Shoreline Locations Research Articles

Equilibrium shoreline modelling of a high-energy meso-macrotidal multiple-barred beach

Abstract 8-year time series of incident wave energy and monthly alongshore-averaged beach surveys at the high-energy meso-macrotidal multiple-barred Truc Vert beach are analysed. We apply two behaviour-oriented equilibrium shoreline models that relate the rate of cross-shore shoreline displacement to the wave energy and the wave energy disequilibrium between the wave energy and the equilibrium wave energy that would cause no change to the present shoreline location. The two models show similar skill. Results show that the equilibrium shoreline model concept works on meso-macrotidal multiple-barred beaches, with similar skill when applied to non-barred and/or micro-mesotidal beaches, provided that a relevant shoreline proxy is used. Simulations show that Truc Vert beach responds predominantly at seasonal timescales rather than at individual storm frequency. The first winter storms drive the most pronounced erosion events because both the wave energy disequilibrium and erosion change potential are large. The best shoreline proxy at Truc Vert beach is the mean high water level, where the inner-bar and berm dynamics have little influence on the shoreline cross-shore displacement. Implications for shoreline monitoring through video imagery on this type of beach are discussed. Results also reveal that the equilibrium shoreline concept can be extended to an equilibrium beach profile concept pending further improvements.

GNSS-based monitoring and mapping of shoreline position in support of planning and management of Matinhos/PR (Brazil)

Monitoring and mapping variations in shoreline location is an activity that can be undertaken using several different techniques of data collection, e.g., photogrammetric restitution, satellite images, LiDAR (Light Detection and Ranging) or classical topographical surveys to support coastal environmental protection such as identifying flood risk areas. The global navigation satellite system (GNSS) has been employed by the Federal University of Parana (UFPR) as part of their research into the application of geodetic survey methods for shoreline mapping in coastal environments since 1996. The advantages of using GNSS are accuracy and productivity, given that a great number of points can be determined within a short period of time at decimeterlevel accuracy. In this work, GNSS relative kinematic positioning approach was applied to monitor Matinhos coastal district of Brazil. Other important data, such as the highand low-tide marks, all obtained using GNSS, and thematic maps have also been incorporated. Through the reanalysis of historical surveys, it is possible to make some conclusions about the shoreline dynamics and to use this information as material in support of the planning and management of the coastal environment, for example, when planning engineering works that set out to minimize coastal erosion and for urban planning. The results achieved in this work include defining the position of the shoreline for 2008, developing the thematic map of the shoreline, the quantification of the advance and retreat of the shoreline between 2001 and 2008, and a map showing those critical areas where the shoreline position is equal to the high-tide water line. GNSS-based method offers quicker, all-weather, highly accurate and continuously updatable shoreline positional time series relevant for monitoring, thus enabling quicker management decisions to be undertaken, which may be of benefit to coastal engineering applications.

Beach response to a fixed sand bypassing system

Indian River Inlet is located at roughly the mid-point of the Atlantic coast of Delaware and connects the ocean to two Delaware inland bays. Jetties constructed in 1940 have maintained the inlet for navigation purposes but have also acted as a barrier to net northerly alongshore sediment transport causing downdrift erosion. A mobile, land-based bypassing system was initiated in 1990 in an effort to counteract this erosion. Beach profile data from 1985 (pre-bypassing) until 2008 are used to investigate the effect of the sand bypassing system on beaches adjacent to the inlet. The downdrift beach experienced horizontal shoreline erosion between 10 and 60m during the pre-bypassing period but accreted 10–20m during the bypassing period. The mean shoreline location on the updrift beach during bypassing is 10–20m landward (erosion) of its position during the pre-bypassing period. Empirical orthogonal function (EOF) amplitudes from analyses performed on mean-removed elevation surfaces during the periods of highest bypassed volume (average of 83% of design rate) showed that the influence of the bypassing system on the downdrift beach extends to about 1500m of the inlet. An EOF analysis showed that different morphologic responses were evident following the initiation of bypass operations. Temporal variations of shoreline and beach morphology were correlated to the temporal variations in bypassing rates on the downdrift beach only. The downdrift beach response was greatest near the inlet for larger bypassing volumes. Correlation in these instances occurred with a roughly 1-year time lag suggesting that the beach quickly redistributes the bypassed sand. EOF amplitude and shoreline response are weakly correlated to bypassed volumes when the system bypassed smaller volumes (average of 56% of design rate) of sand suggesting that there is a minimum bypassing rate, regardless of yearly variability, below which the effect on the downdrift beach is obscured.

