Abstract Worldwide, coastal, and deltaic communities are susceptible to flooding from the individual and combined effects of rainfall excess and astronomic tide and storm surge inundation. Such flood events are a present (and future) cause of concern as observed from recent storms such as the 2016 Louisiana flood and Hurricanes Harvey, Irma, and Maria. To assess flood risk across coastal landscapes, it is advantageous to first delineate flood transition zones, which we define as areas susceptible to hydrologic and coastal flooding and their collective interaction. We utilize numerical simulations combining rainfall excess and storm surge for the 2016 Louisiana flood to describe a flood transition zone for southeastern Louisiana. We show that the interaction of rainfall excess with coastal surge is nonlinear and less than the superposition of their individual components. Our analysis provides a foundation to define flooding zones across coastal landscapes throughout the world to support flood risk assessments.
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Coupling Hydrologic, Tide and Surge Processes to Enhance Flood Risk Assessments for the Louisiana Coastal Master Plan
Flood risk at the coastal land margin is influenced by both hydrologic and tidal processes, especially in deltaic flood plains, which leads to the realization that there exist transitional zones of flood hazard and risk. This coastal flood plain phenomena will be better understood by delineating dominant contributors to flood hazard and risk as they move from surge-only (in the immediate coastal flood zone) to hydrologic and tidal (including both low impact, high frequency events such as winter storms and higher impact lower frequency events such as storm surge) to rainfall-induced-only further from the coast. The intent of the proposed efforts are to demonstrate that while this transitional flood risk zone retreats towards populated areas with coastal land loss, it can also be advanced away from urban centers with the aid of Louisiana Coastal Master Plan projects. To do so will directly address the Rationale from Topic 6: “The Coastal Master Plan recognizes the importance of both future climate change and episodic forcing, such as storms and droughts, in shaping the future of the coast and the success of protection and restoration projects.” The aim of the proposed research is to address these fundamental issues by defining regions where both rainfall runoff and storm surge (both winter and tropical storms) overlap through development of a coupled hydrologic and hydrodynamic model to enable more comprehensive enhanced flood risk assessments and more.
“Coupling Hydrologic, Tide and Surge Processes to Enhance Flood Risk Assessments for the Louisiana Coastal Master Plan.” The Water Institute of the Gulf, Restore Act Center of Excellence for Louisiana, 01/25/2017, $499,882 (PI: S.C. Hagen), Role: Co-PI
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S.C. Hagen, D.L. Passeri, M.V. Bilskie, D.E. DeLorme, D. Yaskowitz (2017). “Systems Approaches for Coastal Hazard Assessment and Resilience.” Oxford Research Encyclopedia of Natural Hazard Science. DOI:10.1093/acrefore/9780199389407.013.28
The framework presented herein supports a changing paradigm in the approaches used by coastal researchers, engineers, and social scientists to model the impacts of climate change and sea level rise (SLR) in particular along low-gradient coastal landscapes. Use of a System of Systems (SoS) approach to the coastal dynamics of SLR is encouraged to capture the nonlinear feedbacks and dynamic responses of the bio-geo-physical coastal environment to SLR, while assessing the social, economic, and ecologic impacts. The SoS approach divides the coastal environment into smaller subsystems such as morphology, ecology, and hydrodynamics. Integrated models are used to assess the dynamic responses of subsystems to SLR; these models account for complex interactions and feedbacks among individual systems, which provides a more comprehensive evaluation of the future of the coastal system as a whole. Results from the integrated models can be used to inform economic services valuations, in which economic activity is connected back to bio-geo-physical changes in the environment due to SLR by identifying changes in the coastal subsystems, linking them to the understanding of the economic system and assessing the direct and indirect impacts to the economy. These assessments can be translated from scientific data to application through various stakeholder engagement mechanisms, which provide useful feedback for accountability as well as benchmarks and diagnostic insights for future planning. This allows regional and local coastal managers to create more comprehensive policies to reduce the risks associated with future SLR and enhance coastal resilience.
Permanent link to this article: http://www.mattbilskie.com/systems-approaches-for-coastal-hazard-assessment-and-resilience/
K. Alizad, S.C. Hagen, J.T. Morris, S.C. Medeiros, M.V. Bilskie, J.F. Weishampel (2016). “Coastal wetland response to sea-level rise in a fluvial estuarine system.” Earth’s Future. In-Press. http://dx.doi.org/10.1002/2016EF000385.
