2025

1. Coupling Coastal and Hydrologic Models through Next Generation National Water Model Framework

   Ebrahim Hamidi, Hart Henrichsen, Abbie Sandquist, Hongyuan Zhang, Hamed Moftakhari, and 4 more authors

   Journal of Hydrologic Engineering, 2025

   DOI
2. Coastal storm-induced flooding risk of the New York City subway amid climate change

   Yuki Miura, Christine Y. Blackshaw, Michelle S. Zhang, Kyle T. Mandli, and George Deodatis

   Transportation Research Part D: Transport and Environment, 2025

   Abs DOI

   Coastal areas face worsening storm-induced flooding due to climate change, threatening critical below-ground infrastructure like subway systems, as seen from Hurricane Sandy’s catastrophic impact on New York City (NYC)’s subway system in 2012. Stakeholders must urgently address these risks to protect infrastructure and assets. Simulating future flood scenarios is crucial for estimating flood risk and damage efficiently and for identifying reliable and effective protective measures. This article uses the GIS-based Subdivision-Redistribution (GISSR) methodology, a high-speed, physics-based flood estimation tool, that is now extended to model subway system flooding and associated economic impacts. It identifies flooded tunnels and stations and quantifies indirect economic losses from subway inoperability using an input–output model. The model is validated against observed subway flooding during Hurricane Sandy. Each analysis, covering both above- and below-ground flooding in Lower Manhattan, takes less than 90 s on a single 4-core Intel Core i7-13620H CPU machine. Scenario analyses were conducted with NYC stakeholders, incorporating sea level rise projections and various protective measures. Results, benchmarked against NYC’s ongoing resiliency projects, demonstrate the effectiveness of adaptation/protective strategies, particularly when subway system-specific and coastal measures are combined, highlighting the model’s value as a practical guide for stakeholders.

3. Impacts of barrier-island breaching on mainland flooding during storm events applied to Moriches, New York

   Catherine R. Jeffries, Robert Weiss, Jennifer L. Irish, and Kyle Mandli

   Natural Hazards and Earth System Sciences, 2025

   Abs DOI

   Barrier islands can protect the mainland from flooding during storms through reduction of storm surge and dissipation of storm-generated wave energy. However, the protective capability is reduced when barrier islands breach and a direct hydrodynamic connection between the water bodies on both sides of the barrier island is established. Breaching of barrier islands during large storm events is complicated, involving nonlinear processes that connect water, sediment transport, dune height, and island width, among other factors. In order to assess how barrier-island breaching impacts flooding on the mainland, we used a statistical approach to analyze the sensitivity of mainland storm surge to barrier-island breaching by randomizing the location, time, and extent of a breach event. We created a framework that allows breaching to develop during the course of a simulation and imposes a breach in an approximation of a Gaussian bell curve that deepens over time. We show that simulating a storm event and varying the size, location, and number of breaches in the barrier island that mainland storm surge and horizontal inundation is affected by breaching; total inundation has a logarithmic relationship with total breach area which tapers off after the entire island is removed. Breach location is also an important predictor of inundation and bay surge. The insights we have gleaned from this study can help prepare shoreline communities for the differing ways that breaching affects the mainland coastline. Understanding which mainland locations are vulnerable to breaching, planners and coastal engineers can design interventions to reduce the likelihood of a breach occurring in areas adjacent to high flood risk.

4. Assessment of Caribbean Coastal Hazard Posed by Tropical Cyclones

   Mona Hemmati, Chia-Ying Lee, Kyle T. Mandli, Adam H. Sobel, Suzana J. Camargo, and 1 more author

   Journal of Applied Meteorology and Climatology, 2025

   DOI

2024

1. Climate Change Contributions to Increasing Compound Flooding Risk in New York City

   Ali Sarhadi, Raphaël Rousseau-Rizzi, Kyle Mandli, Jeffrey Neal, Michael P Wiper, and 2 more authors

   Bulletin of the American Meteorological Society, 2024

   Abs DOI

   

   Abstract Efforts to meaningfully quantify the changes in coastal compound surge- and rainfall-driven flooding hazard associated with tropical cyclones (TCs) and extratropical cyclones (ETCs) in a warming climate have increased in recent years. Despite substantial progress, however, obtaining actionable details such as the spatially and temporally varying distribution and proximal causes of changing flooding hazard in cities remains a persistent challenge. Here, for the first time, physics-based hydrodynamic flood models driven by rainfall and storm surge simultaneously are used to estimate the magnitude and frequency of compound flooding events. We apply this to the particular case of New York City. We find that sea level rise (SLR) alone will increase the TC and ETC compound flooding hazard more significantly than changes in storm climatology as the climate warms. We also project that the probability of destructive Sandy-like compound flooding will increase by up to 5 times by the end of the century. Our results have strong implications for climate change adaptation in coastal communities.

