West Thermaikos Coastal Zone

The coastal zone extending from Thessaloniki City

westwards and southwards to

TERRA INCOGNITA: Eco-Tales for Thessaloniki's sea line

westwards and southwards to

Axios and Aliakmon river mouths.

A coastal engineering point of view

Yiannis Savvidis

Civil Engineer, PhD in Coastal Engineering

Assoc. Prof. of Physical Oceanography, ATEITh.

Thessaloniki's coastline• The coastline extending from Thessaloniki City westwards and southwards to Axios and Aliakmon river mouths- A coastal engineering point of view

• The most characteristic regions and sites of special ecological interest along the north and west coastal zone of Thermaikos Gulf include:

* The Port of Thessaloniki* The Port of Thessaloniki

* The submarine outfall

* The river mouths- The Axios river delta

* The region of Chalastra (North of Axios river delta) –

an area with mussel farms

* The region of Agathoupolis-Methoni - (South-West of

Axios delta) also an area with mussel farms and touristic

beaches for swimming

STRUCTURE OF THE PRESENTATION

(1) The Thermaikos Gulf as the extended area which includes the coastline westwards & southwards of Thessaloniki City

(2) The wind, coastal & oceanographic conditions

TERRA INCOGNITA: Eco-Tales for Thessaloniki's sea line

(2) The wind, coastal & oceanographic conditions

(3) The most important sites and pollution sources and their relation to the environmental conditions of the area

(4) Proposed types of structures due to the physical and environmental conditions of the region

(1) The Gulf of Thermaikos

Thessaloniki City

Axios River Delta

Figure 1. The Thermaikos Gulf. The ellipse depicts the coastal zone extending from Thessaloniki city westwards and southwards

to Axios and Aliakmon river mouths

The Gulf of Thermaikos

The Gulf of Thermaikos is located in the northwestern part of the Aegean Sea, situated north of the line Epanomi- Atherida capes, defining the eastern and western limits of that boundary. Figure 1 illustrates the gulf and its sub-regions :

(a) the Bay of Thessaloniki, occupying the northern part of Thermaikos Gulf, and extending southwards to the line ‘cape Micro Emvolo – Galikos river mouth’ (with depths varying up to 20 m)

(b) the Gulf of Thessaloniki, which extends from the line ‘cape (b) the Gulf of Thessaloniki, which extends from the line ‘cape Micro Emvolo – Galikos river mouth’, to the line ‘cape Megalo Emvolo –Axios river mouth’ (with depths varying up to 27m)

(c) the inner Thermaikos Gulf extending to the south of the line ‘cape Megalo Emvolo –Axios river mouth’ ‘to the line cape Epanomi – cape Atherida’ and (with depths varying up to 40m)

(d) There is also the outer Thermaikos Gulf extending to the south of the Thessaloniki Gulf reaching the southern boundary line ‘cape Posidi – cape Platamonas’ (Figure 2)

Figure 2. The extended area of Thermaikos Gulf

(2) The wind - coastal & oceanographic conditions on the area

–wind conditions

–currents - water circulation

–waves’ climate –waves’ climate

–tides (astronomical tides)

–sediments’ transport

–red tides (algae blooms)

• North and northwestern winds blow with the highest frequency (about 22.9 and 18.17 % respectively).

These winds blow most of the time of the year and mainly during the winter.

• South and southeastern winds are also frequent (with

wind conditions

• South and southeastern winds are also frequent (with frequency about 14.02 % and 11.97% respectively).

