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Prof. Dr. Hafzullah Aksoy
Istanbul Technical University, Department of Civil Engineering, Hydraulics Division 34469, Maslak, Istanbul, Turkey

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0 Hydrology
0 Water Resources
0 Hydrological Modelling
0 stochastic modelling
0 Solid transport

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Research article
Published: 11 June 2021 in Hydrological Sciences Journal
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A methodology using the standardized precipitation index is proposed to develop critical drought intensity-duration-frequency (IDF) curves. We define dry periods within which we recognize droughts of different durations. The most severe drought for each drought duration in each year is called 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. Generalized Extreme Value probability distribution function is found the best to fit the critical drought severity. The methodology is implemented using monthly precipitation data of a meteorological station in Turkey. The critical drought intensity decreases linearly with increasing drought duration while 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 characterize the drought not with an index-based intensity but with its return period. This kind of presentation is physically more understandable in particular for stakeholders and decision makers in practice.

ACS Style

Hafzullah Aksoy; Mahmut Cetin; Ebru Eris; Halil Ibrahim Burgan; Yonca Cavus; Isilsu Yildirim; Murugesu Sivapalan. Critical drought intensity-duration-frequency curves based on total probability theorem-coupled frequency analysis. Hydrological Sciences Journal 2021, 66, 1337 -1358.

AMA Style

Hafzullah Aksoy, Mahmut Cetin, Ebru Eris, Halil Ibrahim Burgan, Yonca Cavus, Isilsu Yildirim, Murugesu Sivapalan. Critical drought intensity-duration-frequency curves based on total probability theorem-coupled frequency analysis. Hydrological Sciences Journal. 2021; 66 (8):1337-1358.

Chicago/Turabian Style

Hafzullah Aksoy; Mahmut Cetin; Ebru Eris; Halil Ibrahim Burgan; Yonca Cavus; Isilsu Yildirim; Murugesu Sivapalan. 2021. "Critical drought intensity-duration-frequency curves based on total probability theorem-coupled frequency analysis." Hydrological Sciences Journal 66, no. 8: 1337-1358.

Preprint content
Published: 03 March 2021
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Drought is one of the extreme hydrological events which may seriously affect the majority of the population in many ways such as economically, socially and environmentally. Researches on the drought analysis may prevent these adverse consequences to a significant extent. Droughts are characterized by using various meteorological and hydrological indicators (i.e. precipitation, temperature, streamflow etc.). These indicators are used to derive drought indices. Spatio-temporal drought is analysed both in time and space by using drought indices based on site-specific precipitation and temperature data. In this study, Standardized Precipitation Index (SPI) using only precipitation data and Standardized Precipitation Evapotranspiration Index (SPEI) using precipitation and temperature data are considered at various time scales changing from 1 to 24 months for a more detailed drought characterization. On the other hand, so-called Dimensionless Precipitation Anomaly Index (DPAI) is introduced at annual scale in this study. The DPAI is used to determine dry periods from the recorded precipitation data. Cases are studied in Kucuk Menderes River Basin located in the Aegean region of Turkey. Precipitation and temperature data obtained from five meteorological stations over the river basin are used to determine drought index time series. Drought risk graphs and drought severity maps are obtained from time series of the drought indices. Drought risk is the likelihood of the drought occurrence that is quantified with the frequency calculated from the SPI and SPEI time series. As for the drought severity maps, they are created to understand its basin-scale variation by using the severities calculated from the dry periods of SPI and SPEI time series. Results show that the prolonged severe historical dry periods of the river basin are correctly identified by the drought indices. These indices used in this study based on easily available meteorological data are simple tools to explain temporal variability at a site or spatial variability over the basin. Also, the spatial distribution of drought severity over the river basin does not show a significant variability though more severe droughts are observed in the inner part of the river basin. Mild drought dominates at each time scale, this stems from the tendency of precipitation fluctuating around the average. Results in the study have considerable importance both in science and practice of drought. Although the methodology established from basic tools using meteorological data, the outcomes of the study are expected to become beneficial for drought management plans.

ACS Style

Yonca Cavus; Ebru Eris; Hafzullah Aksoy; Halil Ibrahim Burgan; Hakan Aksu; Hulya Boyacioglu. Spatio-temporal analysis of precipitation-based drought indices in Kucuk Menderes River Basin, Turkey. 2021, 1 .

AMA Style

Yonca Cavus, Ebru Eris, Hafzullah Aksoy, Halil Ibrahim Burgan, Hakan Aksu, Hulya Boyacioglu. Spatio-temporal analysis of precipitation-based drought indices in Kucuk Menderes River Basin, Turkey. . 2021; ():1.

Chicago/Turabian Style

Yonca Cavus; Ebru Eris; Hafzullah Aksoy; Halil Ibrahim Burgan; Hakan Aksu; Hulya Boyacioglu. 2021. "Spatio-temporal analysis of precipitation-based drought indices in Kucuk Menderes River Basin, Turkey." , no. : 1.

