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Öğe Assessment of drought in SPI series using continuous wavelet analysis for Gediz Basin, Turkey(Elsevier Science Inc, 2021) Yerdelen, Cahit; Abdelkader, Mohamed; Eris, EbruThis study aims to estimate the short and long-term drought periodicities, and trend component using the continuous wavelet transforms. The applied approach introduces a new concept, the maxima line, which defines the most dominant component affecting the trend in Standardized Precipitation Index (SPI) time series. The analysis of the short and long-term drought cycles was performed with data from 15 stations located in Gediz Basin, at western part of Turkey, obtained during the recording period of 1960-2016. The change point in the SPI time series was determined graphically via the continuous wavelet power spectrum, and the obtained results were verified with Pettitt's test. The significant change points, in the northwest, east and southwest part of the basin, occurred by the beginning of 1980s, by the end of 1980s, and by the mid of 1990s, respectively. The most dominating periodicities affecting the trend were varying between 24 and 48 months for the short-term drought cycles, whereas they were varying between 96 and 162 months for the long-term drought cycles.Öğe Critical drought intensity-duration-frequency curves based on total probability theorem-coupled frequency analysis(Taylor & Francis Ltd, 2021) Aksoy, Hafzullah; Cetin, Mahmut; Eris, Ebru; Burgan, Halil Ibrahim; Cavus, Yonca; Yildirim, Isilsu; Sivapalan, MurugesuA methodology using the standardised precipitation index is proposed to develop critical drought intensity-duration-frequency (IDF) curves. We define dry periods within which we recognise droughts of different durations. The most severe drought for each drought duration in each year is called the critical drought. The total probability theorem-coupled frequency analysis is used to determine the best-fit probability distribution function of drought severity, which is then converted to intensity. The generalised extreme value probability distribution function is found to best fit the critical drought severity. The methodology is implemented using monthly precipitation data for a meteorological station in Turkey. The critical drought intensity decreases linearly with increasing drought duration, whereas the return period increases exponentially when the drought becomes more severe. The site-specific IDF curves furnished with an empirical relationship between the intensity and return period allow one to characterise the drought not by an index-based intensity but by its return period. This kind of presentation is physically easier to understand, in particular for stakeholders and decision makers in practice.Öğe Determination of flexible vegetation resistance against the flow with rigid behavior(Pamukkale Univ, 2017) Bombar, Gokcen; Eris, Ebru; Kavakli, UveysIn this study, it is aimed to obtain roughness coefficients of flexible multi-stemmed vegetation standing upright against flow with rigid behavior. Flow depths and discharges are measured; head losses causing from vegetation are calculated at 7 different points in 166 experiments for four different configurations. It is seen that Chezy coefficient C, Darcy-Weisbach friction coefficient f and Manning coefficient n cannot be expressed with a single function for all Reynolds number. Therefore, the data are analyzed for the two different cases of Reynolds number lower and greater than 10000. Dimensionless parameters for the roughness coefficients are determined as Froude number Fr, Reynolds number Re, the relative roughness h/h(v), approach flow energy line slope S-f, and vegetation density k. The most suitable equations for estimating roughness coefficients are obtained by nonlinear regression models. It is evaluated that for the Reynolds number lower than 10000 the roughness coefficients are defined as f = f (h(1)h(v)}, n = [Fr, h/h(v), k} and C = (Fr, SA, and for the Reynolds number greater than 10000 they are given as f = [Fr,/h(v), k}, n = [Fr, h/h(v), k} and C = {Fr, Re, h/h(v) S-f, k}. Also, for relatively low Reynolds numbers, the presence of plants caused an increase in resistance against the flow independently of other parameters as expected. It is observed that the regression equation coefficients could be influenced by factors such as surface area plant in the flow direction and plant density.