Surge Attenuation Research Articles

Conditional Oprk1-dependent Kiss1 deletion in kisspeptin neurons caused estrogen-dependent LH pulse disruption and LH surge attenuation in female rats

The gonadotropin-releasing hormone (GnRH) pulse and surge are considered to be generated by arcuate kisspeptin/neurokinin B/dynorphin A (KNDy) neurons and anteroventral periventricular nucleus (AVPV) kisspeptin neurons, respectively, in female rodents. The majority of KNDy and AVPV kisspeptin neurons express κ-opioid receptors (KORs, encoded by Oprk1) in female rodents. Thus, this study aimed to investigate the effect of a conditional Oprk1-dependent Kiss1 deletion in kisspeptin neurons on the luteinizing hormone (LH) pulse/surge and fertility using Kiss1-floxed/Oprk1-Cre rats, in which Kiss1 was deleted in cells expressing or once expressed the Oprk1/Cre. The Kiss1-floxed/Oprk1-Cre female rats, with Kiss1 deleted in a majority of KNDy neurons, showed normal puberty while having a one-day longer estrous cycle and fewer pups than Kiss1-floxed controls. Notably, ovariectomized (OVX) Kiss1-floxed/Oprk1-Cre rats showed profound disruption of LH pulses in the presence of a diestrous level of estrogen but showed apparent LH pulses without estrogen treatment. Furthermore, Kiss1-floxed/Oprk1-Cre rats, with Kiss1 deleted in approximately half of AVPV kisspeptin neurons, showed a lower peak of the estrogen-induced LH surge than controls. These results suggest that arcuate and AVPV kisspeptin neurons expressing or having expressed Oprk1 have a role in maintaining normal GnRH pulse and surge generation, the normal length of the estrous cycle, and the normal offspring number in female rats.

Mangrove forests as a nature-based solution for coastal flood protection: Biophysical and ecological considerations

Nature-based coastal protection is increasingly recognised as a potentially sustainable and cost-effective solution to reduce coastal flood risk. It uses coastal ecosystems such as mangrove forests to create resilient designs for coastal flood protection. However, to use mangroves effectively as a nature-based measure for flood risk reduction, we must understand the biophysical processes that govern risk reduction capacity through mangrove ecosystem size and structure. In this perspective, we evaluate the current state of knowledge on local physical drivers and ecological processes that determine mangrove functioning as part of a nature-based flood defence. We show that the forest properties that comprise coastal flood protection are well-known, but models cannot yet pinpoint how spatial heterogeneity of the forest structure affects the capacity for wave or surge attenuation. Overall, there is relatively good understanding of the ecological processes that drive forest structure and size, but there is a lack of knowledge on how daily bed-level dynamics link to long-term biogeomorphic forest dynamics, and on the role of combined stressors influencing forest retreat. Integrating simulation models of forest structure under changing physical (e.g. due to sea-level change) and ecological drivers with hydrodynamic attenuation models will allow for better projections of long-term natural coastal protection.

The effects of coastal marsh geometry and surge scales on water level attenuation

Coastal wetlands are an effective natural and nature-based feature to mitigate coastal flood hazards. While the sheltering and attenuation offered by wetlands are recognized, the protection level varies based on wetland and storm characteristics. Here we focus on the effects of the spatial scales of the coastal wetlands (i.e., channel geometry, marsh elevation-gradient) and the temporal scales of storm forcing (i.e., storm surge amplitude and duration) on peak water level attenuation. The study was conducted by performing hydrodynamic simulations on an idealized marsh geometry. One hundred seventy-one hydrodynamic simulations were conducted by varying wetland features under variable hydrodynamic forcing. Increased tidal channel area enhances water flow across marshes by reducing the capacity of vegetated platforms to resist propagation of a storm surge. The level of surge attenuation and channel area shows a non-linear relationship. Storm scales also affect surge attenuation for a given channel geometry. Higher amplitudes and lower surge durations provide greater attenuation of peak water levels. The level of attenuation and surge scales also show a non-linear correlation. A multivariate scaling relationship was developed that successfully integrates the combined effects of channel geometry and surge scales on water level attenuation by salt marsh. This research provides guidance to engineers and coastal managers on salt marsh's flood hazard reduction benefits.

