Urban coastal flood pathways during extreme events
Date
2022
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Publisher
University of Delaware
Abstract
Barrier islands are low-lying, narrow landforms existing parallel to the mainland coast. These landforms are integral to mitigating damage along the mainland as they are the first line of defense against high-impact storm forces. Thus, barrier islands are also susceptible to severe damage by extreme events, particularly if storms occur frequently and the island is unable to recover. Descriptive regimes have been developed to describe damage by only the ocean-side storm surge (Sallenger, 2000). However, barrier island erosion is also affected by bay hydrodynamics on the back side of the island. A much less understood storm-surge ebb flow describes overwash and breaching initiated from the bay side resulting from elevated water levels in the bay and can cause severe erosion and flood damage (Smallegan and Irish, 2017). Understanding the effects of ocean-side and intercoastal water flooding on barrier island communities is lacking in the current body of knowledge because of the paucity in field data on barrier islands during storms. ☐ This study aims to quantify and infer flood magnitudes and map flood pathways through a coastal community and validate a community model to aid in the prevention and mitigation of flood damage. Understanding the threats of flooding and pathways of floodwater in Delaware’s vacation hotspot of Bethany Beach is a complex and pressing phenomenon as nuisance flooding continues to worsen with more frequent and intense storm events. Significant portions of the town’s attractions and infrastructure exist within low elevation areas near waterways whose water levels are controlled by inflow from the bay. Additionally, understanding ocean- side flooding in the case of extreme events is an important aspect of developing a holistic understanding of flood threats to the community. ☐ Noted urban problematic flooding areas from the Bethany Beach Canal Tidal Loop Assessment, ease of deployment access, and ability to obtain permission from private landowners dictated possible station locations (Applied Software & Information Services and Carpenter Engineering, 2020). Long-term monitoring pressure sensors were strategically placed at multiple of these locations within the intersecting canal network that connects to Indian River Bay. ☐ The Nearshore Community Model (NearCoM) (Shi et al., 2015) predicts waves, currents, sediment transport, and bathymetric change in the nearshore ocean. The model’s capability to predict street-level flooding through the urban canopy via quantitative data collected from each station was validated. The validated model is used to determine the flooding patterns, magnitudes, and durations of areas where sensors were not deployed. ☐ The findings of this study will be shared with Bethany Beach City Planners equipping them with the information necessary to improve city planning. The town will be better prepared to lessen nuisance flooding and mitigate damage associated with large-scale coastal storm events such as hurricanes and nor’easters.
Description
Keywords
Delaware, Flood mapping, Flood pathways, Hurricanes, NearCoM