WoS İndeksli Yayınlar Koleksiyonu / WoS Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7150
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Article Citation - WoS: 7Citation - Scopus: 5Meteorological Drought and Trend Effects on Transboundary River Basins in Afghanistan(Springer, 2023) Hayat, Ehsanullah; Tayfur, GökmenAfghanistan, as a landlocked country located within central and southwestern Asia, has an arid to semi-arid climate. Most of the people are involved in agricultural activities, and a major part of the country's gross domestic product depends on agriculture, but the country has the lowest water storage capacity. Consecutive periods of drought and rapid snowmelt due to climate change have made it more challenging for suitable water resource management practices. This study investigates the historical meteorological drought characteristics across the whole country by employing the Reconnaissance Drought Index for the period 1979-2019 using data from 55 meteorological stations. Trends in precipitation and temperature are also investigated using the Mann-Kendall's and the Sen's slope statistical tests. A four-decadal countrywide drought map is generated. Extreme and severe droughts were observed in 1999 and 2000 across the whole country. Moderate drought events have started to occur with a frequency of 3 to 5 years since 1999. The decadal annual rainfall values in each river basin indicate that rainfall has decreased in the last two decades with a significant decline in 1999-2008. The trends of increase in temperature and decrease in precipitation are indications of rapid climate change in the country, especially in the south, west, and southwest regions. Due to the intensity and frequency of the droughts, river flow rates have decreased; and therefore, there is a need for the upstream and downstream neighboring countries to come to terms with the phenomenon of a new normal in the hydrological cycle and accordingly revise new water sharing treaties.Correction 3D modelling of surface spreading and underground dam groundwater recharge: Egri creek subbasin, Turkey(Springer, 2023) Şahin, Yavuz; Tayfur, GökmenArticle Citation - WoS: 4Citation - Scopus: 53d Modelling of Surface Spreading and Underground Dam Groundwater Recharge: Egri Creek Subbasin, Turkey(Springer, 2023) Şahin, Yavuz; Tayfur, GökmenThis study investigated surface spreading and underground dam recharge methods to replenish groundwater in Turkey's Egri Creek Sub-basin of the Kucuk Menderes River Basin. A three-dimensional numerical model was employed for this purpose. Field and lab data are provided to the model for realistic simulations. Pumping test results were used to determine the aquifer parameters. The laboratory works involved sieve analysis, permeability tests, and porosity and water content prediction. The numerical model's boundary conditions were determined from the geological and hydrogeological characteristics of the study area. Initial conditions were expressed regarding water content and pressure head in the vadose zone. The numerical model was satisfactorily validated by simulating water levels in three different pumping wells in the study area. Seven different scenarios, each having a different pool size, were investigated for the surface spreading recharge method. The results showed that a pool size of 30 x 30 m with a 6-m depth basin was the most optimal choice, raising the groundwater level to about 29.3 m. On the other hand, it was found that an underground dam could raise the levels by an average of 9.5 m, which might not be significant to warrant the construction.Article Citation - WoS: 2Citation - Scopus: 2Numerical Simulation of Flow and Dam Body Sediment Over a Movable Bed Due To an Earthfill Dam Break(Yıldız Teknik Üniversitesi, 2022) Tayfur, Gökmen; Issakhov, Alibek; Zhandaulet, YeldosThis paper presents the numerical simulations of flow and dam body sediment transport over a movable bed due to an earthfill dam break. The RANS equations, together with the k-omega SST turbulent model, are employed. The phase characteristic parameter is used as the phases of air, water, sediment, and bulk of dam body. The system of equations is solved numerically using the PISO algorithm. The numerical model is first verified using the dam break experimental data from the literature. The model successfully captures the temporal changes in the measured flow depths, pressures, wave fronts, and arrival times. The ve rified mod el is then app lied to simulate the flow and sediment transport as a result of an artificial earthfill dam break having an obstacle at its downstream section. The simulations show that there is a noticeable decrease in the shock pressures at all points around the obstacle and there is an increase in the water levels. The bulk dam body sediment moves together with the water flow wh ile sp reading. It takes longer time for the sediment laden flow to reach the obstacle. The investigation of dam body formed by different soils shows that the soil type has minor effect while the transport of sediment can raise the water levels and change the morphology of the downstream section.Article Closure To "reverse Flood Routing in Rivers Using Linear and Nonlinear Muskingum Models" by Meisam Badfar, Reza Barati, Emrah Dogan, and Gokmen Tayfur(American Society of Civil Engineers (ASCE), 2022) Badfar, Meisam; Barati, Reza; Doğan, Emrah; Tayfur, GökmenArticle Citation - WoS: 29Citation - Scopus: 31Reverse Flood Routing in Rivers Using Linear and Nonlinear Muskingum Models(American Society of Civil Engineers, 2021) Badfar, Meisam; Barati, Reza; Doğan, Emrah; Tayfur, GökmenOne of the key factors for flood modeling and control is the flood hydrograph, which is not always available due to lack of flood discharge observations. In reverse flow routing, hydraulic or hydrological calculations are performed from the downstream end to the upstream end. In the present study, a reverse flood routing approach is developed based on the Muskingum model. The storage function is conceptualized as linear and five different nonlinear