Civil Engineering / İnşaat Mühendisliği

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

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Author: search.filters.author.Elçi, Şebnem

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  • 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).
  • Research Project
    Tahtalı Baraj Gölü'nde hidrodinamik çevrimin modellenmesinde ve düşeyde akım profilinin sıcaklıkla ilişkilendirilmesi
    (2007) Elçi, Şebnem; Gök, Suzan; Atış, İlker; Sılay, Erdenir Aslı
    [No Abstract Available]
  • Research Project
    Türbülansın askıdaki katı maddenin çökelme hızına etkisinin deneysel olarak araştırılması
    (2018) Elçi, Şebnem
    Türbülanslı akımlarda düşey yönde akı nispeten küçük olsa da, gözlenen biyolojik ve kimyasal değişimlerin açıklanmasında büyük önem taşır. Yüzeysel akımlarda hem karışım hem de askıdaki katı madde modellenmek istendiğinde türbülansın hem karışıma, hem de askıdaki katı madde çökelme hızına etkisinin gerçekçi olarak tanımlanması gerekmektedir. Literatürdeki mevcut denklemler türbülanslı akımın özelliklerini ve etkisini hesaba katmadan parçacık çökelme hızını tahmine yöneliktir, o yüzden de eksik kalmıştır. Bu eksikliği gidermek üzere deneysel bir düzenek tasarlanmış, ve farklı dane boyutlu parçacıklar bir tanka bırakılarak parçacığın çökelme hareketi video ile kaydedilerek sonrasında görüntü işleme tekniği ile çökelme hızları belirlenmiştir. Deneyler esnasında belli derinliklerde 10 MHz akustik Doppler akım ölçer ile akım ölçümleri yapılmış ve akım verileri analiz edilerek akımın türbülans karakteristik bilgileri hesaplanmıştır. Parçacığın akım ölçer probunun yanından geçtiği anın 2 saniye öncesi ve sonrası türbülans karakterizasyonunda kullanılmıştır. Sonraki aşamada türbülans şiddeti, parçacık çökelme hızı ile ilişkilendirilmeye çalışılmıştır. İki farklı motor devir hızıyla yaratılan türbülanslı akım koşullarında dane boyutu 2?den küçük ve 2?den büyük olma durumuna göre çökelme hızının laminer akıma göre farklı davranış gösterdiği gözlenmiştir. Düşük motor devir hızıyla yaratılan türbülanslı akım, dane boyutu 2 mm?den küçük parçacıklara laminer akımda gözlenen çökelme hızlarını ortalama %49 arttırarak etki ederken, daha büyük parçacıklara arttırıcı etkisi olmadığı ve çökelme hızlarının laminer akımda gözlenen çökelme hızlarına benzer olduğu gözlenmiştir. Motor yüksek devir hızıyla çalıştırıldığında ise, dane boyutu 2 mm?den küçük parçacıklara çökelme hızının ortalama %36 arttırarak etki ettiği, ama daha büyük parçacıklarda çökelme hızını azaltıcı bir etkiye sahip olduğu gözlenmiştir. Deneysel çalışmalar, tek bir dane boyutu için farklı derinliklerde ve farklı türbülans koşullarında gözlenen çökelme hızları ve deneyler esnasında yapılan hız ölçümlerinden elde edilen türbülans kinetik enerjilerinde bazı mesafe ve dane boyutları için benzer oranlar olduğunu göstermiştir. Ancak türbülans kinetik enerjileri ve akım hızları arasında oransal bir ilişki olduğunu tüm ölçümlerde gözlemlemek mümkün olmadığından genel bir ilişki kurulamamıştır. Deneyler sonucunda elde edilen tüm sonuçlar toplu olarak değerlendirilerek çökelme hızları ve türbülans şiddeti arasında regresyon analizi aracılığıyla tabandan ölçülen farklı mesafelerde bir ilişki kurulmaya çalışılmıştır. Analiz sonucu regresyon belirleme katsayısı R2 değeri oldukça düşük de olsa, türbülans şiddetinin ivme ve dane boyutundan bağımsız olarak artışı ile çökelme hızı bu artış göstermiştir. Deneyleri takiben sayısal model ile parçacık çökelme hızının laminer akımda ve farklı türbülanslı akım koşullarında simülasyonu gerçekleştirilmiştir. Bu amaçla Fluent modelinde Lagrangian dağınık faz alt modeli uygulanmıştır. Laminer akım için deneysel ve sayısal modellerde benzer sonuçlar elde edilmiştir. Ancak türbülanslı akım koşullarında parçacık çökelme hızı modellendiğinde, deneylerde gözlenen çökelme hızındaki artışın modellenen çökelme hızı değerlerinde gözlenemediği görülmüştür. Bu gözlemler doğrultusunda Fluent modelinde parçacık çökelme hızının hesaplandığı förmüllerde kullanıcı tanımlı fonksiyon yazılarak, türbülans şiddetinin çökelme hızının hesabında kullanılması sağlanmıştır. Sonuç olarak bu yaklaşımla türbülanslı akım koşullarında daha gerçekçi hızlar hesaplandığı düşünülmektedir. Özellikle erozyon etkisiyle askıda katı madde miktarının fazla olduğu baraj göllerinde su alma yapısının askıdaki katı maddeyi dışarıda bırakacak şekilde yeniden tasarımında ve nehirlerde köprü ayakları için koruma yapılarının tasarımında kullanılan modelleme yaklaşımlarının akım türbülans karakteristiğini içerecek şekilde yeniden yapılandırılması daha iyi sonuçlar verecektir.