2023

1. Advances in Morphodynamic Modeling of Coastal Barriers: A Review

   Steven W.H. Hoagland, Catherine R. Jeffries, Jennifer L. Irish, Robert Weiss, Kyle Mandli, and 3 more authors

   Journal of Waterway, Port, Coastal, and Ocean Engineering, 2023

   Abs DOI

   As scientific understanding of barrier morphodynamics has improved, so has the ability to reproduce observed phenomena and predict future barrier states using mathematical models. To use existing models effectively and improve them, it is important to understand the current state of morphodynamic modeling and the progress that has been made in the field. This manuscript offers a review of the literature regarding advancements in morphodynamic modeling of coastal barrier systems and summarizes current modeling abilities and limitations. Broadly, this review covers both event-scale and long-term morphodynamics. Each of these sections begins with an overview of commonly modeled phenomena and processes, followed by a review of modeling developments. After summarizing the advancements toward the stated modeling goals, we identify research gaps and suggestions for future research under the broad categories of improving our abilities to acquire and access data, furthering our scientific understanding of relevant processes, and advancing our modeling frameworks and approaches.

2022

1. A Novel Framework for Parametric Analysis of Coastal Transition Zone Modeling

   Taher Chegini, Gustavo de Almeida Coelho, John Ratcliff, Celso M. Ferreira, Kyle Mandli, and 2 more authors

   JAWRA Journal of the American Water Resources Association, 2022

   Abs DOI

   Vulnerability of coastal regions to extreme events motivates an operational coupled inland‐coastal modeling strategy focusing on the coastal transition zone (CTZ), an area between the coast and upland river. To tackle this challenge, we propose a top‐down framework for investigating the contribution of different processes to the hydrodynamics of CTZs with various geometrical shapes, different physical properties, and under several forcing conditions. We further propose a novel method, called tidal vanishing point (TVP), for delineating the extent of CTZs through the upland. We demonstrate the applicability of our framework over the United States East and Gulf coasts. We categorize CTZs in the region into three classes, namely, without estuary (direct river–coast connection), triangular‐, and trapezoidal‐shaped estuary. The results show that although semidiurnal tidal constituents are dominant in most cases, diurnal tidal constituents become more prevalent in the river segment as the discharge increases. Also, decreasing the bed roughness value promotes more significant changes in the results than increasing it by the same value. Additionally, the estuary promotes tidal energy attenuation and consequently decreases the reach of tidal signals through the upland. The proposed framework is generic and extensible to any coastal region.

2. Inter‐Model Comparison of Delft3D‐FM and 2D HEC‐RAS for Total Water Level Prediction in Coastal to Inland Transition Zones

   David F. Muñoz, Dongxiao Yin, Roham Bakhtyar, Hamed Moftakhari, Zuo Xue, and 2 more authors

   JAWRA Journal of the American Water Resources Association, 2022

   Abs DOI

   Hydrodynamic models play a key role in simulating total water level (TWL), that is, a combination of river flow, tide, surge, wind and wave‐induced water level, and representing flood inundation dynamics in coastal areas. An appropriate selection of two‐dimensional (2D) models that integrate riverine and estuarine interactions with ocean dynamics is crucial to generate accurate TWL predictions and assist stakeholders and federal agencies in decision making and flood emergency responses. In this study, we compare the performance of two widely used hydrodynamic models (e.g., 2D HEC‐RAS and Delft3D‐Flexible Mesh [FM]) with respect to their ability of predicting TWL in Delaware Bay, United States. Based on a previously established model configuration, we simulate Hurricane Sandy and Isabel that affected the Bay and led to considerable damages and economic losses. We then evaluate model capabilities with tidal analysis, compare observed vs. simulated TWL and analyze spatiotemporal variations of TWL through scenario‐based simulations. Our results suggest that atmospheric forcing input in Delft3D‐FM significantly improves TWL predictions as compared to those of 2D HEC‐RAS. Furthermore, model simulations with Delft3D‐FM can be faster than 2D HEC‐RAS by a factor of 6–10. Despite these advantages, 2D HEC‐RAS (version 5.07) is a noncommercial software easier to implement and can be a simpler alternative for modeling extreme events when atmospheric forcing is not relevant in the model domain.

2011

1. The GeoClaw software for depth-averaged flows with adaptive refinement

   Marsha J. Berger, David L. George, Randall J. LeVeque, and Kyle T. Mandli

   Advances in Water Resources, 2011

   Abs DOI

   

   Many geophysical flow or wave propagation problems can be modeled with two-dimensional depth-averaged equations, of which the shallow water equations are the simplest example. We describe the GeoClaw software that has been designed to solve problems of this nature, consisting of open source Fortran programs together with Python tools for the user interface and flow visualization. This software uses high-resolution shock-capturing finite volume methods on logically rectangular grids, including latitude–longitude grids on the sphere. Dry states are handled automatically to model inundation. The code incorporates adaptive mesh refinement to allow the efficient solution of large-scale geophysical problems. Examples are given illustrating its use for modeling tsunamis and dam-break flooding problems. Documentation and download information is available at www.clawpack.org/geoclaw.