These winds are more frequent during the summer period (Katsoulis, 1970)

The seawater circulation and the wave climate of Themaikos Gulf are mainly determined by the wind conditions

currentsThe overall water circulation pattern in Thermaikos Gulf is characterized by northerly water movement, from the central and eastern part of the Gulf; this is compensated by southerly movement along its western part. Current speeds are of the order of 5-20 cm/s near the water surface and up to 9 cm/s near the seabed (Poulos et al. 2000).Water masses from the North Aegean enter through the east part and exit through the west part of the gulf

Figure 3. The overall water circulation in Thermaikos Gulf

currents –water circulation

Prevailing water circulation (a) during winter (left) under the influence of N-NW prevailing winds (b) during summer (right) under the influence of S-SE >> windsSurface circulation is depicted with vectors of elliptical shape (eddies) while deep circulation with single vectors (Ganoulis, 1994)

Figure 4. The prevailing water circulation in Thermaikos Gulf

waves

Waves in the region (mean in the year) are of the order of 20 cm according to numerical models (HCMR, 2005)

Wave heights, and especially the direction of wave propagation, are governed by the existing wind regime; Waves related to southerly winds are considered to be the most important in terms of their magnitude; these are associated with the longest fetches. Hence, high waves of long wavelength are to be expected only from high waves of long wavelength are to be expected only from southerly directions. In contrast, the northerly components of the wind spectrum have a high frequency of occurrence but smaller fetches; despite these smaller fetches, they generate surface gravity waves influencing the general water surface circulation of Thermaikos Gulf (Poulos et al. 2000)

Only for SE strong winds we can expect wave heights more than 2 m on the coastal zone south of Axios and Aliakmon rivers’ mouth.

tide

Tide, of 12hrs period, in the region is small like all over the Aegean Sea and the Mediterranean generally. According to the tide recorder of Thessaloniki Port (Variangin, 1979)

• mean tidal height 0,25 m above MSL (mean sea level)

• maximum high tide 0,72 m >>

• minimum low tide 0,74 m >>• minimum low tide 0,74 m >>

• mean high tide 0,14 m >>

• mean low tide 0,10 m >>

sediment transport

The main rivers of the area outflow to the west coasts of the Thermaikos Gulf and the sediments transported (sand and silt and clay) settle mainlyalong the west coasts. While a small amount of fine suspended particulate matter escapes through the south boundary of through the south boundary of the Gulf

For this reason the waters along the west coastline, (waters of Pieria coasts) are more turbid and less clear than the waters on the opposite coasts at Chalkidiki.

Figure 5. The figure shows the sedimentation over the gulf after a period of one year – with the suspended particulate matter entering the gulf from the rivers’ mouth (Savvidis, 2000)

red tides

• Red tide is a common name for a phenomenon also known as an algal bloom (large concentrations of micro-organisms). It is an event in which marine or fresh water algae accumulate rapidly in the water column resulting in discoloration of the surface water. (It is usually found in coastal areas)

• Thermaikos gulf is one of the most eutrophic greek basins due to the rivers eutrophic greek basins due to the rivers discharging organic matter. Therefore according to the weather conditions red tides appear frequently.

• Harmful algae bloom were recorded in low population densities, all over the year in Thermaikos Gulf.

• A mathematical model was developed to simulate the dispersion in space and time of the algae after the appearance of a bloom episode (Patoucheas and Savvidis, 2010)

Figure 6. Thermaikos Gulf and the A & B points which depict the locations of algae bloom (Patoucheas and Savvidis, 2010)

red tides

Figure 7 - The concentrations of algae (cells /L) a week after the bloom in position A under the influence of N and S winds of speed 7 m/s

red tides

Figure 8 - The concentrations of algae (cells /L) a week after the bloom in position B under the influence of N and S winds of 7 m/s

(3) The most important sites and pollution sources and their relation to the environmental

conditions of the area

Figure 9.

1 Port of Thessaloniki (dendropotamos), 2 Submarine Outfall, 3 Axios, 4 Loudias, 5 Aliakmon

General

• Pollution and eutrophication of the nearshore marine environment have resulted from the:

inputs of industrial wastes,

urban untreated sewage and

The main environmental pressures and the main pollution sources

(depicted in the previous slide)

urban untreated sewage and

agricultural activities on the coastal plains

• The construction of dams along the routes of the main rivers has reduced dramatically the water sediment fluxes; this caused, for example, retreat of the deltaic coastlines and seawater intrusion into the groundwater aquifers.

