L’ evolution paléogéographique du bassin d’ Athènes pendant 6.000 ans BP

The Athenian basin is a very interesting area not only from archaeological point of view, since a large number of important archeological sites are situated, but also from geographical position. It is inhabited since Neolithic time. The human impact on the landscape is shown by the ancient constructions such as the Long Walls and the canalization of the rivers, in the area of the Athenian Basin and Piraeus. Its morphological variations such as, basins and coastal areas help the development (cultural, military) of the ancient (Athenian) greek civilization. The most important period of the antiquity was the Golden Age of Pericles (5th century BC) when Athens was the dominant city-state. The greatest buildings were constructed in that period such as Parthenon, the Long Walls and the complex of the Harbours (Mounichia, Zea, Kantharos).Except the human impact on the environment it is necessary to be mentioned the action of the fluvial and the coastal processes that acted in the broader area, in that geological period (Upper Holocene). So in this basin the sediments are fluvial, alluvial, anthropogenic, lagoonal and coastal in origin. Except the sea level rise which was about 2-3m below present time, climate variations (hot-wet, cold-dry periods) were observed during Holocene affecting the sedimentation. Lots of historical reports and maps were found through literature review in order to represent the paleogeography of the area.The available obtained information of the depositional environments in the Athenian basin, has been received by previous studies, 217 geotechnical boreholes were collected from literature review (Marinos, 1999), 10 sampling boreholes from the area of Piraeus and 14 geotechnical boreholes from the New Cultural Center of Athens (Funding By Stavros Niarchos Foundation). In addition topographic and geological maps were collected.A GIS database established to manipulate and analyze the collected data (spatial, sedimentological). A DEM created through the ArcGis v. 9.3. platform, to represent the recent topography of the study area. Also a geological and a geomorphological map were created for the representation of the landforms.The results obtained from the sedimentological analysis of the core samples (Cores form Piraeus P1-P10) were put into the software Grafistat for statistical analysis. Two deferent sedimentological methods were used (Method of sedimentological indicators and Passega Method) in order to determine the depositional environment, the river dynamics and the combination with others processes. The results of these sedimentological methods showed that the depositional environment was a combination of a low energy fluvial environment with the contribution of a coastal-lagoonal environment.After the interpretation of the boreholes, six lithostratigraphic units were defined (Anthropogenic sediments: Unit A, Holocene sediments: Units B1, B2, Pleistocene sediments: Unit C, Neogene sediments: Unit D, Substratum of the Athenian basin: Unit E). The lithostratigraphy of the boreholes is represented through the Rockworks v.15 software. Images, Cross-sections and 3d models of each lithostratigraphic unit were drawn to correlate them. Cross sections were drawn to represent and correlate the lithostratigraphic units of the study area (A-A’, B-B’, C-C’, D-D’, E-E’, F-F’). Six images of the structure of each lithostratigraphic unit (Unit A, Unit B1, Unit