Historical Shoreline Change of the Sele Plain (Southern Italy): The 1870–2009 Time Window

Abstract Alberico, I.; Amato, V.; Aucelli, P.P.C.; D'Argenio, B.; Di Paola, G.; and Pappone, G., 2012. Historical shoreline change of the Sele Plain (southern Italy): the 1870–2009 time window. In the Mediterranean, the coastal population was estimated at 146 million in 1990 and the urban coastal population alone is projected to rise to 176 million by 2025, with an addition of 350 million of tourists per year. In coastal zones, forecasting shoreline location and changes in time is a basic tool for decisional making regarding land management and future planning. Historical maps, aerial photography, topographic maps and a beach survey were used as data sources to detect the shorelines of the Sele Plain coastline between the towns of Salerno and Agropoli (southern Italy) and define its change from 1870 to 2009. By using the potential of ArcGIS release 8.3 software and its extension digital shoreline analysis system, we followed two main stages. The first required identification of the shorelines, reducing to...

Coastal Impacts of the March 11th Tohoku, Japan Tsunami in the Galapagos Islands

On March 11, 2011 at 5:46:23 UTC (March 10 11:46:23 PM Galapagos Local Time), the Mw 9.0 Great East Japan Earthquake occurred near the Tohoku region off the east coast of Japan, spawning a Pacific-wide tsunami. Approximately 12,000 km away, the Galapagos Islands experienced moderate tsunami impacts, including flooding, structural damage, and strong currents. In this paper, we present observations and measurements of the tsunami effects in the Galapagos, focusing on the four largest islands in the archipelago; (from west to east) Isabela, Santiagio, Santa Cruz, and San Cristobal. Access to the tsunami affected areas was one of the largest challenges of the field survey. Aside from approximately ten sandy beaches open to tourists, all other shoreline locations are restricted to anyone without a research permit; open cooperation with the Galapagos National Park provided the survey team complete access to the Islands coastlines. Survey locations were guided by numerical simulations of the tsunami performed prior to the field work. This numerical guidance accurately predicted the regions of highest impact, as well as regions of relatively low impact. Tide-corrected maximum tsunami heights were generally in the range of 3–4 m with the highest runup of 6 m measured in a small pocket beach on Isla Isabela. Puerto Ayora, on Santa Cruz Island, the largest harbor in the Galapagos experienced significant flooding and damage to structures located at the shoreline. A current meter moored inside the harbor recorded relatively weak tsunami currents of less than 0.3 m/s (0.6 knot) during the event. Comparisons with detailed numerical simulations suggest that these low current speed observations are most likely the result of data averaging at 20-min intervals and that maximum instantaneous current speeds were considerably larger. Currents in the Canal de Itabaca, a natural waterway between Santa Cruz Island and a smaller island offshore, were strong enough to displace multiple 5.5-ton navigation buoys. Numerical simulations indicate that currents in the Canal de Itabaca exceeded 4 m/s (~8 knots), a very large flow speed for a navigational waterway.