Can Managed Realignment Buffer Extreme Surges? The Relationship Between Marsh Width, Vegetation Cover and Surge Attenuation

Managed realignment (MR) involves the landward relocation of sea defences to foster the (re)creation of coastal wetlands and achieve nature-based coastal protection. The wider application of MR is impeded by knowledge gaps related to lacking data on its effectiveness under extreme surges and the role of changes in vegetation cover, for example due to sea-level rise. We employ a calibrated and validated hydrodynamic model to explore relationships between surge attenuation, MR width(/area) and vegetation cover for the MR site of Freiston Shore, UK. We model a range of extreme water levels for four scenarios of variable MR width. We further assess the effects of reduced vegetation cover for the actual MR site and for the scenario of the site with the largest width. We show that surges are amplified for all but the largest two site scenarios, suggesting that increasing MR width results in higher attenuation rates. Substantial surge attenuation (up to 18 cm km−1) is only achieved for the largest site. The greatest contribution to the attenuation in the largest site scenario may come from water being reflected from the breached dike. While vegetation cover has no statistically significant effect on surge attenuations in the original MR site, higher coverage leads to higher attenuation rates in the largest site scenario. We conclude that at the open coast, only large MR sites (> 1148 m width) can attenuate surges with return periods > 10 years, while increased vegetation cover and larger MR widths enable the attenuation of even higher surges.

Improved modeling of the role of mangroves in storm surge attenuation

Mangroves have been proven to be effective in storm surge attenuation but it remains an important challenge to accurately quantify such bio-shielding effects using numerical simulations, as it is very difficult to comprehensively represent the ecological characteristics of mangroves at both large and small scales. In this study, a numerical method is developed and implemented in the Coastal and Estuarine Storm Tide (CEST) model in order to investigate the attenuation effect of mangroves on storm surge. This numerical method employs an improved drag force formula, which involves the development of new abstract tree models and use of a landscape scale data map of mean mangrove tree height for the study area. The storm surge observed in the South Florida mangrove zone caused by Hurricane Wilma (2005) is used to verify the numerical model. The numerical results indicate a maximum surge of approximately 4.3 m, and a decay rate of peak storm surge height of approximately 18 cm/km across the areas with a mixture of mangrove islands and open water, and nearly 24 cm/km through areas with dense mangrove forest. Results also show that short mangroves (< 4 m) can outperform tall mangroves on surge attenuation when the water depth is low (< 4 m). Extensive comparisons are also made with the conventional Manning coefficient based method that incorporates the mangrove drag force into bed friction; it is found that the current method predicts better inundation extents for Wilma (2005), hence a more accurate quantification of the attenuation of storm surge due to mangroves.

Coastal wetlands mitigate storm flooding and associated costs in estuaries

As storm-driven coastal flooding increases under climate change, wetlands such as saltmarshes are held as a nature-based solution. Yet evidence supporting wetlands’ storm protection role in estuaries—where both waves and upstream surge drive coastal flooding—remains scarce. Here we address this gap using numerical hydrodynamic models within eight contextually diverse estuaries, simulating storms of varying intensity and coupling flood predictions to damage valuation. Saltmarshes reduced flooding across all studied estuaries and particularly for the largest—100 year—storms, for which they mitigated average flood extents by 35% and damages by 37% ($8.4 M). Across all storm scenarios, wetlands delivered mean annual damage savings of $2.7 M per estuary, exceeding annualised values of better studied wetland services such as carbon storage. Spatial decomposition of processes revealed flood mitigation arose from both localised wave attenuation and estuary-scale surge attenuation, with the latter process dominating: mean flood reductions were 17% in the sheltered top third of estuaries, compared to 8% near wave-exposed estuary mouths. Saltmarshes therefore play a generalised role in mitigating storm flooding and associated costs in estuaries via multi-scale processes. Ecosystem service modelling must integrate processes operating across scales or risk grossly underestimating the value of nature-based solutions to the growing threat of storm-driven coastal flooding.

