BOAK, E.H. and TURNER, I.L., 2005. Shoreline Definition and Detection: A Review. Journal of Coastal Research, 21(4), 688‐703. West Palm Beach (Florida), ISSN 0749-0208. Analysis of shoreline variability and shoreline erosion-accretion trends is fundamental to a broad range of investigations undertaken by coastal scientists, coastal engineers, and coastal managers. Though strictly defined as the intersection of water and land surfaces, for practical purposes, the dynamic nature of this boundary and its dependence on the temporal and spatial scale at which it is being considered results in the use of a range of shoreline indicators. These proxies are generally one of two types: either a feature that is visibly discernible in coastal imagery (e.g., highwater line [HWL]) or the intersection of a tidal datum with the coastal profile (e.g., mean high water [MHW]). Recently, a third category of shoreline indicator has begun to be reported in the literature, based on the application of imageprocessing techniques to extract proxy shoreline features from digital coastal images that are not necessarily visible to the human eye. Potential data sources for shoreline investigation include historical photographs, coastal maps and charts, aerial photography, beach surveys, in situ geographic positioning system shorelines, and a range of digital elevation or image data derived from remote sensing platforms. The identification of a ‘‘shoreline’’ involves two stages: the first requires the selection and definition of a shoreline indicator feature, and the second is the detection of the chosen shoreline feature within the available data source. To date, the most common shoreline detection technique has been subjective visual interpretation. Recent photogrammetry, topographic data collection, and digital image-processing techniques now make it possible for the coastal investigator to use objective shoreline detection methods. The remaining challenge is to improve the quantitative and process-based understanding of these shoreline indicator features and their spatial relationship relative to the physical land‐water boundary.

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Shoreline Definition and Detection: A Review

The effects of global climate change on seagrasses

Seagrasses are able to modify current flow and sediment composition, yet little information exists describing their effect on waves. Four species of seagrass, Halodule wrightii, Syringodium filiforme, Thalassia testudinum and Zostera marina were evaluated for their ability to reduce wave energy under various combinations of shoot density and water depths over a 1 m test section in a wave tank. Percent wave energy reduction per meter of seagrass bed equaled 40% when the length of these seagrasses was similar to the water depth. Seagrasses are approximately equal to saltmarshes in reducing wave energy on a unit distance basis, but only when water depth is scaled to plant size. When seagrass beds occur as broad, shallow meadows, the influence of seagrasses on wave energy will be substantial.

A preliminary evaluation of wave attenuation by four species of seagrass

Environmental impacts of dredging on seagrasses: a review.

The role of Posidonia oceanica in promoting sediment stability and accretion was studied in a 15 m deep meadow at Fanals Point (NW Mediterranean, Spain) by comparing particle deposition within the meadow and adjacent bare sediment. Small sediment traps were used to measure deposition within and above the meadow and over bare sand. A model, based on measurements of particle deposition at increasing distances from the bottom, was used to partition the total depositional flux between primary (sediment particles deposited for the first time at the measuring site) and resuspended deposition (sediment particles that have been previously deposited at the measuring site). Measurements were conducted monthly over a year to establish the magnitude and seasonality of deposition, and to form a balance of particle transport at the annual time scale. Significant differences in total deposition were found over time, ranging from 1·5 to 500 g DW m−2 d−1, including those between bare and vegetated sediments. The effect of P. oceanica in increasing primary deposition at an annual scale was modest, however, P. oceanica significantly buffered sediment resuspension, which was reduced more than three fold compared to the unvegetated bottom. The annual flux of deposition was dominated by settling of resuspended materials, which represented 85% of the total flux within the meadow, but 95% of the total deposition on bare sand. Thus, seagrass meadows reduce resuspension in the NW Mediterranean littoral, thereby contributing to increased sediment retention and, therefore, reducing erosion in the coastal zone.

Sediment Retention by a Mediterranean Posidonia oceanica Meadow: The Balance between Deposition and Resuspension

Measurements of velocity profiles, bathymetry, and surface sediment characteristics across eelgrass (Zostera marina L.) meadows yielded information on community development processes and functional attributes of this ecosystem. Height/length ratios of the meadows were positively correlated with tidal current velocity. Low, medium, and high current regimes were separated by surface current velocities of approximately 50 and 90 cm s−1. Z. marina can tolerate approximately 120–150 cm/sec current velocities in the areas studied. Per cent silt-clay and organic matter content of the surface sediments are negatively associated with shear velocity, suggesting that meadows in high current areas are sources while meadows in low current areas are sinks of autochthonous detritus. Current velocity maintains seagrass meadows at different equilibrium levels (relative climaxes). We theorize these different equilibrium levels provide unequal habitat utilization potentials for the associated faunal community.

The role of current velocity in structuring eelgrass (Zostera marina L.) meadows

This paper describes the development of a new parameter to characterize dune vulnerability to storm-induced erosion. Existing indicators of dune erosion vulnerability are examined, including expected cross-sectional erosion values calculated using storm characteristics. We extract a series of 110 pre- and poststorm profiles at cross-shore transects, spaced at approximately 300 m alongshore on digital terrain models of a North Carolina barrier island. Dune failure and survival are designated based on a percentage of the cross-sectional area eroded—50% or greater erosion indicates failure, less than 50% erosion, survival. Crest height does not prove to be an effective predictor of dune vulnerability. Existing cross-sectional area based parameters show some success in predicting erosion vulnerability. We improve the dune failure and survival prediction success rate using a new parameter, a surrogate moment of inertia, the erosion resistance.

Vulnerability indicators for coastal dunes

A review of some of the potential sources of error associated with the use of aerial photographs to map shoreline change is presented. The influence of both tides and waves in the estimation of the position of the wet sand line on the subaerial beach is included. The use of the relatively new digital photogrammetry as applied to shoreline mapping is discussed and suggested as having the potential for being a superior method for this application.

https://icce-ojs-tamu.tdl.org/icce/index.php/icce/article/download/5088/4766

Interpretation of shoreline position from aerial photographs

A model predicting dune erosion under storm conditions has been developed using data from SUPERTANK laboratory experiments. In this model, the swash approach is applied with the basic assumption that the volume eroded from the dune is a function of the swash force acting on the dune. The swash force is characterized with swash parameters, specifically the swash height, the swash velocity and the swash period. For given storm conditions, the model predicts wave height variation across-shore, swash height variation on the beach face, swash velocity, swash period, swash forces and finally volume eroded at the dune. Predictions of swash parameters and dune erosion are compared with measurements from SUPERTANK laboratory experiments.

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John S. Fisher

Papers

The role of current velocity in structuring eelgrass (Zostera marina L.) meadows

Vulnerability indicators for coastal dunes

Interpretation of shoreline position from aerial photographs

Development of a dune erosion model using supertank data

Factors influencing faecal contamination in coastal marinas