Flood events increase tremendously due to uncontrolled urbanization, global warming, and climate change. As a result, countries suffer not only from the loss of life but also from direct and indirect economic losses. To reduce the adverse effects caused by the flood, it is of great importance to learn from past events and understand the causes and consequences of the flood. Therefore, investigating and assessing extreme flood events and large-scale structural damages caused by flood flow play an important role in explaining the physical mechanism.
Flood events deeply affect many countries on a global scale and cause one-third of the total economic losses due to natural disasters (Chikwiramakomo et al., 2021; Loucks and Van Beek, E., 2017; Moel and Aerts, 2011; Uddin et al., 2013; Koç et al., 2021; Ozmen, 2019; Mogollon at al., 2016; Abdo et al., 2012). The most common cause of flooding is heavy rainfall or snowmelt (Paveluc et al., 2021). In addition to natural causes, human intervention in nature plays a vital role in the emergence of floods (Cai et al., 2016). With the increase in population and urbanization, uncontrolled construction interferes with the river beds (Jian et al., 2021). Therefore, the cross-sectional area of the stream decreases, and a flood occurs as a result of the construction on the floodplain (Dang et al., 2011).
Flood disaster poses a significant risk for the environment and human life (Siddiqui, 2011; Cook and Merwade, 2009). Millions of people lose their lives, and financial losses are experienced due to floods in various parts of the world. For example, Pakistan, India, and China were severely affected by floods in 2010 and Australia between 2010 and 2011 (Mueller et al., 2019; Kundzewicz, 2019; Atta-ur-Rahman., Khan, 2013). In 2008, the flood occurred due to the heavy rain and snowmelt severely affected the US State of Iowa; damaged many residences and workplaces, and 40,000 people had to leave their homes (Sönmez et al., 2013). The maximum damage caused by river flooding in a country in one year was seen in China in 2010 with 51 billion dollars (Kundzewicz, 2019). In 2010, almost 2000 people lost their lives due to monsoon floods in Pakistan (Kundzewicz et al. 2014). In May and June 2016, extreme storms in Europe caused heavy rains; the Sen River overflowed in France and flooded Germany. These disasters caused an economic loss of approximately US$ 4 billion (URL 1). In Serbia, the floods affected 1 million people and resulted in 51 casualties, of which 23 were due to drowning (Dottori et al., 2017). In Bosnia-Herzegovina, over a million people were affected by flooding, almost 90,000 were displaced, and 25 casualties were recorded (Dottori et al., 2017). In Romania, more than 11 million hectares of agricultural land was affected by floods; more than 2,000 bridges and more than 700 km of roads were destroyed; 85,000 houses were affected by floods from which 13,000 were destroyed, and 215 humans lost their lives in the flood event between May and July 1970 (Urzica and Grozavu, 2021; Chendeș et al., 2015).
Many flood events were also observed in Turkey. The Turkey Disaster Database (TABB), which was established in 2009 to collect all documents related to both natural and anthropogenic disasters, reported 1076 flood events that caused 795 deaths and economic losses of US$ 800 million from 1960 to 2014 (Koç et al., 2021; Koç and Thieken, 2018). The Black Sea, Mediterranean, and Western Anatolia regions are the most sensitive places to floods in Turkey (SYGM, 2019; Oğuz et al., 2016). The highest event frequency highest economic and human losses due to flood hazards are seen in the Black Sea region (Koç, 2021). During the flood events in Istanbul, Ankara, and Senirkent in 1995, 74 people lost their lives; 46 people were injured; 2000 people lost their homes, and 65 million dollars of economic loss occurred (Ertek, 2014; Korkanç and Korkanç, 2006). More than 2 million people were affected by the flood disasters that occurred in the Western Black Sea Region in 1998; more than 30 lives were lost, and 478 houses were completely inundated (Kömüşçü and Çelik, 2013; Ceylan et al., 2007, Ergunay, 2007; Zeybek, 1998). During the Ayamama flood, which took place in Istanbul between 8–12 September 2009, 32 people lost their lives, 3816 houses and 1490 workplaces were damaged (Kömüşçü et al. 2011). Fourteen people lost their lives in the flood in Rize on August 26, 2010 (AFAD, 2018). In addition, 77 and 30 flood incidents in Kastamonu and Sinop Provinces of Turkey from January 01, 1950, to June 01, 2018, are observed (AFAD, 2018). A review of national reports on natural disasters shows that floods are the most economically damaging natural disasters after earthquakes (Ozmen, 2019). Based on these events, it is crucial and necessary to carry out studies on floods to prevent and reduce the damages and losses in Turkey.
The hydrodynamic forces resulting from flooding cause damage to structures such as bridges, culverts, roads, revetment walls, and buildings. The direct flood damage to the structures is typically observed in two ways, i.e., wall failure or scour under foundations (Chung and Adeyeye, 2018). Flood actions that result in scour are a leading cause of bridge and structural failure (Prendergast et al., 2018). For example, washing away the soil from around bridge foundations by hydraulic action causes bridge collapse since it reduces the stiffness and capacity of foundations of bridges located in waterways (Prendergast et al., 2018; Prendergast & Gavin, 2014; Arneson et al., 2012). Therefore, there are many examples of scouring failure at bridges and culverts due to flooding (Dyke et al., 2021; Sung and Wang, 2013). Moreover, roads and highways are commonly damaged by flooding, resulting in their dysfunctionality or reducing their serviceability (Fathy et al., 2020; Ismail et al., 2019; Lertworawanich, 2012; Keller and Ketcheson, 2011). The damage on the road and highway due to flood is particularly critical since the road and highway are used to assess the area affected by the flood. Therefore, precautions should be taken to prevent damages caused by flooding, especially on roads.
Observations and site assessments of Bozkurt and Ayancık regions in the Western Black Sea Basin were reported after the flood disaster on August 11, 2021, to contribute and shed light on the existing studies on flooding. For this purpose, first, the flooded region and the flood event were explained and assessed, along with the photographs taken during the two-day site visit. Then, the causes and effects of flood and damages of flood on infrastructures, bridges, culverts, revetment walls, and highways were discussed. Finally, recommendations were made on the design guidelines of the structures located in or nearby the floodplain, which were subject to potential frequent flooding.