Numerical Investigation on Coastal Inundation of Storm Surges in Estuarine Wetland Waters

Zhang, H.; Zhang, M.; Shen, Y., and Xu, T., 2020. Numerical investigation on coastal inundation of storm surges in estuarine wetland waters. In: Malvarez, G. and Navas, F. (eds.), Proceedings from the International Coastal Symposium (ICS) 2020 (Seville, Spain). Journal of Coastal Research, Special Issue No. 95, pp. 1383-1388. Coconut Creek (Florida), ISSN 0749-0208.Coastal flooding caused by storm surges poses serious threats to coastal areas, communities and ecosystems. Plants that widely distributed in tidal flats play an important role in protecting the coastline from erosion, and mitigating extreme nature hazards. In this paper, based on the finite volume method (FVM), an explicit depth-averaged 2D model is established to investigate the interaction between salt marsh plants and storm surges in estuarine wetland waters. The Roe approximate Riemann solver, coupled with a drying-wetting boundary technique, is proposed in order to evaluate the effectiveness of interface fluxes for tracking the moving coastline and calculating storm surge land intrusions. The drag force induced by vegetation is added to momentum equations as an internal source to express the vegetation resistance to storm surges. The Jelesnianski 65 typhoon model is adopted to simulate the wind and pressure fields of the storm surges, and the background wind field is included in the total wind field. The proposed model is applied to investigate tidal levels, storm surges and flow currents during Typhoon Winnie and Typhoon Matsa in the Bohai Sea. Moreover, the model is used to explore the land intrusion and storm surge attenuation in Liao River Estuary (LRE) wetlands during Typhoon Winnie. Numerical predictions are found to match perfectly with those given by the measured data. The storm surge model can accurately reproduce the storm surge inundation process in wetland waters. The simulated results also indicate that salt marsh plants can reduce the flow current in vegetated regions, thus effectively attenuating the potential threats of storm surges.

Modeling Storm Surge Attenuation by an Integrated Nature-Based and Engineered Flood Defense System in the Scheldt Estuary (Belgium)

There is increasing interest in the use of nature-based approaches for mitigation of storm surges along coasts, deltas, and estuaries. However, very few studies have quantified the effectiveness of storm surge height reduction by a real-existing, estuarine-scale, nature-based, and engineered flood defense system, under specific storm surge conditions. Here, we present data and modelling results from a specific storm surge in the Scheldt estuary (Belgium), where a hybrid flood defense system is implemented, consisting of flood control areas, of which some are restored into tidal marsh ecosystems, by use of culvert constructions that allow daily reduced tidal in- and outflow. We present a hindcast simulation of the storm surge of 6 December 2013, using a TELEMAC-3D model of the Scheldt estuary, and model scenarios showing that the hybrid flood defense system resulted in a storm surge height reduction of up to half a meter in the estuary. An important aspect of the work was the implementation of model formulations for calculating flow through culverts of restored marshes. The latter was validated comparing simulated and measured discharges through a physical scale model of a culvert, and through a real-scale culvert of an existing restored marsh during the storm surge.

Engaging coastal community members about natural and nature-based solutions to assess their ecosystem function

Hazards in coastal ecosystems, such as flooding and land loss, demand natural and nature-based solutions from local communities due to the protective and non-protective services they provide when compared with traditionally engineered approaches. In this context, natural solutions are those that consider conserving existing habitats whereas nature-based solutions are those created by humans. These solutions support important coastal ecosystem functions, such as nutrient uptake, fisheries habitat, soil carbon storage, and surge attenuation. Our main research questions were: (1) Based on community engagement, what are the possible natural and nature-based solutions to address coastal hazards in Breton Sound Estuary, Louisiana? and (2) How do these community co-designed nature-based solutions support various ecosystem functions? To help answer these questions, we leveraged the competency group methodology to incorporate the local needs and traditional ecological knowledge of community stakeholders into collaborative ecosystem modelling. In total, fifteen members regularly met five times over an eight-month period to design nature-based solutions to address coastal hazards. Two nature-based solutions, created marshes and restored ridges, were identified most frequently by the competency group (>75% occurrence) in a final survey. Associated ecosystem functions of the identified solutions were assessed with simulation models to determine future ecosystem functions of nutrient uptake, fisheries habitat, soil carbon storage, and surge attenuation after 20 years. By adding created marshes to an ecosystem, our model results indicate slight increases in nutrient uptake, likely increases to fisheries habitat and soil carbon storage capacity, as well as storm surge attenuation in some areas following ridge restoration. Quantifying these ecosystem functions with management actions has been limited and is needed to assess how natural and nature-based solutions impact local communities and resource users. This novel approach to modeling ecosystem-based solutions through a collaborative modeling process with researchers and residents can be applied elsewhere to assess the viability of natural and nature-based solutions.

