Civil Engineering / İnşaat Mühendisliği
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Article Citation - WoS: 10Citation - Scopus: 11Experimental Investigation of Sediment Movement as a Result of Homogeneous Earth-Fill Dam Overtopping Break Over a Simplified Urban Area(Elsevier, 2023) Taşkaya, Ebru; Bombar, Gökçen; Tayfur, GökmenWhen an earth-fill dam breaks, dam body sediment and water flow simultaneously move to downstream area causing devastation. Dam break studies in the literature have concentrated mostly on the water flow part while ignoring the sediment movement by designing the dam body as a movable metal gate. This study, however, is the first one experimentally investigating flow and sediment transport due to an earth-fill dam break by constructing the dam body from sediment. Sediment propagation as a result of homogenous earth-fill dam overtopping break was experimentally studied in a laboratory flume of 18.4 m long and 2.0 m wide, and 0.88 m in height in the Hydraulics Laboratory of Izmir Katip Celebi University, Izmir, Turkey. Downstream section right after the dam body was designed as a smooth bed and rough bed. The rough bed, resembling a simplified urban area, was created by using thirteen 10 × 10 × 10 cm sized concrete blocks. The dam body was constructed as homogenous with uniform material having D50 = 0.441 mm. The earth-fill dam body was built using the standard compression methods; each layer of sediment with a thickness of 10 cm was laid in layers, and the body was prepared with a crest width of 10 cm, a transverse base width of 200 cm, a longitudinal base width of 202 cm and height of 60 cm with upstream and downstream slopes of 1:1.6. The water level behind the dam was gradually raised until it overtopped the crest level. A pre-breach was formed at the top of the dam to trigger the break. During each dam break event, water depths were measured by three ULS-40D level meter sensors at different locations, and the final sediment bathymetry map was generated using the ULS-40D Probes at 10 × 10 cm grids. The results showed that, in both smooth and rough downstream bed cases, the dam body eventually collapsed while a great portion of it was carried away by the flood flow. The sediment spreading occurred all over the downstream area, showing significant non-uniform variation in thickness both longitudinally and transversely, especially in the simulated urban area. All the residential areas, while breaking in motion, were submerged under the muddy flow. Some blocks were almost submerged while sediment heights reached half level of some blocks at the end of the experiment. Sediment heights were higher in the urban area.Conference Object 14th of the International Conference on Hydroscience and Engineering, Iche 2022: Proceeding Book(Izmir Institute of Technology, 2022) Elçi, Şebnem; Bombar, Gökçen14th 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.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.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: 60Citation - Scopus: 69Experimental and Numerical Investigation of Bed-Load Transport Under Unsteady Flows(American Society of Civil Engineers (ASCE), 2011) Bombar, Gökçen; Elçi, Şebnem; Tayfur, Gökmen; Güney, M. Şükrü; Bor, AslıThe dynamic behavior of bed-load sediment transport under unsteady flow conditions is experimentally and numerically investigated. A series of experiments are conducted in a rectangular flume (18 m in length, 0.80 m in width) with various triangular and trapezoidal shaped hydrographs. The flume bed of 8 cm in height consists of scraped uniform small gravel of D 50=4.8 mm. Analysis of the experimental results showed that bed-load transport rates followed the temporal variation of the triangular and trapezoidal hydrographs with a time lag on the average of 11 and 30 s, respectively. The experimental data were also qualitatively investigated employing the unsteady-flow parameter and total flow work index. The analysis results revealed that total yield increased exponentially with the total flow work. An original expression which is based on the net acceleration concept was proposed for the unsteadiness parameter. Analysis of the results then revealed that the total yield increased exponentially with the increase in the value of the proposed unsteadiness parameter. Further analysis of the experimental results revealed that total flow work has an inverse exponential variation relation with the lag time. A one-dimensional numerical model that employs the governing equations for the conservation of mass for water and sediment and the momentum was also developed to simulate the experimental results. The momentum equation was approximated by the diffusion wave approach, and the kinematic wave theory approach was employed to relate the bed sediment flux to the sediment concentration. The model successfully simulated measured sedimentographs. It predicted sediment yield, on the average, with errors of 7% and 15% of peak loads for the triangular and trapezoidal hydrograph experiments, respectively.Article Citation - WoS: 7Citation - Scopus: 9Calculation of the Time-Varying Mean Velocity by Different Methods and Determination of the Turbulence Intensities(Academic Journals, 2010) Bombar, Gökçen; Güney, Mehmet Şükrü; Tayfur, Gökmen; Elçi, ŞebnemThe raw velocity data for both stream-wise and transversal directions in unsteady flows, which are formed by generating input hydrograph, are obtained by using a flow tracker. The same hydrograph is generated 15 times and the mean values are found by calculating the average of all hydrographs. The time varying mean is obtained by using FFT, moving average, wavelet and EMD methods. The best time varying mean is selected according to prescribed criteria. Then, the 15 time series are processed and the stream-wise and transversal turbulence intensities are obtained. The mean of the product of fluctuations is also determined. © 2010 Academic Journals.