Abstract Coastal wetlands are likely to lose productivity under increasing rates of sea-level rise (SLR). This study assessed a fluvial estuarine salt marsh system using the Hydro-MEM model under four SLR scenarios. The Hydro-MEM model was developed to apply the dynamics of SLR as well as capture the effects associated with the rate of SLR in the simulation. Additionally, the model uses constants derived from a 2-year bioassay in the Apalachicola marsh system. In order to increase accuracy, the lidar-based marsh platform topography was adjusted using Real Time Kinematic survey data. A river inflow boundary condition was also imposed to simulate freshwater flows from the watershed. The biomass density results produced by the Hydro-MEM model were validated with satellite imagery. The results of the Hydro-MEM simulations showed greater variation of water levels in the low (20 cm) and intermediate-low (50 cm) SLR scenarios and lower variation with an extended bay under higher SLR scenarios. The low SLR scenario increased biomass density in some regions and created a more uniform marsh platform in others. Under intermediate-low SLR scenario, more flooded area and lower marsh productivity were projected. Higher SLR scenarios resulted in complete inundation of marsh areas with fringe migration of wetlands to higher land. This study demonstrated the capability of Hydro-MEM model to simulate coupled physical/biological processes across a large estuarine system with the ability to project marsh migration regions and produce results that can aid in coastal resource management, monitoring, and restoration efforts.
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Publication | Data and numerical analysis of astronomic tides, wind-waves, and hurricane storm surge along the northern Gulf of Mexico
M.V. Bilskie, S.C. Hagen, S.C. Medeiros, A.T. Cox, M. Salisbury, D. Coggin (2016). “Data and numerical analysis of astronomic tides, wind-waves, and hurricane storm surge along the northern Gulf of Mexico.” Journal of Geophysical Research, In Press. doi: 10.1002/2015JC011400.
Abstract The northern Gulf of Mexico (NGOM) is a unique geophysical setting for complex tropical storm-induced hydrodynamic processes that occur across a variety of spatial and temporal scales. Each hurricane includes its own distinctive characteristics and can cause unique and devastating storm surge when it strikes within the intricate geometric setting of the NGOM. While a number of studies have explored hurricane storm surge in the NGOM, few have attempted to describe storm surge and coastal inundation using observed data in conjunction with a single large-domain high-resolution numerical model. To better understand the oceanic and nearshore response to these tropical cyclones, we provide a detailed assessment, based on field measurements and numerical simulation, of the evolution of wind waves, water levels, and currents for Hurricanes Ivan (2004), Dennis (2005), Katrina (2005), and Isaac (2012), with focus on Mississippi, Alabama, and the Florida Panhandle coasts. The developed NGOM3 computational model describes the hydraulic connectivity among the various inlet and bay systems, Gulf Intracoastal Waterway, coastal rivers and adjacent marsh, and built infrastructure along the coastal floodplain. The outcome is a better understanding of the storm surge generating mechanisms and interactions among hurricane characteristics and the NGOM’s geophysical configuration. The numerical analysis and observed data explain the ∼2 m/s hurricane-induced geostrophic currents across the continental shelf, a 6 m/s outflow current during Ivan, the hurricane-induced coastal Kelvin wave along the shelf, and for the first time a wealth of measured data and a detailed numerical simulation was performed and was presented for Isaac. This article is protected by copyright. All rights reserved.
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Publication | Dynamic simulation and numerical analysis of hurricane storm surge under sea level rise with geomorphologic changes along the northern Gulf of Mexico
M.V. Bilskie, S.C. Hagen, K. Alizad, S.C. Medeiros, D.L. Passeri, H.F. Needham, A. Cox (2016). “Dynamic simulation and numerical analysis of hurricane storm surge under sea level rise with geomorphologic changes along the northern Gulf of Mexico.” Earth’s Future, In Press. doi: 10.1002/2015EF000347
Abstract This work outlines a dynamic modeling framework to examine the effects of global climate change, and sea level rise (SLR) in particular, on tropical cyclone-driven storm surge inundation. The methodology, applied across the northern Gulf of Mexico, adapts a present day large-domain, high resolution, tide, wind-wave, and hurricane storm surge model to characterize the potential outlook of the coastal landscape under four SLR scenarios for the year 2100. The modifications include shoreline and barrier island morphology, marsh migration, and land use land cover change. Hydrodynamics of ten historic hurricanes were simulated through each of the five model configurations (present day and four SLR scenarios). Under SLR, the total inundated land area increased by 87% and developed and agricultural lands by 138% and 189%, respectively. Peak surge increased by as much as 1 m above the applied SLR in some areas, and other regions were subject to a reduction in peak surge, with respect to the applied SLR, indicating a nonlinear response. Analysis of time-series water surface elevation suggests the interaction between SLR and storm surge is nonlinear in time; SLR increased the time of inundation and caused an earlier arrival of the peak surge, which cannot be addressed using a static (“bathtub”) modeling framework. This work supports the paradigm shift to using a dynamic modeling framework to examine the effects of global climate change on coastal inundation. The outcomes have broad implications and ultimately support a better holistic understanding of the coastal system and aid restoration and long-term coastal sustainability.
