Abstract
While beach erosion and sand loss are typically of great concern to the tourism industry, managing rapid morphological changes linked to large amounts of moving sediments is the challenge facing Grado, an important seaside resort in the northern Adriatic, Italy. The cause of the unusual management conflict is the presence of the Mula di Muggia Bank, a nearshore depositional system made up of relict and active migrating sandbanks extending up to 2 km seawards from the touristic beachfront. A reconstruction of the morpho-sedimentary evolution of the coastal system over a 200-year period was done using a large dataset which includes historical cartography, topographic maps, aerial photos and topo-bathymetric surveys. The results show the growth of a significant urban development aimed at creating a tourist destination by occupying the waterfront along fetch-limited coastal tracts with very shallow water and scarce hydrodynamics. Furthermore, a number of sandy dynamic landforms (longshore migrating bars, a bypass corridor, an ebb-tidal delta) and accumulation zones attest to a sediment excess which can be mostly attributed to the eastern river supplies. The progressive constant migration rate of 12.6 my−1 allowed the bank to induce the expansion of the low-energy silty backbarrier environment, characterised by abundant seagrass meadows a short distance directly in front of the tourist beaches of Grado. As a result of historical analysis and more current observations, areas with diverse morphosedimentary features and with varying tourist/recreational, ecological, and conservation values have been identified. These can be considered as basic units for future accurate planning and re-evaluation of coastal management choices to balance environmental protection and tourist use. A soft coastal defence approach is proposed which includes either the preservation of specific environments or the proper use of excess sand for beach nourishment via periodic dredging or sediment bypassing.
Highlights
IntroductionCoastal systems are the most densely populated locations on the planet, as well as the most vulnerable to sea-level rise (SLR) caused by global warming
The bank’s apex is defined by barely emerging bars (0.57 m), whereas another emerging bank can be found near the tourist beach; (c) the Primero Inlet area (PI sector), representing the Primero tidal inlet system, which is characterised by the main ebb channel separating the MMB from (d) the Isonzo
The gathered and analysed data allowed for two major outcomes: on the one hand, the multidecadal analysis highlighted the evolution of the MMB and adjacent coasts over time, beginning with the earliest and most likely cartographic representations and progressing to modern high-resolution surveys; on the other hand, it was possible to describe the evolution of coastal landforms in relation to contemporary anthropogenic and tourist development
Summary
Coastal systems are the most densely populated locations on the planet, as well as the most vulnerable to sea-level rise (SLR) caused by global warming. Continued accelerated global SLR, along with potential increases in the frequency and intensity of extreme sea-level events [1,2], will cause rapid coastal changes in many parts of the world. Erosion, drowning and increased vulnerability involve sedimentary bodies such as beaches, coastal dunes, barrier island systems and deltas. The definition of the temporal scale is critical for assessing coastal evolution and distinguishing coastal change caused by episodic, seasonal, or longterm processes [16,17]. A multidecadal analysis of the shoreline is a basic requirement for coastal management and one of the classic geomorphological methodologies [18,19,20,21,22,23]
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