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Examples of Morphological Changes


Case Study 1: Morphological evolution of the R. Alfios deltaic shoreline by G.Ghionis and S. Poulos 2005.

The mouth area of the R. Alfios located at the northern part of the Kyparissiakos Gulf, which lies along the west coast of Peloponnese, facing to the NE Ionian Sea. The catchment area of the R. Alfios covers an area of some 3665 km2, being mountainous with elevations exceeding 2200 m.

Figure 3. The mouth area of R. Alfios (NW Peloponnese, Ionian Sea) Topgraphic map published by the Hellenic Army Geographical Service, in 1972.)

Fluvial water and sediment fluxes are rather high, with mean annual discharge in the order of 67 m3/s (maximum=145 m3/s) (Therianos, 1974) whilst during flood events discharges oftenly exceed the 1000 m3/s. In accordance to high amounts of water discharge, the temperate type of climate, the relatively erodible lithology (Quaternary deposits + flysch ~52%), and the mountainous relief, the amounts of sedimentary material available for transport by the river network are expected also to be significant. Although, no direct measurements exist for the sediment fluxes of the R. Alfios, on the basis of monthly suspended sediment flux data available for other Greek rivers discharging into the Ionian Sea i.e . R. Acheloos (2.5x106 t), R Arachthos (7.3x106 t), R. Kalamas (1.9x106 t) and published information regarding sediment fluxes in the northeastern Mediterranean Sea (e.g. Poulos & Collins, 2002) an amount of some 2.5x106 tonnes per year of suspended sediment (i.e. SSL) and more than 3x106 tonnes of total sediment load are expected to be transported towards its deltaic coast by the R. Alfios, annually(Poulos et al., 2002). The delta is exposed primarily to wind-induced waves approaching from the S, SW and W and NW involving due to very long (hundreds of km) fetches a wave regime with wave heights >5 m, during storms and a potential longshore northward sediment transport in front of the river mouth in the order of 0.5 106 m3/yr (Ghionis et al., 2005). Over the last decades the major human interference to the natural deltaic evolution was the construction of the Ladona and Floka dams; the former is a gravity-type of dam producing 750.000 Volt of electric power, whilst the latter is an irrigation dam, that establishes a steady flow of fresh water of approximately 40 m3/hr, throughout the year. The Ladonas dam got in operation in 1955 cutting off an upstream area of some 900 km2, which represents the 25% of the total drainage basin. The second dam (Flokas), put in operation in 1967, being only 6 km away from the coastline and having upstream of it the 97% of the catchment, have reduced drastically the sediment fluxes, at least those related to that transported as bed load and most of the suspended sediment load. The consequences on the deltaic evolution, as revealed from the comparison of aerial photographs, incorporate a relatively rapid and spatially important shoreline retreat (see Fig. 4), which in the river mouth exceeds 300 m becoming smaller to the north and south but not being insignificant for distances larger than a few km.

Figure 4. Shoreline retreat of the Mouth area of R. Alfios following the construction of dams (Ghionis et al., 2005)

Bibliography sited

Ghionis G., Poulos S.E., Gialouris P. & Gianopoulos Th., 2005. Recent morphological evolution of the deltaic coast of R. Alfios due to natural processes and human impact. Proceedings of the 7th Panehellenic Geographical Congress, Mytilini, Oct. 2004, v.1, p.302-308 (in Greek)

Poulos S.E. and Collins M.B., 2002. Fluvatile sediment fluxes to the Mediterranean Sea: a quantitative approach and the influence of dams. In: S.J Jones.and L.E Frostick (eds),. Sediment Flux to Basins: Causes Controls and Consequences. Geological Society of London Special Publications, 191, 227-245.

Poulos S.E., Voulgaris G., Kapsimalis V., Collins M. and Evans G., 2002. Sediment fluxes and the evolution of a riverine-supplied tectonically-active coastal system: Kyparissiakos Gulf, Ionian Sea (eastern Mediterranean). (In:) Jones S.J. & Frostick L.E. (eds) Sediment Flux to Basins: Causes, Controls and Consequences. Geological Society, London, Special Publications, 191, 247-266.

Therianos A.D., 1974 The geographical distribution of the river water supply in Greece. Bulletin Geological Society, Greece, 11, 28-58 (in Greek).

