Serafim E. Poulos

Recent evolution of a Mediterranean deltaic coastal zone: human impacts on the Inner Thermaikos Gulf, NW Aegean Sea

The Inner Thermaikos Gulf is located in the northwestern Aegean Sea, receiving water and sediment fluxes from the Axios, Aliakmon, Gallikos and Loudias Rivers. The geomorphological and sedimentological evolution of the system is reconstructed for the last 150 years (1850–2000), on the basis of detailed analysis of historical bathymetric charts. Late Holocene history is considered within the context of changing riverine sediment supply and human activities. Three evolutionary stages are identified. Stage I (1850–1916) corresponds to a natural phase of rapid deltaic progradation and sea-floor deposition, with an average sediment accumulation rate of 6.5 × 106 m3 a−1. During Stage II (1916–1956), human interference (e.g. artificial changes in river delta plains, realignment of channels and land reclamation schemes) to the deltaic system increased sediment delivery to the coastal waters by a factor of three; this, in turn, enhanced the progradation of the active river mouth areas. In contrast, Stage III (1956–2000) is characterized by significant coastline (deltaic) retreat and erosion of the adjacent sea floor (net loss of 2.5 × 106 m3 a−1); this was as a result of extensive river damming, which trapped a significant part of the sediment moving seaward. Furthermore, these human impacts have affected the character of the surficial sea-bed sediments of the Gulf, by reducing the proportion of mud. The response of the deltaic margin of the Inner Thermaikos Gulf to various anthropogenic interventions seems to be analogous to that of other deltas in the Mediterranean region where large drainage projects, the development of irrigation networks and dam construction have taken place within their river basins.

Sedimentation processes in a tectonically active environment: the Kerkyra-Kefalonia submarine valley system (NE Ionian Sea)

The Kerkyra–Kefalonia valley system is the northwestern extension of the Hellenic arc–trench system, representing the collision zone of the Apulian Platform and the Hellenides. The system is distinguished by two different physiographic regions: the northern part, U-shaped, and oriented NNW–SSE, with relatively gentle slopes and a wide floor; and the southern part, oriented NE–SW, V-shaped, and with much steeper side walls and a narrow floor. Both parts are formed tectonically, with the former coinciding with a collision zone, and the latter being the morphometric expression of the Kefalonia strike–slip fault. Sediments recovered in the piston cores from the region consist of fine-grained material, deposited by a variety of sedimentation processes such as: gravity-driven mass movements, associated with seismic activity (i.e., slumping, sliding, debris flows, grain flows, turbidites–seismoturbidites); and, to a lesser extent, by hemipelagic deposition. Measured near-bed currents and their associated shear stresses indicate resuspension of the material, mainly within the northern part of the valley. Sub-bottom acoustic (seismic) profiling data reveal various sedimentary provinces, related to different mechanisms of sediment accumulation: (i) the eastern margin of the Apulian Platform with hemipelagic sedimentation, together with possible advection of suspensates from the Adriatic, in response localised to seabed erosion; (ii) the western Hellenic margin, with down-slope episodic sliding and slumping, induced primarily by earthquake activity, together with an input from hemipelagic settling; (iii) the collision zone, coinciding with the northern part of the Kerkyra–Kefalonia valley system, with deposition mostly from resuspension, the occurrence of local mass gravity flows and the advection of some material from the north; and (iv) the Kefalonia strike–slip fault region, where mass gravity flows are the dominant mechanisms, related to erosion/deposition from resuspension. Overall sedimentation within the tectonically-active Kerkyra–Kefalonia valley system is characterised by the coupling of the mass gravity-driven flows, which are the predominant mechanisms, with the near-bed current regime related with resuspension phenomena and the advection of suspensates. These latter mechanisms is likely more pronounced during the winter period, when dense water masses formed in the Adriatic inflowing into the Ionian Sea.

An holistic approach to beach erosion vulnerability assessment.

