Floods are among the most devastating disasters in terms of socio-economics and casualties. However, these natural disasters can be managed and their effects can be minimized by flood modeling performed before the occurrence of a flood. In this study, flood modeling was developed for the Göksu River Basin, Mersin, Türkiye. Flood hazard and risk maps were prepared by using GIS, HEC-RAS, and HEC-HMS. In hydraulic modeling, Manning’s n values were obtained from 2018 CORINE data, return period flow rates (Q25, Q50, Q100, Q500) were obtained from HEC-HMS, and the application was carried out on a 5 m resolution digital surface model. In the study area, the water depths could reach up to 10 m, and water speeds were approximately 0.7 m/s. Considering these values and the fact that the study area is an urban area, hazard maps were obtained according to the UK Department for Environment, Food and Rural Affairs (DEFRA) method. The results indicated that possible flood flow rates from Q25 to Q500, from 1191.7 m³/s to 1888.3 m³/s, were detected in the study area with HEC-HMS. Flooding also occurred under conditions of the Q25 flow rate (from 4288 km² to 5767 km²), and the impacted areas were classified as extremely risky by the DEFRA method.

Rapid development in a watershed affects both surface water and groundwater resources. Urbanization results in an increase in surface runoff and volume of water collected downstream of the watershed. Low-impact development (LID) best management practices (BMPs) such as bioretentions, vegetated rooftops, rain barrels, vegetative swales, permeable pavements, and stormwater wetlands have been implemented to diminish adverse effects of urbanization such as flood by reducing peak flows on the surface and thus managing stormwater runoff. The objective of this study is to investigate the hydrological performance of bioretentions, which may also be considered as a small-size local constructed wetland, by conducting experimental analyses under various rainfall intensities and durations. For this purpose, an experimental setup called a rainfall-watershed-bioretention (RWB) system is constructed, which involves an artificial rainfall system, drainage area, and four bioretention columns with different soil textures and organic content. Inflow rate at the entrance of bioretentions and ponding depth on bioretention columns are measured during selected artificial rainfall events and durations. In addition, the outflow rate at the exit of bioretention columns is measured to understand the role of soil types in hydrological behavior of bioretention columns. Experimental results show that different soil types and organic content under various rainfall intensities and durations affect hydrological performance of bioretentions considerably.

The aim of this study is to analyze the effects of a possible dam failure under various scenarios and to generate a flood hazard map for two consecutive dams located in a study area with a dense-residential region and a heavy-traffic highway. Two consecutive dams consist of Elmalı 2, a concrete-buttress dam and Elmalı 1, an earth-fill gravity dam in the upstream and downstream, respectively. Hydrologic Engineering Center-River Analysis System (HEC-RAS) was used to develop a dam failure model. Dam failure scenarios were examined regarding three main criteria: the Breach Formation Time (BFT), the Number of Failed Buttresses (NFB) of Elmalı 2, and the Reservoir Volume Ratio (RVR) of Elmalı 1. Accordingly, flood peak depth (Hp), peak flow rate (Qp), peak velocity (vp), and time to reach the peak (tp) are discussed. The results showed that BFT and NFB of Elmalı 2 were highly effective on these values, whereas RVR of Elmalı 1 had no significant effect. Moreover, the total area affected by potential floods was calculated with a comparative areal change analysis using flood inundation and flood hazard maps obtained. Estimated damage costs indicate that in the worst-case scenario, more than 500 buildings will be affected in the region.