An Improved Statistical Method for Calculating Lightning Overvoltages in HVDC Overhead Line/Cable Systems

HVDC cable systems connected to HVDC overhead lines are subject to fast front overvoltages emanating from the line when lightning strikes a shield wire (backflashover) or a pole conductor (shielding failure). Representative fast front overvoltage levels for HVDC cable systems are usually established without considering their statistical characteristics. A statistical method to determine overvoltages related to the acceptable mean time between failure (MTBF) for the cable system was developed previously. The method accounts for the statistical distribution of lightning current magnitudes as well as the attenuation of the overvoltage wave due to corona discharges on the line, since this effect dominates for system voltages up to about ±320 kV. To make the method suitable for higher system voltages as well, this article introduces an improved statistical method which also accounts for surge attenuation through resistive effects, soil ionization, and statistical treatment of overvoltages due to shielding failures. To illustrate the improved method, it is applied to a case study for a ±525 kV DC line.

Exploring the performances of the dual technique-based water hammer redesign strategy in water supply systems

Abstract This paper explored and compared the effectiveness of the inline and branching redesign strategies-based dual technique, implemented to enhance the conventional technique skills in terms of attenuation of positive and negative pressure surge magnitudes and limitation of the spreading of pressure wave oscillation period. Basically, this technique is based on splitting the single inline or branched plastic short-section, used in the conventional technique, into a couple of two sub-short-sections made of two distinct plastic material types. Investigations addressed positive and negative surge initiated water hammer events. Additionally, high and low density polyethylene materials were utilized for sub-short-section material. Results illustrated the reliability of the dual technique in protecting hydraulic systems from excessive pressure rise and drop, and evidenced that the (HDPE/LDPE) sub-short-sections' combination (where the former sub-short-section is attached to the sensitive region of the steel piping system parts, while the latter is attached to the second extremity of the steel piping system) is the most prominent configuration providing the best trade-off between pressure surge attenuation, and pressure wave oscillation period spreading. Lastly, it was found that the pressure head peak (or crest) and the pressure wave oscillation period values were markedly sensitive to the (HDPE) sub-short-section length and diameter.

Lightning Propagation Analysis on Telecommunication Towers Above the Perfect Ground Using Full-Wave Time Domain PEEC Method

Lightning surge propagation on telecommunication towers is essential to lightning protection design. Analysis of very fast surges in a telecommunication tower requires a full-wave solution of Maxwell's equations. This paper proposes a full-wave time domain partial element equivalent circuit (PEEC) method considering the effect of ground to evaluate the surge currents and voltages on vertical structures. The PEEC of the formulation is provided by using the method of image. This method can take into account the attenuation of the lighting surges, and has the potential to be implemented as a new type of solution for general lightning surge analysis. The proposed method is validated numerically with the finite-difference time domain method, and is used to analyze the surge propagation on cables mounted on two typical grounded telecommunication towers. The simulation shows that both the location of cable installations and the type of towers have a significant influence on the lightning protection performance.