B2, Unit C, Unit D, Unit E) were created in order to represent the paleogeography of the different geological period, as mentioned above.Five images of the thickness of each unit were created to understand and separate the depositional dynamics of each geological period, in order to detect the thickest deposition comparing the different units.From the observation of these cross sections, images and 3d models, the Holocene evolution of the Athenian basin and the human impact on the paleo-landscape were detected and described.Through the GIS and data base platform, these results were combined and paleogeographic maps-images were created in order to represent the landscape for each lithostratigraphic unit (geological period) of the Athenian basin, and extract results for the temporal and spatial changes of the paleo-landscape and the involvement of the human impact on the depositional process in the Athenian basin during Holocene.Αντικείμενο της παρούσας Διδακτορικής διατριβής αποτέλεσε η παλαιογεωγραφική εξέλιξη της πεδιάδας των Αθηνών τα τελευταία 6.000 έτη. Ύστερα από βιβλιογραφική ανασκόπηση επιλέχτηκε η εφαρμογή της κατάλληλης μεθοδολογίας εμπλουτισμένης με την χρήση νέων τεχνολογιών και πολυπαραγωντικής ανάλυσης.Ειδικότερα, η έρευνα επικεντρώθηκε σε μεθόδους παλαιογεωγραφικής αναπαράστασης της περιοχής μελέτης προκειμένου να δοθεί μια εικόνα της κατάστασης της περιοχής τελευταία 6000 έτη.Για να επιτευχθεί ο στόχος αυτός χρησιμοποιήθηκε μεγάλο εύρος δεδομένων κα στοιχείων.Συλλέχθηκαν γεωλογικά, τοπογραφικά, βυθομετρικά, ιστορικά, γεωτρητικά (227 γεωτρήσεις) και κοκκομετρικά-ιζηματολογικά δεδομένα (P2-P4) για την περιοχή μελέτης.Από την ανάλυση και αποτύπωση των χωρικών δεδομένων προέκυψε η χαρτογραφική απεικόνιση της περιοχής με τη χρήση σύγχρονων λογισμικών Γεωγραφικών Συστημάτων Πληροφοριών, γεγονός που συνέβαλλε στη δημιουργία ενός ακριβούς τοπογραφικού υποβάθρου που βοήθησε στην αναπαράσταση της παλαιογεωγραφίας της περιοχής.Τα κοκκομετρικά-ιζηματολογικά δεδομένα των δειγμάτων των γεωτρήσεων P2-P4 αναλύθηκαν μέσω των μεθόδων Passega και ιζηματολογικών δεικτών προκειμένου να προσδιοριστεί το περιβάλλον καθώς και το μέσο απόθεσης των ιζημάτων.Από την ενδελεχή μελέτη και ανάλυση των δειγμάτων σε συνδυασμό με την στρωματογραφία όλων των γεωτρήσεων που συλλέχθηκαν, έγινε διαχωρισμός και αρχειοθέτηση των 6 λιθοστρωματογραφικών ενοτήτων που προέκυψαν.Η απεικόνιση των ενοτήτων αυτών σε δισδιάστατα και τρισδιάστατα μοντέλα είχε ως αποτέλεσμα την εξαγωγή συμπερασμάτων για την παλαιογεωγραφία της αντίστοιχης περιόδου.Τα αποτελέσματα της εν λόγω έρευνας ερμηνεύτηκαν, συσχετίστηκαν και εμπλουτίστηκαν τόσο με τις ιστορικές πηγές όσο και με τα σύγχρονα δεδομένα της περιοχής της πεδιάδας των Αθηνών.Ειδικότερα, όπως προκύπτει από τα παραπάνω παρατηρείται μια λιμνοθαλάσσια περιοχή με μεγάλα πάχη των λιμνοθαλάσσιων αποθέσεων στην παράκτια περιοχή του διδακτορικού, η οποία χώριζε τον Πειραιά από την υπόλοιπη Αθήνα. Η περιοχή αυτή προσχώθηκε κυρίως από ποταμοχειμάρρια ιζήματα καθώς και από την ανθρώπινη παρέμβαση.Παράλληλα παρατηρήθηκαν έντονες επεμβάσεις και στο υδρογραφικό δίκτυο της περιοχής, αφού σημειώθηκαν εκτροπές καθώς και επικαλύψεις των κοιτών.Τα νέα δεδομένα που προέκυψαν κατά την εκπόνηση της διδακτορικής αυτής διατριβής έδωσαν τη δυνατότητα, της παλαιογεωγραφικής αναπαράστασης μιας τελείως αστικής περιοχής, και συγχρόνως οδήγησαν στην δημιουργία μιας πολύτιμης βάσης δεδομένων που περιλαμβάνει τόσο ποσοτικά όσο και ποιοτικά στοιχεία