Öğe Determination of Spatial Distribution of Precipitation on Poorly Gauged Coastal Regions: Eastern Black Sea Region(Turkish Chamber Civil Engineers, 2017) Eris, Ebru; Agiralioglu, NecatiDeteimination of spatial distribution of precipitation has an importance in teams of hydrological applications and water resources assessment. Particularly, the effects of orography and coastline on precipitation distribution should be taken into account in mountainous and/or coastal regions. This necessity is complicated by the limited number of rain gauges which have also a nonhomogenous distribution. In this study, it is aimed to determine the spatial distribution of precipitation for the coastal part of the Eastern Black Sea Region. It can be said that this study is the first in terms of combination of precipitation distribution on both hillside and coastal part by using two different approaches. One of these approaches is the water balance that reflects the precipitation distribution on hillside. The other one depends on the regression equations which explains the precipitation variability on coastline and valleys, for the coastal part of the Eastern Black Sea Region.Öğe Empirical Sediment Transport Models Based on Indoor Rainfall Simulator and Erosion Flume Experimental Data(Wiley, 2017) Aksoy, Hafzullah; Eris, Ebru; Tayfur, GokmenLand degradation processes start with accelerated runoff and sediment delivery. In this study, rainfall-runoff induced sediment transport is investigated using data from an indoor laboratory experimental setup consisting of a rainfall simulator and an erosion flume. The data are analysed to develop empirical models using sediment discharge, slope, flow discharge, rainfall intensity and sediment size. Fine and medium sands are considered as bare soil in experiments. Four rainfall intensities (45, 65, 85 and 105mmh(-1)) are applied with combinations of lateral and longitudinal slopes of 5%, 10%, 15% and 20%. Eighty experiments are conducted. Flow is measured, and sediment within flow is separated and weighted. Experimental data are used for developing empirical models through multiple regression with parameters optimized by genetic algorithm. Results show that slope is the main contributing variable to the sediment transport over hillslopes. Accommodating variables among slope, rainfall intensity, flow discharge and median diameter of sediment as independent variables, one-variable, two-variable and four-variable models are developed considering also that higher number of parameters increases the performance of the model with higher cost of parameterization. Copyright (c) 2016 John Wiley & Sons, Ltd.Öğe Evaluation of an erosion-sediment transport model for a hillslope using laboratory flume data(Springer Heidelberg, 2014) Arguelles, Anya Catherine C.; Jung, MinJae; Mallari, Kristine Joy B.; Pak, GiJung; Aksoy, Hafzullah; Kavvas, Levent M.; Eris, Ebru; Yoon, JaeYoung; Lee, YoungJoon; Hong, SeonHwaClimate change can escalate rainfall intensity and cause further increase in sediment transport in arid lands which in turn can adversely affect water quality. Hence, there is a strong need to predict the fate of sediments in order to provide measures for sound erosion control and water quality management. The presence of microtopography on hillslopes influences processes of runoff generation and erosion, which should be taken into account to achieve more accurate modelling results. This study presents a physically based mathematical model for erosion and sediment transport coupled to one-dimensional overland flow equations that simulate rainfall-runoff generation on the rill and interrill areas of a bare hillslope. Modelling effort at such a fine resolution considering the flow connection between interrill areas and rills is rarely verified. The developed model was applied on a set of data gathered from an experimental setup where a 650 cmx136 cm erosion flume was pre-formed with a longitudinal rill and interrill having a plane geometry and was equipped with a rainfall simulator that reproduces natural rainfall characteristics. The flume can be given both longitudinal and lateral slope directions. For calibration and validation, the model was applied on the experimental results obtained from the setup of the flume having 5% lateral and 10% longitudinal slope directions under rainfall intensities of 105 and 45 mm/h, respectively. Calibration showed that the model was able to produce good results based on the R (2) (0.84) and NSE (0.80) values. The model performance was further tested through validation which also produced good statistics (R (2)=0.83, NSE=0.72). Results in terms of the sedigraphs, cumulative mass curves and performance statistics suggest that the model can be a useful and an important step towards verifying and improving mathematical models of erosion and sediment transport.