Attenuation of Storm Surges by Coastal Mangroves

AbstractThe interaction between mangroves and storm surges is explored using an analytical solution. A simplified momentum equation, balancing vegetation drag and pressure gradient, is combined with the continuity equation resulting in a diffusion equation. Assuming a simplified environment, a one‐dimensional analytical solution is obtained to predict peak surge level across a forest. The solution accurately reproduces peak water level of a 10‐year return period flood event in mangroves in the Firth of Thames, New Zealand, and in Ten Thousand Islands, Florida, during Hurricane Charley. Vegetation properties that determine the capacity of mangroves to reduce surges are forest density and cross‐shore extent. Storm characteristics—flood duration and peak water level at the forest fringe—also influence surge attenuation. Mangroves are shown to be an effective form of coastal flood protection if forests are sufficiently wide/dense, relative to the surge decay length scale, to restrict water exchange during a storm.

HOW VEGETATED FORESHORES AFFECT PROBABILITIES AND CONSEQUENCES OF DIKE FAILURE

Coastal ecosystems, such as salt marshes, mangrove forests and reefs, can contribute to flood risk reduction by surge attenuation, wave energy dissipation and erosion reduction (Temmerman et al. 2013). Such ecosystems can work stand-alone, but here we consider hybrid engineering solutions, where ecosystems are utilized as vegetated foreshores along engineered structures (Fig. 1).

Hydrodynamic storm surge model simplification via application of land to water isopleths in coastal Louisiana

The Mississippi River Delta ranks the seventh largest delta in the world. It provides a habitat for the Louisiana seafood industry, navigation canals and rivers that support five of the 15 largest cargo ports by volume in the United States, and hurricane storm surge protection for coastal cities and oil and gas industry infrastructure that facilitates 90% of the outer continental oil and gas extraction. Due to substantial coastal wetland loss since 1900, the risk of damage to these industries and infrastructure has increased through time. The goal of this research is to develop a methodology to analyze the historical and future evolution of coastal hazards, such as hurricane storm surge, across a complex, low-lying coastal landscape. To accomplish this task, the change in coastal hazards is analyzed through historical changes in coastal wetlands. Specifically, isopleths, defined as lines on a map indicating a constant value of a given variable, are developed to describe areas of constant values of the ratio of land to water (L:W) across coastal Louisiana.In this analysis, a methodology is developed that utilizes land to water (L:W) isopleths to simplify the modern day Louisiana coastal landscape as represented in a state-of-the-art high resolution storm surge model. L:W isopleths are derived for the year 2010 and used to construct 36 storm surge models, each featuring variations of three distinct coastal zones: “High” (i.e. high wetland), “Intermediate” (i.e. wetland), and “Submersed” (i.e. region between open water and wetland). The ADvanced CIRCulation (ADCIRC) code is used to compute water surface elevations and depth-averaged currents forced by hurricane wind and pressures from Hurricanes Rita, Gustav, and Katrina for each model. Peak water levels and volume of inundation are quantified within hydrologic unit code watersheds (HUC12) in order to compare storm surge models featuring high resolution and simplified coastal landscapes.A L:W isopleth permutation of 99%–90%–40%–1% with areas labeled “High” (99%–90%), “Intermediate” (90%–40%) and “Submersed” (40%–1%) is found to best represent simulated storm surge that most closely reproduces the high resolution storm surge model. Simulation results reveal the methodology developed in this analysis is effective in identifying an isopleth permutation that accurately simplifies a high resolution storm surge model. This result may lead to future analyses of the historical evolution of storm surge attenuation in the Mississippi River Delta (MRD) as well as other complex, low-lying deltas. These possibilities include developing storm surge models for the years 1930 and 1970, for instance, with the same isopleth permutation to examine the changes in storm surge attenuation through time. This analysis could also be applied in other similar low-lying coastal regions to conduct past and future analyses of the evolution of coastal hazards.

