Civil Engineering / İnşaat Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/13
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Article Citation - Scopus: 1Assessment and Transport of Sediment-Bound Estuarine Contaminants(Springer, 2015) Work, P. A.; Haas, K. A.; Warren, D. A.; Elçi, ŞebnemEstuaries 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.Conference Object Experimental Investigation of Flow Characteristics of Discretized Triangular Hydrographs(International Association for Hydro-Environment Engineering Research, 2015) Pulat, Aytaç; Ata, Cem; Altınsoy, Sinem; Bombar, Gökçen; Elçi, ŞebnemIn this study effect of discretization of triangular hydrographs on flow characteristics is investigated. All experimental tests are carried out in a rectangular flume of 70 cm width and 18 m length and having a slope of 0.004. The flow rate is measured by an electromagnetic flow meter mounted on the inlet pipe and the time variation of flow depth is monitored at various locations. The point velocities are measured by a side-looking ultrasonic velocity meter at 17 different elevations along the water column by repeating the same hydrograph 17 times in unsteady flows, so that the velocity time series could be obtained at each location. A pump speed control unit (PSCU) is used to generate the hydrograph. The results of a three step discretized hydrograph and a continuous triangular shaped hydrograph generated in the flume are compared. Rising and falling periods of both hydrographs are 5.5 minutes and the base and peak flow rates are 14 l/s and 62 l/s respectively. The time varying mean of velocity time series in both stream-wise and vertical directions are investigated. The velocity profiles as well as the turbulence characteristics are compared with the ones obtained from the triangular hydrograph and the discretized hydrograph at unsteady flow conditions. The effect of discretization of the triangular hydrograph on flow velocities and turbulence characteristics is also discussed.Book Part Suspended Sediment Concentration in Stratified Lakes Estimated by Acoustic Methods(Springer, 2012) Elçi, Şebnem[No abstract available]Article Citation - WoS: 4Citation - Scopus: 3Baraj Yıkılması Sonrası İki Boyutlu Taşkın Yayılımının Yerleşim Bölgeleri için Modellenmesi(Turkish Chamber of Civil Engineers, 2017) Elçi, Şebnem; Tayfur, Gökmen; Haltaş, İsmail; Kocaman, BülentHer ne kadar baraj yıkılması nadiren gerçekleşse de, aniden yıkılan bir barajın taşkın dalgasının mansapta bulunan yerleşim bölgelerinde etkisi felaketle sonuçlanabilmektedir. Bu sebeble muhtemel bir baraj yıkılmasının sonuçlarını öngörmek risk yönetimi açısından gereklidir. Bu çalışmada baraj yıkılması sonucunda oluşan taşkın dalgasının tahmini ve mansapta ilerlemesinin analizine yönelik bir yaklaşım sunulmuştur. Sunulan yaklaşım, barajların aniden yıkılma varsayımı ile baraj haznesindeki su hacminin bir-boyutlu model ile dar bir vadi boyunca ötelenmesini ve ötelenmiş hidrograf sınır şartı kabul edilerek mansabında yerleşim bölgeleri yer alan iki ayrı çalışma alanında taşkın dalgasının iki boyutlu yayılımının modellenmesini içermektedir. Önerilen yaklaşım mansabında Eskişehir bulunan Porsuk Barajı ile mansabında İstanbul olan Alibey Barajına uygulanmıştır.Article Citation - WoS: 76Citation - Scopus: 84Two-Dimensional Numerical Modeling of Flood Wave Propagation in an Urban Area Due To Ürkmez Dam-Break, Izmir, Turkey(Springer Verlag, 2016) Haltas, İsmail; Tayfur, Gökmen; Elçi, ŞebnemThis study investigated flood inundation in an urban area due to a possible failure of Ürkmez Dam in İzmir, Turkey. The estimation of flood hydrograph upon partial failure of the dam and routing of the flood hydrograph along the narrow valley downstream were first performed by the one-dimensional hydraulic routing model HEC-RAS. The two-dimensional hydraulic routing model FLO-2D is then used to simulate the spreading of the dam-break flood after the flood wave exits the valley. Land use and land cover digital maps were utilized to find the spatially varying roughness coefficient for the floodplain. The influence of the buildings on the flood propagation was represented in the numerical model by the area reduction factor as well as the width reduction factor. The peak flow depth, peak flow velocity and time moment of the peak flow depth maps were shown in the GIS environment. The results reveal that flow depths can reach about 3 m in the residential area. In