Assessment of Wave Storm-Induced Flood Vulnerability in Rhodes Island, Greece

Coastal areas are threatened by extreme meteorological phenomena, such as wave storms. Therefore, the analysis of such events, such as providing information for their potential hazards assessment, is a key element in coastal management. In this study, a preliminary assessment of flood vulnerability due to storms was performed in Rhodes Island, Greece. Firstly, storm events were defined in terms of significant wave height, peak period, and duration, and they were grouped by means of cluster analysis into five classes (from weak to extreme) reflecting the intensity of each event. Subsequently, flood hazard was assessed by using an empirical formula for wave run-up calculations on cross-shore profiles and storm surge data at the region. Finally, a Flood Vulnerability Index (FVI) was used for assessing vulnerability according to a scale from very low to very high. The most intense storms were found to occur in the eastern, southeastern, and southern part of the island. More than 60% of storms were classified as weak, while extreme events were found to occur with a frequency of less than 2.5%. Regarding flood hazard and vulnerability, the maximum values of wave run-up were calculated in the southeastern region, but the most vulnerable part was found to be the northwestern region, as the FVI was assessed as very high for weak and extreme events

Geomorphological changes in the coastal area of Farasan Al-Kabir Island (Saudi Arabia) since mid Holocene based on a multi-proxy approach

International audienc

Geomorphological changes in the coastal area of Farasan Al-Kabir Island (Saudi Arabia) since mid Holocene based on a multi-proxy approach

International audienc

The Role of Sea State to the Morphological Changes of Prasonisi Tombolo, Rhodes Island, Greece

Wave-induced morphodynamic processes that cause formation, preservation, and destruction of the Prasonisi tombolo in Rhodes Island are investigated, based on satellite image analysis and numerical modeling. A new method is developed for extracting wave events that consist of successive wave data of similar characteristics. The wave events refer either to wind seas or swell seas. This process combined with the satellite image analysis is then utilized for the derivation of the most representative wave scenarios that affect tombolo and salient formation. In particular, the main factors that play a significant role in tombolo and salient evolution are the offshore wave conditions, the location and width of the surf zone, the maximum value of the wave breaking index in the study area, and the initial bottom bathymetry before the study area is exposed to a new sea state. In general, the proposed method provides a realistic insight into tombolo morphodynamics and can be used to provide a cost-effective approach and a wave data-reduction technique for coastal engineering studies

Cross-Comparison of the “BathySent” Coastal Bathymetry to Sonar Measurements and Ratio Model Technique: Pilot Sites in the Aegean Sea (Greece)

The proposed novel “BathySent” approach for coastal bathymetric mapping, using the Copernicus Sentinel-2 mission, as well as the assessment and specification of the uncertainties of the derived depth results, are the objectives of this research effort. For this reason, Sentinel-2 bathymetry retrieval results for three different pilot sites in Greece (islands of Kos, Kasos, and Crete) were compared with ground-truth data. These data comprised high-resolution swath bathymetry measurements, single-beam echosounder measurements at very shallow waters (1–10 m), and the EMODnet DTM 2018 release. The synthetic tests showed that the “BathySent” approach could restitute bathymetry in the range of 5–14 m depth, showing a standard deviation of 2 m with respect to the sonar-based bathymetry. In addition, a comparison with the “ratio model” multispectral technique was performed. The absolute differences between conventional Earth Observation-based bathymetry retrieval approaches (i.e., linear ratio model) and the suggested innovative solution, using the Sentinel-2 data, were mainly lower than 2 m. According to the outcome evaluation, both models were considered to provide results that are more reliable within the depth zone of 5–25 m. The “ratio model” technique exhibits a saturation at ~25 m depth and demands ground calibration. Though, the “BathySent” method provides bathymetric data at a lower spatial resolution compared to the “ratio model” technique; however, it does not require in situ calibration and can also perform reliably deeper than 25 m

Assessment of the physical impact of a short-term dredging operation on a semi-enclosed environment: South Euboean Gulf, Greece

