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Kriebel, D.L. and Geiman, J.D., 2014. A coastal flood stage to define existing and future sea-level hazards. This paper explores the possible definition of a generic coastal flood stage (FS), an elevation at which significant flooding of local infrastructure is initiated, for regional or nationwide use in flood hazard analysis. By using monthly National Oceanic and Atmospheric Administration tidal gauge data from several coastal locations, a coastal FS based on the statistics of extreme high water events is proposed. This statistical FS is then compared to moderate and major FSs established by the National Weather Service with good agreement. Once adopted, the FS serves as a less ambiguous reference elevation or threshold to which the flooding potential of future storm events and sea-level rise can be compared and allows for consistent comparison between different sites. [ABSTRACT FROM AUTHOR]

Thirty years of monitoring surveys and shoreline erosion studies (1980-2010) along the South Carolina coast show that artificial beach nourishment and the natural process of inlet shoal bypassing have advanced the shoreline along most of the developed beaches and barrier islands. Of the ~98 mi (~161 km) of developed beaches (including public parks), fully 80% were much healthier in 2010 than in 1980, as evidenced by burial of seawalls, wider berms, and higher dunes. About 15% of the developed beaches are in approximately the same condition as in 1980; the remaining ~5% are considered in worse condition. The balance of South Carolina beaches (~89 mi, ~146 km) are principally wilderness areas with limited public access. The dominant condition of wilderness beaches is high erosion; limited new sand inputs, particularly via inlet bypassing; and accelerated recession as many of these sand-starved beaches wash over salt-marsh deposits. High erosion results from a combination of sand losses to the lagoon, winnowing of muddy marsh deposits outcropping across the receding beach, and longshore transport losses to the adjacent inlet. An estimated 75% of the undeveloped beaches in 2010 were well landward of their 1980 positions. Between 1980 and 2010, -39.4 million yd³ (~30.1 million m³) of beach nourishment from external sources was added to developed and park beaches (~62.6 mi, ~102.6 km). This is equivalent to an addition of ~168 ft (~51 m) of beach width in the nourished areas. Natural shoal bypassing events appear to have added a similar magnitude of new sand along accreting beaches. Bypassing events at some beaches involved -2~5 million yd³ (1.5-3.8 million m³). Ebb dominance at many South Carolina inlets is shown to play an important role in preserving the littoral sand budget, maintaining large sand reservoirs for bypassing and helping maintain the developed beaches in the state. Low rates of erosion in other areas, such as the Grand Strand, combined with large-scale nourishment have advanced those beaches well beyond historic conditions. [ABSTRACT FROM AUTHOR]

As sea level rise accelerates and land development intensifies along coastlines, tidal wetlands will become increasingly threatened by coastal squeeze. Barriers that protect inland areas from rising sea level prevent or reduce tidal flows, and impermeable surfaces prevent wetland migration to the adjacent uplands. As vegetation succumbs to submergence by rising sea levels on the seaward edge of a wetland, those wetlands prevented from inland migration will decrease in area, if not disappear completely. Tools to identify locations where coastal squeeze is likely to occur are needed for coastal management. We have developed a ''Coastal Squeeze Index'' that can be used to assess the potential of coastal squeeze along the borders of a single wetland and to rank the threats faced by multiple wetlands. The index is based on surrounding topography and impervious surfaces derived from light detection and ranging and advanced spaceborne thermal emission and reflection radiometry imagery, respectively, and uses a fuzzy logic approach. We assume that coastal squeeze varies continuously over the coastal landscape and tested several fuzzy logic functions before assigning a continuous weight, from 0 to 1, corresponding to the influence of slope and impervious surfaces on coastal squeeze. We then combined the ranked variables to produce a map of coastal squeeze as a continuous index. Using this index, we compare the present and future threat of coastal squeeze to marshes in Wells and Portland, Maine, in the United States and Kouchibouguac National Park in New Brunswick, Canada. [ABSTRACT FROM AUTHOR]

Coastal flood risk in California is concentrated around urbanized embayments that are protected by infrastructure, such as levees, pumps, and flood walls, which pose a challenge to accurate flood prediction. A capability to predict coastal urban flooding at the parcel-scale (individual home or street) from high ocean levels (extreme high tides) is shown here by coupling a regional ocean forecasting system to an embayment-scale hydrodynamic model that incorporates detailed information about flood defenses. A unique flooding data set affords the rare opportunity to validate model predictions and allows us to identify model data that are essential for accurate forecasting. In particular, results show that flood defense height data are critical, and here, that information is supplied by a Real Time Kinematic Global Positioning System (RTK-GPS) survey, which yields ca. 1-cm, vertical root mean-squared error accuracy. Bathymetry surveys and aerial Light Detection and Ranging (LIDAR) data characterizing the embayment also prove essential. Moreover, hydrodynamic modeling of flood inundation is shown to significantly improve on planar surface models, which overestimate inundation, particularly when manipulated to account for run-up in a simplistic way. This is attributed to the transient nature of overtopping flows and motivates the need for dynamic, spatially-distributed overtopping models that are tailored to the urban environment. [ABSTRACT FROM AUTHOR]