Erosion is a major threat for coasts worldwide, beaches in particular, which constitute one of the most valuable coastal landforms. Vulnerability assessments related to beach erosion may contribute to planning measures to counteract erosion by identifying, quantifying and ranking vulnerability. Herein, we present a new index, the Beach Vulnerability Index (BVI), which combines simplicity in calculations, easily obtainable data and low processing capacity. This approach provides results not only for different beaches, but also for different sectors of the same beach and enables the identification of the relative significance of the processes involved. It functions through the numerical approximation of indicators that correspond to the mechanisms related to the processes that control beach evolution, such as sediment availability, wave climate, beach morhodynamics and sea level change. The BVI is also intended to be used as a managerial tool for beach sustainability, including resilience to climate change impact on beach erosion.

Sediment fluxes and the evolution of a riverine-supplied tectonically-active coastal system: Kyparissiakos Gulf, Ionian Sea (eastern Mediterranean)

Abstract Kyparissiakos Gulf, located in the southwestern part of Greece (northeastern Ionian Sea), is a riverine-coastal system that has developed over the southern flank of the Alpine orogenic belt (Hellenides). Some 4 km in the vertical separates the heights of the mountain peaks to the depths of the adjacent offshore deep-water basin. This system extends horizontally over approximately 100 km. The area experiences intensive tectonism (e.g. seismicity), a Mediterranean type of climate and microtidal and moderate wave-energy oceanographic settings. Large quantities of sediments (>2.5 × 106t year−1), transferred principally by the River Alfios, are the product of denudation of the high relief (in excess of 2000 m), developed on erodible lithology (with siliciclastics and carbonates >90%) under moderate climatological conditions. The large amounts of sediments produced in the hinterland, in association with land-ocean process interaction, have led to the formation of a coastal zone that includes deltaic plains and coastal barriers with dune fields, which enclose lagoons. The shape and morphological characteristics of the shore zone indicate, clearly: (a) the dominance of the wave activity; (b) an overall northward longshore sediment movement; and (c) a major depocentre at the northern, naturally sheltered, end of the Gulf. Seawards, the coastal zone includes a narrow continental shelf covered with a blanket of recent sediments, which are terrigenous in origin; these extend down a steep slope, where materials is transferred to the deep (approximately 1800 m) offshore basin (the northward component of the Hellenic Trench) primarily by gravitational mass movements; these are triggered often by earthquake activity. To a first approximation, some 50% of the riverine sediment fluxes accumulate over the shelf, whilst another 25% is transported over the slope to the deeper ocean waters. The construction of (two) dams has led to a dramatic reduction in the sediment supply to the coast, having already caused the retreat of the River Alfios deltaic coastline, by >100 m. Similarly, artificial drainage of the lagoons (for the development of agricultural land) has affected the overall ecosystem (altering the the fauna and flora) of the coastal zone Thus, the Upper Quaternary (mostly Holocene) evolution of this particular coastal system is attributed, primarily, to processes and balances between sediment fluxes (e.g. terrestrial transportation, seaward dispersion) and, recently, to human interference.

Late Quaternary Evolution of Amvrakikos Gulf, Western Greece

Amvrakikos Gulf is a Neogene basin, formed during a late extensional tectonic phase within the Plio-Quaternary period. It is a semienclosed embayment, separated from the Ionian Sea by a shallow (< 10 m) channel. The analysis of 3.5-kHz seismic reflection profiles shows that, during the last (Würm) glacial period, the parts of the Gulf that lie at water depths >41 m (below present sea level) were a paleo-lake while the rest were exposed to subaerial erosion. Subsequent offshore depositional sequences accumulated at rates of 1.2–2.3 m/ka.

