Ospino, S.; Restrepo, J.C.; Otero, L.; Pierini, J., and Alvarez-Silva, O., 2018. Saltwater intrusion into a river with high fluvial discharge: A microtidal estuary of the Magdalena River, Colombia.

The Magdalena River (Bocas de Ceniza) forms a microtidal estuary subjected to numerous interventions aimed to guarantee navigability towards the port of Barranquilla, Colombia. Significant sedimentation processes are still frequent in this area, however. Understanding the dynamics of both saltwater intrusion and mixing conditions is a fundamental requisite to understanding the sedimentation dynamics in these types of estuaries. The effects of river discharge, tide, and winds on stratification patterns, and mixing and saltwater intrusion dynamics in the estuary of the Magdalena River were evaluated, focusing on the effects of river discharge variability. The three-dimensional hydrodynamic model MOHID was implemented, and calibration and validation of the model were carried out using in situ velocity, temperature, and salinity data, obtaining Skill values greater than 0.90. To cover a wide range of variability in the main forcing factors (fluvial discharge, tide, and wind), the conditions recorded in 2010 were simulated when both phases of the El Niño–Southern Oscillation phenomenon occurred. During that year, the river discharge ranged between 2465 and 16,463 m³ s⁻¹. Results revealed a stratified, saltwater wedge estuary, the dynamics of which were mainly dominated by river discharge. Tide and winds altered saltwater intrusion dynamics, mainly during low-discharge periods.

Kelley, J.T.; Kelley, A.R.; Sorrell, L.; Bigelow, G., and Bampton, M., 2018. Evidence for a former transgressive dune field: Shetland Islands, United Kingdom.

Transgressive sand dunes result from a large disturbance of a significant coastal sand dune field. Sand blows landward, covering whatever it encounters, including agricultural fields, forests, or human habitations. This investigation is of a beach-dune system in the Shetland Islands of northern Scotland that is known from historic documents and archaeological excavations to have experienced a sand invasion during the Little Ice Age (LIA). Ground-penetrating radar observations suggest remnants of pre-LIA dunes and buried soils. Excavation of dunes and optically stimulated luminescence (OSL) dating of sand deposits confirm historic accounts but also document that the “event” lasted centuries. Geomorphological observations and OSL dates also indicate that earlier events occurred in this region, sometimes in association with known archaeological sites like Old Scatness and Jarlshof. Although the site studied is stable now, a sand invasion could occur again owing to increased storminess, removal of dune vegetation, or both. Mining of the dunes for aggregate places the contemporary beach in a more vulnerable position than earlier.

Sherwood, C.R.; Warrick, J.A.; Hill, A.D.; Ritchie, A.C.; Andrews, B.D., and Plant, N.G., 2018. Rapid, remote assessment of Hurricane Matthew impacts using four-dimensional structure-from-motion photogrammetry.

Timely assessment of coastal landforms and structures after storms is important for evaluating storm impacts, aiding emergency response and restoration, and initializing and assessing morphological models. Four-dimensional multiview photogrammetry, also known as structure from motion (4D SfM), provides a method for generating three-dimensional reconstructions of landscapes at two times (before and after events) using only photos and existing information for ground control points. Here, these techniques were applied using National Oceanic and Atmospheric Administration (NOAA)-obtained oblique aerial photos taken before (2015) and immediately after Hurricane Matthew (2016) to assess coastal changes near Matanzas, Florida. This work demonstrated that 3D digital elevation models can be constructed within 48 hours of postevent photo collection without on-site ground control measurements. One advantage of timely SfM elevation-change assessments is that they avoid confusion of storm impacts with changes that occur after the event but before LIDAR surveys can be performed. The accuracy and precision of the 4D SfM maps were assessed a posteriori using the first-available LIDAR data, which were collected more than a month after the hurricane, and 11 independent ground-truth survey points measured a week after the hurricane. Horizontal coordinates of the 4D SfM reconstruction were biased by an average of 0.79 m (0.83 m root-mean-square difference; RMSD) compared with the ground-truth points, but vertical elevations were more accurate. They were biased from the LIDAR by −0.09 to −0.25 m, with ∼0.20 m RMSD from both the LIDAR data and five ground-truth points with good vertical positioning and 0.25 m RMSD from LIDAR data along a 60-m stretch of pavement. This level of precision was sufficient to quantify geomorphological change that was often in excess of 1 m. The methodology is conducive for rapid assessment of changes along short stretches (tens of kilometers) of coast with modest resources and could be scaled up for larger regions.