Case Study 2: Sediment dynamics in the nearshore zone of Gouves (Heraklio, Crete) in relation to erosion, by S. Poulos (unpublished data 2006).

The area under examination is located between the torrential rivers of Gouvianos and Gournianos, on the North shores of the Heraklion Prefecture of Crete. The area is under an intense wave and wind regime (wave heights >5m during a storm) with the dominant winds being from N and NW and with wave runup (R) reaching elevations of up to of 2.9m on the beach face, resulting in erosion and shoreline retreat. These phenomena have been aggravated by human interventions such as the blockage of sediment fluxes of the aforementioned torrenrs, the construction of small ports, marinas and seawalls. The seabed is covered by sandy material, with the eastward longshore sediment transport to be in the order of 28x103m3 (Poulos et al., 1998).

Figure 5. Geomorphological and sedimentological characteristics of the study area (Poulos et al, 1998). Sampling stations for the present study are indicated (G1, G2, G3). Note: (n=1,2,..), bathymetry in metres.

The present contribution describes the effect of a ‘Meltemi’ event, on the resuspension and transportation of the nearshore sediments. The ‘Meltemi’ or etesians (in Greek means northern wins of yearly occurrence) appear at the beginning of May with low but also fluctuating frequency and with short duration; they preserve their character until the end of June. From the beginning of July, the frequency of Etesians increases reaching its greatest values towards the end of the month, which it then preserves until about mid-September, and then reduces at the end of October. According to the mean daily velocity the Etesians have been distinguished in 3 categories: weak (mean velocity 0-3.3m/s) moderate (3.4-7.9 m/s) and strong (≥ 8m/s) (Carapiperis, 1981). The outcome of this investigation is based upon the deployment of Autonomous Benthic Recorders (ABRs) equipped with an electromagnetic current meter (EMCM), a pressure sensor (wave height and period), and an optical backscatter sensor (OBS) for measuring turbidity (sediment resuspension). The deployment took place in July 2003 and covered a ‘Etesian’event with winds >6 B for a period of approximately 5 days. Figure 6 illustrates the current directions at each station during the study period together with the associated current speeds. It can be noted from Figure 6 that the current speeds increase and decrease relative to the development of the Meltemi event. The highest current speeds are experienced at G1 reaching a maximum of 16 cm/s in peak conditions. It can be seen that at station G1 and G2 there is a strong northerly component, this represents the reverse undertow currents that are produced as waves hit the coastline. The strength of this current is less at G2 due to the frictional effects on the seabed between the two stations. G3 on the other hand shows a more random distribution of current directions. There is still a northerly component but, once again, the strength of the flow has been reduced. Wave-generated currents can also be noted at G3 in terms of the south-easterly direction, this being the predominant wave direction in the area at this time of year.

Figure 6. Current directions and speeds for each station G1 (inshore), G2, and G3 (offshore) during the study period. Values on the ‘x’ axis refer to time in hours from the starting time of 15:52 on the 24th July 2003


The explanation for the occurrence of undertow involves the elevation of the main water level within the surf zone. This produces a seaward-directed pressure gradient of water, which on average is balanced by the momentum of the waves directed toward the shore (Komar, 1998). Wave height was seen to increase during the storm period reaching a maximum late on the 27th July (1.4-1.8m) after which it decreased to its previous level. The graphs of wave height (Figure 7) show that there is some degree of correlation between this significant wave height (Hs) and the amount of suspended sediment in concentration (SSC); this is most apparent at Stations G1 and G3 where the peaks of Hs and SSC coincide. At G2, there appears to be a time lag between the peak Hs and the peak in SSC; this time difference at Station G2 shows a lag of approximately 11 hours. It could be possible that the time lag related to the peak seen in G2 represents the movement of the breaker zone. Similarly to Hs, wave period (T) was seen to increase over the duration of the storm, with the SSC distribution appearing also to be related to T, as both parameters rise and fall with the progression of the Meltemi event.

Figure 7. Graphs representing the significant wave height (Hs) and suspended sediment concentration (SSC) over the study period.