Öğe Experimental investigation of scouring around a single spur under clear water conditions(Iwa Publishing, 2022) Ozyaman, Cansu; Yerdelen, Cahit; Eris, Ebru; Daneshfaraz, RasoulThis study presents the effect of different parameters on scouring process around spur dikes. Our research group's stated objective was to evaluate the effects of sediment gradation, flow depth, spur angle and spur length on scouring process. Since most existing studies generally employed uniform sediment; in this study uniform and non-uniform sediment were selected. Experiments were made in a rectangular open channel in uniform flow conditions. Results showed that the effect of the spur dike length and the orientation angle on sediment scour varies with the type of sediment used. Scour volumes were 40% greater in uniform sediments than in non-uniform sediments. Measured scour depth was maximum at spurs perpendicular to the flow, whereas the scour volume was maximum at spurs directed upstream. The scour depth increased with an increase in the spur length; however, effect of spur length on scouring varied at a contraction rate of 0.29 for uniform sediments and 0.36 for non-uniform sediments. A multiple regression analysis was also performed, and four equations were suggested to predict the scour depth and scour volume. Comparisons were made with the literature equations applicable for clear-water scouring to check the suggested equation. Because of a wide range of contraction ratios considered in this study, the equations which considered the contraction effect yielded better estimates.Öğe Frequency analysis of low flows in intermittent and non-intermittent rivers from hydrological basins in Turkey(Iwa Publishing, 2019) Eris, Ebru; Aksoy, Hafzullah; Onoz, Bihrat; Cetin, Mahmut; Yuce, Mehmet Ishak; Selek, Bulent; Aksu, Hakan; Burgan, Halil Ibrahim; Esit, Musa; Yildirim, Isilsu; Karakus, Ece UnsalThis study attempts to find out the best-fit probability distribution function to low flows using the up-to-date data of intermittent and non-intermittent rivers in four hydrological basins from different regions in Turkey. Frequency analysis of D = 1-, 7-, 14-, 30-, 90- and 273-day low flows calculated from the daily flow time series of each stream gauge was performed. Weibull (W2), Gamma (G2), Generalized Extreme Value (GEV) and Log-Normal (LN2) are selected among the 2-parameter probability distribution functions together with the Weibull (W3), Gamma (G3) and Log-Normal (LN3) from the 3-parameter probability distribution function family. Selected probability distribution functions are checked for their suitability to fit each D-day low flow sequence. LN3 mostly conforms to low flows by being the best-fit among the selected probability distribution functions in three out of four hydrological basins while W3 fits low flows in one basin. With the use of the best-fit probability distribution function, the low flow-duration-frequency curves are determined, which have the ability to provide the end-users with any D-day low flow discharge of any given return period.Öğe Frequency curves of high and low flows in intermittent river basins for hydrological analysis and hydraulic design(Springer, 2024) Sarigil, Gokhan; Aksoy, Hafzullah; Cavus, Yonca; Eris, EbruUpper and lower percentiles of Flow Duration Curves (FDCs) of daily streamflow data were investigated to develop frequency curves. Upper percentiles with exceedance probability of 1, 5 and 10% (Q1, Q5, Q10) were used for high flows, and lower percentiles with non-exceedance probability of 10, 5 and 1% (Q90, Q95, Q99) for low flows. Median value (Q50) was covered to represent the average conditions of streamflow. A mixed frequency analysis based on the total probability theorem taking zero values into account was applied for the lower percentiles of FDC. Case studies were performed for three intermittent Streamflow Gauging Stations (SGSs) from Kucuk Menderes River Basin in western Turkey. An overall assessment of results shows that the best-fit probability distribution function does not change from one SGS to another considerably for low flows while each SGS has its own probability distribution function for high flows. Upper and lower percentiles, and median value were calculated at various return periods by using the identified probability distribution functions. The calculated values were plotted in the form of frequency curves of high flow percentiles and low flow percentiles. The frequency curves have a practically significant potential use in hydrological analysis, water resources management and hydraulic design under high and low flow conditions. They are yet open to further development for regionalization and their applicability can be extended to ungauged sites in river basins.