Jennifer L. Irish

The Influence of Storm Size on Hurricane Surge

Over the last quarter-century, hurricane surge has been assumed to be primarily a function of maximum storm wind speed, as might be estimated from the Saffir–Simpson hurricane scale. However, Hurricane Katrina demonstrated that wind speed alone cannot reliably describe surge. Herein it is shown that storm size plays an important role in surge generation, particularly for very intense storms making landfall in mildly sloping regions. Prior to Hurricane Katrina, analysis of the historical hurricane record evidenced no clear correlation between surge and storm size, and consequently little attention was given to the role of size in surge generation. In contrast, it is found herein that, for a given intensity, surge varies by as much as 30% over a reasonable range of storm sizes. These findings demonstrate that storm size must be considered when estimating surge, particularly when predicting socioeconomic and flood risk.

Scanning laser mapping of the coastal zone: the SHOALS system

The SHOALS system uses lidar technology to remotely measure bathymetry and topography in the coastal zone. During five years of survey operations, SHOALS has demonstrated airborne lidar bathymetrys benefits to the coastal community by providing a cost-effective tool for comprehensive assessment of coastal projects. This paper discusses the application of lidar technology for water-depth measurement, specifically outlining the SHOALS system and introducing a SHOALS survey from Saco River, ME.

Uncertainty in hurricane surge simulation due to land cover specification

Hurricane storm surge is one of the most costly natural hazards in the United States. Numerical modeling to predict and estimate hurricane surge flooding is currently widely used for research, planning, decision making, and emergency response. Land cover plays an important role in hurricane surge numerical modeling because of its impacts on the forcing (changes in wind momentum transfer to water column) and dissipation (bottom friction) mechanisms of storm surge. In this study, the hydrodynamic model ADCIRC was used to investigate predicted surge response in bays on the central and lower Texas coast using different land cover data sets: (1) Coastal Change Analysis Program for 1996, 2001, and 2006; (2) the National Land Cover Dataset for 1992, 2001, and 2006; and (3) the National Wetlands Inventory for 1993. Hypothetical storms were simulated with varying the storm track, forward speed, central pressure, and radius to maximum wind, totaling 140 simulations. Data set choice impacts the mean of maximum surges throughout the study area, and variability in the surge prediction due to land cover data set choice strongly depends on storm characteristics and geographical location of the bay in relation to storm track. Errors in surge estimation due to land cover choice are approximately 7% of the surge value, with change in surge prediction varying by as much as 1 m, depending on location and storm condition. Finally, the impact of land cover choice on the accuracy of simulating surges for Hurricane Bret in 1999 is evaluated.

Tropical Cyclone Storm Surge Risk

Tropical cyclone storm surge represents a significant threat to communities around the world. These surge characteristics vary spatially and temporally over a range of scales; therefore, conceptual frameworks for understanding and mitigating them must be cast within a context of risk that covers the complete range of hazards, their consequences, and methods for mitigation. A review of primary overlapping time scales and associated spatial scales for tropical cyclone surge hazards covers two scales of particular interest: (1) synoptic-scale predictions used for warnings and evacuation decisions and (2) long-term estimation of hazards and related risks needed for coastal planning and decision-making. Factors that can affect these estimates, such as episodic variations in tropical cyclone characteristics and longer-term climate change and sea-level rise are then examined in the context of their potential impacts on hazards and risks related to tropical cyclone surges.

ACCURACY OF SAND VOLUMES AS A FUNCTION OF SURVEY DENSITY

A study of alternatives including a shoreline evolution numerical modelization has been carried out in order to both diagnose the erosion problem at the beaches located between Cambrils Harbour and Pixerota delta (Tarragona, Spain) and select nourishment alternatives.

Method for Estimating Future Hurricane Flood Probabilities and Associated Uncertainty

AbstractReliable hurricane flood probability estimates are essential for effective management and engineering in the coastal environment. However, uncertainty in future climate conditions presents a challenge for assessing future flood probabilities. Studies suggest that in the future, sea-level rise may accelerate, and hurricanes may intensify and occur less or more often. Here, methods are presented for incorporating sea-level rise and future hurricane conditions into extreme-value flood statistics analysis. By considering an idealized coast, surge response functions are used with joint probability statistics to define time-varying continuous probability mass functions for hurricane flood elevation. Uncertainty in the flood estimates introduced by uncertainty in future climate is quantified by considering variance in future climate and sea level projections. It will be shown that future global warming can increase the flood elevation at a given return period by 1–3% per decade, but that climate-related ...

