Sea-Level Rise Induced Multi-Mechanism Flooding and Contribution to Urban Infrastructure Failure

Abstract

Sea-level rise (SLR) induced flooding is often envisioned as solely originating from a direct marine source. This results in alternate sources such as groundwater inundation and storm-drain backflow being overlooked in studies that inform planning. Here a method is developed that identifies flooding extents and infrastructure vulnerabilities that are likely to result from alternate flood sources over coming decades. The method includes simulation of flood scenarios consisting of high-resolution raster datasets featuring flood-water depth generated by three mechanisms: (1) direct marine flooding, (2) storm-drain backflow, and (3) groundwater inundation. We apply the method to Honolulu's primary urban center based on its high density of vulnerable assets and present-day tidal flooding issues. Annual exceedance frequencies of simulated flood thresholds are established using a statistical model that considers predicted tide and projections of SLR. Through assessment of multi-mechanism flooding, we find that approaching decades will likely feature large and increasing percentages of flooded area impacted simultaneously by the three flood mechanisms, in which groundwater inundation and direct marine flooding represent the most and least substantial single-mechanism flood source, respectively. These results illustrate the need to reevaluate main sources of SLR induced flooding to promote the development of effective flood management strategies.

Sea‐level rise drives wastewater leakage to coastal waters and storm drains

“…The Honolulu tide gage record (NOAA; station ID: 1612340) has a semi-diurnal range of 0.58 m with a 1.51 ± 0.21 mm/year (30-year average) rate of local SLR. Models show that nuisance flooding can occur when tides exceed 0.20-0.35 m above the mean higher high water datum (Sweet et al 2014;Thompson et al 2019;Habel et al 2020).…”

Beach nourishment has complex implications for the future of sandy shores

“…For example, storms can cause groundwater salinization [107][108][109][110][111] -especially concerning for low-lying islands with limited freshwater supplies such as the barrier islands along subsiding coasts 112 and Pacific atolls [113][114] -and contribute to coastal flooding 115 . For example, a sea level rise model assessment for urban Honolulu, Hawaii (USA) at the end of the century, found that including groundwater processes doubles the size of the flood-prone area compared to when considering marine inundation alone 116,117 .…”

Identifying oceanographic conditions conducive to coastal impacts on temperate open coastal beaches and the importance of empirical impact data

“…Hence, the public perception of increasingly frequent and severe impacts could be skewed by the shifting baselines of normalcy, against which the extremeness and remarkability of a particular event are assessed. However, such news and social media-based assessments of impacts have been shown to deliver comparable results to those using conventional threshold-based (Moore and Obradovich 2020) or modelling (Habel et al 2020;Yagoub et al 2020) approaches. Moore and Obradovich (2020) identi ed some circumstances where ood thresholds derived using social media observations were more representative of the vertical height at which impacts typically associated with minor ood occur, than the actual de ned minor thresholds.…”