• Area of Port of Thessaloniki (Fig.10)

• Rivers and drainage canals (Fig.11)

……….the main pollution sources

• The submarine outfall (Fig.12)

• Mussel Farms (Fig.13)

Port of Thessaloniki

Area of Port of Thessaloniki(pollution from rare accidental oil slicks, ore and other stored

Figure 10. Port of Thessaloniki

ore and other stored bulk cargo blown by the wind to the sea, and untreated sewage disposal of the west part of the city) Fig.10

Figure 10a.

East side of the port

Figure 10b.

West side of the port

Axios

Loudias

Aliakmon

Rivers and drainage canals receiving the waters from the cultivated land adjacent to the coastal line (pollution source of toxic and other elements). More specifically the intensive cultivation and drainageof the irrigation water of the City of Thessaloniki and

Figure 11. The rivers outflowing to the west coasts of the gulf

AliakmonCity of Thessaloniki and adjacent areas of Imathia and Pieria, burden uncontrollablythe gulf with nutrients from the drainage of fertilizers that farmers use without control (these outflows usually contain toxic elements from the pesticides). Fig.11

Submarine Outfall

The submarine outfall that transports the treated wastewaters and outflows in the gulf, away from the

submarine outfall

Figure 12. Disposal of the wastewaters to 20m depth at a distance 2km from the coast

gulf, away from the coast (pollution source of nutrients and heavy metals) Fig.12

Wastewaters from Thessaloniki western areas and the submarine outfall

• The company of water supply and drainage of Thessaloniki that manages the liquid wastes of the city has already constructed two Central Sewage main Collectors. The major transfers the sewage of the greater Thessaloniki area to the west coast of the Gulf (northeast of Axios delta) and the minor one referring to Thermaikos municipality, to the east coast of the gulf.the gulf.

• The one of the west coast, collects the wastewaters from the Thessaloniki City and the industries on the west areas of the city, and transfers them to the treatment plant near the Gallikos river mouth. From there, the treated waste waters are transferred by an underground pipe entering the sea as a submarine outfall and dispose the wastewaters northeast of Chalastra bay (northeast of Axios delta) via a Y shape diffuser

Axios Delta – Mussel Farms

Figure 13. Axios Delta and the mussel farms

Intensive Mussel Cultures

The main environmental pressures, which affected negatively the delta’s area ecological conditions, are : water discharge decrease, drainage works, urbanization, and imported pollution (Karageorgis et al., 2004).

Figure 14.

Photo of the floating barrels (enhancing the buoyancy)which constitute the upper part of the system of mussel farms with the mussel

clusters hanging underwater (not seen)

Water quality in the area of mussel farms

and further south of the river mouths

• There are important impacts of the mussel units on the waters of northwest gulf of Thessaloniki. The environmental parameters of water quality, measured during a recent research program (Alexander TEI of Tessaloniki, 2007), showed the following results: The concentration of dissolved oxygen was in the limits of hypoxia (mean value of dissolved oxygen 3 mg/l). Values of dissolved oxygen less than 4 mg/l describe, according to the dissolved oxygen less than 4 mg/l describe, according to the international literature , correspond to a mediocre to bad water

quality.

• The nutrients entering the gulf mainly from the Aliakmon river’s mouth (coming from agricultural activities) have caused, along the coasts, south of the rivers’ mouths, to the open sea of Pieria coastline, a circular area of trapped “green” waters which reminds a sea marsh (fig. 15).

south of Axios river mouth and

south of Aliakmon river mouth

Aliakmon river mouth

Axios river mouth

stagnant

waters

Figure 15. Axios and Aliakmon river mouths and the adjacent coastal areas

(4) Proposed structures due to the particular

conditions of the region

Special conditions and parameters to be considered :

• Conventions for the protection of this environment of special ecological interest (Ramsar, Natura e.t.c.)

• Shallow coastal waters with mild slopes of the seafloor

• Unconsolidated sediments easily re-suspended by currents and waves waves

• Semi-enclosed coastal area with low water renewal rates

• Intense activity of mussel farming

• Mild wind and wave conditions most of the time in the year

The above factors lead to the consideration of alternative structural solutions of

Light harbor and coastal structures friendly to the specific physical and environmental characteristics of this region.