The present study has investigated the effect of an ‘Etesian’ event, on the resuspension of sediments in Northern Crete. The results indicate that wave action is the dominant process in the resuspension of sediments as the nearbed unidirectional flow (current speeds ≤ 0.18 m/s) throughout the ‘Etesian’ event, never exceeding the critical velocity (Ucr) for the threshold of sediment movement. The nearshore wave heights also increased over the event from 0.2 to 1.7m with the larger of the deepwater waves were breaking, prior to their arrival in the nearshore region. The wave heights demonstrated a strong linear or exponential relationship to SSC, before peak storm conditions were attained. On the basis of the above, it may be concluded that in addition to the reduction in supply of sediment to the area (terrestrial and longshore), the ‘Etesian’ events during the summer months result in a further offshore transport of nearshore sediment. Although, in the absence of such strong events during the summer period months some of the sediment lost during winter storm events would perhaps allow for to be replenished. However, the observed continuous erosion along this section of the coastline over the last decade suggests that it is unlikely that calm periods, between the summer ‘Etesian’ events and the winter storms to be sufficient in order to replenish lost sediment.

Bibliography sited

Carapiperis L.N. (1968). The Etesian Winds: On the daily variation of the velocity of the Etesian winds in Athens.20pp

Komar P.D. (1998). Beach Processes and Sedimentation, Second edition. Prentice Hall, Upper Saddles River New Jersey, 544pp

Poulos S.E., Dounas K., Petihakes G. (1998) Study of the sedimentological and hydrological conditions of the Gournes shorezone (province of Heraklio, Crete). Proceedings of the 6th Panhellenic Geographical Congress, Thessaloniki, Oct. 2002, p. 304-311 (in Greek).

Case Study 3: Long-term geomorphological changes on the coastal area of the Inner Thermaikos Gulf (Greece),by Kapsimalis Vasilios, Dr. Geologist, Assitant Researcher, Hellenic Centre for Marine Research, Institute of Oceanography

The long-term geomorphological evolution of the deltaic coastal zone of the Inner Thermaikos Gulf, northern Greece, is studied for the last 150 years (1850–2000), based on detailed analysis of historical bathymetric charts (Albanakis et al., 1993; Poulos et al., 1994; Kapsimalis et al., 2005). These changes are affected by human-induced modifications in the basins of two main rivers (Axios and Aliakmon) and two smaller rivers (Gallikos and Loudias), which discharge into the Gulf (Poulos et al., 2000; Karageorgis et al., 2005; Karageorgis et al., 2006). In general, over the past 150 years, the Gulf has accumulated a net sediment volume of 1230 x 106 m3, at an average rate of accretion of 8 x 106 m3 a-1 or 12 x 106 t a-1. Some 85% of this load is deposited around the active river mouths, with approximately 15% being dispersed offshore (Kapsimalis et al., 2005). Over this period of time, three evolutionary ‘stages’ are identified on the basis of changes in sediment supply and associated human interference.

  1. From the middle of the 19th century to the early 20th century (Stage I: 1850–1916), the coastal system of the Gulf was controlled naturally, with a net marine sediment supply of some 430 x 106 m3, at an average fluvial discharge of 6.5 x 106 m3 a-1 or 10 x 106 t a-1 (Kapsimalis et al., 2005; Karageorgis et al., 2006). This input resulted in progradation of the delta complex, especially near the active river mouths.
  2. Subsequently, during Stage II (1916–1956), especially in its second part (1934–1956), human intervention to the natural system of the deltaic plain was at a maximum through: (a) artificial realignment of the main river channels (1934); (b) drainage of the Yiannitsa Lake and the Loudias Swamps (1935); (c) the instigation of other land reclamation projects (Karageorgis et al., 2006). The net riverine sediment supply increased considerably to 900 x 106 m3; this corresponds to an average input of 18 x 106 m3 a-1 or 28 x 106 t a-1 (Kapsimalis et al., 2005). Over this period, rapid progradation occurred at the active mouths of the Axios and Aliakmon Rivers. At the same time, some of the fine-grained components of the sediment load were dispersed over the Inner Thermaikos Gulf.
  3. Stage III (1959–2000) is strongly characterized by a further ‘cycle’ of human interference (Georgas and Perissoratis, 1992; Poulos et al., 2000; Karageorgis et al., 2005). This incorporates the construction of irrigation reservoirs and hydroelectric dams. Such structures have caused a significant reduction in sediment supply, leading to an overall erosional phase over the Gulf and a mean sediment loss of 2.5 x 106 m3 a-1 or 4 x 106 t a-1 (Kapsimalis et al., 2005). During this period, the river mouths underwent rapid retreat. The ‘active’ rivers prograded only minimally, with the lower reaches of the deltaic plain being subjected to coastal flooding. Furthermore, human activities have affected the circulation pattern of the Gulf (Nikolaidis et al., 2006) and texture of the offshore sea-bed sediments (Kapsimalis et al., 2005) resulting in the alteration of the associated benthic habitat (Voutsinou-Taliadouri and Varnavas, 1995).

