Coastal erosion Turkey
Vulnerabilities - The Turkish coast
The Turkish coastline is 8,333 km long and is bordered by four different seas: the Mediterranean Sea, the Black Sea, the Aegean Sea, and the Marmara Sea, which is connected to the Black Sea by the Bosphorus Strait and to the Aegean Sea by the Dardanelles Strait (3).
Coastal erosion along Turkish shores may yield about 6% of GNP for capital loss. Although coastal cities cover less than 5% of the total surface area of Turkey, they comprise 51% of the population, 80% of industrial activities and 90% of tourism income (7).
The Turkish coast consists of three main types: (i) erosional rocky and softer cliff coastlines (5752 km or 69%), (ii) accretional sandy coasts (1546 km or 19%), (iii) accretional, partly swampy, deltaic coasts (1035 km or 12%) (4). Turkey has well-developed coastal dunes, especially along the western Black Sea coast and in the deltas of the Aegean and Mediterranean Seas. These natural barriers to storms provide some defence against the consequences of accelerated sea-level rise (ASLR), at least in the short term. Elsewhere, beach rock has developed along numerous low soil cliffs, notably on the Aegean and Mediterranean coasts and the Black Sea coasts of Istanbul province.
The Seyhan, Ceyhan and Goksu deltas are where the most active shoreline changes have been occurring in the northeastern Mediterranean (5):
- Seyhan: Construction of a dam in the Seyhan River in 1954 greatly reduced sedimentation in the delta and erosion started. As a result, from 1954 to 1995, an area of about 1,012,536 m2 has been lost due to coastal erosion, and the delta became retrogradational.
- Ceyhan: On the mouth of the Ceyhan River, however, the total amount of progradation from 1947 to 1995 is about 3,097,745 m2 . About 90% of this progradation occurred with a rate of 74,977 m2 /year before the construction of a dam on the river in 1984. The rate of progradation after 1984 reduced to about 29,418 m2 /year, and only 323,597 m2 prograding occurred from 1984 to 1995. To the northeast, an area of 835,779 m2 was eroded by the sea due to no sediment influx on the abandoned Ceyhan River channel in Yumurtalik Bay between 1948 and 1995.
- Goksu: The total amount of progradation, from 1956 to 1995, on the mouth of the Goksu River is 398,445 m2. To the southwest, due to coastal erosion at a rate of 4,548 m2/year from 1951 to 1995, the lighthouse at Cape Incekum is now lying under the sea. The total amount of retrogradation here is about 200,125 m2.
Only eight out of the 485 dams were built before 1960, and 89% of dams hold sediment, reducing sediment flux to the coast. Although it has not been investigated, the effect of this reduction of sediment supply is expected to have adverse long-term effects, which will exacerbate the effects of sea level rise (erosion) (3).
Vulnerabilities - European coasts
All European coastal states are to some extent affected by coastal erosion. About twenty thousand kilometres of coasts, corresponding to 20% face serious impacts in 2004. Most of the impact zones (15,100 km) are actively retreating, some of them in spite of coastal protection works (2,900 km). In addition, another 4,700 km have become artificially stabilised (1).
The risk of coastal flooding due to the undermining of coastal dunes and sea defences potentially affects several thousands of square kilometres and millions of people. Over the past 50 years, the population living in European coastal municipalities has more than doubled to reach 70 millions inhabitants in 2001 and the total value of economic assets located within 500 meters from the coastline has multiplied to an estimated 500-1000 billion Euros in 2000 (1).
The cost of coastal erosion (coastline protection against the risk of erosion and flooding) has been estimated to average 5,400 million euro per year between 1990 and 2020 (2).
Coastal erosion results in three different types of impacts (or risks):
- Loss of land with economical value
- Destruction of natural sea defences (usually a dune system) as a result of storm events, which may result in flooding of the hinterland.
- Undermining of artificial sea defences as a result of chronic sediment shortage
Coastal erosion is influenced by several human factors, including:
- Coastal engineering. The waterfronts of urban, tourism or industrial zones have usually been engineered by way of seawalls, dykes, breakwaters, jetties, or any hard and rock-armoured structures, which aims at protecting the construction or other assets landwards the coastline from the assault of the sea. Such structures modify wave and flow patterns in the near shore zone and therefore cause a redistribution of sediment. The net sediment volume in the coastal zone may not be strongly affected, but the sediment redistribution can induce erosion in some places and accretion in others.
- Land claim. Within tidal basins or bays (where land reclamation projects are most easily undertaken), land reclamation results in a reduction of the tidal volume and therefore a change in the ebb and flood currents transporting sediments. As a result, relatively stable coastal stretches may begin to erode.
