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Flash floods and Urban flooding Turkey

Vulnerabilities

Floods are the second most destructive type of natural disaster in Turkey, after earthquakes. Nearly 30 % of all the natural disasters in the country consist of flood events. 34 flood events occurred in Turkey between 1950 and 2007 and 1,016 people died, and about 1.5 million people were affected (1). Temporal trends of Turkish flood occurrences do not portray steady increases or decreases rather they fluctuate, but they are on rise since the mid-1990s (2).

Flash floods associated with intense and prolonged rainstorms are a common phenomenon,especially in coastal parts of Turkey. Flood impacts in Turkey are felt more severely in major cities of the country which suffer from frequent floods as a result of combined effects of intense rainfalls, occupation of flood plains by residential and commercial buildings, high coverage of impervious surfaces, and inadequate drainage. A flash flood prevention program, implemented since 1970, has been successful in reducing the number of annual flash floods. However, a lot of structural and mitigation efforts are still needed especially in urban areas of the country to prevent the occurrences of flash floods and to minimize their impacts (3).

Marmara floods (Istanbul), 7–10 September 2009

The Marmara region in north-western Turkey suffered from a series of floods during 7–10 September 2009, with 32 human losses and more than $100 million of economic damage. The flash floods were due to intense rain storms that swept the region, amounting to its heaviest rainfall in decades. The 24-h rainfall amounts varied between 100 and 253 mm during the flooding period. Additional factors such as land use changes, urbanization, poor drainage, and construction and settling in the flood-prone areas worsened consequences of the floods, especially in major urban areas of the region. Istanbul, the largest city of Turkey with 14 million inhabitants, suffered most from the flash floods. The floods submerged some suburban districts of the city and the city’s highways turned into rivers and transportation and communication infrastructures were damaged. A total of 35,000 people were affected by the floods in the Marmara region (3). The 9 September flood event is categorized as an event greater than the 500-year return period (4). 

Istanbul historically has been vulnerable to natural disasters. Since 1967, the city suffered 13 major floods. The city has grown rapidly over the last 40 years due to internal migration. In order to absorb the increasing population, new settlements have been built, mostly illegally on the outskirts of the city. The rapid urbanization led people to occupy flood plains to open up new spaces for development. Natural hydrologic pattern of the city changed considerably due to expansion in the transportation network and more impervious surface were added to the city’s land use. Flood control structures and channel improvements in creeks were not able to accommodate the increasing urban pressure resulted expansion of the settlements and industrial sites due to internal migration. Capacity of the storm sewers and flood detention structures in the city remained inadequate to control a large flood as in case of the September 2009 flood and consequences were devastating. Infrastructure in the newly established residential and commercial areas of the city did not grow in parallel to the population, and therefore, the current infrastructure of the city is not adequate even to accommodate runoff from a moderate rainfall (3).

Adaptation strategies

Istanbul

Disastrous flood events are inevitable in Istanbul in the future unless necessary measures are taken by the local governments and authorities (3):

  • An initial step should be developing a comprehensive flood mitigation plan within a framework of integrated flood plain management. Flood inundations maps should be prepared, based on different recurrence intervals and zones under risk of flooding, before taking any structural measures.
  • Once the risk areas prone to floods are identified, further development in those known flood risk areas should be prevented by enforcing specific building codes. In particular, no construction activities should be allowed in the flood zones of rivers which are exposed to high risk of flooding.
  • Present industrial facilities and residential buildings in flood zones of Ayamama and Kağıthane Rivers should be relocated to other parts of the city where the risk of flooding is lower or non-existent.
  • Some structural measures also should be taken to control the flows in main rivers of the city, especially the Ayamama and Kağıthane Rivers which frequently overflows following intense rainfalls.
  • A more important step would be setting up flash flood early warning system to monitor water levels in the main creeks in and around Istanbul, monitor and assess spatial and temporal distribution of rainfall, and issue warning when necessary to act promptly to evacuate the areas where there is risk of being flooded.

The proposed measures will not be successful unless they are supported by legislative measures including specific building codes for flood-prone areas, political efforts, and public awareness to enhance their effectiveness.

References

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.

  1. EM-DAT (2010)
  2. Kömüşcü and Ceylan (2007)
  3. Kömüşcü and Ҫelik (2012)
  4. Yucil (2015)
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