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Water quality modeling is very important for the management of water resources. In this study, the upper part of the Porsuk Basin in Türkiye is analyzed using SWAT. In the analysis, in addition to the data provided by the General Directorate of State Hydraulic Works (DSI), the freely available flow and water quality data from the GEMStat data portal were used. This study presents a discussion of the practicality of GEMStat data for a water quality model. For this purpose, firstly, the SWAT model was constructed with freely available global data sources on elevation, land use/land cover, and soil type. Then, the model flow outputs were calibrated and validated for both DSI and GEMStat data in three different time periods. As a result, the flow calibration and validation success in the daily time step is 0.64 and 0.44 according to the Nash–Sutcliffe efficiency (NSE). The model was also validated using GEMStat flow data and calibrated using GEMStat water quality data such as nitrate (NO3), total suspended solids (TSS), and dissolved oxygen (DO) with a reasonable value. Hence, the results showed that GEMStat flow and water quality data can be used as auxiliary open-source data in the modeling process.

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.

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.

Recent techniques should be investigated in detail to avoid present and future problems of urbanization like flood, drought and water pollution. Low Impact Development (LID) Best Management Practices (BMPs) such as bioretentions, green roofs, rain barrels, vegetative swales, and permeable pavements have been implemented to diminish the adverse effects of urbanization. In this study, a hydrological model for a Rainfall-Watershed-Bioretention (RWB) system is developed by using the Environmental Protection Agency Storm Water Management Model (EPA SWMM). RWB system is an experimental setup which consists of an artificial rainfall system, a drainage area and four bioretention columns with different soil mixtures. The hydrological modeling capability of SWMM for bioretentions is presented using the experimental data obtained from the experiments conducted in the RWB system under different rainfall events and for bioretentions with different designs. Finally, the modeling results of SWMM are compared with the results of the Hydrological Model of RWB (HM-RWB) system. Results show that EPA SWMM performs well in modeling bioretentions whereas the results of HM-RWB are in better agreement with the experimental data.

Sustainable water management is crucial in the reduction of water pollution and floods. New techniques should be investigated in order to avoid present and future problems such as flood, drought, and water contamination. For this purpose, Low Impact Development-Best Management Practice (LID-BMP) has recently come into the stage in storm water management. Vegetative swales, green roofs, bioretentions, storm water wetlands, rain barrels, permeable asphalts and pavements are among LID-BMPs. Bioretention type of LID is implemented to diminish adverse effects of urbanization such as flood by reducing peak flows on surface and thus managing storm water runoff. The aim of this study is to investigate the hydrological performance of bioretentions by developing a hydrological model based on the data obtained using experimental setup called Rainfall-Watershed-Bioretention (RWB). The hydrological model of RWB (HM-RWB) consists of two main components: (i) rainfall-runoff model in which kinematic wave theory is used for simulation of surface runoff generated over the drainage area that reaches the bioretention as inflow; (ii) runoff-bioretention flow model in which Green-Ampt method under unsteady rainfall is employed and further improved by incorporating the effect of ponding depth on bioretention for the simulation of outflow at the exit of the bioretention. It is observed that the results of the hydrological model developed herein are in good agreement with the measured data obtained in the RWB experimental setup.

This study aims to conduct a comparative analysis of global precipitation products and ground station data using a hydrological model. The effects of different gridded precipitation datasets and topographic model inputs, such as subbasin delineation and elevation band details, on streamflows were investigated. The study focused on the mountainous Nilüfer Basin in Türkiye. Ground station data (GSD) and three different global precipitation datasets —Climate Forecast System Reanalysis (CFSR), Climate Hazards Group InfraRed Precipitation with Station (CHIRPS), and National Aeronautics and Space Administration–Prediction of Worldwide Energy Resources (NASA–POWER)— were used. The Soil and Water Assessment Tool (SWAT) was employed for hydrological modelling and Nash-Sutcliffe Efficiency (NSE) was utilized as the performance criterion for model calibration. The results showed that GSD, CHIRPS, and NASA–POWER achieved reasonable NSE levels (>0.5) without calibration, whereas CFSR performed poorly (NSE<0.2). After calibration, all models indicated successful results (NSE>0.70), with a notable improvement in CFSR (NSE increased from 0.12 to 0.71). Increasing the number of subbasins slightly improved the results, with the highest change in NSE of 0.09. Generating too many subbasins, though, lead to longer processing times without further improvements. However, introducing elevation bands significantly enhanced model performance (NSE increased by 0.21–0.27 across all datasets). An increase in the number of bands yielded only slight improvements, with NSE increasing by 0.03 at most.