References

Albanakis K., Vavliakis E., Psilovikos A., Sotiriadis L., 1993. Mechanisms and evolution of the delta of Axios River during the 20th Century. Proceedings of the 3rd Hellenic Geography Conference, Hellenic Geographical Society, Athens, 311–325.

Georgas D., Perissoratis C., 1992. Implications of future climatic changes on the Inner Thermaikos Gulf. In: Jeftic L., Milliman J. (eds.), Climatic change and the Mediterranean. UNEP, Edward Arnold, London, 495–534.

Kapsimalis V., Poulos S.E., Karageorgis A.P., Pavlakis P., Collins M.B., 2005. Recent evolution of a Mediterranean deltaic coastal zone: human impacts on the Inner Thermaikos Gulf, NW Aegean Sea. Journal of Geological Society, London, 162: 897-908.

Karageorgis, A.P., Skourtos M.S., Kapsimalis V., Kontogianni A.D., Skoulikidis N.T., Pagou K., Nikolaidis N.P., Drakopoulou P., Zanou B., Karamanos H., Levkov Z., Anagnostou C., 2005. An integrated approach to watershed management within the DPSIR framework: Axios River Catchment and Thermaikos Gulf. Regional Environmental Change, 5:138–160.

Karageorgis A.P., Kapsimalis V., Kontogianni A., Skourtos M., Turner K.R., Salomons W., 2006. Impact of 100-year human interventions on the deltaic coastal zone of the Inner Thermaikos Gulf (Greece): a DPSIR framework analysis. Environmental Management, 38(2): 304-315.

Nikolaidis N.P., Karageorgis A.P., Kapsimalis V., Marconis G., Drakopoulou P., Kontoyiannis H., Krasakopoulou E., Pavlidou A., Pagou K., 2006. Circulation and nutrient modeling of Thermaikos Gulf, Greece. Journal of Marine Systems, 60: 51-62.

Poulos S.E., Papadopoulos A., Collins M. B., 1994. Deltaic progradation in Thermaikos Bay, Northern Greece and its socio-economic implications. Ocean and Coastal Management, 22: 229–247.

Poulos, S.E., Chronis G.T., Collins M.B., Lykousis V., 2000. Thermaikos Gulf coastal system, NW Aegean Sea: an overview of water/sediment fluxes in relation to air–land–ocean interactions and human activities. Journal of Marine Systems, 25: 47–76.

Voutsinou-Taliadouri F., Varnavas S.P., 1995. Geochemical and sedimentological patterns in the Thermaikos Gulf, North-west Aegean Sea, formed from a multisource of elements. Estuarine and Coastal Shelf Science, 40: 295–320.


The implications of the expected sea level rise on the low lying areas of continental Greece in the next century. By Kosmas Pavlopoulos

A natural hazard that is expected to influence on a global scale the earth in the near future, is the anticipated rapid sea level rise by the to continental and glacier ice melt and expansion of the oceanic water masses triggered by a rise in air temperature due to the Greenhouse effect. Based on world-wide climatic data of the U.S. Environmental Protection Agency and the use of mathematical models, it is calculated that by the year 2050, the temperature will rise by 1C and sea level will be 15 cm higher while by the year 2100 the temperature will be 2C higher than today and sea level will have risen by about 34 cm. Thus, the rate of sea level rise will be 4,2 mm/year in 2100. In the case of deltaic deposits, an additional land subsidence due to sediment compaction should be taken into account.

Given the extensive stretches of low lying coastal areas that continental Greece possesses in the form of deltas ,lagoons,coastal alluvial plains and pocket beaches and their significant settlement, tourist and industrial development in the last decades, the implications of the expected sea level rise are examined for the coasts of continental Greece. Furthermore, the specific economic and social implications of the land use pattern of the coastal zones such as farmland, saltworks, fisheries, tourist installations, airports, etc. are also studied.

