Identifying causes of the 2015 Hopa flash flood in NE Turkey and mitigation strategies

A severe thunderstorm occurred in the Sundura watershed, located in Hopa district in North Eastern Turkey on August 24, 2015. The thunderstorm generated torrents, floods, and landslides and caused the loss of eight lives as well as extensive damage to property. Hydrometeorological, physiographic, hydraulic, and socioeconomic causes of the Hopa catastrophe were investigated in the study. Precipitation records were checked by weather satellite images. The frequency of this thunderstorm was estimated to be close to 100 years. Due to morphometric parameters and land misuse by tea cultivation in the steep upper watershed, the Sundura Creek has a high flood generating potential. The part of the Sundura Creek passing through the urban area has been channeled, but the channel capacity was not sufficient for a 100-year flow, and therefore some parts of the city were inundated. Another reason for flooding is clogging of inadequate culvert sections at conjunction points of the creek or Black Sea, by debris. Some tributaries could not join the Sundura Creek or the sea due to clogged culverts or the elevated Black Sea highway and Hopa-Artvin highway road embankments. In order to control torrents and floods in the Sundura watershed, afforestation is needed for non-productive forest and tea cultivation areas in the upper watershed. In the lower part of the watershed, the main channel should be redesigned according to the Q₅₀₀ years flow. Some debris trapping structures should be constructed to prevent clogging of culverts and bridges. Unnecessary road constructions on the slopes should be prevented, and buildings below the Q₁₀₀ flood level should be encouraged to relocate to safer/higher elevations.