Greek case studies: Morphological evolution of the R.Alfios deltaic shoreline

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Examples of Morphological Changes

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

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

Figure 1. The mouth area of River 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 often exceed the 1000 m3/s. In accordance to high amounts of water discharge, the temperate climate, the relatively erodible lithology (Quaternary deposits and flysch ~52%), and the mountainous relief, the amounts of sedimentary material available for transport by the river network are expected to be significant. No direct measurements exist for the sediment fluxes of the River Alfios. On the basis of monthly suspended sediment flux data available for other Greek rivers discharging into the Ionian Sea, i.e . River Acheloos (2.5x106 t), River Arachthos (7.3x106 t), River Kalamas (1.9x106 t) and on the basis of published information on sediment fluxes in the NE Mediterranean Sea (e.g. Poulos & Collins, 2002), an amount of some 2.5x106 tonnes per year of suspended sediment and an amount of more than 3x106 tonnes of total sediment load are expected to be transported annually by the River Alfios towards its deltaic coast (Poulos et al., 2002). The delta is exposed primarily to wind waves approaching from the S, SW and W and NW. Due to very long (hundreds of km) fetches, a wave regime with wave heights >5 m during storms drives a longshore northward sediment transport in front of the river mouth in the order of 0.5 106 m3/yr (Ghionis et al., 2005).

Figure 2. Shoreline retreat of the Mouth area of River Alfios following the construction of the dams (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, operational in 1955, has an upstream catchment area of some 900 km2, representing 25% of the total drainage basin. The second dam (Flokas), operational in 1967, is only 6 km away from the coastline; 97% of the catchment is situated upstream of the dam. The dam has reduced drastically the sediment fluxes: almost all the bed load transport and most of the suspended sediment transport. The consequence on the deltaic evolution, as revealed from the comparison of aerial photographs, is a fairly rapid large scale shoreline retreat (see Fig. 2), which in the river mouth exceeds 300 m. The retreat decreases to the north and south, but for distances larger than a few km it remains significant .

Bibliography sited

Ghionis G., Poulos S.E., Gialouris P. & Gianopoulos Th., 2005. Recent morphological evolution of the deltaic coast of River 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).

The main authors of this article are Ghionis, George and Poulos, Serafim
Please note that others may also have edited the contents of this article.