Human interference has influenced the natural evolution not only of the coastal environment but also the fluvial. An almost certain sea level rise will enhance the risks involved in the well-being of the coasts and the rivers. River channel diversions or cut-offs, irrigation, hydroelectric or regulation dams as well as coastal works such as jetties, wharfs, piers, landfills, highways, harbours and marinas constitute important elements that disrupt the coastal environment.

Coastal classification of Continental Greece

The coastline of continental Greece presents not only a great length but also a complex configuration. It is possible to group them in deltaic plains, lagoons, coastal plains, pocket beaches and steep coasts

Coastal classification of Continental Greece. We measured the coastal lengths of the five aforementioned categories of continental Greece at scale 1:50000. The coastal lengths correspond to steep coasts (48,04 %), coastal plains (38,27%) and to a much lesser degree, deltaic plains (6,39 %), lagoons (3,73 %) and pocket beaches (3,57 %) (fig 1.).


Figure 1. .

The distribution of the five coastal types by geographical department. Worthnoting is the great extent of low lying coasts (deltaic plains and lagoons) in Thrace (88 %). On the contrary, the steep coasts comprise about 2/3 of the coasts of Thessaly. The main region where deltaic plains have considerable extend are in Epirus (24,23%, Kalamas - Arakhthos and in Thrace (25,69 %, Evros).

Table 1.
Figure 2.


Expected sea level rise in the next 100 years

Given the vulnerability of low lying coastal areas by an expected sea level rise in the next 100 years, four deltaic plains were studied, namely Sperkhios, Evinos, Arakhthos and Kalamas. Using topographic maps at a scale 1:5000 and delineating the land below the 0.50 m contour line, the area that will be inundated by the sea by the year 2100 was calculated. In these 50 cm an anticipated sea level rise of 0.34 m by EPA (1995) is included together with more than 0.15 m of natural sediment compaction of the deltas (fig. 3).

Figure 3.

Generalizing for the 15 most important deltaic plains of continental Greece (Kalamas, Louros, Arakhthos, Akheloos, Evinos, Mornos, Pinios of Peloponnesus, Alfios, Sperkhios, Pinios of Thessaly, Aliakmonas, Axios, Strymonas, Nestos and Evros) and applying the mean land expected to be covered by the sea (13,16%), we come to the conclusion that about 306,63 km2 of land will be lost by the year 2100. In the case of the coastal plains, it is estimated and hoped that negligible amounts of land will be lost to the sea mainly due to steeper slopes and narrower land. In northern and western Peloponnesus for example, the coastline retreat will be insignificant due to the high elevations and slopes of the dunes and alluvial cones and fans. Costal wetlands will be covered by the rising sea level and an important natural resource of the environment of Greece will diminish dramatically cease to exist. The lagoons of Kotyhi, Messologi, Amvrakikos, and Porto Lagos that are important fishing grounds, will become shallow bays or gulfs. The extensive saltworks of Messologi and other areas of Greece will have to move farther inland.

References

Karybalis, E. 1996. Geomorphologic observations in the drainage basin of Evinos river, Ph.D. University of Athens (In Greek).

Maroukian H, 1990. Implications of sea level rise for Greece, Report of the I.P.C.G., Miami Conference, vol.2, pp. 161-181.

Maroukian, H., K. Gaki-Papanastasssiou, K. Pavlopoulos & A. Zamani 1995. Comparative geomorphological observations in the Kalamas delta in western Greece and the Sperkhios delta in eastern Greece. Rapp.Comm.int. Mer. Medit., 34, 110 (Abstract).

Maroukian, H., K. Gaki-Papanastassiou, K. Pavlopoulos, & V. Sabot 2004. The assumed future sea level rise as a natural Hazard threatening the coastlines of continental Greece. AGPH, v. XXXX, pp. 69-82.

Moutzouris, K. & H. Maroukian 1988. Greece In: Artificial Structures and Shorelines. H. J. Walker ed. New York: Academic Publishers, pp. 207-215.

Titus G.J. & V.K. Narayanan 1995. The probability of sea level rise. U.S. E.P.A., Washignton D.C.

