Bozkurt Flood Disaster Causes and Findings

Istanbul Technical University (ITU) announced an evaluation report on the flood disaster that occurred in the Bozkurt district of Kastamonu. The report, which is supported by ITU Center for Satellite Communications and Remote Sensing (CSCRS) images, includes striking findings.

In the report prepared by ITU’s scientists Prof. Dr. Ali Deniz, Prof. Dr. Ahmet Duran Şahin, Prof. Dr. Azime Tezer and Assoc. Prof. Dr. İsmail Dabanlı, main causes of loss of life and property as a result of the flood and inundation in the Western Black Sea Region on 11 August 2021 are presented to the public in an objective framework with scientific evidences and approaches by evaluating the findings through precipitation records and on-site observations.

The highlights of the report’s conclusion part are:

• A meteorological system deepened in convective structure has resulted in excessive precipitation in the region.
• The extreme precipitation values observed in the region exceeded the maximum precipitation amounts recorded for many years at many stations.
• Attributing the occurrence of the disaster directly to climate change will lead to misconceptions. Correct settlement planning should be kept on the agenda before climate change.
• Extreme value analyses of the region should be re-performed in terms of precipitation and flow.
• The fact that the topography consists of steep slopes, the slope is high and the water-saturated soil has transferred almost all of the precipitation to the surface flow on the 2nd day has increased the scale of the disaster.
• The feet of the bridges built on rehabilitated stream beds in the residential area narrowed the cross-section and the sediment and logs drifted by the flood blocked the cross-section, causing the stream to swell and overflow to the residential areas many times.
• Bridges could not withstand the dynamic load behind them as a result of the swelling and collapsed, causing the damage to increase.
• It is thought that the cross-section, which is normally expected to carry a flow rate of Q₅₀₀, did not function as planned due to blockage of sections with bridges by the sediment, erosion and logs.
• It was found out that as a result of the partial or complete collapse of the right and left coast masonry walls, the foundations of the collapsed buildings could more easily be hollowed out.
• It was found out that of the buildings built on sediment, buildings with raft foundation and shear wall survived intact, and the buildings that were thought to have been built on spread or strip footing and whose foundations were undermined were partially or completely damaged.
• It was observed that in the region there is an irregular settlement, which is not based on inundation.
• As it can be understood from the satellite photographs, it was found out that floods originating from the upper basin of the Ezine Stream, which had a very high flow rate and speed as a result of excessive rainfall, brought logs and sediment and left them in the stream bed and the city center at the end of the flood, as well as forming a delta in the sea in a way that will change the coastline.
• Due to the forecasting of precipitation anomalies, especially in the Black Sea Region, it is urgent to carry out a spatial risk analysis in the settlements located on the valley floors, to transform the settlements in critically risky areas, to re-plan them in safer areas, and to establish the safety of life, property and public services.
• Rehabilitation of streams passing through settlements should be done with an ecological and sustainable approach by leaving their surroundings empty to be used as recreation areas instead of using classical masonry walls or concrete box sections.
• Since the greatest impact of flood damage was caused by sediment control, in order to prevent future floods, in case the region is suitable, check dams and flood protection dams to be built in the upper basins, and stream rehabilitation and zoning practices in residential areas should be considered as holistic scientific participatory projects.
• Spatial and engineering applications such as restriction of construction activities in areas with flood/inundation risk, determination of emergency water retention areas/alternative waterways, use of natural/structural solutions necessary for sediment control in surface flow should be scientifically addressed, planned and implemented.
• It is important to keep the damage under control with flood-resistant structural measures (such as raising buildings, keeping the ground floors open, using water-resistant construction materials, using flood-resistant building types).
• In flood risk management, spatial planning measures are a rational solution for areas with medium or low flood risk while in areas with high risk, spatial/structural solutions should be handled with more integrated approaches.