Dao, T.; Stive, M.J.F.; Hofland, B., and Mai, T., 2018. Wave damping due to wooden fences along mangrove coasts.

In the Mekong Delta, as in many other mangrove settings, wooden fences are considered beneficial coastal structures to provide sheltering for mangrove replantation efforts by reducing waves and currents and promoting sedimentation. One of the most quantitative previous studies on fence-induced wave reduction offered a first understanding of relevant process parameters. The present application of the advanced numerical time-domain wave model SWASH increases this understanding substantially and explains previously unexplained phenomena that were encountered in this earlier study. The findings reveal that wave damping increases with increasing fence thickness and with increasing density of the woody material in the fences. It further shows that the transmitted wave height (represented by the transmission coefficient) is inversely proportional to the Ursell number, implying that nonlinear waves are damped more effectively.

Mattheus, C.R. and Yovichin, R.D., III, 2018. Hurricane trajectory and irregular bedrock topography as drivers of washover fan geomorphology on an isolated carbonate platform.

Although washover fan geomorphology is widely studied along sandy passive continental margins, little is known about rocky carbonate platform analogs. This paper addresses the multidecadal evolution of a compound washover fan complex on San Salvador Island, an isolated and hurricane impact–prone Bahamian carbonate platform. Its geomorphic development is assessed from pre– and post–Hurricane Joaquin topographic measurements, historic aerial photographs, ground-penetrating radar imagery, and sediment cores. Survey information provides insight into event-based surficial processes, while subsurface mapping and aerial photography offers a window into past events. Hurricane Frances left the fan largely unmodified in 2004, whereas the comparably strong Hurricane Joaquin was affiliated with heavy scouring of the fan apex and extensive accretion across the distal fan in 2015. Mimicking the surficial geomorphic changes affiliated with Joaquin, a superposition of five distinct event-based depositional units is elucidated from subsurface architectures. Cores from the distal, subaqueous fan sample interbedded lagoon muds and overwash sands, while truncated subsurface radar units near the fan apex map erosional events. The susceptibility of this particular island locale to repeated modification relates to the irregularity of the carbonate bedrock terrain, which funnels surge waters inland through low topography under favorable hydrodynamic conditions. These were met during the NE-trending Hurricane Joaquin, but not the NW-trending Frances. Storm characteristics, particularly trajectory, appear to play a significant role in determining overwash potentials along highly irregular bedrock-dominated coastlines. These implications for overwash dynamics must be considered and reconciled when attempting to reconstruct regional storm histories from coastal sedimentary archives.

Conlin, M.; Cohn, N., and Ruggiero, P., 2018. A quantitative comparison of low-cost Structure from Motion (SfM) data collection platforms on beaches and dunes.

Observations of beach and dune geomorphology are critical for characterizing coastal processes and hazards. A relatively new approach for monitoring the coastline is Structure from Motion photogrammetry (SfM), a technique that uses overlapping photographs to reconstruct three-dimensional surfaces. In this study, a quantitative comparison of multiple low-cost kite-, pole-, and unmanned aerial vehicle (UAV)–based SfM data collection platforms is performed to illuminate important considerations when choosing an SfM platform for use in measuring beach and dune topography. A multicriteria analysis based on SfM results and platform usability is used to complete this comparison. Results show that UAV-based platforms received high performance scores, largely because these stable, high-flying platforms provide images with adequate texture to allow accurate three-dimensional topographic reconstruction. Although data extracted from the kite- and pole-based systems are less accurate, these platforms possess increased usability because of decreased barriers to entry and fewer environmental limitations (in the case of the pole), which increases their overall performance. These results illustrate that the overall effectiveness of a platform is based on many factors beyond vertical error of extracted data, and factors of platform usability can be important to consider when choosing an SfM platform. Furthermore, this multiplatform analysis reveals the important idea that different platforms can be optimal for different applications depending on the study site and environmental conditions. As the technology progresses, many improvements to platforms are likely to emerge, allowing SfM to become an even more useful tool for the coastal scientist.