Case Study 5: Long term geomorphological changes in the coastal zone of the Thermaikos Gulf, Salonika Region, North Greece by K.G.Vouvalides

Department of Physical & Environmental Geography, School of Geology, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece

Abstract

During late Pleistocene (Würm Glacial) the area surrounding the city of Thessaloniki and the northern part of Thermaikos Gulf was a low-lying valley bounded by a hilly terrain and drained by the Axios River and its tributaries (rivers Gallikos, Aliakmon and Anthemoundas at present). The Holocene transgression caused the inundation of the lower parts of the valley and gradually led to the present shoreline configuration. Along the north and northwestern parts of the area the coastal zone has been impacted by depositional processes of the Gallikos – Axios – Aliakmon rivers forming a very extensive deltaic complex. Thessaloniki delta plain is the largest (~2 000 km²) deltaic area of Greece. In contrast, along the eastern part of the region beaches are backed by coastal terraces and with some exceptions are characterized by erosional trends. A number of both prehistoric and historic coastal settlements existed in the region and have been affected in many ways and various degrees by the prolongation or the retreat of the coastline. The city of Thessaloniki is built on a hilly terrain in the upper most part of Thermaikos gulf, around a smaller embayment where the harbor and the seafront of the city are. Generally, the morphology of the city’s surrounding area involves a hilly terrain at the north and two lowland areas at the west, where the big deltaic plain of Axios is formed and at the east, between the capes Mikro Emvolo and Megalo Emvolo where is the Anthemuntas basin.


Introduction

The present morphology of both Thessaloniki Bay and Thermaikos Gulf is the result of numerous natural processes having taken place during the past 10,000 years. The most important of these processes has been the rise of the sea level resulted from glacial melting after the last glacial maxima (Würm) and the continuous sediment deposition from the Gallikos, Axios and Aliakmon Rivers which formed a large deltaic complex on the north and western parts of the Gulf. As the sea level rose the low lying regions were inundated and new equilibrium was established in the area. In particular, along the northern part of the advancing shoreline numerous river deltas were formed. The base level migration resulted in changing erosion/deposition conditions both on terrestrial and marine environments. Humans have appeared in the region during the past 7000 years (Grammenos, 1991; French, 1967). As expected, human settlements been filled with sediments delivered by the main rivers whereas others have been destroyed by coastal erosion and the retreating shoreline. Natural processes have been shaping the landscape until the beginning of the 20th century. Major human impacts include a series of hydraulic works as dam constructions, drainage of the floodplains, sand quarrying, canalization, land reclamation, and construction of levees and weirs. As a result, the evolution of the present landscape is not related to the sequence of natural processes but to the intensity of human impacts (Konstantinidis, 1989; Psilovikos & Psilovikos, 1997).


Study area

The study area includes Thessaloniki Bay and the northern part of Thermaikos Gulf (Fig. 1). The morphology of the northern and eastern parts of the study area is characterized by rolling hills composed by Tertiary and Quaternary sediments. Erosional trends exist there with only exception the coastal zone of Anthemoundas River.

Figure 1. Location of the study area together with the type of coasts found in the North Thermaikos Gulf and the Thessaloniki Bay.

In contrast to the eroding coasts on the north and eastern parts the western part of the study area is dominated by the prograding deltas of Gallikos –Axios – Aliakmon Rivers (Lykousis et al., 1981; Poulos et al., 1994). The present location of their channels and deltas is the result of numerous human interventions that have been taking place since the 1930’s (Albanakis et al., 1993). Most important the mouth of Axios River has been displaced from its natural course outside Thessaloniki Bay across cape Megalo Emvolo. The displacement of the river mouth was important in that it decelerated the siltation of Thessaloniki port (Evmorphopoulos, 1961). The low relief prograding coasts on the western part give place to the eroding coastal terraces on the eastern part even though deposition along the coastline occurs on isolated parts. Finally, deposition caused by humans along numerous parts of the coast of Thessaloniki Bay has resulted in manmade coasts.

Morphological changes in the coastal zone

The deltaic complex of the Aliakmon, Loudias, Axios, & Galikos Rivers

By the end of the last glacial age the study area comprised the lower part of a low lying river valley drained by the Axios River and its tributaries Gallikos, Aliakmon and Anthemoundas rivers together with other minor streams. The river mouth was located in the center of the present-day Thermaikos Gulf and below the 100m-depth contour (Lykousis and Chronis, 1989). The rise of the sea level flooded the river valleys and the coastline begun retreating to the north. Sea inundation reached beyond the present coastline about 30 km to the northwest totally drowning the area occupied today by the Thessaloniki – Giannitsa plain. The main port of the Macedonian era, Pella is found today 25 km inland. The higher base level shifted the accumulation area of river discharge more inland. Continuous sediment deposition took place in deltaic, lagoonal and marine environments (Fig. 2) (Fouache et al., in press). Today, the river deltas are characterized by relatively narrow prodelta slopes whereas their deltaic platforms extend much across the study area (Lykousis and Chronis, 1989).