Potential of marshes to attenuate storm surge water level in the Chesapeake Bay

AbstractStorm surges from tropical and extratropical storms frequently impact coastal communities globally. While the potential of natural and nature‐based features for coastal defenses has gained increased attention as a viable option for coastal flood protection, the lack of in situ measurements of storm surge attenuation has delayed their widespread utilization. We present the findings of a 3‐yr water level monitoring campaign that resulted in a large collection (52 flood events) of attenuation rates from marsh transects located in two natural preserves in the U.S. mid‐Atlantic region. Results show that the overall marsh attenuated water levels, exhibiting values up to 0.02 cm/m at Eastern Shore of Virginia National Wildlife Refuge (ES) and 0.03 cm/m at Magothy Bay Natural Preserve (MGB). In general, the greatest attenuation rates were observed at the marsh edge section. The reach close to the coastline revealed an amplification of the water level followed by water level attenuation toward the backside of the marsh. However, analyses of five major storms at ES demonstrated that, within each event, the ability of the upper marsh to attenuate water level decreased with higher inundation heights. Additionally, small spatial scales of the marsh platform, geomorphological features such as channels, elevated surrounding forests and levees seem to play a major role in reducing the attenuation rates provided by the marshes. These results indicate that, while this type of marshland would provide storm surge attenuation during low inundation heights, these ecosystems would be less effective attenuating higher water depths from extreme events.

Numerical modeling of storm surge attenuation by mangroves in protected area of mangroves of Qheshm Island

With the experience of storm surges along Persian Gulf of Iran it is needed to simulate storms in coastal areas and study the protection techniques in order to protect communities and industrial facilities in coastal areas. Mangrove forests play a unique role in attenuating storm surge during tropical cyclones. MIKE21 FM is an applicable software for simulating cyclones within coastal environments. A hydrodynamic model is used to analyze the attenuating role of the protected area of mangroves between Gheshm Island and Khamir Port mangroves under a realistic conditions by updating the calibrated Manning's coefficient based on the land cover data to incorporate the mangrove effect with modifying bottom friction and characteristics of cyclone Gonu 2007 which is the strongest cyclone recorded in the Arabian Sea and Persian Gulf. In this research we measured the maximum surge levels in both scenarios (in situ conditions and the condition which mangrove forest is neglected); maximum storm tide reduction by mangroves (MSTRM) by mangroves and maximum storm tide reduction rate by mangroves (MSTRRM). Also inundation maps are presented aiming to measure the areas rescued from inundation and the areas inundated caused by mangroves. The simulations shows that the minimum and maximum storm tide reduction rate by mangroves are 5.32% and 34.88% respectively.

Quantification of the Attenuation of Storm Surge Components by a Coastal Wetland of the US Mid Atlantic

Coastal wetlands are receiving increased consideration as natural defenses for coastal communities from storm surge. However, there are gaps in storm surge measurements collected in marsh areas during extreme events as well as understanding of storm surge processes. The present study evaluates the importance and variation of different processes (i.e., wave, current, and water level dynamics with respect of the marsh topography and vegetation characteristics) involved in a storm surge over a marsh, assesses how these processes contribute to storm surge attenuation, and quantifies the storm surge attenuation in field conditions. During the Fall of 2015, morphology and vegetation surveys were conducted along a marsh transect in a coastal marsh located at the mouth of the Chesapeake Bay, mainly composed of Spartina alterniflora and Spartina patens. Hydrodynamic surveys were conducted during two storm events. Collected data included wave characteristics, current velocity and direction, and water levels. Data analysis focused on the understanding of the cross-shore evolution of waves, currents and water level, and their influence on the overall storm surge attenuation. Results indicate that the marsh area, despite its short length, attenuates waves and reduces current velocity and water level. Tides have a dominant influence on current direction and velocity, but the presence of vegetation and the marsh morphology contribute to a strong reduction of current velocity over the marsh platform relative to the currents at the marsh front. Wave attenuation varies across the tide cycle which implies a link between wave attenuation and water level and, consequently, storm surge height. Storm surge reduction, here assessed through high water level (HWL) attenuation, is linked to wave attenuation across the front edge of the marsh; this positive trend highlights the reduction of water level height induced by wave setup reduction during wave propagation across the marsh front edge. Water level attenuation rates observed here have a greater range than the rates observed or modeled by other authors, and our results suggest that this is linked to the strong influence of waves in storm surge attenuation over coastal areas.