Ludeno, G.; Reale, F.; Raffa, F.; Dentale, F.; Soldovieri, F.; Carratelli, E.P., and Serafino, F., 2018. Integration between X-band radar and buoy sea state monitoring.

This article presents the results of an integrated buoy and X-band radar sea state monitoring activity carried out on the southern coast of Sicily. The work involved the integration of buoy and radar data, as well as the simultaneous acquisition of significant wave height (SWH) values from two similar radar sets located at a slight distance from each other—a rare and fortunate circumstance that took place during two storms in the winter 2014–2015. Good consistency and repeatability was reached between the two radars, and the reliability of X-band radar as a wave monitoring system was confirmed by the comparison with the buoy wave meter. Some knowledge has also been gained on the short spatial and temporal fluctuations of the sea state: while such “gustiness” or small scale storm variation (SSSV) cannot be easily discriminated from electromagnetic effects and from algorithm artefacts, some important progress has been made toward the identification of this phenomenon. Integration of various sensors is the key to a definite improvement of sea state monitoring for most coastal applications.

Bujan, N.; Cox, R.; Lin, L.-C.; Ducrocq, C., and Hwung, H.-H., 2018. Semiautomatic digital clast sizing of a cobble beach, Nantian, Taiwan.

Surface sediment data is scarce for beaches that are made of material close to the cobble size range, partly because of the difficulty of direct sampling for sediment size analysis. An object-detection tool for semiautomatic analysis of clast geometry, originally developed for riverbeds, was applied to the coarse-clastic beach of Nantian, Taiwan. Comparison of the software with digital point counts for the common size percentiles D₅, D₁₆, D₃₀, D₅₀, D₇₀, D₈₄, and D₉₅ indicated an average coefficient of determination of 0.990 over 10 test pictures. The surface sediment was digitally sampled at three cross-shore locations along the beach: near the shoreline, on the steep part of the beach face, and on the beach crest. Clast-size distributions, including clast area and elongation ratio, were computed from the geometry of 1000 clasts for each location and the cross-shore variance was captured. The combination of sediment characteristics with topographic measurements showed significant relations between bidimensional size and elongation of the sediments and morphology of the beach. The method can only access the clast geometry that is visible on pictures and cannot describe the full tridimensional shape. Despite this limitation, semiautomatic digital sizing is well suited to coarse-clastic beaches and has the potential to increase the understanding of coastal sedimentology over a wide range of sediment sizes.

Amante, C.J., 2018. Estimating coastal digital elevation model uncertainty.

Integrated bathymetric–topographic digital elevation models (DEMs) are representations of Earth's solid surface that extend across the coastal land–water interface. DEMs are fundamental to the modeling of coastal processes, including tsunami, storm-surge, and sea-level-rise inundation. Vertical errors in coastal DEMs are deviations in elevation values from the actual seabed or land surface, which originate from the (1) elevation measurements, (2) datum transformation that converts bathymetric and topographic measurements to a common vertical reference system, (3) spatial resolution of the DEM, and (4) interpolative gridding technique that estimates elevations in areas unconstrained by measurements. The magnitude and spatial distribution of the vertical errors are typically unknown, and a DEM uncertainty surface is a statistical assessment of the likely magnitude of these errors. The National Oceanic and Atmospheric Administration National Centers for Environmental Information develops DEMs for United States' coastal communities. This study describes a methodology to derive uncertainty surfaces that estimate coastal DEM vertical errors at the DEM cell–level. A coastal DEM south of Sarasota, Florida is the case study for deriving uncertainty surfaces. Results indicate that large vertical uncertainty exists in deeper waters offshore with sparse echo-sounder measurements, and small vertical uncertainty exists on flat terrains with dense light detection and ranging measurements. The estimated uncertainty can be propagated into the modeling of coastal processes that utilize DEMs by deriving numerous plausible DEM realizations within the uncertainty bounds. The numerous DEMs realizations can then produce an ensemble of coastal modeling results, and in turn, better-informed coastal management decisions.

Moskalski, S.; Floc'h, F.; Verney, R.; Fromant, G.; Le Dantec, N., and Deschamps, A., 2018. Sedimentary dynamics and decadal-scale changes in the macrotidal Aulne River estuary, Brittany, France.