  • Article
    Citation - WoS: 4
    Citation - Scopus: 4
    Destratification of Thermally Stratified Water Columns by Air Diffusers
    (Elsevier, 2023) Elçi, Şebnem; Hazar, Oğuz; Bahadıroğlu, Nisa; Karakaya, Derya; Bor, Aslı
    This study aims at improving the understanding in order to optimise an aeration system for artificial destratification to control cyanobacteria growth in the reservoirs. Previous applications for artificial destratification in reservoirs were based on installations based on computational methods, where neither the effect of air bubble size and configuration nor the effect of air density in the bubble plume could be investigated. This study seeks for an optimized design with the help of experimental and numerical analyses. In order to perform experimental studies, a novel water tank enabling the heating/cooling of the water column as desired and a diffuser system were manufactured. During the experimental studies, effect of bubble size, bubble slip velocity, and other parameters of air diffuser on destratification efficiency were investigated. Based on the nondimensional parameters, a new destratification efficiency formula is obtained by the Genetic Algorithm (GA) approach. Additionaly, the hydrodynamics of the water tank during the mixing process by air diffuser was simulated via 3D numerical model and validated with experimental results. The Eulerian multiphase model with the ‘degassing’ boundary condition and k-ω turbulence model are found to be suitable for the purposes of the study. Based on the error analysis of comparisons of the model and observations, the best configuration of air diffuser is proposed, and the numerical model is found to be successful in simulating the destratification of thermally stratified water columns by air diffuser.
  • Article
    Citation - WoS: 5
    Citation - Scopus: 5
    Developing Predictive Equations for Water Capturing Performance and Sediment Release Efficiency for Coanda Intakes Using Artificial Intelligence Methods
    (MDPI, 2022) Hazar, Oğuz; Tayfur, Gökmen; Elçi, Şebnem; Singh, Vijay P.
    Estimation of withdrawal water and filtered sediment amounts are important to obtain maximum efficiency from an intake structure. The purpose of this study is to develop empirical equations to predict Water Capturing Performance (WCP) and Sediment Release Efficiency (SRE) for Coanda type intakes. These equations were developed using 216 sets of experimental data. Intakes were tested under six different slopes, six screens, and three water discharges. In SRE experiments, sediment concentration was kept constant. Dimensionless parameters were first developed and then subjected to multicollinearity analysis. Then, nonlinear equations were proposed whose exponents and coefficients were obtained using the Genetic Algorithm method. The equations were calibrated and validated with 70 and 30% of the data, respectively. The validation results revealed that the empirical equations produced low MAE and RMSE and high R2 values for both the WCP and the SRE. Results showed outperformance of the empirical equations against those of MNLR. Sensitivity analysis carried out by the ANNs revealed that the geometric parameters of the intake were comparably more sensitive than the flow characteristics.
  • Article
    Citation - WoS: 10
    Citation - Scopus: 12
    Impacts of Construction of Dam on the Flow Regimes and Water Quality: a Case Study From Turkey
    (Springer, 2022) Bor, Aslı; Elçi, Şebnem
    Dam construction has important positive and negative effects on the environment, including physical changes of the riverbed morphology, changes in sediment transport patterns and water quality, and the river ecosystem in general. The primary objective of this study is to present a methodology to assess the impacts of construction and operation of Çine Dam, in Aydin, Turkey, on the river flow regimes, sedimentation, and water quality of the downstream reach of Büyük Menderes River. Construction of the dam significantly reduced the sediment load from the Çine tributary to the main reach, as expected. To evaluate changes in the water quality of the Çine River, five different water quality index methods are compared before and after the dam operation: Weighted Arithmetic Index (WAI-WQI), Canadian Council of Ministers of the Environment Water Quality Index (CCME-WQI), Universal Water Quality Index (UWQI), Oregon Water Quality Index (OWQI) and Aquatic Toxicity Index (ATI). ATI and CCME-WQI methods are found to be more appropriate for the 10-year water quality assessment of the river.
