Flood Risk Mitigation in Highly Urbanized Area by Nature Based Solutions: The Case of Istanbul Esenyurt

As in the rest of the world, floods have devastating socio-economic effects in Turkey as well. Especially, highly urbanized areas do not enable the implementation of structural measures, properly. In addition, in recent years, structural measures have been replaced by nature-based and eco-friendly approaches. Therefore, it is essential to investigate the effectiveness of nature-based solutions (NBSs) in such places in order to eliminate the negative effects of floods. This study covers the area of Esenyurt District in Istanbul, which is highly urbanized and frequently affected by floods. The main channel of the Haramidere Creek and its six branches were studied with a total length of approximately 25 km. Firstly, 2, 5, 10, 50, 100, 500 and 1000 year recurrence interval of flow rates were calculated by using a hydrological model and extreme value analysis. Next, flood inundation area and depths were determined using 1D and 2D hydrodynamic models. Social and economic risks were estimated by combining the related studies mentioned above with the road, vehicle, building etc. inventory. Following this, the basin was divided into regions according to its NBS characteristics. The approaches such as rainwater harvesting in areas with insufficient infrastructure and permeable pavement in suitable areas having gentle slopes were modeled both individually and in combinations. In the literature, the effects of NBS have been revealed by examining the flood volume and peak flow values. In some similar studies, there is more decrease in peak flow rates while implementing a combination of NBSs rather than applied alone as a solution. In our study, in addition to the changes in flood volume and peak values, changes in flood inundation boundary, depth, social and economic risk will also be quantitatively revealed for the relevant recurrence interval of flow rates.