Studies of macrotidal estuaries have been dominated by large, high-turbidity systems like the Gironde and Severn, but some macrotidal estuaries are different from these systems. The goal of this study was to document the state of hydrosedimentary processes in the macrotidal, low-turbidity Aulne River estuary and, where possible, compare it to a previous study. Study sites from a 1977 study were revisited in 2013. Observations of velocity, salinity, and suspended sediment concentration were analyzed and compared to the 1977 study, with particular attention given to hourly data. The results illustrate the impact of shallowing on hydrosedimentary processes. The estuary is strongly dominated by spring–neap variability and shallowing, with increasing tidal distortion in the landward direction and a turbidity maximum zone created by sediment resuspension. The maximum flooding and ebbing velocity were stronger and tidal velocity distortion was more pronounced than in 1977. The salinity intrusion moved farther landward during low discharge in 2013 than in 1977, but not during average and high discharge. Other hydrosedimentary processes remained consistent with the previous study. This study also illustrates potential problems that can occur when attempting to use historical analyses.

Li, J.; Pu, R.; Yuan, Q.; Liu, Y.; Feng, B.; Guo, Q.; Jiang, Y., and Ye, M., 2018. Spatiotemporal change patterns of coastlines in Xiangshan Harbor (Zhejiang, China) during the past 40 years.

As special and important landscape bodies, tidal inlets possess many coastal resources. Consideration of the maintenance and protection of coastline resources and the environment is a challenging research topic, i.e. how to reasonably and scientifically exploit and use coastal resources. In this study, multitemporal Landsat images were used to explore and quantify relationships between the intensity of human activities and coastline changes. Specifically, (1) the spatial location, length, and tortuosity of coastlines in Xiangshan Harbor (XH; Zhejiang Province, China) tidal inlets, from 1974 to 2014, were extracted from satellite images; (2) the coastline change indices and the intensity of human activities in the tidal inlet areas of XH were calculated and assessed; and (3) the relationships between coastline change characteristics and human activities during the past 40 years were explored and analyzed. The results demonstrated that, during the past four decades, as human activities have intensified, the natural coastlines in XH continuously shrank, whereas artificial coastlines increased and then gradually became stable. Various human activities have changed the morphology of local coastlines in XH, and the overall coastline tortuosity has been continuously reduced. The intensity of human activities increased from 1974 to 1998, and the intensity slowed after 1998. However, the impacts of human activities are extensive and almost cover the entire coastlines of the harbor. The correlations between the intensity of human activities and the overall length and tortuosity of the coastlines were significantly negative, which means that, as human activities intensified, the length and tortuosity of the coastlines decreased.

Kowalski, J.L.; DeYoe, H.R.; Boza, G.H., Jr.; Hockaday, D.L., and Zimba, P.V., 2018. A comparison of salinity effects from hurricanes Dolly (2008) and Alex (2010) in a Texas lagoon system.

Hurricanes are not uncommon along the Gulf of Mexico coast, but there are few studies of the effects they have on coastal embayments. Hurricanes Dolly (2008) and Alex (2010) were both Category 2 storms affecting the Lower Laguna Madre (LLM) of Texas. Surveys were performed to assess poststorm water quality after landfall of both storms at up to 18 sample stations. The main difference between storm effects was salinity reduction because of stormwater input from the watershed. Effects from Hurricane Dolly were of short duration and small magnitude, whereas the effects from Hurricane Alex were extensive and lasted more than a month. Differences in spatial patterns in salinity were significantly more pronounced across the LLM than were temporal differences. Precipitation of 50–100 cm caused stormwater discharge to exceed 1000 m s⁻¹ to the LLM during the Alex event and depressed salinity over more than three-fourths (ca. 500 km²) of the estuary for 2 months. Storm-related effects on water-column physiochemistry were persistently lowest near freshwater drains (Arroyo Colorado). Salinity remained less than 5 for more than 2 months during the Alex freshet. Freshwater input from Hurricane Dolly was relatively minor because the storm precipitation was largely restricted to the small Arroyo Colorado watershed. Effects from Alex were delayed but were greater because of the bulk of the precipitation falling in the Rio Grande/Rio Bravo drainage basin in México. The greatest impact from that freshwater disturbance was the loss of seagrasses after prolonged exposure to hyposalinity. Hurricanes Dolly and Alex both affected the LLM but with contrasting impacts that reflected spatial and meteorological differences between the two storms.