Sensitivity considerations and the impact of spatial scaling for storm surge modeling in wetlands of the Mid-Atlantic region

Among the many activities in the recent efforts to evaluate coastal resiliency is the study of the capacity of wetlands and coastal marshes to attenuate storm surge. The development of an acceptable index or attenuation rate for coastal flooding is complicated by the many factors that contribute to maximum surge elevation, inundation extent and duration, including storm characteristics (e.g. track, size, forward speed, duration, central low pressure) and local features including topo-bathymetry, land-cover, barrier islands, channels, lagoons and inlets. For this study, we investigated the impact of spatial scaling, mesh resolution, storm characteristics and bottom friction on storm surge in wetland areas in the barrier island system of the Delmarva Peninsula using the coupled hydrodynamic-wave model (ADCIRC + SWAN). Synthetic storms derived from hindcasts of historical storms affecting this region were used for model forcing through multi resolution meshes recreating the complex wetland areas exposed to varying degrees of ocean surge through natural breaks in the barrier islands. Sensitivity to mesh resolution and bottom friction were evaluated for regional attributes and storm characteristics, confirming the results of previous studies. Results suggest inlet configuration and exposure to ocean surge are dominant factors for surge propagation through small scale wetlands and barrier island systems for weak to moderate storms. Attenuation rates observed for weaker storms, were influenced secondarily by the complex geometry of channels, lagoons and the presence and continuity of marshes. Results evaluating greater surge produced by stronger storms, even of less than a meter of storm surge increase, indicate that the mitigating impacts of local features are greatly diminished. Our results indicate that although the back bays systems in the Delmarva Peninsula and similar ecosystems in the US East Coast could provide storm surge attenuation for annual storm events, its use in coastal engineering protection may require a case by case analysis due to the high dependence on local characteristics.

Assessing the relevance of wetlands for storm surge protection: a coupled hydrodynamic and geospatial framework

The expectation that wetlands can protect coastal communities has been a major topic in the effort to evaluate innovative methods of mitigating coastal impacts from storm surge. Recent investigations have shown that there is a potential flood mitigation benefit to be gained from the presence of marshes. Though the extent of that benefit is not yet clearly defined, prioritizing wetland systems for coastal protection requires a consideration of the interactions between communities at risk of storm surge damage and wetland areas of sufficient spatial scales to reliably attenuate storm surge. Here, a framework is proposed for geospatial characterization of these interactions based on numerical model results and is applied to Virginia’s Chesapeake Bay region. Spatial identification of Chesapeake Bay wetlands was derived from four nationally available datasets (National Wetland Inventory, National Land Cover Dataset, Coastal Change Analysis Program, and NOAA’s Wetland Potential database). Maps of maximum storm tides for four historical storms were generated based on a coupled hydrodynamic wave model (ADCIRC–SWAN), validated for those storms with a mean root mean square error of 0.44 m. Population information was extracted from US Census block data in FEMA’s HAZUS Multi-Hazard geodatabase. Results from geospatial analysis of the relationships between wetland land cover, inundation, and population were used to identify where interactions with coastal populations are relevant for the study area when spatial limitations are considered. Approximately 1160 sq. km of wetlands were inundated by all four storms. Total population present in a range of proximities (200, 400, and 600 m) to flooded wetlands was used as a metric to evaluate the effect of a range of limitations on wetland size (5–50 sq. km) on potential population protected. A high level of uncertainty was seen due to wetland dataset selection (number of standard deviations from the mean ranged from 0.04 to 1.37), owing to high variability in spatial delineation/configuration of wetlands. Applying the framework to the Virginia Chesapeake Bay region yields an index of potential protection based on spatial scale limitations. For example, such an evaluation for wetlands meeting the 5 sq. km limitation (disregarding wetlands <5 sq. km) indicates that the presence of wetlands offers a potential protection for 3.4 % of the population. An application of the index on a more local scale indicates that the interaction of the flooded wetlands with more populated localities is such that the coastal marshes in Hampton Roads and Gloucester may offer protection to nearby coastal communities. This framework demonstrates that effective surge protection from wetlands and marshes is related to a combination of the incidence of storm surge inundation, proximity to coastal communities, and the relationship of sufficient spatial scales for surge attenuation.