about 40 min after the dam-break, houses in the large section of the town would be under the maximum flow depths. The two-dimensional hydrodynamic model results were tested against experimental dam-break flow data of the distorted physical model of Ürkmez Dam, which is consisted of the reservoir, dam body and downstream area including Ürkmez Town. The model successfully simulated experimental flow depth data measured at different measurement locations.Article Citation - WoS: 49Citation - Scopus: 51Numerical Simulation of Flood Wave Propagation in Two-Dimensions in Densely Populated Urban Areas Due To Dam Break(Springer Verlag, 2016) Haltaş, İsmail; Elçi, Şebnem; Tayfur, GökmenDams are important structures having many functions such as water supply, flood control, hydroelectric power and recreation. Although dam break failures are very rare events, dams can fail with little warning and the damage at the downstream of the dam due to the flood wave can be catastrophic. During a dam failure, immense volume of water is mobilized at very high speed in a very short time. The momentum of the flood wave can turn to a very destructive impact force in residential areas. Therefore, from risk point of view, understanding the consequences of a possible dam failure is critically important. This study deals with the methodology utilized for predicting the flood wave occurring after the dam break and analyses the propagation of the flood wave downstream of the dam. The methodology used in this study includes creation of bathymetric, DEM and land use maps; routing of the flood wave along the valley using a 1D model; and two dimensional numerical modeling of the propagation and spreading of flood wave for various dam breaching scenarios in two different urban areas. Such a methodology is a vital tool for decision-making process since it takes into account the spatial heterogeneity of the basin parameters to predict flood wave propagation downstream of the dam. Proposed methodology is applied to two dams; Porsuk Dam located in Eskişehir and Alibey Dam located in Istanbul, Turkey. Both dams are selected based on the fact that they have dense residential areas downstream and such a failure would be disastrous in both cases. Model simulations based on three different dam breaching scenarios showed that maximum flow depth can reach to 5 m at the border of the residential areas both in Eskişehir and in Istanbul with a maximum flow velocity of 5 m/s and flood waves having 0.3 m height reach to the boundary of the residential area within 1 to 2 h. Flooded area in Eskişehir was estimated as 127 km2, whereas in Istanbul this area was 8.4 km2 in total.Article Citation - WoS: 2Citation - Scopus: 2Observational and Numerical Methods for Quantifying and Modeling of Turbulence in a Stratified Reservoir(Isfahan University of Technology, 2016) Elçi, Şebnem; Ekmekçi, Hüseyin BurakThe 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: 46Citation - Scopus: 53Distorted Physical Model To Study Sudden Partial Dam Break Flows in an Urban Area(American Society of Civil Engineers (ASCE), 2014) Güney, Mehmet Şükrü; Tayfur, Gökmen; Bombar, Gökçen; Elçi, ŞebnemA distorted physical model, based on Ürkmez Dam in Izmir, Turkey, was built to study sudden partial dam break flows. The distorted model had a horizontal scale of 1/150 and a vertical scale of 1/30, containing dam reservoir, dam body, and downstream area-from dam body to Ürkmez urban area until the sea coast. In the model, the reservoir is approximately 12 m3, the dam body has a width of 2.84 m and a height of 1.07 m, and the downstream area is nearly 200 m2. The Ürkmez Dam was chosen because Ürkmez Town is located right at its downstream area, allowing the study of dam break flows in an urban area. Furthermore, the dimensions were suitable such that it allowed the construction of a physical model (dam reservoir, dam body, and downstream area) having a horizontal scale of 1/150 in the available space of 300 m2. The features creating roughness such as buildings, bridge, and roads were also reflected in the physical model. The dam break flow was investigated for sudden partial collapse, which was simulated by a trapezoidal breach on the dam body. The water depths at downstream area were measured at eight different locations by using e+ WATER L (level) sensors. The velocities were measured at four different locations by ultrasonic velocity profiler (UVP) transducers. The