An Example for the Disasters Caused by Improper Land Use: The Kayaköy Polje Flood of January 31, 2019
Cihan Bayrakdar, Mehmet Fatih Döker, Ferhat KeserciKayaköy Polje is a typical karst depression 6 km south of the city of Fethiye, extending for a length of 5 km, with a width of 2 km, and covering an area of 5 km2 at 140 m from the sea level. On January 31, 2019, heavy rainfall occurred in Fethiye, which is on the southwestern coast of Turkey, flooding settlements and agricultural areas on the nearby Kayaköy Polje. Following the process whereby a flood escalates into a disaster, a study was performed to investigate the roles of precipitation, karst processes, and land use, and solutions were proposed. Within the scope of the land surveying work that followed, the spatial information obtained with the help of drones, satellite images, and data collected by meteorological stations were analyzed using geographic information systems to create maps and other outputs. These findings implicated rapid development in the basin, in addition to the strong torrents that accelerated in a very short time, causing flooding in the region. The development activities altered the natural drainage and slope conditions, rendering flood protection structures useless, clogging sinkholes, or turning them into concrete wells. It was concluded that as long as improper land use, which triggered the flood, continued, flood and other disasters were bound to repeat.
Polyelerde Hatalı Arazi Kullanımların Sebep Olduğu Afetlere Bir Örnek: 31 Ocak 2019 Kayaköy Polyesi Taşkını
Cihan Bayrakdar, Mehmet Fatih Döker, Ferhat KeserciKayaköy Polyesi Fethiye’nin 6 km güneyinde deniz seviyesinden 140 m yükseklikte, 5 km uzunluğunda, 2 km eninde ve 5 km2 alana sahip dolomitler içinde oluşmuş dış drenaja kapalı tipik bir karstik depresyondur. Kayaköy Polyesi Havzası ise 43 km2 alan kaplayıp doğuda yer alan Ovacık-Hisarönü ovalarını da kapsar ve havzanın suları polyenin batısında tespit edilen iki düden ile dış drenaja bağlanır. 31 Ocak 2019 tarihinde Fethiye ve yakın çevresinde aşırı yağışlar sonucu Kayaköy Polyesi’nde oluşan taşkın, yerleşmeler ile tarım alanlarını sular altında bırakmış, taşkının etkisi birkaç ay süre ile devam etmiştir. Bu taşkının afete dönüşmesinde yağış faktörü, karstik süreçler ve arazi kullanım özelliklerinin etkilerini araştırılmış ve çözüm önerileri getirilmiştir. Bu kapsamda arazi çalışmaları, insansız hava aracı, uydu görüntüleri ve meteoroloji istasyonlarının verilerinden elde edilen mekânsal veriler coğrafi bilgi sistemleri kullanılarak analiz edilmiş, sonuç harita ve çıktılar oluşturulmuştur. Elde edilen veriler sonucunda taşkının oluşmasında kısa sürede gelişen kuvvetli sağanak yağışların yanında havzadaki hızlı yapılaşma sonucunda doğal sızma ve eğim koşullarının değişmesi, taşkın koruma yapılarının işlevini yitirmesi, düdenlerin tıkanması ya da beton kuyulara dönüştürülmesi etkili olmuştur. Taşkın oluşumunu tetikleyen bu yanlış arazi uygulamaları devam ettiği sürece taşkının tekrarlanabileceği sonucuna varılmıştır.
Kayaköy Polje is a typical karst depression 6 km south of the city of Fethiye, extending for a length of 5 km, with a width of 2 km, and covering an area of 5 km2 at 140 m from the sea level. Formed inside the dolomite formation, it has a karst drainage system. Kayaköy Polje basin covers an area of 43 km2 including the Ovacık–Hisarönü plains to the east. Its waters drain outside through two ponors to the west side of the polje. On January 27, 2019, a cyclone system of North Atlantic origin developed and moved toward the Mediterranean Basin, collecting moisture along the way through interaction with warm sea waters, eventually initiating a downpour on the South Aegean line between January 31 and February 1 of 2019. The heavy rainfall (170 mm) in Fethiye and its immediate surroundings on these dates caused small-scale flooding in the region; however, its destructive impact peaked to reach proportions of a disaster in the Kayaköy Polje. In the aftermath of the heavy rainfall, 110 hectares of agricultural land and settlement areas were flooded for several months.