Öğe Impact of climate change on meteorological and hydrological droughts for Upper Coruh Basin, Turkey(Springer, 2022) Yilmaz, Muhammet; Alp, Harun; Tosunoglu, Fatih; Asikoglu, Omer Levend; Eris, EbruDrought is a multifaceted natural hazard that occurs in almost every component of the hydrological cycle. This study investigated future hydro-meteorological droughts using climate projections from an ensemble of 13 European Coordinated Regional Downscaling Experiments (CORDEX) domain outputs under two alternative scenarios of representative concentration pathways (RCP 4.5 and RCP 8.5) for the 2030-2059 and 2070-2099 periods across Upper Coruh Basin, Turkey. The bias-corrected CORDEX climate projections were incorporated into the Soil and Water Assessment Tool (SWAT) hydrological model. In this study, two optimisation algorithms (the sequential uncertainty fitting algorithm of SWAT calibration and uncertainty and the shuffled complex evolution (SCE) algorithm in parameter estimation tool (PEST)) were tested for the automatic parameter calibration of a complex hydrologic model, SWAT, in the study area. Results show that SCE reached better parameter solutions than the other algorithm. This study investigated for the first time a comprehensive analysis of the projected droughts in the Upper Coruh Basin, Turkey. The standardised precipitation index and standardised streamflow index were used to evaluate the meteorological and hydrological droughts, respectively. Overall, the future annual precipitation and the maximum and minimum temperatures are projected to change from - 15.46% to 8.74%, 0.02 degrees C to 8.74 degrees C and - 2.69 degrees C to 5.27 degrees C, respectively. The results show that the frequency of hydrological drought durations will be higher under RCP4.5 and RCP8.5 during the period 2030-2059. In addition, the frequency of hydrological high-severity droughts (> similar to 5) and low-severity droughts (< similar to 2) will be more likely under RCP4.5 and RCP8.5 during the period 2030-2059 and 2070-2099, respectively. Other than this, not enough evidence exists to claim that hydrological and meteorological drought will become more significant in the twenty-first century.Öğe Laboratory experiments of sediment transport from bare soil with a rill(Taylor & Francis Ltd, 2013) Aksoy, Hafzullah; Unal, N. Erdem; Cokgor, Sevket; Gedikli, Abdullah; Yoon, Jaeyoung; Koca, Kaan; Inci, S. Boran; Eris, Ebru; Pak, GijungMathematical models developed for quantification of sediment transport in hydrological watersheds require data collected through field or laboratory experiments, but these are still very rare in the literature. This study aims to collect such data at the laboratory scale. To this end, a rainfall simulator equipped with nozzles to spray rainfall was constructed, together with an erosion flume that can be given longitudinal and lateral slopes. Eighty experiments were performed, considering microtopographical features by pre-forming a rill on the soil surface before the start of each experiment. Medium and fine sands were used as soil, and four rainfall intensities (45, 65, 85 and 105 mm h(-1)) were applied in the experiments. Rainfall characteristics such as uniformity, granulometry, drop velocity and kinetic energy were evaluated; flow and sediment discharge data were collected and analysed. The analysis shows that the sediment transport rate is directly proportional to rainfall intensity and slope. In contrast, the volumetric sediment concentration stays constant and does not change with rainfall intensity unless the slope changes. These conclusions are restricted to the conditions of experiments performed under rainfall intensities between and 105 mm h(-1) for medium and fine sands in a 136-cm-wide, 650-cm-long and 17-cm-deep erosion flume with longitudinal and lateral slopes varying between 5 and 20%.Öğe PRACTICAL METHODS FOR THE ESTIMATION OF HYDROELECTRIC POWER POTENTIAL OF POORLY GAUGED BASINS(Yildiz Technical Univ, 2017) Agiralioglu, Necati; Eris, Ebru; Andic, Gokhan; Cigizoglu, H. Kerem; Coskun, H. Gonca; Yilmaz, Levent; Alganci, Ugur; Toprak, Z. FuatDetermining the hydroelectric power potential of ungauged or poorly gauged basins gains importance parallel with the increasing electricity consumption. This study presents some simple methods to predict flow to determine the hydroelectric power potential of poorly gauged basins, such as the precipitation-elevation, average precipitation, and average basin elevation methods. Results of these methods are compared with the available flow measurements. The poorly gauged Solakli Basin, which is located in Trabzon, in the Eastern Black Sea Region of Turkey, is selected as the pilot area. The hydroelectric power potential of the planned small hydroelectric power plants in this area is estimated using different flow prediction methods.