Automatic extraction of shorelines from Landsat TM and ETM+ multi-temporal images with subpixel precision

A high precision geometric method for automated shoreline detection from Landsat TM and ETM+ imagery is presented. The methodology is based on the application of an algorithm that ensures accurate image geometric registration and the use of a new algorithm for sub-pixel shoreline extraction, both at the sub-pixel level. The analysis of the initial errors shows the influence that differences in reflectance of land cover types have over shoreline detection, allowing us to create a model to substantially reduce these errors. Three correction models were defined according to the type of gain used in the acquisition of the original Landsat images. Error assessment tests were applied on three artificially stabilised coastal segments that have a constant and well-defined land-water boundary. A testing set of 45 images (28 TM, 10 ETM high-gain and 7 ETM low-gain) was used. The mean error obtained in shoreline location ranges from 1.22 to 1.63m, and the RMSE from 4.69 to 5.47m. Since the errors follow a normal distribution, then the maximum error at a given probability can be estimated. The results confirm that the use of Landsat imagery for detection of instantaneous coastlines yields accuracy comparable to high-resolution techniques, showing the potential of Landsat TM and ETM images in those applications where the instantaneous lines are a good geomorphological descriptor.

Equilibrium shoreline response of a high wave energy beach

[1] Four years of beach elevation surveys at Ocean Beach, San Francisco, California, are used to extend an existing equilibrium shoreline change model, previously calibrated with fine sand and moderate energy waves, to medium sand and higher-energy waves. The shoreline, characterized as the cross-shore location of the mean high water contour, varied seasonally by between 30 and 60 m, depending on the alongshore location. The equilibrium shoreline change model relates the rate of horizontal shoreline displacement to the hourly wave energy E and the wave energy disequilibrium, the difference between E and the equilibrium wave energy that would cause no change in the present shoreline location. Values for the model shoreline response coefficients are tuned to fit the observations in 500 m alongshore segments and averaged over segments where the model has good skill and the estimated effects of neglected alongshore sediment transport are relatively small. Using these representative response coefficients for 0.3 mm sand from Ocean Beach and driving the model with much lower-energy winter waves observed at San Onofre Beach (also 0.3 mm sand) in southern California, qualitatively reproduces the small seasonal shoreline fluctuations at San Onofre. This consistency suggests that the shoreline model response coefficients depend on grain size and may be constant, and thus transportable, between sites with similar grain size and different wave climates. The calibrated model response coefficients predict that for equal fluctuations in wave energy, changes in shoreline location on a medium-grained (0.3 mm) beach are much smaller than on a previously studied fine-grained (0.2 mm) beach.

Physical, Chemical, and Mineralogical Characteristics of a Reservoir Sediment Delta (Lake Powell, USA) and Implications for Water Quality during Low Water Level

Lake Powell is a large reservoir in Utah and Arizona that has experienced large changes in water level during a recent drought. As a first step in assessing the connection between hydrologic and chemical changes at Lake Powell, we characterized the particle size and solid-phase bulk concentrations for 31 elements and 25 minerals in sediment from the inflow region and some shoreline locations by using laser diffractometry, X-ray fluorescence, elemental analysis, and X-ray diffraction Our results are consistent with previous results that show a negative correlation between particle size and concentrations of most elements and most minerals other than quartz and some feldspars. In our samples, however, solid-phase iron, rather than particle size or organic carbon, is the best predictor variable for the solid-phase concentrations of elements and minerals. Sediment characteristics vary on a scale of tens of kilometers, with fine sediment that is enriched in trace elementsnearer to the dam. These trends allow formulation of an algorithm for determining a water-level threshold below which sediment resuspension may alter water chemistry in a generic reservoir with a long and narrow sediment delta.

LONG-TERM MONITORING ON THE SAND SPIT MORPHODYNAMICS AT THE TENRYU RIVER MOUTH

In this study, long-term monitoring on the sand spit morphodynamics at the Tenryu River mouth was carried out based on the time series of sand spit profiles extracted from the field camera recorded images between Apr 2007 and Dec 2009. Time stack images were applied to qualitatively characterize the variation of sand spit morphology at the representative longshore location. Primarily analyses were conducted by focusing on the bulk statistical properties of the recorded sand spit profile data. Detailed insight into the evolution process of the sand spit shoreline location was estimated through the Empirical Orthogonal Function (EOF) analysis. Sand spit riverside morphodynamics presents a short-term, but intensive variation pattern and is found to be closely related to the overtopping or flood events. Modification on the sand spit shoreline location shows an asymmetric nearshore process. In the first two years, slow beach accretion accompanying with the eastward longshore sand movement prevailed; whereas, rapid shoreline erosion, together with the westward longshore sand movement, became predominant in the following half year.