The role of coastal morphology in influencing sea level variations induced by meteorological forcing in microtidal waters: examples from the Island of Crete (Aegean Sea, Greece)

ABSTRACT Poulos, S.E.; Plomaritis, T.A.; Ghionis, G.; Collins, M.B., and Angelopoulos, C., 2013. The role of coastal morphology in influencing sea level variations induced by meteorological forcing in microtidal waters: examples from the Island of Crete (Aegean Sea, Greece). Sea surface variations due to strong (northerly) onshore winds are compared over three different geomorphological settings of the essentially tideless (tidal range < 10 cm) northern coast of Crete (southern Aegean Sea): (i) an open beach zone; (ii) a beach zone with the same offshore characteristics as the previous zone, but protected by a shore-parallel reef; and (iii) a pocket beach located in the cove of a semienclosed gulf. Even though the three beach zones are exposed to similar meteorological forcing (strong northerly winds with speeds > 10 m s−1), they developed different water level variations depending on the local morphological conditions. The beach zone situated in the semienclosed gulf experienced a 3.3 times larger offshore sea surface rise (10 cm) than the unprotected open beach. The presence of the reef, on the third beach, caused a 2.7 times higher increase of the nearshore sea surface elevation (i.e., up to 24.5 cm) than the nearshore sea surface rise (9 cm) measured at the nearby unprotected open coast that experiences similar offshore hydrodynamic conditions. The sea surface variations in the offshore zone are induced primarily by wind forcing and, secondarily, by barometric pressure fluctuations: their corresponding ratios vary from 3.2 ∶ 1 in the unprotected open beach, to 2.2 ∶ 1 in the pocket beach located in the semienclosed gulf. Sea surface rise within the nearshore zone is controlled mainly by the wave set-up, due to breaking waves; this, at the open coast, is about 1.3 times larger than the wind set-up. Finally, the presence of the reef amplifies sea surface rise along the shoreline, which can easily exceed 0.4 m (15 times the offshore sea surface rise).

Assessment of island beach erosion due to sea level rise: the case of the Aegean archipelago (Eastern Mediterranean)

The present contribution constitutes the first comprehensive attempt to (a) record the spatial characteristics of the beaches of the Aegean archipelago (Greece), a critical resource for both the local and national economy, and (b) provide a rapid assessment of the impacts of the longterm and episodic sea level rise (SLR) under different scenarios. Spatial information and other attributes (e.g., presence of coastal protection works and backshore development) of the beaches of the 58 largest islands of the archipelago were obtained on the basis of remote-sensed images available on the web. Ranges of SLR-induced beach retreats under different morphological, sedimentological and hydrodynamic forcing, and SLR scenarios were estimated using suitable ensembles of cross-shore (1-D) morphodynamic models. These ranges, combined with empirically derived estimations of wave runup induced flooding, were then compared with the recorded maximum beach widths to provide ranges of retreat/erosion and flooding at the archipelago scale. The spatial information shows that the Aegean “pocket” beaches may be particularly vulnerable to mean sea level rise (MSLR) and episodic SLRs due to (i) their narrow widths (about 59 % of the beaches have maximum widths < 20 m), (ii) their limited terrestrial sediment supply, (iii) the substantial coastal development and (iv) the limited existing coastal protection. Modeling results indeed project severe impacts under mean and episodic SLRs, which by 2100 could be devastating. For example, under MSLR of 0.5 m – representative concentration pathway (RCP) 4.5 of the Fifth Assessment Report (AR5) of the Intergovernmental Panel on Climate change (IPCC) – a storm-induced sea level rise of 0.6 m is projected to result in a complete erosion of between 31 and 88 % of all beaches (29–87 % of beaches are currently fronting coastal infrastructure and assets), at least temporarily. Our results suggest a very considerable risk which will require significant effort, financial resources and policies/regulation in order to protect/maintain the critical economic resource of the Aegean archipelago. Published by Copernicus Publications on behalf of the European Geosciences Union. 450 I. N. Monioudi et al.: Assessment of island beach erosion due to sea level rise

The Effect of Beach Rock Formation on the Morphological Evolution of a Beach. The Case Study of an Eastern Mediterranean Beach: Ammoudara, Greece

