Unpacking storm damages on a developed shoreline: Relating dune erosion and urban runoff

Hurricane Matthew (2016) caused significant beach and dune erosion from Cape Hatteras, North Carolina, USA, to Cape Canaveral, Florida, USA. At Myrtle Beach, South Carolina, the storm caused beach recession, and much of the southern half of the city’s beaches appeared to be overwashed in post-storm surveys. Around half of the city’s beaches appeared overwashed following the storm; however, the Storm Impact Scale (SIS; Sallenger 2000) applied to a pre-storm elevation model suggests less than 10% of the city’s beaches should have experienced overwash. Spatial analysis of elevation and land cover data reveals dunes that were “overwashed” during Matthew drain from watersheds that are >35% impervious, where those showing only dune recession are <5% impervious. The densely developed downtown of Myrtle Beach sits on a low seaward-sloping terrace. Additionally, indurated strata beneath the downtown area can prevent groundwater from draining during excessive rain events. As a result, the most continuous impervious surface cover and near-surface strata lie within a half-kilometer of the beach and drain directly to the backshore. Along the U.S. Southeast coast, this is somewhat rare; many coastal systems feature a lagoon or low-lying bottomland along their landward border, which facilitates drainage of upland impervious surfaces following storm passage. At Myrtle Beach, all of the stormwater runoff is drained directly to the beach through a series of outfall pipes. Many of the outfall pipes are located along the backshore, near the elevation of storm surge during Matthew. Runoff from Matthew’s heavy rains was observed causing ponding on the landward side of the foredune and scouring around beach access walkways. Based on these observations, the severe dune erosion experienced near downtown Myrtle Beach during Hurricane Matthew may have been caused by runoff and/or groundwater flux rather than overwash. These results highlight an unexpected relationship between upland conditions and dune erosion on a developed shoreline. That is, dune erosion can be caused by mechanisms beside overwash during storm events.

Myrtle Beach: A history of shore protection and beach restoration

The City of Myrtle Beach (South Carolina, USA) initiated a three-phase plan for beach restoration in the 1980s: Phase 1 — small-scale beach scraping; Phase 2 — mediumscale nourishment by trucks using inland sand; and Phase 3 — large-scale nourishment by dredge using offshore sand. Phases 1 and 2 were locally funded and served as interim measures (1981-1996) until a 50-year federal project could be constructed (1997 to present). In the course of this work, the city pioneered several approaches to beach management and became a model for the state. These include: the prototype SC beach survey program; the profile volume method for determining shorelines in the presence of seawalls, which was codified in the Beach Management Act (BMA) of 1988; the first locally funded nourishment (1986-1987) and FEMA-funded postdisaster renourishment after Hurricane Hugo 1989-1990; and the first surveys of offshore deposits for nourishment. Before restoration, nearly 65% of the 9-mile (14.5 kilometer) oceanfront was armored with seawalls, bulkheads, and revetments (1981). After nourishment, erosion control structures are now buried and fronted by a vegetated storm berm, while a wider beach accommodates millions of visitors each year. Total volumes and adjusted costs of nourishment from 1986 to early 2018 are 4,997,201 cubic yards (3,820,360 m3) and ~$70.8 million ($2018), respectively. On a unit annual beach length basis, the cost of beach restoration and improvement has averaged $46.80 per one foot of shoreline per year (~$153.50/m/yr) ($2018). Oceanfront property values on a unit length of shoreline basis presently range from ~$15,000/ft (~$49,200/m) for single-family homes to ~$75,000/ft (~$250,000/m) for high-rise buildings, suggesting that beach maintenance has cost well under 0.5% of oceanfront property values per year. Sand loss rates have averaged ~0.8 cy/ft/yr (2.0 m3/m/yr), and the rate of nourishment has been more than adequate to keep up with the ~0.37 ft (0.11 m) sea level rise between 1980 and 2018.

Hydrodynamic Drivers of Dissolved Oxygen Variability within a Tidal Creek in Myrtle Beach, South Carolina

Beach erosion and water quality degradation have been observed in Singleton Swash, a tidal creek that traverses the beach-face connecting land and ocean in Myrtle Beach, SC. The objective of this study in Singleton Swash is to explore relationships between water quality and hydrodynamics, where the latter are influenced by beach face morphology. We measure water velocities, water levels, and dissolved oxygen concentrations (DO) (a proxy for water quality) and apply correlation analysis to examine the relationships between physical processes and dissolved oxygen variations. Results show that larger tidal ranges are associated with higher mean levels of DO in the tidal creek. The larger tidal ranges are linked to larger magnitude currents, which increase both the DO transport via larger fluxes of oxygenated oceanic water into the swash and the magnitude of Reynolds shear stresses; due to tidal asymmetries, flood currents are stronger than ebb currents in this system. Based on these results, it is concluded that the combined transport of oxygenated waters into the tidal creek from the ocean on large flood tides and subsequent mixing due to large Reynolds shear stresses result in the observed net DO concentration increases in the creek over tidal cycles.

