MODELING OF URBAN FLOODING AND WATERFALL EFFECT ON STEPPED STREETS IN ISTANBUL, TURKEY

Flood is one of the most common and deadly natural disasters. Most of the cities are under the threat of flash floods due to precipitation regime changes with global climate change. The existing infrastructure and the stepped streets that were not previously risky in the city create a waterfall effect in heavy rain and reduce street safety. Today, there are more than a hundred stepped streets in the settlement as by topography conditions such as Beyoglu, Sisli and Uskudar, with different type of stepped streets that form a short path in the transportation network. Many researchers studied to calculate discharges through spillways or dam break flows using numerical models. In the study, different step streets related vertically with Meclis-i Mebusan Street in Istanbul are examined in terms of flooding after heavy rains. The data was obtained through on-site observation. Physical properties such as stair length, width, slope, stair shape and railing were taken into consideration during the on-site examination. The step street as staircase models was analyzed with FLOW 3D software according to the selected flood height. In the numerical models examined by CFD method, the maximum speed zones occurring on the staircase during the flood were determined and the critical zones were specified. In this way, it is possible to comment on the impact assessment of stairs by considering water heights and speeds in critical areas. Some precautions are suggested to be taken in line with the data against the flash floods.