propagation of the flood was recorded by a high-defnition camera. The experimental results show that the Ürkmez area can be flooded in a matter of minutes, at depths reaching up to 3 m in residential areas in 4 min. The flood wave front can reach the residential areas in 2 min and to the sea coast in 4 min. Flow velocities can reach 70.9 km/h in sparse residential areas, close to dam body. Away from the dam body in the sparse buildings part of the town, the velocities can reach 27.7 km/h. In dense residential areas of the town, the velocities are too low (2.8 km/h) but flow depths can reach 3 m. Velocity profiles show similar behavior like unsteady and nonuniform open channel flow in nonresidential areas close to the dam body. In residential areas away from the dam body, the velocity profiles are more uniform, having lower velocity values. Vertical variations of velocities show markedly different behavior during rising and recession stages. The profiles are smooth during the rising stage in sparse residential area, yet it shows fluctuating behavior during the recession stage.Article Citation - WoS: 19Citation - Scopus: 21Effects of Basin Activities and Land Use on Water Quality Trends in Tahtali Basin, Turkey(Springer Verlag, 2013) Elçi, Şebnem; Selçuk, PelinBi-weekly water quality data from seven monitoring stations located within Tahtali Watershed, İzmir, Turkey and digital land use/land cover data of the same watershed are analyzed in this study. To examine the changes in land use associated with urbanization, the satellite images of the main pool of the Tahtali reservoir prior to filling and subsequent to filling, respectively, are analyzed. Aerial photos of the basin taken in 1995 (October) are compared with images taken in 2005 (November) from the IKONOS satellite through use of several GIS techniques. New residential buildings, greenhouses, and industrial buildings are presented in separate layers, and changes in basin activities are quantified. The effects of urbanization on the water quality are investigated through statistical analysis. The seasonal Kendall test is applied to the water quality parameters monitored bi-weekly at seven stations within the basin for the duration 1997-2005. There was no trend in phosphorus, but there was a negative trend in boron and nitrate and a positive trend in the parameters of biological oxygen demand (BOD) and chemical oxygen demand (COD). The improvement in nitrate concentrations is attributed to the new regulations on the use of fertilizers in greenhouses. However, increase of BOD and COD concentrations is related to the growing settlement areas and industrial zones, which point to the insufficient wastewater treatment within the basin. Soil erosion within the basin is also quantified by the universal soil loss equation using available maps. Estimated total soil loss rate increased about 2. 5 times that of 1995 when the changed land use composition in 2005 is considered in the calculations.Article Citation - WoS: 1Citation - Scopus: 2How Do Contaminated Reservoir Bottom Sediments Affect Water Quality? an Assessment Using Swim Model(Water Environment Federation, 2013) Elçi, Şebnem; Şimşek, Sinem ElifIn this study, an approach for the assessment of long term effects of contaminated sediments on the surface water quality of a future reservoir is presented. A one-dimensional sediment-water interaction model designed to simulate contaminants associated with the sediments, and the transfer of these contaminants to the overlying water column, was developed. The effect of contaminated bottom sediments on water quality was investigated under different stratification conditions. The numerical model was applied to an existing reservoir (Tahtali Reservoir) for validation and projected contaminant concentrations based on the soil and water samples collected before inundation of the land. Results were compared with the concentrations obtained from water samples collected during its operation. Next, transfer to a planned reservoir (Çamli Basin, Izmir) of four heavy metals - copper, zinc, chromium, and lead - existing in bottom sediments of the planned reservoir is modeled. A ten year projection of heavy metal concentrations for the Çamli Reservoir showed concentrations to be higher than those acceptable by the World Health Organization (WHO). Construction of a treatment facility is recommended if the reservoir is to be utilized for providing domestic water.