On August 11, 2021, one of the most destructive flood disasters occurred in the Western Black Sea Basin of Turkey. The flood resulted in the death of 76 individuals, 30,000 people being affected by the disaster. A maximum precipitation depth of 400 mm/day was recorded at one station, indicating a return period exceeding 500 years for the rainfall event. During a two-day site visit immediately following the flooding event, damages to infrastructures, water structures, bridges, retaining walls, roads, and private houses were observed in the Bozkurt and Ayancık regions. Based on the observations, the flood wave propagated through the initial meandering river bed and floodplain, exceeding the channelized river bed capacity. Due to the massive sediment transport and drifting of trees, several bridges have been blocked and overflown where the basements of the structures in these regions were flooded. The enormous flood flow triggered extensive scouring on bridge piers, building foundations, and retaining walls, eventually causing the walls and bridges to collapse. The collapse of structures blocked the waterway and amplified the backwater effect when combined with the sediment transport. The total collapse of the retaining walls in some sections of the stream caused accelerated scouring in the foundations of the nearby buildings. Damages were also observed on the side roads along the river beds. This paper evaluated the driving mechanism of damages caused by flood flow from hydrological, structural, and geotechnical perspectives. Based on these observations and assessments, recommendations on engineering design guidelines for structures close to the floodplain, such as bridges, retaining walls, and side roads, were elaborated. Emphasis was placed on the flood-resistant design of these structures to develop a comprehensive approach for flood risk management.

The land development and increase in urbanization in a watershed affect water quantity and water quality. On one hand, urbanization provokes the adjustment of geomorphic structure of the streams, ultimately raises peak flow rate which causes flood; on the other hand, it diminishes water quality which results in an increase in Total Suspended Solid (TSS). Consequently, sediment accumulation in downstream of urban areas is observed which is not preferred for longer life of dams. In order to overcome the sediment accumulation problem in dams, the amount of TSS in streams and in watersheds should be taken under control. Low Impact Development (LID) is a Best Management Practice which may be used for this purpose. It is a land planning and engineering design method which is applied in managing storm water runoff in order to reduce flooding as well as simultaneously improve water quality. Consequently, the authors observe the possible effects of LID on surface runoff and TSS in Sazlidere Watershed.

In this study, the impact of low-impact development (LID) methods implementation on total suspended solids (TSS) is investigated by developing a hydrologic-water quality model for Alibeyköy Watershed located in Istanbul, Turkey. For this purpose, the US Environmental Protection Agency Storm Water Management Model (EPA SWMM) was used, which was calibrated in this watershed. Then, several LID types, such as bioretention, vegetative swales, infiltration trenches and permeable pavements were incorporated into the model, in an effort to evaluate the impacts of distinct and combined LIDs on TSS removal in the Alibeyköy Watershed for different scenarios. Both distinct and combined impacts of LID-BMPs on the reduction of TSS concentration in Alibeyköy Watershed are observed. It is found that bioretention, vegetative swales, permeable pavements, and infiltration trenches have significant effects on TSS removal both in case of distinct and combined implementations. Moreover, it is seen that bioretention and vegetative swales are slightly more effective on TSS removal under a strong rainfall.

Bioretention is one of the most common low-impact development (LID) types but there is lack of knowledge in the capacity and local behavior of bioretentions. In this study, laboratory-scale experiments are conducted in order to investigate the heavy metal removal capacity of bioretentions. Batch sorption experiments were first performed to determine the sorption parameters and retardation factor of copper (Cu), lead (Pb), and zinc (Zn) on various bioretention media, namely mulch, turf, vegetative soil, sand, and gravel. Reaction kinetics of Cu, Pb, and Zn were determined in order to assess the sorption equilibrium time of these metals for the five different bioretention media. The results of the batch tests show that turf has the highest sorption capacity followed by mulch and vegetative soil. For the range of concentrations considered in this study, linear sorption isotherm was found to best represent the metal sorption for all bioretention media. Metal removal percentages were highest for Pb and lowest for Zn. The time required to reach equilibrium ranged from 1 to 6 h depending on the type of bioretention media and metal. In addition to batch sorption experiments, column sorption experiments were also conducted in order to investigate effects of soil textures and organic content on removal of heavy metal in bioretention columns. For this purpose, four bioretention columns with different vegetative soil, turf, and sand ratios were prepared. The column tests were conducted for a period of 127 days under continuous boundary source, i.e., constant flow rate is supplied to each column with a concentration of 5 mg/L for each metal. Results show that different local soil types in bioretention design affect removal of heavy metal concentration considerably. Breakthrough analysis indicates that the removal of Zn reaches almost zero in about 127 days, while Cu and Pb are almost fully retained in all columns until the end of the experiment.