ABSTRACT Alexandrakis, G.; Ghionis, G., and Poulos, S. 2013. The effect of beach rock formation on the morphological evolution of a beach. The case study of an eastern Mediterranean beach: Ammoudara, Greece. The present work investigates the decadal morphological evolution of a microtidal, perched beach and the effect that beach rock formations can have on coastal morphology. Using historical and recent morphological observations from Ammoudara Beach on the island of Crete, Greece, and numerical modeling, the interaction of beach rock formation and retreating coastline are investigated. The principal feature of the morphological evolution of the coastal zone under investigation has been the transformation of a beach rock formation, initially attached to the shoreface (1950s), to a submerged reef that is aligned subparallel to the present-day shoreline. At present, the beach rock is attached to the shoreface at sea level at the western part of the beach, but it has evolved to a submerged reef toward the east, being approximately 40 m off the shoreline at the central part and ∼70 m off the coastline at the eastern part of the beach. This kind of beach evolution is attributed to the interplay of natural hydrodynamic and sediment transport processes (that have been changing as the beach rock formation evolved to an offshore submerged reef) and to human intervention. The latter is exhibited mainly as changes in the sediment supply to the coastal zone (e.g., reduction in terrestrial freshwater/sediment influx, deterioration of sand dune field, and arbitrary abstraction of beach material). After a period of readjustment of the nearshore hydrodynamics to the changing morphology and vice versa, it seems that, at present, Ammoudara Beach has attained a new morphodynamic equilibrium where the shore-parallel reef acts as a submerged breakwater.

Hydrodynamic, neotectonic and climatic control of the evolution of a barrier beach in the microtidal environment of the NE Ionian Sea (eastern Mediterranean)

The existence of barrier beaches is crucial, as they act as a buffer zone to the associated wetlands, whilst they are sensitive to climate change. The present study offers an insight into the processes controlling the formation and evolution of the Gyra barrier beach (NW coast of the island of Lefkada) in the microtidal, tectonically very active Ionian Sea under the influence of regional climate change and human interference. Such investigations are sparse in the literature. Existing information regarding regional geology, sediment availability and human intervention is combined with the collection of geophysical data, field observations and simulations of nearshore hydro- and sediment dynamics, analysis of climatic variations with respect to offshore wind/wave patterns (including storminess), in situ measurements of recent morphometric changes (2006–2008) and historical shoreline changes (since the 1960s). The recent formation and evolution (mostly under retreat) of the Gyra barrier beach is shown to be the combined result of the regional seismotectonic setting, relative increase of sea level, coastal sediment transport patterns, as well as human impact (negative) on primarily terrestrial sediment influxes. The current erosional trend of the barrier beach is associated with a shift in the wind and wave direction (from SW to NW) of extreme storm events in the Ionian Sea since the 1980s. The regional climatic variations of the last decades are well correlated with the trend of the North Atlantic Oscillation.

Deltaic coastline retreat due to dam construction: The case of the River Alfios mouth area (Kyparissiakos Gulf, Ionian Sea).

ABSTRACT Ghionis, G., Poulos, S.E. and Karditsa, A., 2013. Deltaic coastline retreat due to dam presence: The case of river Alfios mouth area, Kyparissiakos Gulf, Ionian Sea. The deltaic coast of the Alfios river, and especially its mouth area, is undergoing intense erosion over the last decades. This erosion has been caused primarily by the dramatic reduction of the fluvial sediment fluxes, following the construction of two dams (in 1954 and 1967), with the second dam being located at a distance of only 6 km from the river mouth. A further decrease in sediments reaching the sea is induced by the extended (even not continuous) abstraction of sand and gravel from the rivers lower route. The resulting sediment deprivation in association with the highly energetic nearshore hydrodynamic regime has caused a retreat of approximately 450 m (from 1945 to 2003) of the mouth area of the R. Alfios. The northern part of the mouth has been affected more heavily by the erosional processes (shoreline retreat between 200 and 445 m) than the southern part (100–240 m retreat), the sediment losses of which are partially replenished by the northward longshore sediment transport of Kyparissiakos Gulf. Shoreline retreat at distances >1 km on either side of the rivers mouth is approximately equal, becoming minimal at distances >2 km. The erosional trend of the Alfios River deltaic coast, that has caused significant property losses and damage to coastal infrastructure, is expected to continue and may become more intense as a response to the anticipated future sea level rise.