Civil Engineering / İnşaat Mühendisliği

Permanent URI for this collectionhttps://hdl.handle.net/11147/13

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Institution Author: search.filters.institutionAuthor.Elçi, ŞebnemWoS Q: search.filters.wosQuartile.Q3

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Now showing 1 - 5 of 5
  • Article
    Citation - WoS: 2
    Citation - Scopus: 2
    Assessment of Future Water Demand in a Semiarid Region of Turkey: a Case Study of Tahtali–seferihisar Basin
    (Springer, 2023) Karahan, S. M.; Elçi, Şebnem
    Water is a vital resource for society and nature, and its scarcity has consequences in all aspects of existence. Today, issues including the inability to preserve the status of existing water resources and excessive water withdrawal are causing the amount of water to diminish day by day. Furthermore, factors such as urbanization and industrialization, population growth, water quality degradation owing to agricultural pesticides, and climate change, all have a negative impact on water supplies. A basin-based water management analysis was carried out in this study by applying the "Integrated Water Resources Management" strategy to the Tahtalı–Seferihisar sub-basin in Turkey, where water stress is expected in the future. Using the WEAP (Water Evaluation and Planning System) model, the hydrological (precipitation, flow, evaporation) data of important water resources for the basin and Izmir (Tahtalı, Seferihisar, Ürkmez, and Kavakdere Dams) were used to predict the availability of water resources in the future, and several possible scenarios for water demands/supplies were analyzed. The water budget balances projected in 2050 have been calculated by considering six different scenarios: Reference Scenario, Report Consumption Scenario, Optimistic Case Scenario, Pessimistic Case Scenario, Return Flow Scenario, and Various Forecast Scenario. The water balances that can be obtained in each scenario under various situations were computed and compared. For all considered scenarios, unmet water demand in the basin is found to be significant (157.52 hm3 in the Optimistic Case Scenario and 373.16 hm3 in the Pessimistic Case Scenario).
  • Article
    Citation - WoS: 3
    Citation - Scopus: 3
    Design of Coanda Intakes for Optimum Sediment Release Efficiencies
    (Korean Society of Civil Engineers, 2020) Hazar, Oğuz; Elçi, Şebnem
    When the water has to be diverted from a turbid source having a great amount of suspended materials in it, bottom intake structures such as Coanda and Tyrolean types are preferred. To perform this task, diverted water is captured by a transversal rack, and a gallery located in the control crest is utilized. This study was motivated by a search for the best design where the quality of the diverted water can be increased by screening out most of the sediments in the flow. Current work focuses on the water capture and sediment release efficiencies of both Tyrolean and Coanda type intakes through experimental work. It complements and extends existing experimental studies by considering sediment-laden flow. We used a novel sediment feeding system designed specifically for this study in the experiments. Study results pointed out that when sediment release efficiency is considered, all types of Coanda intakes having different design parameters performed better as compared to Tyrolean intakes. Water capture and sediment release efficiencies are related to parameters used in the experiments including Coanda type, rack angle, void ratio, sediment amount, and flow rate based on the statistical analyses of these parameters. An optimum design is proposed with the maximum sediment release efficiency to prevent clogging during the operation of the intakes. © 2020, Korean Society of Civil Engineers.
  • Article
    Citation - WoS: 2
    Citation - Scopus: 2
    Observational and Numerical Methods for Quantifying and Modeling of Turbulence in a Stratified Reservoir
    (Isfahan University of Technology, 2016) Elçi, Şebnem; Ekmekçi, Hüseyin Burak
    The interplay between stratification and shear in lakes controls the vertical mixing, which is the mostimportant mechanism affecting the transport of heat, salt, momentum and suspended and dissolvedsubstances. This study attempts to quantify and characterize the turbulence from direct measurementsconducted in a reservoir. A 3D numerical model is used to investigate the water column hydrodynamics forthe duration of measurements and the performance of various turbulence models used in the CFD model areinvestigated via simulation of mixing in the reservoir. The drawdown curves produced by the turbulencemodels are formulized through linear equations. Although, use of different turbulence models do not havesignificant effects on the flow hydrodynamics away from the intake structure; significant effects especially onturbulence kinetic energy production are observed at the orifice. Therefore, for simulation of withdrawalflow, either use of shear stress transport (SST) k-omega models solving equations all the way to the wall or kepsilonmodels with the nonequilibrium wall function is recommended to account for the changes in thepressure gradient. In this study, the methods using quantified turbulent characteristics of the flow toreformulate the Stokes' settling velocity to be applied in turbulent flows are also investigated. An approach topredict setting velocity in turbulent flows that utilizes acoustic Doppler instruments for quantification ofturbulent characteristics is presented. Modification of the Stokes' settling velocity with thenondimensionalized turbulent kinetic energy production profiles lead better results than other turbulencecharacteristics (buoyancy flux and by Richardson number flux) widely used in characterizing turbulentmixing.
  • Article
    Citation - WoS: 20
    Citation - Scopus: 23
    Estimation of Suspended Sediment Concentration in Rivers Using Acoustic Methods
    (Springer Verlag, 2009) Elçi, Şebnem; Aydın, Ramazan; Work, Paul A.
    Acoustic Doppler current meters (ADV, ADCP, and ADP) are widely used in water systems to measure flow velocities and velocity profiles. Although these meters are designed for flow velocity measurements, they can also provide information defining the quantity of particulate matter in the water, after appropriate calibration. When an acoustic instrument is calibrated for a water system, no additional sensor is needed to measure suspended sediment concentration (SSC). This provides the simultaneous measurements of velocity and concentration required for most sediment transport studies. The performance of acoustic Doppler current meters for measuring SSC was investigated in different studies where signal-to-noise ratio (SNR) and suspended sediment concentration were related using different formulations. However, these studies were each limited to a single study site where neither the effect of particle size nor the effect of temperature was investigated. In this study, different parameters that affect the performance of an ADV for the prediction of SSC are investigated. In order to investigate the reliability of an ADV for SSC measurements in different environments, flow and SSC measurements were made in different streams located in the Aegean region of Turkey having different soil types. Soil samples were collected from all measuring stations and particle size analysis was conducted by mechanical means. Multivariate analysis was utilized to investigate the effect of soil type and water temperature on the measurements. Statistical analysis indicates that SNR readings ob tained from the ADV are affected by water temperature and particle size distribution of the soil, as expected, and a prediction model is presented relating SNR readings to SSC mea surements where both water temperature and sediment characteristics type are incorporated into the model. The coefficients of the suggested model were obtained using the multivariate anal ysis. Effect of high turbidity conditions on ADV performance was also investigated during and after rain events.
  • Article
    Citation - WoS: 184
    Citation - Scopus: 233
    Effects of Thermal Stratification and Mixing on Reservoir Water Quality
    (Springer Verlag, 2008) Elçi, Şebnem
    In this study, the effect of thermal stratification on water quality in a reservoir has been investigated by field observations and statistical analysis. During the summer period, when stratification is evident, field observations indicate that the observed dissolved oxygen concentrations drop well below the standard limit of 5 mg l-1 at the thermocline, leading to the development of anoxia. The reasons for variations in the dissolved oxygen concentrations were investigated. Variations of air temperature and other meteorological factors and lateral flows from side arms of the lake were found to be responsible for the increase of dissolved oxygen concentrations. It was also observed that turbidity peaked mostly in the thermocline region, closely related to the location of the maximum density gradient and thus low turbulence stabilizing the sediments in the vertical water column. Relatively cold sediment-laden water flowing into the lake after rain events also resulted in increased turbidity at the bottom of the lake. Nondimensional analysis widely used in the literature was used to identify the strength of the stratification, but this analysis alone was found insufficient to describe the evolution of dissolved oxygen and turbidity in the water column. Thus correlation of these parameters was investigated by multivariate analysis. Fall (partial mixing), summer (no mixing), and winter (well mixed) models describe the correlation structures between the independent variables (meteorological parameters) and the dependent variables (water-quality parameters). Statistical analysis results indicate that air temperature, one day lagged wind speed, and low humidity affected variation of water-quality parameters. © The Japanese Society of Limnology 2008.