Are sea otters being exposed to subsurface intertidal oil residues from the Exxon Valdez oil spill?

Twenty years after the Exxon Valdez oil spill, scattered patches of subsurface oil residues (SSOR) can still be found in intertidal sediments at a small number of shoreline locations in Prince William Sound, Alaska. Some scientists hypothesize that sea otters continue to be exposed to SSOR by direct contact when otters dig pits in search of clams. This hypothesis is examined through site-specific examinations where SSOR and otter-dug pits co-occur. Surveys documented the exact sediment characteristics and locations on the shore at the only three subdivisions where both SSOR and otter pits were found after 2000. Shoreline characteristics and tidal heights where SSOR have persisted are not suitable habitat for sea otters to dig pits during foraging. There is clear separation between areas containing SSOR and otter foraging pits. The evidence allows us to reject the hypothesis that sea otters encounter and are being exposed by direct contact to SSOR.

A Multichamber Oscillating Water Column Using Cascaded Savonius Turbines

This paper describes a small segmented oscillating water column (OWC) with three sections and the modelling techniques that can be used to simulate its performance. The turbine uses cascaded Savonius rotors and the unit is developed and tested for validation of the performance algorithms. It is shown that the systems can be easily described and developed. It would be suitable for a shoreline location such as a harbor wall, where waves are random and not orthogonal to the column. Conversion rates in the region of 20% are tabulated for the system with an output of 25-W peak. A full algorithm used for the system is put forward and solved using the Runge-Kutta-Nystrom (RKN) method.

Effect of changes in water level on sediment pore water redox geochemistry at a reservoir shoreline

Pore water samplers with high vertical resolution were used to evaluate the response of sediment redox geochemistry during transient hydrologic conditions at Lake Powell, a large reservoir in Utah and Arizona, USA. Samplers were deployed at two different yet proximal shoreline locations, White and Farley Canyons, before and after exposure of sediment to air and subsequent resubmersion, which resulted from fluctuations in the water level of the reservoir. Before exposure to air, an observed increase in dissolved Mn concentrations and, at Farley Canyon, an observed decrease in dissolved U concentrations across and immediately below the sediment–water interface indicated reducing conditions in the sub-surface. After exposure and resubmersion of the sediment, pore water profiles at each site differed distinctly from those observed before the fluctuation in water level. At White Canyon, an increase in U concentrations and a decrease in Mn concentrations in pore water after exposure and subsequent resubmersion are suggestive of oxidative processes occurring during the period of sediment exposure. Data from Farley Canyon suggest that the same processes may be occurring, but to a lesser extent. Depth profiles of As and Pb were also examined, but were relatively featureless compared to those of Mn and U. At both sites, sediment evaluated for pore water chemistry in the second sampling was only fully resubmerged for 2–5 days prior to the second sampling event, yet reducing conditions were clearly evident in the Mn pore water profiles. This suggests that the dynamics of the biogeochemical processes occurring in surface sediment at Lake Powell are responsive on the timescale defined by the fluctuating water levels in the reservoir.

A Small Segmented Oscillating Water Column Using a Savonius Rotor Turbine

This paper describes a project which addresses the use of a small segmented oscillating water column with three sections. The turbine utilizes cascaded Savonius rotors (one for each section), and this system is developed and tested for validation of the performance algorithms. This paper shows that the system is easily described using a simulation, while a small-scale wave-tank-based system is shown to generate electrical power. The system is suitable for a shoreline location such as a harbor wall, where waves are random and not orthogonal to the column. Conversion rates in the region of 20% are tabulated with an output of 25 W peak. This paper reports on the operation of the column with respect to the wave frequency and wavelength. The peak tip speed ratio of the turbine is investigated in the application and found to correlate with published data when the turbine operates in free (rather than ducted) airflow conditions. The turbine is fully characterized - the generator is a brushless permanent-magnet machine connected to a diode bridge rectifier and a variable load.

