwater inundation; Groundwater modeling; Hazard assessment; Sea-level rise; Tidal flooding