The potential influence of short-period (May-June 2012) dredging activities (for the installation of a submarine gas pipeline) on physical properties of the marine environment of two shallow-water sites in the Aliveri and Varnavas areas of South Euboean Gulf (Greece) has been evaluated. During the dredging operation in Varnavas, the induced dredge plume traveled up to 750 m from the shoreline, featured by light attenuation coefficient (c(p)) maxima of 4.01-4.61 m(-1) and suspended particulate matter (SPM) concentrations up to 6.01 mg L-1. After dredging the previous parameters reduced to the ambient seawater condition, 0.45 m(-1) and < 2.8 mg L-1 on average, respectively. Likewise in Aliveri, the dredging-associated sediment plume drifted offshore up to 400 m from the shoreline, characterized by c(p) maxima of 2.11-4.86 m(-1) and SPM concentrations up to 13.07 mg L-1. After the completion of the excavation and trenching activities, the c(p) and SPM values were restored to the pre-disturbance condition, 0.6 m(-1) and < 2.2 mg L-1 on average, respectively. The migration of the dredge plume in both dredging sites was accomplished through the formation of intermediate and benthic nepheloid layers, whose development and evolution were governed by seawater stratification and flow regime. The dredging-derived SPM levels appeared to increase within a distance of no more than 300 m from the shoreline (near-field zone). Based on data from the literature, this SPM enhancement together with the deposition of a post-dredging residual mud veneer in the near-field zone could deteriorate local marine biota, but in a reversible way

Paleoenvironmental Evolution and Sea Level Change in Saronikos Gulf (Aegean Sea, Greece): Evidence from the Piraeus Coastal Plain and Elefsis Bay Sedimentary Records

International audienceThorough faunal (benthic foraminifera, ostracods, molluscs) and palynomorph analyses as well as magnetic susceptibility measurements performed on the Piraeus coastal plain sedimentary sequences have shed light on the paleoenvironmental evolution of the area since ca. 9000 cal BP. Benthic and palynomorph assemblages along with magnetic susceptibility suggest a typical lagoonal environment with significant freshwater inputs at the eastern part of the plain after 8700 cal BP. Between 7500 and 5400 cal BP, microfaunal assemblages, mollusc fauna and magnetic susceptibility suggest a shallow marine paleoenvironment, with Piraeus forming a tied island in the center of the bay. Since ca. 4800 cal BP a closed oligohaline lagoon is evidenced in the western part of the Piraeus plain further developed to a marsh after 2800 cal BP, while a coastal environment associated with the fluvio-deltaic system of Kifissos and Korydallos Rivers is continually developing to the west. Signs of cultivation and grazing activities in the area are evidenced since the Early Bronze Age, culminating during the Classical Period. A comparison with a well-dated marine record, recovered from the nearby shallow Elefsis Bay, provides a reasonable estimation of ~5 mm/yr for the absolute sea level rise rate in the inner Saronikos Gulf during the Mid-Holocene

Evidence from the Piraeus coastal plain and Elefsis bay sedimentary y records. Water

International audienc

Paleoenvironmental Evolution and Sea Level Change in Saronikos Gulf (Aegean Sea, Greece): Evidence from the Piraeus Coastal Plain and Elefsis Bay Sedimentary Records

International audienceThorough faunal (benthic foraminifera, ostracods, molluscs) and palynomorph analyses as well as magnetic susceptibility measurements performed on the Piraeus coastal plain sedimentary sequences have shed light on the paleoenvironmental evolution of the area since ca. 9000 cal BP. Benthic and palynomorph assemblages along with magnetic susceptibility suggest a typical lagoonal environment with significant freshwater inputs at the eastern part of the plain after 8700 cal BP. Between 7500 and 5400 cal BP, microfaunal assemblages, mollusc fauna and magnetic susceptibility suggest a shallow marine paleoenvironment, with Piraeus forming a tied island in the center of the bay. Since ca. 4800 cal BP a closed oligohaline lagoon is evidenced in the western part of the Piraeus plain further developed to a marsh after 2800 cal BP, while a coastal environment associated with the fluvio-deltaic system of Kifissos and Korydallos Rivers is continually developing to the west. Signs of cultivation and grazing activities in the area are evidenced since the Early Bronze Age, culminating during the Classical Period. A comparison with a well-dated marine record, recovered from the nearby shallow Elefsis Bay, provides a reasonable estimation of ~5 mm/yr for the absolute sea level rise rate in the inner Saronikos Gulf during the Mid-Holocene