Within the scope of the land surveying work that followed, the spatial information obtained with the help of drones, satellite images, and data collected by meteorological stations were analyzed using geographic information systems to create maps and other outputs. The image classification work performed to track the changes in land use and land cover in the basin over time involved using Landsat satellite images from four different periods. They consist of Landsat 5 TM for the years 1985, 1995, and 2005, and Landsat 8 OLI/TIRS for 2019. Similarly, 10 m terrestrial resolution Sentiel-2 satellite data from February 4, March 16, and April 30, 2019 were analyzed using image enhancement techniques to study the effects of the flood.
Kayaköy Polje basin has been an area of intensive human activity in all periods. Its fertile soil provides favorable conditions for agricultural activities. Moreover, being home to several civilizations throughout its history, the basin has turned into a hotspot of tourist activities. While the basin floor was used only for agriculture in the past, it has been opened to settlements in modern times, causing serious problems such as floods. An analysis of the land cover and land use maps obtained from satellite imaging shows that the settlement area in the basin grew by almost six times after 1985, reaching a total area of 440 hectares.
These findings implicated rapid settlement development in the basin in addition to strong torrents that accelerated in a very short time, making this flood to be categorized as a natural disaster of hydrometeorological origin. A total precipitation of 588.2 mm was reported in December (134.4 mm) and January (426 mm), including the date of the flood incident and the pre-flooding period, which was effective at the onset of this process, and in February (58.2 mm) when the flood continued. This precipitation value shows that the climate during 2018–2019 was quite rainy compared with the corresponding period in previous years for the same region. For example, while the total precipitation in December, January, and February in 2015–2016 was 340.8 mm, it was 353.6 mm in 2016–2017, 503.3 mm in 2017–2018, and 364.8 mm in 2019–2020. As stated above, the precipitation for 2019 was reported to be 1047.1 mm, which far exceeds the average rainfall value of 862 mm reported for many years both periodically and throughout the year. In this context, rainfall above seasonal averages as of October in the climate period 2018–2019 peaked in January and became one of the most significant factors in the occurrence of the flood incident. The constructions and settlement activities in the region altered the natural drainage and slope conditions, rendering flood protection structures useless, clogging ponors, or turning dolines into concrete wells. In consideration of the long time required for complete drainage of the polje, the full extent of the damage is far worse than observed. Following the flood of January 31, 2019, it was not possible to talk about normalization of life or economic activities in the Kayaköy Polje before April 2019.
Kayaköy Polje is an area with a high risk of flooding, as it lacks a superficial drainage system, and human activities in the catchment basin are rampant. Considering these risk factors, watershed rehabilitation and flood prevention structures can be constructed (transferring water out of the basin, creating small dams, creating new water escape areas with boreholes, reactivating closed sinkholes, and discharging the water in the base of the polje using motor pumps). Furthermore, existing ponors should be maintained and kept active, and relevant underground cracks and cavities should be identified using geophysical methods to form new water escape pathways for drainage. In the flooding period, the water accumulated in the polje floor can be drained from lower levels using motopumps. All these suggestions should be evaluated in coordination with public institutions and organizations legally authorized to implement measures against flood and to reclaim floodplains in the aftermath of a disaster.
The ancient ghost town of Kayaköy itself, which saw settlements until as recent as the turn of the 20th century, is a clear indication that settlements should be built on the slopes, not on the polje floor. However, following the migration of people between Greece and Turkey in the early 20th century, in the absence of adequate regulations, new settlements have spread on the polje floor instead of the slopes, making present-day disasters inevitable. Therefore, in all types of natural disaster prevention measures, taking historical precedents into consideration appears to be the most rational and economic solution.