A Meteotsunami Climatology along the U.S. East Coast

Meteotsunamis are atmospherically forced ocean waves with characteristics similar to seismic tsunamis. Several recent hazardous meteotsunamis resulted in damage and injuries along U.S. coastlines, such that the National Oceanic and Atmospheric Administration (NOAA) is investigating ways to detect and forecast meteotsunamis to provide advance warning. Better understanding meteotsunami occurrence along U.S. coastlines is a necessary step to pursue these objectives. Here a meteotsunami climatology of the U.S. East Coast is presented. The climatology relies on a wavelet analysis of 6-min water-level observations from 125 NOAA tide gauges from 1996 to 2017. A total of 548 meteotsunamis, or about per year, were identified and assessed using this approach along the U.S. East Coast. There were a total of 30 instances when gauges observed waves of more than 0.6 m, which is assumed to be a potentially impactful event, and several cases with wave heights more than 1 m. Tide gauges along the open coast observed the most frequent events, including more than five events per year at Atlantic City, New Jersey; Duck, North Carolina; and Myrtle Beach, South Carolina. The largest waves were observed by gauges in estuaries that amplified the meteotsunami signal, such as those in Providence, Rhode Island, and Port Canaveral, Florida. Seasonal trends indicate that meteotsunamis occur most frequently in the winter and summer months, especially July. This work supports future meteotsunami detection and warning capabilities at NOAA, including the development of an impact catalog to aid National Weather Service forecasters.

Aviation Connectivity Impacts on Regional Economies in the United States

This paper uses applied microeconomics techniques to investigate the impact of aviation connectivity on 548 regional economies in the United States. Using lagged socioeconomic variables to instrument for future aviation connectivity, the paper finds a significant impact of connectivity on long-run economic growth. An increase of 100 in the city’s Global Connectivity Index is associated with an increase in long-term total personal income of the city by up to $254,350,000, and up to 613 more jobs. For a city like Myrtle Beach, SC, with a connectivity index close to the mean connectivity levels of core-based statistical areas, a 100-point increase in the index represents a 1.03% increase in air connectivity. The paper also finds evidence suggesting that the impact of connectivity on regional economies is significantly more pronounced in the largest 100 cities, whereas these effects vanish in smaller cities.

Model Results and Software Comparisons in Myrtle Beach, SC Using Virtual Beach and R Regression Toolboxes

Utilizing R software and a variety of data sources, daily forecasts of bacteria levels were developed and automated for beach waters in Myrtle Beach, SC. Modeled results are then shown for beach locations via a website and mobile device app. While R provides a robust set of tools for use in forecast modeling, the software has an extensive learning curve and requires skilled statistical interpretation of results. The Environmental Protection Agency (EPA) created the “Virtual Beach” software package to address these concerns. To evaluate the utility of the more user-friendly Virtual Beach modeling toolbox, predictive models were developed and model results were analyzed using the two software suites. Recommendations were made based on ease of use and several performance measures. Model results indicate the two software toolboxes yield comparable outputs. However, Virtual Beach tends to create more robust model forecasts, while R provides more options for model setup and outputs.

Long Bay Hypoxia Monitoring Consortium

In October 2011, the coastal municipalities of North Myrtle Beach, Myrtle Beach, Surfside, and Horry County signed a resolution, under the aegis of their Coastal Alliance of mayors, to develop and implement the Long Bay Hypoxia Monitoring Consortium. The goal of this consortium is to support monitoring and studies that further characterize hypoxia and its causes in Long Bay. The baseline data will enable assessments of water quality management efforts. Monitoring stations are to be maintained at three piers, Cherry Grove (NMB), Apache (Horry County), and Second Ave N. Pier (Myrtle Beach). Turbidity and chlorophyll sensors will be deployed at two piers and radon detectors at three piers. All piers will have weather stations. Data will be accessible via a real-time public website. Biological responses to low dissolved oxygen (DO) will be assessed via monitoring of larval recruitment and net plankton. The S.C. Department of Natural Resources (SCDNR) is also conducting creel surveys at the piers. These efforts are being coordinated with a marine education outreach campaign that includes signage at the piers, presentations at pier events, and web-based content.