Öğe Prediction of rainfall runoff-induced sediment load from bare land surfaces by generalized regression neural network and empirical model(Wiley, 2020) Tayfur, Gokmen; Aksoy, Hafzullah; Eris, EbruBased on three rainfall run-off-induced sediment transport data for bare surface experimental plots, the generalized regression neural network (GRNN) and empirical models were developed to predict sediment load. Rainfall intensity, slope, rainfall duration, soil particle median diameter, clay content of the soil, rill density and soil particle mass density constituted the input variables of the models while sediment load was the target output. the GRNN model was trained and tested. the GRNN model was found successful in predicting sediment load. Sensitivity analysis by the GRNN model revealed that slope and rainfall duration were the most sensitive parameters. in addition to the GRNN model, two empirical models were proposed: (1) in the first empirical model, all the input variables were related to the sediment load, and (2) in the second empirical model, only rainfall intensity, slope and rainfall duration were related to the sediment load. the empirical models were calibrated and validated. At the calibration stage, the coefficients and the exponents of the empirical models were obtained using the genetic algorithm optimization method. the validated empirical models were also applied to two more experimental data sets: (1) one data set was from a field experiment, and (2) one set was from a laboratory experiment. the results indicated the success of the empirical models in predicting sediment load from bare land surfaces.Öğe PrefaceSpecial Issue: Facets of Uncertainty(Taylor & Francis Ltd, 2016) Carsteanu, Alin; Eris, Ebru; Volpi, Elena; Weijs, StevenÖğe A rainfall simulator for laboratory-scale assessment of rainfall-runoff-sediment transport processes over a two-dimensional flume(Elsevier Science Bv, 2012) Aksoy, Hafzullah; Unal, N. Erdem; Cokgor, Sevket; Gedikli, Abdullah; Yoon, Jaeyoung; Koca, Kaan; Inci, S. Boran; Eris, EbruA rainfall simulator is an ideal tool for infiltration, soil erosion, and other related research areas for replicating the process and characteristics of natural rainfall. In this study, a laboratory-scale rainfall simulator is developed. Rainfall characteristics including the rainfall intensity and its spatial uniformity, raindrop size, raindrop velocity, and kinetic energy confirm that natural rainfall conditions are simulated with sufficient accuracy. Pressure nozzles are used to spray water corresponding to rainfall intensities ranging from 45 to 105 mm h(-1). The simulator produces rainfall with uniformity coefficient changing between 82 and 89%. The raindrops falling with an initial velocity from a height of 2.43 m have median diameters of 2.2-3.1 mm. The impact velocities of the median size raindrops deviate from their terminal velocities with a relative error between 6 and 15%. The accompanying erosion flume can be given slope up to 20% in lateral and longitudinal directions. During the experiments, flow measurement is taken from two outlets at the end of the flume to distinguish the contribution of interrill areas into rills. Experiments result in typical rainfall-induced hydrographs and sedigraphs observed under natural conditions. This shows the ability of the rainfall simulator for use in sediment transport processes over hillslopes. (c) 2012 Elsevier B.V. All rights reserved.Öğe Rainfall-Runoff Model Considering Microtopography Simulated in a Laboratory Erosion Flume(Springer, 2016) Aksoy, Hafzullah; Gedikli, Abdullah; Unal, N. Erdem; Yilmaz, Murat; Eris, Ebru; Yoon, Jaeyoung; Tayfur, GokmenA comprehensive process-based rainfall-runoff model for simulating overland flow generated in rills and on interrill areas of a hillslope is evaluated using a laboratory experimental data set. For laboratory experiments, a rainfall simulator has been constructed together with a 6.50 m x 1.36 m erosion flume that can be given adjustable slopes changing between 5 % and 20 % in both longitudinal and lateral directions. The model is calibrated and validated using experimental data of simulated rainfall intensities between 45 and 105 mm/h. Results show that the model is capable of simulating the flow coming from the rill and interrill areas. It is found that most of the flow occurs in the form of rill flow. The hillslope-scale model can be used for better prediction of overland flow at the watershed-scale; it can also be used as a building block for an associated erosion and sediment transport model.Öğe RAINFALL-TRIGGERED LIMITED DATA-BASED ANALYSIS OF LANDSLIDES IN TRABZON PROVINCE, TURKEY(Parlar Scientific Publications (P S P), 2017) Eris, EbruRainfall is one of the most important triggering factors of landslides. Researchers carry out various scientific studies on identification of the rainfall amount that trigger landslides. The Eastern Black Sea region is a landslide-prone area in Turkey. The population of the region is affected by the landslides because of high rainfall and the steep topography of the region. The aim of this study is to investigate the relationship between rainfall and landslide for the Trabzon province the most vulnerable city to landslides in the region. For this purpose, rainfall and rainfall-induced landslides data are used. The relation between rainfall and landslide events is analyzed considering meteorological records of rain gauge stations.