Equilibrium shoreline response: Observations and modeling

Shoreline location and incident wave energy, observed for almost 5 years at Torrey Pines beach, show seasonal fluctuations characteristic of southern California beaches. The shoreline location, defined as the cross‐shore position of the mean sea level contour, retreats by almost 40 m in response to energetic winter waves and gradually recovers during low‐energy summer waves. Hourly estimates of incident wave energy and weekly to monthly surveys of the shoreline location are used to develop and calibrate an equilibrium‐type shoreline change model. By hypothesis, the shoreline change rate depends on both the wave energy and the wave energy disequilibrium with the shoreline location. Using calibrated values of four model free parameters, observed and modeled shoreline location are well correlated at Torrey Pines and two additional survey sites. Model free parameters can be estimated with as little as 2 years of monthly observations or with about 5 years of ideally timed, biannual observations. Wave energy time series used to calibrate and test the model must resolve individual storms, and model performance is substantially degraded by using weekly to monthly averaged wave energy. Variations of free parameter values between sites may be associated with variations in sand grain size, sediment availability, and other factors. The model successfully reproduces shoreline location for time periods not used in tuning and can be used to predict beach response to past or hypothetical future wave climates. However, the model will fail when neglected geologic factors are important (e.g., underlying bedrock limits erosion or sand availability limits accretion).

Methodology for Location of Shorelines using 3D-GPS Positioning: A Case Study at Sauaçui Beach, Northeast Brazil

Many research studies have tried to improve the techniques for effective control of changes in coastal spaces caused by natural or human-induced phenomena. Such alterations modify the capacity for natural regeneration of beaches, and because of the growing population in these areas coastal management must pay close attention to the subject. The method used in this study case at Sauaçui Beach establishes a terrestrial digital model using topographic software fed by a georeferenced data bank generated by a three-dimensional global positioning system (GPS) whose vertical coordinates are referred to as tidal datum. The GPS technology can be used for the accommodation dynamic of the earth's crust of tectonic displacements. This method is able to identify the level curve equivalent to the maximum elevation of the wave run-up line, as well as the position of the waterline, during any stage of tidal elevation through curves of higher or lower levels of elevation, depending on the specific need of the study. Besides determining a baseline for future observations at Sauaçui Beach, this study allows us to evaluate the occurrence of alterations in the volume of sediments at the beach through differences among the generated land surfaces during different periods of time, as well as the risk of substantial variations in the shoreline position caused by eventual sea-level changes.

Quantifying Seasonal Shoreline Variability at Rehoboth Beach, Delaware, Using Automated Imaging Techniques

Abstract We describe a seven-camera video system deployed at Rehoboth Beach on the Atlantic coast of Delaware that was used to monitor and quantify the evolution of a nourished beach. Shorelines along 6 km of beach were automatically identified using pixel-intensity gradients from time-exposure and variance imagery. Correlations between automatically identified and user-defined shorelines from images with various wave and atmospheric conditions exceed r2 values of 0.92. Small variations in camera azimuth and tilt were found to significantly affect apparent shoreline locations and were automatically corrected through image-correlation procedures. Hourly shoreline data were tidally and seasonally averaged to quantify seasonal morphodynamic variability. Over a summer-winter-summer monitoring period, the shoreline exhibited erosional and accretional variations of ∼10 m dependent in the alongshore direction on permanent man-made structures and subject to seasonally characteristic littoral transport variations....