- River basin regulation works. Damming has effectively sealed water catchments locking up millions of cubic metres of sediments per year. For some southern European rivers (e.g. Ebro, Douro, Urumea, Rhone), the annual volume of sediment discharge represents less than 10% of their level of 1950; for the Ebro this is even less than 5%. This results in a considerable sediment deficit at the river mouth, and subsequent erosion downstream as illustrated in Ebro delta, Playa Gross, Petite Camargue (Rhone delta) and Vagueira.
- Dredging. Dredging may affect coastal processes by removing from the foreshore materials (stones, pebbles) which protect the coast against erosion, and by contributing to the sediment deficit in the coastal sediment cell.
- Vegetation clearing. A significant number of cases have highlighted the positive role of vegetation to increase the resistance to erosion.
- Gas mining or water extraction. Gas mining or water extraction may induce land subsidence, causing sediment deficit and a retreat of the coastline.
Direct anthropogenic effects on effective sea-level rise (ESLR)
From an assessment of contemporary effective sea-level rise (ESLR) for a sample of 40 deltas distributed worldwide it was concluded that direct anthropogenic effects determine ESLR in the majority of deltas studied, with a relatively less important role for eustatic sea-level rise. According to this study, serious challenges to human occupancy of deltaic regions worldwide are conveyed by other factors than the climate change–sea-level rise (6).
For any delta, ESLR is a net rate, defined by the combination of eustatic sea-level rise, the natural gross rate of fluvial sediment deposition and subsidence, and accelerated subsidence due to groundwater and hydrocarbon extraction. The deltas in this study represent all major climate zones, levels of population density, and degrees of economic development. The study includes the European deltas of Danube, Ebro, Po, Rhine, and Rhone. Collectively, the sampled deltas serve as the endpoint for river basins draining 30% of the Earth's landmass, and 42% of global terrestrial runoff. Nearly 300 million people inhabit these deltas. For the contemporary baseline, ESLR estimates range from 0.5 to 12.5 mm per year (6).
Decreased accretion of fluvial sediment resulting from upstream siltation of artificial impoundments and consumptive losses of runoff from irrigation are the primary determinants of ESLR in nearly 70% of the deltas. Approximately 20% of the deltas show accelerated subsidence, while only 12% show eustatic sea-level rise as the predominant effect. Extrapolating contemporary rates of ESLR through 2050 reveals that 8.7 million people and 28,000 km2 of deltaic area in the sample set of deltas could suffer from enhanced inundation and increased coastal erosion (6).
Adaptation strategies - Four key recommendations
Four key recommendations have been proposed to make coastal erosion problems and risks in Europe manageable (1):
- Increase coastal resilience by restoring the sediment balance and providing space for coastal processes. A more strategic and proactive approach to coastal erosion is needed for the sustainable development of vulnerable coastal zones and the conservation of coastal biodiversity. In light of climate change it is recommended that coastal resilience is enhanced by: (a) restoring the sediment balance; (b) allocating space necessary to accommodate natural erosion and coastal sediment processes and (c) the designation of strategic sediment reservoirs (supplies of sediment of ‘appropriate’ characteristics that are available for replenishment of the coastal zone, either temporarily (to compensate for losses due to extreme storms) or in the long term (at least 100 years)).
- Internalise coastal erosion cost and risk in planning and investment decisions. Public responsibility for coastal erosion risk should be limited and an appropriate part of the risk should be transferred to direct beneficiaries and investors. Risks should be monitored and mapped, evaluated and incorporated into planning and investment policies. Current practices observed in Europe reveal that the tax payer – through expenditures executed by public authorities - supports the major part of the costs associated with coastal erosion risk. Almost no cases are found were the parties responsible for coastal erosion or the owners of assets at risk paid the bill. The contribution of private funding for coastal erosion management in European member states probably does not reach 10% of the public expenditure (except for Denmark: a contribution from private owners up to 50% of the overall cost of coastal defence).
- Make responses to coastal erosion accountable. Coastal erosion management should move away from piecemeal solutions to a planned approach based upon accountability principles, by optimising investment costs against values at risk, increasing social acceptability of actions and keeping options open for the future.
- Strengthen the knowledge base of coastal erosion management and planning. Over the past hundred years the limited knowledge of coastal sediment transport processes at the local authority level has often resulted in inappropriate measures of coastal erosion mitigation. In many cases, measures may have solved coastal erosion locally but have exacerbated coastal erosion problems at other locations – up to tens of kilometres away – or have generated other environmental problems.
The references below are cited in full in a separate map 'References'. Please click here if you are looking for the full references for Turkey.
- Salman et al. (2004)
- Salman et al. (2002), in: Salman et al. (2004)
- Güven, C. (2007)
- Karaca and Nicholls (2008)
- Cetin et al. (1999)
- Ericson et al. (2006)
- Albayrakoğlu (2011)