forms. The Euler and the fourth-order Runge-Kutta numerical methods are used for solving the storage models. The shuffled complex evolution (SCE) algorithm is used for optimization of the flood routing parameters. The models are calibrated and validated with theoretical and actual hydrographs. The results indicate that the proposed methodology could substantially (up to almost 82%) improve comparison with observed inflows. The practical applicability of the proposed methodology is also validated in real river systems.Article Two dimensional bed deformation model in turbulent streams(Taylor & Francis, 2019) Gharehbaghi, Amin; Kaya, Birol; Tayfur, GökmenA coupled model is developed to simulate two dimensional water surface profile, suspended sediment load and bed deformation in unsteady open channels. The hydrodynamical component employs the two dimensional shallow water equations to obtain the hydraulic variables. These, in turn, are used in the morphdynamical component to determine the bed deformation. For the turbulence variables; two turbulence models are supervened to the governing equations. Triangular meshes were developed to discretize the domain of open channel. In order to discretize the governing equations, the explicit finite volume method is used by the total variation diminishing (TVD) schemes. The performance of the developed model is compared to that of the Flow3D software. The comparison results are in good agreement.Article Citation - WoS: 16Citation - Scopus: 20Groundwater Recharge Estimation Using Hydrus 1d Model in Alaşehir Sub-Basin of Gediz Basin in Turkey(Springer Verlag, 2019) Tonkul, Serhat; Baba, Alper; Şimşek, Celalettin; Durukan, Seda; Demirkesen, Ali Can; Tayfur, GökmenGediz Basin, located in the western part of Turkey constituting 2% land of the country, has an important groundwater potential in the area. Alasehir sub-basin, located in the southeast of the Gediz Basin and subject to the extensive withdrawal for the irrigation, constitutes the study area. Natural recharge to the sub-basin due to precipitation is numerically investigated in this study. For this purpose, 25 research wells, whose depths range from 20 to 50 m, were drilled to observe the recharge and collect the necessary field data for the numerical model. Meteorological data were collected from 3 weather stations installed in the study area. The numerical model HYDRUS was calibrated using the field water content data. Soil characterization was done on the core samples; the aquifer characterization was performed, and the alluvial aquifer recharge due to precipitation was calculated. As a result, the computed recharge value ranges from 21.78 to 68.52 mm, with an average value of 43.09 mm. According to the numerical model, this amount of recharge corresponds to 10% of the amount of annual rainfall.Article Citation - WoS: 3Citation - Scopus: 3Simulating Transient Sediment Waves in Aggraded Alluvial Channels by Double-Decomposition Method(American Society of Civil Engineers (ASCE), 2011) Tayfur, Gökmen; Singh, Vijay P.By using the double-decomposition (DD) method, this study simulates transient sediment waves caused by aggradation described by a diffusion-type partial differential equation (PDE). The DD method solves the PDE by decomposing the solution function for sediment rate into a summation of M number of components, where M stands for the order of approximation. The solution was approximated by considering only the first three terms. The model satisfactorily simulated laboratory-measured aggradation bed profiles with, on average, a mean absolute error (MAE) of 0.70 cm, a root-mean-square error (RMSE) of 0.84 cm, a mean relative error (MRE) of 1.11%, and R2=0.95. The model performance was also tested by using numerical and error-function solutions. In addition, the results obtained from application of the DD solution to hypothetical field cases were found to be theoretically compatible with what may be observed in natural streams. However, sediment wave fronts in later periods of the simulation time reached equilibrium bed levels more quickly, around in the middle section of the channel.Article Citation - WoS: 73Citation - Scopus: 84Groundwater Contamination and Its Effect on Health in Turkey(Springer Verlag, 2011) Baba, Alper; Tayfur, GökmenThe sources of groundwater pollution in Turkey are identified, and pathways of contaminants to groundwater are first described. Then, the effects of groundwater quality on health in Turkey are evaluated. In general, sources of groundwater contamination fall into two main categories: natural and anthropogenic sources. Important sources of natural groundwater pollution in Turkey include geological formations, seawater intrusion, and geothermal fluid(s). The major sources of anthropogenic groundwater contamination are agricultural activities, mining waste, industrial waste, on-site septic tank systems, and pollution from imperfect well constructions. The analysis results revealed that natural contamination due to salt and gypsum are mostly found in Central and Mediterranean regions and arsenic in Aegean region. Geothermal fluids which contain fluoride poses a danger for skeleton, dental, and bone problems, especially in the areas of Denizli, Isparta, and AydIn. Discharges from surface water bodies contaminate groundwater by infiltration. Evidence of such contamination is found in Upper KIzIlIrmak basin, Gediz basin, and Büyük Melen river basin and some drinking water reservoirs in Istanbul. Additionally, seawater intrusion causes groundwater quality problems in coastal regions, especially in the Aegean coast. Industrial wastes are also polluting surface and groundwater in industrialized regions of Turkey. Deterioration of water quality as a result of fertilizers and pesticides is another major problem especially in the regions of Mediterranean, Aegean, Central Anatolia, and Marmara. Abandoned mercury mines in the western regions of Turkey, especially in Çanakkale, Izmir, Muǧla, Kütahya, and BalIkesir, cause serious groundwater quality problems. © 2011 Springer Science+Business Media B.V.