Secular cange of the area and the location of shoreline at the Fukiage beach in Awaji island

Secular cange of the area and the location of shoreline at the Fukiage beach in Awaji island

Estimating hinterland exhumation from late orogenic basin volume, NW Borneo

A new approach for restoring sediment volumes onto the sediment source area to estimate uplift timing and magnitude is discussed and used in the context of late Tertiary basin and topographic development in NW Borneo. Sediment volumes for the Baram Deltaic Province were estimated for four time periods (latest Early, Middle and Late Miocene, and Pliocene–Recent), using 2D and 3D seismic horizons, wells and outcrops. Volume restoration onto the palaeo-sediment source area determined exhumation amount at the drainage divide ( c . 5 km from 17 Ma to Recent) and provided a reasonable match with other denudation estimation methods (cooling ages and an older, regional sediment restoration study using 1979 vintage sediment isopach maps). Restoration took into account: (1) changing sediment densities during the erosion–deposition cycle; (2) changing area of the sediment source province with time (e.g. changing shoreline location as a result of eustacy, uplift and delta progradation, tectonic shortening); (3) uplift and partial erosion of Baram Deltaic Province sediment. Denudation at the drainage divide for the Middle Miocene, Late Miocene and Pliocene–Recent has proceeded at a similar rate for each period. Initial uplift of central Borneo has been attributed to buoyancy of thinned continental crust that jammed the subduction zone under NW Borneo in the Early Miocene. However, the absence of decay in the erosion rates with time from the Middle Miocene to Recent suggests operation of an additional uplift mechanism that may be related to delamination of mantle lithosphere; slab detachment is the favoured explanation.

Frequent occurrence of the human‐specific Bacteroides fecal marker at an open coast marine beach: relationship to waves, tides and traditional indicators

Molecular genetic markers, such as those from fecal Bacteroides microorganisms, can link microbial pollution with its source, and have been used successfully in studies of sheltered aquatic environments. Their applicability to wave-driven, open coast environments has not been tested. We assessed the contribution of a tidal outlet to surf zone water quality in coastal Orange County, California, USA by measuring three traditional culture-based fecal indicator bacteria (FIB) as well as the human-specific Bacteroides molecular marker (HF marker) at four shoreline locations. We found that total and fecal coliform levels were higher during low tides than high tides at two of the four stations, and that this effect was strongest at the mouth of the tidal lagoon and decayed with distance from the outlet. The HF marker was detected in 23% and 47% of samples from the tidal outlet and 26% and 41% of samples from an adjacent recreational beach in 2005 and 2006 respectively. Surprisingly, the station farthest from the tidal outlet had the highest occurrence of the HF marker. We found no relationship between FIB abundance and occurrence of the HF marker for individual samples, but that when the data were considered together by year, higher FIB abundance was correlated with a higher incidence of the HF marker. DNA sequences of the HF marker recovered from this site were > 99% similar to those recovered from other states and countries, suggesting low global diversity of this marker. These data provide strong support for the idea that multiple time points and physical conditions should be considered when assessing coastal water quality.

Incision of alluvial channels in response to a continuous base level fall: Field characterization, modeling, and validation along the Dead Sea

The dramatic lake level drop of the Dead Sea during the twentieth century (∼ 30 m) provides a field-scale experiment in transport-limited incision of gravel-bed channels in response to quasi-continuous base level fall at approximately constant rate. We apply a one-dimensional numerical incision model based on a linear diffusion equation to seven ephemeral channels draining into the Dead Sea. The model inputs include the measured twentieth century lake level curve, annual shoreline location (i.e., annual channel lengthening following the lake level drop), reconstructed longitudinal profiles of each of the channels based on mapped and surveyed terraces, and the current profiles of the active channels. The model parameters included the diffusion coefficient and the upstream-derived sediment flux. Both were first calibrated using a set of longitudinal profiles of known ages and then validated using additional sets of longitudinal profiles. The maximum at-station total incision observed at each of the studied channels was significantly less then the total lake level drop and varied in response to both drainage area and lake bathymetry. The model applied predicted degradation rates and the pattern of degradation with high accuracy. This suggests that sediment flux in the modeled channels is indeed linearly dependent on slope. Further support for this linear dependency is provided by a linear correlation between the diffusion coefficient and the mean annual rain volume over each basin (a proxy for discharge). The model presented could be a valuable tool for planning in rapid base level fall environments where incision may risk infrastructure.