Öğe Soil erosion model tested on experimental data of a laboratory flume with a pre-existing rill(Elsevier, 2020) Aksoy, Hafzullah; Gedikli, Abdullah; Yilmaz, Murat; Eris, Ebru; Unal, N. Erdem; Yoon, Jaeyoung; Tayfur, GokmenPrediction of sediment discharge transported within flow is strongly needed in order to provide measures for a well-established erosion control and water quality management practice. Initiated by runoff generation and erosion processes sediment transport is influenced by microtopography over hillslopes of hydrological watersheds. Consideration of microtopography provides more accurate results. in this study, a process-based two-dimensional rainfall-runoff mathematical model is coupled with erosion and sediment transport component. Both the rainfall-runoff and sediment transport components make simulations in rills and over interrill areas of a bare hillslope. Models at such fine resolution are rarely verified due to the complexity of rills and interrill areas. the model was applied on a data set compiled from laboratory experiments. Erosion flume was filled with granular sand to replace a bare soil. A longitudinal rill and an interrill area were pre-formed over the soil in the flume before the simulated rainfall exerted on. the flume was given both longitudinal and lateral slopes. the simulated rainfall was changed between 45 mm/h and 105 mm/h and exerted on granular uniform fine and medium sand in the erosion flume with longitudinal and lateral slopes both changing from 5% to 20%. Calibration of the model shows that it is able to produce good results in terms of sedigraphs, which suggest also that the model might be considered an important step to verify and improve watershed scale erosion and sediment transport models.Öğe Spatial Variability of Sediment Yield in Turkish Basins(Hard, 2019) Asikoglu, Omer Levend; Eris, EbruIt is of great importance to know the amount of sediment transported to water structures and/or irrigation facilities during their planned lifetime. The amount of sediment transported is used in the design of such facilities, thus minimizing sedimentation losses. Determining sediment amount is generally based on empirical and physical modeling and on the relationship between sediment load and stream flow, where the sediment concentration measurements are correlated with flow characteristics. Each of these methods has some weaknesses. This study aimed to prepare a sediment yield map using suspended sediment measurements obtained from the State Hydraulic Works in 114 observation stations with a recording length of 15 years or more. Since the relationship between the amount of sediment and flow rate is known, the flow rate is considered as secondary data and sediment yield is mapped by the co-kriging method. The map showing spatial variation of the sediment yield was evaluated with the calibration and validation stages, and satisfactory results were obtained. Thus, sediment yield can be estimated at a project site where there is no suspended sediment measurement.Öğe Spatiotemporal analysis of drought by CHIRPS precipitation estimates(Springer Wien, 2022) Aksu, Hakan; Cavus, Yonca; Aksoy, Hafzullah; Akgul, Mehmet Ali; Turker, Seyhmus; Eris, EbruDrought is one of the most devastating natural hazards causing considerable losses in all climatic zones of the world. It is one of the most complex and the least understood hazards at the same time because of its spatially heterogeneous and temporally variable character. Spatially dense and uniformly distributed ground-based meteorological data are needed for proper spatial and temporal drought analysis. In practice, such data are lacking in general due either to the nonexistence of ground stations or their uneven and scarce distribution over a region. This creates a great potential in the use of satellite precipitation estimates (SPEs) such as the long-period high-resolution Climate Hazards Group Infrared Precipitation with Station (CHIRPS) data in drought analysis. In this study, we aim to analyze drought over the Kucuk Menderes River Basin in the western part of Turkey by using the CHIRPS data, which were found highly correlated with precipitation in the local ground stations. The analysis was performed by considering the spatial variability and temporal change in the drought characterization based on the Standardized Precipitation Index (SPI) calculated at the 3-month (seasonal) timescale. Drought in the river basin was found to have a within-year variability from month to month, and a spatial variability over the basin in any given month. Also, an over-year variability with a decreasing trend exists, which could be considered a signal for more strengthened droughts in the future. The study eventually demonstrates how the CHIRPS SPEs could be useful in the spatial and temporal drought analysis for regions with limited ground-based meteorological data.