This is in line with the concept of “minimum footprint”.

Light structures - floating breakwaters or large scale pontoons, friendly to the environment

Figure 16. Floating breakwaters for mild wave climates.

Other proposed structures

• Positioning of devices for the harnessing of the wind and wave energy at sites where the wind fetch can be sufficiently large e.g. south of the region of Axios Delta

This is also in line with the concept of “minimum footprint” by offering lightweight autonomous infrastructure that returns energy to the city through the reuse of natural resources: water, wind and solar power

(website of the workshop)

• Construction of vertical seawalls along coastal zones where the • Construction of vertical seawalls along coastal zones where the stagnation of the sea water is obvious and constitutes a very serious and unpleasant problem. This practice aims to cause reflection of the waves' energy enhancing the waters’ circulation and finally avoiding the unpleasant situation of stagnant waters and accumulation of floating pollutants.

• Construction of breakwater – pier to protect enclosed bays from the accumulation of algae transported there by the prevailing local water circulation

Example of construction of a breakwater on the coastal zone south of Axios river mouth for the protection of a

coastal strip against the accumulation of algae(based on modeling studies)

3000

4000S-SE wind 5m/sa

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breakwater

S-SE wind 5m/s

breakwaterSavvidis Y. & C. Koutitas (2000)

References

Alexander Technological Educational Institution of Thessaloniki (ATEITH). 2007. Water circulation in Organized Areas of Aquaculture Development and land-planning and environmental management interventions. Final Technical Report. Archimedes II. Scientific coordinator A. Moriki. 344 pages (in Greek).

Ganoulis, J.G., Engineering Risk Analysis of Water Pollution: Probabilities and Fuzzy Sets, VCH: Weinheim, Germany, 1994.

Hellenic Center of Marine Research (HCMR), 2005. State of Hellenic Marine Environment. Editors: Papathanassiou E. & A. Zenetos,

Katsoulis (1970), ‘Wind Conditions over the Aegean Sea’, Doctorate Dissertation, University of Athens, Athens (in Greek).

Karageorgis, A. P., Skourtos, M. S., Kapsimalis, V., Kontogianni, A.D., Skoulikidis, N.Th., Pagou, K., Nikolaidis, N.P, Drakopoulou, P., Zanou, B., Karamanos, H., Levkov, Z. & Anagnostou., Ch. (2005). An intergrated approach to watershed management within the DPSIR framework: Axios River catchment and Thermaikos Gulf. Reg. Environ. Change, 5, 138-160.

Kourafalou, V.H., Savvidis, Y.G., Krestenitis Y.N. & Koutitas, C.G. (2004). Modelling studies on the processes that influence matter transfer on the Gulf of Thermaikos (NW Aegean Sea). Continental Shelf Research, 24, 203-222.

Koutitas C. (1988), ‘Mathematicall models in Coastal Enginnering’, Pentech Press Limited, London (UK)Koutitas C. (1988), ‘Mathematicall models in Coastal Enginnering’, Pentech Press Limited, London (UK)

Poulos, S. E., Chronis, G. Th., Collins, M.B. & Lycousis 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.

Patoucheas D.P. and Savvidis Y. G (2010) “A HYDROBIOLOGICAL MODEL AS A TOOL FOR THE DETECTION OF HAB EPISODES. APPLICATION TO THERMAIKOS GULF”, Fresenius Environmental Bulletin Volume 19 – No 9b, pp. 2100-2108

Savvidis Y., C. Koutitas &Y. Krestenitis, (2001). ‘Development and application of a three dimensional cohesive sediment transport mathematical model.’ Journal of Marine Environmental Engineering, Vol. 6, pp. 229-255

Savvidis Y. & C. Koutitas, ‘Simulation of transport & fate of suspended matter along the coast of Agathoupolis (N. Greece)’, Proceedings of the 5th International Conference Protection and Restoration of the Environment, Thassos, Greece, July, 2000

Variangin M., 1972. Tides and Tidal heights of Greek Harbors, Hydrographic Service (in Greek).

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TERRA INCOGNITA: Eco-Tales for Thessaloniki's sea line