Permanent link to this article: http://www.mattbilskie.com/publication-dynamic-simulation-and-numerical-analysis-of-hurricane-storm-surge-under-sea-level-rise-with-geomorphologic-changes-along-the-northern-gulf-of-mexico/
Publication | Tidal hydrodynamics under future sea level rise and coastal morphology in the northern Gulf of Mexico
D.L. Passeri, S.C. Hagen, M.V. Bilskie, S.C. Medeiros, K. Alizad (2016). “Tidal hydrodynamics under future sea level rise and coastal morphology in the northern Gulf of Mexico.” Earth’s Future, Online 4/4/2016.
Abstract This study examines the integrated influence of sea level rise (SLR) and future morphology on tidal hydrodynamics along the Northern Gulf of Mexico (NGOM) coast including seven embayments and three ecologically and economically significant estuaries. A large-domain hydrodynamic model was used to simulate astronomic tides for present and future conditions (circa 2050 and 2100). Future conditions were simulated by imposing four SLR scenarios to alter hydrodynamic boundary conditions and updating shoreline position and dune heights using a probabilistic model that is coupled to SLR. Under the highest SLR scenario, tidal amplitudes within the bays increased as much as 67% (10.0 cm) due to increases in the inlet-cross-sectional area. Changes in harmonic constituent phases indicated tidal propagation was faster in the future scenarios within most of the bays. Maximum tidal velocities increased in all of the bays, especially in Grand Bay where velocities doubled under the highest SLR scenario. In addition, the ratio of the maximum flood to maximum ebb velocity decreased in the future scenarios (i.e., currents became more ebb dominant) by as much as 26% and 39% in Weeks Bay and Apalachicola, respectively. In Grand Bay, the flood-ebb ratio increased (i.e., currents became more flood dominant) by 25% under the lower SLR scenarios, but decreased by 16% under the higher SLR as a result of the offshore barrier islands being overtopped, which altered the tidal prism. Results from this study can inform future storm surge and ecological assessments of SLR, and improve monitoring and management decisions within the NGOM.
Permanent link to this article: http://www.mattbilskie.com/publication-tidal-hydrodynamics-under-future-sea-level-rise-and-coastal-morphology-in-the-northern-gulf-of-mexico/
Permanent link to this article: http://www.mattbilskie.com/publication-a-coupled-two-dimensional-hydrodynamic-marsh-model-with-biological-feedback/
M.V. Bilskie, S.C. Hagen, D.L. Passeri, K. Alizad, S.C. Medeiros, J.L. Irish, H. Needham, and A. Cox, “A dynamic flood inundation model framework to assess coastal flood risk in a changing climate.” 2015 AGU Fall Meeting, San Francisco, CA, Dec. 14-18, 2015.
Session GC032: Field/Laboratory Analysis, Modeling, and Stakeholder Involvement to Assess Impacts of the Coastal Dynamics of Sea Level Rise in Low Gradient Coastal Landscapes
Session ID: 8261
Abstract: Coastal regions around the world are susceptible to a variety of natural disasters causing extreme inundation. It is anticipated that the vulnerability of coastal cities will increase due to the effects of climate change, and in particular sea level rise (SLR). A novel framework was developed to generate a suite of physics-based storm surge models that include projections of coastal floodplain dynamics under climate change scenarios: shoreline erosion/accretion, dune morphology, salt marsh migration, and population dynamics [Bilskie et al., 2014; Passeri et al., 2014; Passeri et al., 2015].
First, the storm surge inundation model was extensively validated for present day conditions with respect to astronomic tides and hindcasts of Hurricane Ivan (2004), Dennis (2005), Katrina (2005), and Isaac (2012). The model was then modified to characterize the future outlook of the landscape for four climate change scenarios for the year 2100 (B1, B2, A1B, and A2), and each climate change scenario was linked to a sea level rise of 0.2 m, 0.5 m, 1.2 m, and 2.0 m [Parris et al., 2012]. The adapted model was then used to simulate hurricane storm surge conditions for each climate scenario using a variety of tropical cyclones as the forcing mechanism. The collection of results shows the intensification of inundation area and the vulnerability of the coast to potential future climate conditions. The methodology developed herein to assess coastal flooding under climate change can be performed across any coastal region worldwide, and results provide awareness of regions vulnerable to extreme flooding in the future.
Bilskie, M. V., S. C. Hagen, S. C. Medeiros, and D. L. Passeri (2014), Dynamics of sea level rise and coastal flooding on a changing landscape, Geophysical Research Letters, 41(3), 927-934.
Parris, A., et al. (2012), Global Sea Level Rise Scenarios for the United States National Climate AssessmentRep., 37 pp.
Passeri, D. L., S. C. Hagen, M. V. Bilskie, and S. C. Medeiros (2014), On the significance of incorporating shoreline changes for evaluating coastal hydrodynamics under sea level rise scenarios, Natural Hazards, 1599-1617.
Passeri, D. L., S. C. Hagen, S. C. Medeiros, M. V. Bilskie, K. Alizad, and D. Wang (2015), The dynamic effects of sea level rise on low gradient coastal landscapes: a review, Earth’s Future, 3.
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