Long, A.; Xie, Q.; Yu, X.; Xiao, H., and Zhou, W., 2018. Nutrient exchange between sediments and overlying waters in the Modaomen estuary (China) over a complete semidiurnal tide cycle: Implications of saltwater intrusion.

Spatial and temporal variations of inorganic nutrients (, , , , and ) and some relevant environmental parameters, including temperature, salinity, pH, Eh, dissolved oxygen (DO), in surface sediments and overlying waters were investigated during the cruise held on 16 to 19 April 2016 over a complete tidal cycle (a spring and neap tide together) in the Modaomen estuary, Pearl River, China. It was found that the dominant component of dissolved inorganic nitrogen (DIN, expressed as sum of , , and ) was in sediment interstitial waters and in overlying waters. Overlying waters contained higher concentration of and lower concentrations of and than interstitial waters. The exchange flux of inorganic nutrients between sediments and overlying waters was calculated using the Fick diffusion equation. Exchange flux calculations revealed that sediments were the sources of , , and but the sink of and . However, nutrimental exchange flux variations were not obvious during the present tidal cycle. Results of correlation analysis of single factor and principal component analysis revealed that nutrimental exchange fluxes mainly depend on the nutrient concentration gradient and overlying water chemical environment due to high stratification of waters, obvious homogeneity of sediments, and relative weakness of bioturbation in the Modaomen estuary.

Choi, J.; Roh, M., and Hwang, H., 2018. Observing the laboratory interaction of undertow and nonlinear wave motion over barred and nonbarred beaches to determine beach profile evolution in the surf zone.

A vertically two-dimensional laboratory experiment was performed with a movable bed to investigate the interaction of undertow and sawtooth-shaped nonlinear wave motion over the cross-shore evolution of barred (storm) and nonbarred (normal) beach profiles. The bottom elevations, free-surface motion, and flow velocity were measured under regular wave conditions, excluding infragravity waves, over a movable bed. The observations were conducted in the surf zone during alternate repeats of the two wave conditions until each quasiequilibrium state was reached. From the net sediment transport of the observation area, it was shown that the storm case was in an erosion state and that the normal case was in an accretion state. The measurements confirmed that the strong undertow, which is a dominant factor in the offshore migration mechanism, was developed in the erosion state but that the undertow in the accretion state was weaker. The measurements also showed that in the shoaling zone, the symmetry of wave motion of the storm-erosion case was larger than that of the normal-accretion case; however, in the surf zone, the symmetry of wave motion of the normal-accretion case was larger than that of the storm-erosion case. In addition, the asymmetry of wave motion of the storm-erosion case was larger than that of the normal-accretion case in both regions. The onshore migration effect of the sawtooth-shaped nonlinear wave motion, which was relatively weak in the accretion state, was more significant than that in the erosion state, because the undertow was not enough strong in the accretion state.

Wernette, P.; Thompson, S.; Eyler, R.; Taylor, H.; Taube, C.; Medlin, A.; Decuir, C., and Houser, C., 2018. Defining dunes: Evaluating how dune feature definitions affect dune interpretations from remote sensing.

Coastal resiliency is the ability of a beach–dune system to recover to a previous state after a storm, and this resiliency is affected by prestorm beach and dune morphology and storm climate (i.e. storm frequency and intensity). Improvements in remote sensing technology such as LIDAR and structure from motion have enabled rapid collection and production of digital elevation models used to assess storm impact and recovery. Although rapid poststorm assessment requires a consistent approach for extracting dune morphology, relatively little attention has focused on defining the different parts of a dune. The goals of this paper are to examine how the definition of a dune feature drives the methodology used to extract dunes and to synthesize a comprehensive definition of dune features. An analysis of existing approaches for extracting beach and dune morphology demonstrates that there is considerable variation in how the beach–dune transition (i.e. dune toe) is defined. Many definitions are recursive or include ambiguous terminology, resulting in a dune toe or crest line position dependent on user interpretation of the definition. Other definitions rely heavily on user interpretation of dune features at varying stages in the feature extraction process. Reliance on visual interpretation can result in substantially different feature locations across different interpreters. Given the impact of varying definitions on dune resiliency assessments and legal implications for dune features location, this study proposes a series of semantic models for dune features. Semantic modelling of coastal morphology is vital for consistently and accurately assessing coastal recovery and predicting future coastal assessments on the basis of a consistent set of criteria.