  • Conference Object
    14th of the International Conference on Hydroscience and Engineering, Iche 2022: Proceeding Book
    (Izmir Institute of Technology, 2022) Elçi, Şebnem; Bombar, Gökçen
    14th of the International Conference on Hydroscience & Engineering, ICHE 2022 will be held in Izmir, Turkey on 26-27 May, 2022. The International Conference on Hydroscience & Engineering began in Washington DC in 1993, and followed by Beijing hosted ICHE in 1995, Cottbus (1998), Seoul (2000), Warsaw (2002), Brisbane (2004), Philadelphia (2006), Nagoya (2008), Chennai (2010), Orlando (2012), Hamburg (2014) Tainan (2016) and Chongqing (2018). These conferences provided a common ground researchers and engineers to report and discuss the latest scientific advancements and practitioner’s solutions in hydroscience and engineering. ICHE 2022 conference aims to bring together researchers and practicing engineers to share the latest scientific and technological advancements in hydroscience and engineering, and will provide networking opportunities for future activities. Participants will be able to hear experts in the field discuss the latest achievements in issues relevant to Hydro-Engineering for Sustainable Development.
  • Article
    An Experimental Study on Release Mechanism of Iron and Manganese From Sediments To the Water Column in Reservoirs
    (2021) Vural, Buse; Elçi, Şebnem; Ökten, Hatice Eser
    Iron and manganese accumulation in drinking water reservoirs is a challenging issue and should be controlled to prevent their adverse effects on human health. Accumulation of these elements not only clogs pipeline systems but also causes stains on fixtures and laundry. Also, high concentrations of iron and manganese may lead to various health problems when ingested. This study focuses on the release mechanism of iron and manganese from sediments to the water column in reservoirs and investigates methods to prevent this release. Effects of hypoxia, hypolimnetic aeration, alkalinity of water, and thermal stratification on iron and manganese concentrations were investigated through laboratory experiments. Experiments done simulating the water column showed that hypoxia caused more dissolution of ferrous iron when compared with that of manganese. Accordingly, aeration of the water column in hypoxic conditions lead to a significant decrease in ferrous iron concentrations (in our case reaching zero). However, manganese and total iron levels were not affected by the aeration of the water column. Alkalinity level of the water column was observed to have a great effect on the solubility of iron and manganese. Concentrations of total Fe and total Mn measured for acidic (pH = 5) conditions were considerably greater than concentrations measured at neutral conditions. As for alkaline (pH = 11) conditions, the opposite was observed with measured concentrations of total Fe and total Mn being lower than the ones measured for neutral conditions. Thermal stratification had an enhancing effect on the solubility of both iron and manganese ions. While aeration of the stratified water column slightly decreased the concentrations of Total Fe and Mn, it had a greater impact on decreasing $Fe^{2+}$ concentrations.
  • Article
    Citation - Scopus: 1
    Assessment and Transport of Sediment-Bound Estuarine Contaminants
    (Springer, 2015) Work, P. A.; Haas, K. A.; Warren, D. A.; Elçi, Şebnem
    Estuaries and coastal bays frequently receive anthropogenically sourced contaminants. Many of these contaminants (e.g. most metals) have low solubility and tend to sorb to sediment particles, so that sediment transport driven by fluid mechanics becomes an important part of the contaminant transport problem. The chosen strategy for mitigation of the contaminant(s) will depend on the potential for migration away from the affected region, or the build-up of concentrations within the receiving area if loading rate exceeds decay or transport rates, and the potential impact on environmental and human health both within and outside the receiving area. Two case studies are considered here in which data describing instantaneous contaminant concentrations in estuarine environments were acquired via field sampling. Both sites feature estuaries dominated by tidal forcing, with smaller, adjacent upland regions also impacted. Metals, particularly copper and lead, are the primary focus in each case. Contaminant transport processes, including diffusion, advection, and bioturbation, are treated together to develop analytical and numerical solutions for time-dependent contaminant concentrations using a spatially varying, time-dependent, effective diffusion coefficient that is influenced by local surface water flow speeds. Different initial, boundary, and loading conditions are considered to illustrate the relative importance of the various transport processes. Implications of future contaminant loading and sea level rise scenarios are demonstrated and discussed.
  • 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.