Figure 2. Holocene reconstruction of the growth of the deltaic plain of Thessaloniki (Fouache et al., in press).

According to Fouache et al. (in press), the main stages in sedimentary and environmental conditions of the Thessaloniki plain are the following:

  • The first stage corresponds to the maximum extension of the sea intrusion. This stage is dated around 4000 B.C., which corresponds to the peak of the Holocene transgression. * From 4000 B.C. and 3000 B.C., we have the maximum extension of the shoreline in the actual alluvial plain.
  • During the second stage dated approximately from 3000 B.C. to 2700 B.C., we have a shallow marine to lagoonal environmental conditions all around the bay
  • The third stage shows a lacustrine occupation around 1600 B.C.
  • The fourth stage around 400 A.D. represents the initial formation of the present shoreline. In this stage we have archaeological evidences of Roman constructions (Bridge) very close to the coastal zone.
  • The last stage is till the beginning of the 20th century. At early 30’s we have the human interference with public works in the channels of the rivers and the coastal zone.


Erosional processes and shoreline migration

On the other hand along the eastern sides of northern Thermaikos Gulf and Thessaloniki Bay, sediment deposition was localized and was taking place only near the Anthemoundas river mouth. But as the sea was advancing and filling the Bay the remaining beaches were subjected to the erosional action of waves. The case when beach formations and sediments are not cohesive enough to resist to wave action is considered identical for the formation of steep beaches and coastal terraces. The terrace front is subjected to continuous wave action, which creates a scour at its base and hence leads to the collapse of the upper part. In this way the shoreline is gradually retreating backwards and the eroded sediments are deposited along the beach (Fig. 3).

Figure 3. The coastal terraces formation due to the erosional action of waves on the eastern coast of the Thermaikos Gulf.

The sea front of the Salonica city

Stratigraphical data from boreholes drilled along the coastal area of the city of Thessaloniki (Vouvalidis et al., 2005) showed that there was a surface layer of human debris up to 8 m thick above marine sediments. It is remarkable that the marine sediments are covered immediately by human debris of various ages (hellenistic, - roman – ottoman - recent). This suggests that the shoreline was initially inshore and shifted offshore due to debris deposition. The human impact was focused primary on the seafront of the old city of Thessaloniki (from the harbour to White Tower). The city of Thessaloniki has evolved as a harbour for more than 23 centuries, ancient and recent human debris lies directly on top of marine sediments. The coastline along the city’s seafront, in the absence of significant sedimentation from river input, should have been inshore its present position as transgression proceeded. But borehole data suggested that human activity over the centuries not only kept the seafront stable but both the city and the harbour extended seawards in order to provide more space to the inhabitants. The Thessaloniki case provides a good example of how humans were protected from increasing sea level and can be used as a reference for future reaction of major cities to sea level rise.


Concluding Remarks

This article is an attempt to be described the long term geomorphological changes on the coastal zone of the Thermaikos Gulf. The case study of the Thermaikos Gulf is a very typical example, of the wide range geomorphological changes could take place in the coastal zone. The human occupation has been adapted to the shoreline displacements since Neolithic times. During the historical period, Macedonian and Roman occupation let in the coastal zone numerous archaeological remains. According to literature, we know that the configuration of the coastal zone changed frequently. The descriptions of the landscapes from ancient authors confirm a strong spatial evolution and a human adaptation to the changes. This contribution of the palaeogeographical reconstruction of the Thermaikos coastal zone, it will be a useful tool to predict the future changes in the coastal zone due to global warming.

References

Albanakis, K., Vavliakis, E., Psilovikos, A. & Sotiriadis, L., 1993. Mechanisms and evolution of the delta of Axios River during the 20th century. Proceedings, 3rd National Geography Conference, 311-325.

Evmorphopoulos, L., 1961. The changes in Thessaloniki Bay. Technical Annal of Greece, 205-208, 51-76.

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