Investigation of flood risk maps under the influence of urbanisation of floodplains in cities, study area: İstanbul Göksu deresi

Floods in the world and in Turkey day by day cause a great deal of damage and loss of people and living things. The biggest reasons are uncontrolled urbanisation activities and intervention in river beds. The main purpose of this thesis is to examine the flood risk maps under the influence of urbanisation and to examine whether the buildings built on floodplains have an effect on floods. In this research, Göksü stream located within the borders of Beykoz District of Istanbul Province was selected as a sample region. The purpose of the selection of this stream is the Elmalı I and II dams located downstream. The floods in this stream are under the control of the spillways of Elmalı I dam. Assuming that the Elmalı I dam is full, the water flow rate of the dam is taken into consideration when the 14 weirs of the dam are open by 25%, 50%, 75% and 100%. The building status (distribution and number) in 2002, 2007, 2012, 2017 and 2023 in the residential area around the Göksu stream river bed located in the downstream region of Elmalı I dam is included in the numerical model and the effect of the increase in the number of buildings in this region on flood propagation is analysed. The increase in the number of buildings in this region varies according to the years and even if this increase does not affect the flood propagation map on a large scale, it is concluded that there is a significant increase in the number of buildings affected by flooding. In order to reduce the flood risk in this and similar urban areas, construction in the floodplain should be prevented. In addition to this, it should be ensured that the floods that are more likely to occur should not overflow out of the river bed by making stream rehabilitation. Flood embankments can be constructed in the areas where flooding occurs outside the river bed to increase the carrying volume of the stream and prevent it from overflowing into the residential area.