Comparison of Shoreline Change Rates along the South Atlantic Bight and Northern Gulf of Mexico Coasts for Better Evaluation of Future Shoreline Positions under Sea Level Rise

ABSTRACT Passeri, D.L.; Hagen, S.C.; and Irish, J.L., 2014. Comparison of shoreline change rates along the South Atlantic Bight and Northern Gulf of Mexico coasts for better evaluation of future shoreline positions under sea level rise. Shoreline change rates established by the USGS Coastal Vulnerability Index (CVI) (Thieler and Hammar-Klose, 1999; Thieler and Hammar-Klose, 2000), the USGS National Assessment of Shoreline Change (Morton et al., 2004; Morton and Miller, 2005) and erosion rates estimated using the Bruun Rule (Bruun, 1962) are compared along sandy shorelines of the U.S. South Atlantic Bight and Northern Gulf of Mexico coasts. The intent of the study is not to regard one method better than another, but rather to explore similarities and differences between the methods. Based on the comparison, the following recommendations are offered for quantifying future shoreline positions under sea level rise(SLR). In areas where long-term erosion rates correspond well with rates predicted by the Bruun Rule, shoreline retreat can be assumed to be completely attributed to forces related to SLR and the Bruun Rule can be applied to estimate future shoreline positions under SLR scenarios. If long-term erosion rates are higher than the rates predicted by the Bruun Rule, a hybrid approach can be taken to include a factor for background erosion due to influences other than SLR. Lastly, care should be taken when extrapolating shoreline change rates determined by the CVI or National Assessment of Shoreline Change to predict future shoreline positions. CVI rates may be projected when considering extreme future SLR scenarios, as they are typically larger than the long-term historic rates.

Experimental study of wave dynamics in coastal wetlands

This paper presents laboratory experiments of wave-driven hydrodynamics in a three-dimensional laboratory model of constructed coastal wetlands. The simulated wetland plants were placed on the tops of conically-shaped mounds, such that the laboratory model was dynamically similar to marsh mounds constructed in Dalehite Cove in Galveston Bay, Texas. Three marsh mounds were placed in the three-dimensional wave basin of the Haynes Coastal Engineering Laboratory at Texas A&M University, with the center of the central wetland mound located in the center of the tank along a plane of symmetry in the alongshore direction. The experiments included two water depths, corresponding to emergent and submerged vegetation, and four wave conditions, typical of wind-driven waves and ocean swell. The wave conditions were designed so that the waves would break on the offshore slope of the wetland mounds, sending a strong swash current through the vegetated patches. Three different spacings between the wetland mounds were tested. To understand the effects of vegetation, all experiments were repeated with and without simulated plants. Measurements were made throughout the nearshore region surrounding the wetland mounds using a dense array of acoustic Doppler velocimeters and capacitance wave gauges. These data were analyzed to quantify the significant wave height, phase average wave field and phase lags, wave energy dissipation over the vegetated patches, mean surface water levels, and the near-bottom current field. The significant wave height and energy dissipation results demonstrated that the bathymetry is the dominant mechanism for wave attenuation for this design. The presence of plants primarily increases the rate of wave attenuation through the vegetation and causes a blockage effect on flow through the vegetation. The nearshore circulation is most evident in the water level and velocity data. In the narrowest mound spacing, flow is obstructed in the channel between mounds by the mound slope and forced over the wetlands. The close mound spacing also retains water in the nearshore, resulting in a large setup and lower flows through the channel. As the spacing increases, flow is less obstructed in the channel. This allows for more refraction of waves off the mounds and deflection of flow around the plant patches, yielding higher recirculating flow through the channel between mounds. An optimal balance of unobstructed flow in the channel, wave dissipation over the mounds, and modest setup in the nearshore results when the edge-to-edge plant spacing is equal to the mound base diameter.

Physical Characteristics of Coastal Hazards

Coastal hazards are among the world’s most threatening hazards. With half of the world’s population living near the coast, an immense threat is posed by these hazards to life and health, livelihood, and the economy. In this chapter, characteristics of coastal hazards are described, first by presenting a historical context, then by laying out our current understanding of the physical problems of interest for coastal design, and finally by presenting simple methods for initial interpretation of the hazard. A number of natural processes and anthropogenic activities adversely impact coastal communities, critical infrastructure, and port facilities along the coast. Natural coastal hazards may generally be classified into those that are episodic and those that occur over long periods of time. Episodic hazards include coastal storms and tsunamis while long-term hazards include, for example, sea-level rise . Many anthropogenic activities also result in long-term impacts at the coast. For example, inland dam construction produces long-term impacts on coastal sediment supply. In the following, we describe the most common coastal hazards and then discuss methods for evaluating their impacts at the coast.

Observations from the 2009 Samoa Tsunami: Damage Potential in Coastal Communities

The September 2009 tsunami devastated the Samoan Islands. Damages observed in eighteen coastal villages following this natural disaster are presented. Using observations and idealized numerical simulations, four main conclusions are drawn regarding tsunami damage patterns in these communities. First, for coastal regions with steep terrain, damage to structures is a function of distance from the shoreline, elevation, construction, and topographic conditions. Second, in those villages where inundation is confined by topography (steep bluffs or mountains), damage is more severe. Third, when inundation is unconfined by topography, damage potential (capacity to cause damage, should buildings of a certain construction be present) in these villages increases with decreasing mean topographic slope. Fourth, run-up height and flood elevation may not be the best indicator of damage potential in these villages, which are characterized by irregular topography. Finally, a damage potential formulation is presented which...