Global distribution of nearshore slopes with implications for coastal retreat

Abstract

Abstract. Nearshore slope, defined as the cross-shore gradient of the subaqueous profile, is an important input parameter which affects hydrodynamic and morphological coastal processes. It is used in both local and large-scale coastal investigations. However, due to unavailability of data, most studies, especially those that focus on continental or global scales, have historically adopted a uniform nearshore slope. This simplifying assumption could however have far reaching implications for predictions/projections thus obtained. Here, we present the first global dataset of nearshore slopes with a resolution of 1 km at almost 620,000 points along the global coastline. To this end, coastal profiles were constructed using global topo-bathymetric datasets. The results show that the nearshore slopes vary substantially around the world. An assessment of sea level rise (SLR) driven coastline recession (for an arbitrary 0.5 m SLR) with a globally uniform coastal slope of 1:100, as done in previous studies, and with the spatially variable coastal slopes computed herein shows that, on average, the former approach would under-estimate coastline recession by about 40 %, albeit with significant spatial variation. The final dataset has been made publicly available at https://doi.org/10.4121/uuid:a8297dcd-c34e-4e6d-bf66-9fb8913d983d.

High-Resolution Intertidal Topography from Sentinel-2 Multi-Spectral Imagery: Synergy between Remote Sensing and Numerical Modeling

“…Our approach yields a DEM that can also be used to cross-evaluate other near-shore topography datasets, such as the global digital surface model ALOS World 3D (AW3D30, 30 m of resolution, [51]) or newly available topography datasets provided by ICESat-2 (Ice, Cloud, and Land Elevation Satellite-2) altimetry mission carrying the advanced topographic laser altimeter system (ATLAS) instrument, which is very promising for estimating the elevation of coastal and intertidal areas at low tide [5]. Funding: This research was funded by CNES through the "BANDINO" TOSCA grant.…”

On the need for a new generation of coastal change models for the 21st century

“…The non-availability of (or lack of free access to) long term morphological and hydrodynamic data has been for decades a frustrating bottleneck in terms of achieving robust validation of, especially, longer term coastal change models. However, the recent emergence of open source satellite image based global data sets of coastal morphology and topography 24,[60][61][62][63][64] and the general worldwide trend towards open source in-situ data (e,g. EMODNET, CEFASWavenet, SISMER, SHOM, Open Earth, DUCK FRF, Narrabeen-Collaroy) represents a step-change in the availability of/access to long term data, greatly improving opportunities for the validation of long term coastal change models.…”

Uncertainties in projections of sandy beach erosion due to sea level rise: an analysis at the European scale

“…The use of the SVNS dataset instead of the uniform slope assumption resulted in an increased estimate of European average shoreline retreat. This is due to the fact that the SVNS based slopes are on average milder than 1:100 across Europe 41 . On the other hand, the differences in the European coastal land loss predictions (Fig.…”

“…The classes that were used are (a) sandy beaches, (b) unerodable coasts, (c) muddy coastlines and (d) rocky coasts with pocket beaches. The EUROSION classes were then regrouped in these four classes according to the highest occurrence as described in Athanasiou et al 41 . Ultimately, only the alongshore points that were classified as sandy beaches were used for the assessment of future shoreline retreat and coastal land loss.…”