Mylroie, J.E., 2018. Superstorms: Comments on Bahamian fenestrae and boulder evidence from the Last Interglacial.

Sea level during the last interglacial (Marine Isotope Substage 5e [MIS 5e]) was ∼6 m above present, interpreted to represent a warmer climate, with increased storm intensity and storm frequency. Two hypotheses have been advanced to demonstrate an increase in storm intensity during MIS 5e. The first considers fenestrae in eolian calcarenites at elevations up to 43 m in the Bahama Archipelago to be evidence of superstorm washover. Additional observations include rip-up clasts and loss of bedform and root structures as a result of wave scour. Such an event should produce a tempestite with a wide-ranging footprint, but none exists above 10 m. This paper argues that the fenestrae are rainfall slurries, rip-up clasts are weathering products of calcarenite protosol development, and bed-form and root structure absence or presence reflects transgressive-phase vs. regressive-phase eolian formation, respectively. In the second case, a 2-km section of the coast of Eleuthera Island contains boulders proposed to have been tossed upward onto the land by superstorm waves, creating an age inversion of older boulders lying on younger rock. These boulders are now karrentisch and rest on pedestals produced by denudation. To emplace them would require extreme energies, but other interpretations such as fossil tower karst and boulders rolling downslope remain viable alternatives. The proposed chronology of boulder emplacement at the end of MIS 5e conflicts with the field evidence of a terra rossa paleosol separating the pedestals and the boulders. A recent paper has argued that normal hurricane activity could have emplaced the boulders. Both of these interpretations fail to explain the lack of similar-sized boulders elsewhere in the Bahama Archipelago. The failure to account for past coastline configuration, cave development in the boulders, and post-MIS 5e boulder denudation makes both boulder analyses incorrect, as discussed herein.

Lindner, B.L.; Johnson, J.; Alsheimer, F.; Duke, S.; Miller, G.D., and Evsich, R., 2018. Increasing risk perception and understanding of hurricane storm tides using an interactive, web-based visualization approach.

Previous studies have shown that much of the public misinterprets standard hurricane storm surge text advisories or standard color-coded storm surge maps. A supplemental approach is proposed that allows users to simulate storm tide for various locations, tidal amounts, and hurricane scenarios and then visualize the estimated water depth on photographs of neighborhood landmarks. Potentially, the visual nature of this approach could enhance risk perception and understanding. The interactive aspect of this approach may engage users more than standard approaches, in addition to providing users with more information. Showing the threats at the neighborhood scale could make the risk more apparent and discourage development of risk-prone areas. Vulnerable groups such as the elderly, transient, or non-English speakers could benefit from the visual representation of the risk. Graphics could be useful for broadcasters and emergency management. However, as is the case with current techniques, this approach has difficulty representing uncertainty. One major shortfall of all current approaches is the parameterization and inclusion of waves as the storm surge travels inland. Waves could be easily visualized with this approach, should the science provide an adequate parameterization.

Li, S. and Liu, Y., 2018. Analytical and explicit solutions to implicit wave friction-factor equations based on the Lambert W function.

Calculation of the friction factor of turbulent oscillatory fluid flow is a significant issue in accessing bed shear stress and sediment entrainment in coastal areas. A fast, robust calculation is necessary for intensive scientific simulations. However, some widely used friction-factor equations belong to the group of implicit and transcendental equations. Common procedures for obtaining accurate solutions are based on root-solving techniques such as the Newton–Raphson iterative method, with substantial computation cost and potential failure of solution convergence. The present note offers a simple and highly accurate procedure for explicitly calculating the friction factors. First, explicit analytical solutions of the friction-factor equations are derived using the Lambert W function, which is a newly recognized elementary transcendental function. Then, the analytical solutions are numerically calculated by simply calling the fast algorithms of the Lambert W function that is available in the libraries of many kinds of software of widely applied numerical computing environments. For practical purposes, this note also compares several fast algorithms of the function.