Original paper
Published: 25 September 2020 in Theoretical and Applied Climatology
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Meteorological drought is analyzed both in time and space by using drought indices based on site-specific precipitation and temperature data. Departure of precipitation from its normal called in this study as the Dimensionless Precipitation Anomaly Index (DPAI) is used at annual scale, while the Standardized Precipitation Index (SPI) using precipitation and the Standardized Precipitation Evapotranspiration Index (SPEI) using precipitation and temperature are considered at monthly time scale. Five meteorological stations over Kucuk Menderes River Basin in the western part of Turkey are selected for the case study. Results are presented in the forms of drought index time series, drought risk graphs, and drought severity maps. The prolonged severe historical dry periods of the river basin are correctly identified by the drought indices. It is seen that simple tools such as the drought indices used in this study based on easily available meteorological data could explain temporal variability at a site or spatial variability over a river basin. They are therefore important not only for the scientific community dealing with drought as a research problem but also for decision-makers, stakeholders, and end-users making practice about the drought through water allocation studies and drought management plans.

ACS Style

Ebru Eris; Yonca Cavus; Hafzullah Aksoy; Halil Ibrahim Burgan; Hakan Aksu; Hulya Boyacioglu. Spatiotemporal analysis of meteorological drought over Kucuk Menderes River Basin in the Aegean Region of Turkey. Theoretical and Applied Climatology 2020, 142, 1515 -1530.

AMA Style

Ebru Eris, Yonca Cavus, Hafzullah Aksoy, Halil Ibrahim Burgan, Hakan Aksu, Hulya Boyacioglu. Spatiotemporal analysis of meteorological drought over Kucuk Menderes River Basin in the Aegean Region of Turkey. Theoretical and Applied Climatology. 2020; 142 (3):1515-1530.

Chicago/Turabian Style

Ebru Eris; Yonca Cavus; Hafzullah Aksoy; Halil Ibrahim Burgan; Hakan Aksu; Hulya Boyacioglu. 2020. "Spatiotemporal analysis of meteorological drought over Kucuk Menderes River Basin in the Aegean Region of Turkey." Theoretical and Applied Climatology 142, no. 3: 1515-1530.

Technical note
Published: 21 August 2020 in Journal of Hydraulic Research
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Self-cleansing is a hydraulic design concept for drainage systems for mitigation of sediment deposition. Experimental studies in the literature have mostly been performed in circular channels. In this study, experiments were conducted in five cross-section channels: trapezoidal, rectangular, circular, U-shape and V-bottom to investigate the non-deposition condition of sediment transport in rigid boundary channels. Deficiencies of conventional self-cleansing design based on a single value of velocity or shear stress and Camp criteria are highlighted in terms of channel cross-section shape; considering a higher number of hydraulic parameters, self-cleaning models are proposed for each cross-section channel; and finally, in order to make a general practical tool by incorporating a cross-section shape factor, a self-cleansing model is proposed to calculate the flow mean velocity at non-deposition conditions of sediment transport. The general self-cleaning model outperforms its alternatives when applying experimental data collected in this study and five datasets taken from the literature.

ACS Style

Mir Jafar Sadegh Safari; Hafzullah Aksoy. Experimental analysis for self-cleansing open channel design. Journal of Hydraulic Research 2020, 59, 500 -511.

AMA Style

Mir Jafar Sadegh Safari, Hafzullah Aksoy. Experimental analysis for self-cleansing open channel design. Journal of Hydraulic Research. 2020; 59 (3):500-511.

Chicago/Turabian Style

Mir Jafar Sadegh Safari; Hafzullah Aksoy. 2020. "Experimental analysis for self-cleansing open channel design." Journal of Hydraulic Research 59, no. 3: 500-511.

Articles
Published: 19 February 2020 in Hydrological Sciences Journal
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Sediment accumulation in a river reservoir is studied by stochastic time series models and analytical approach. The first-order moving average process is found the best for the suspended sediment discharge time series of the Juniata River at Newport, Pennsylvania, USA. Synthetic suspended sediment discharges are first generated with the chosen model after which analytical expressions are derived for the expected value and variance of sediment accumulation in the reservoir. The expected value and variance of the volume of sediment accumulation in the reservoir are calculated from a thousand synthetic time series each 38 years long and compared to the analytical approach. Stochastic and analytical approaches perfectly trace the observation in terms of the expected value and variability. Therefore, it is concluded that the expected value and variance of sediment accumulation in a reservoir could be estimated by analytical expressions without the cost of synthetic data generation mechanisms.

ACS Style

Tanju Akar; Hafzullah Aksoy. Stochastic and analytical approaches for sediment accumulation in river reservoirs. Hydrological Sciences Journal 2020, 65, 984 -994.

AMA Style

Tanju Akar, Hafzullah Aksoy. Stochastic and analytical approaches for sediment accumulation in river reservoirs. Hydrological Sciences Journal. 2020; 65 (6):984-994.

Chicago/Turabian Style

Tanju Akar; Hafzullah Aksoy. 2020. "Stochastic and analytical approaches for sediment accumulation in river reservoirs." Hydrological Sciences Journal 65, no. 6: 984-994.

Journal article
Published: 24 January 2020 in Water
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Flow duration curve (FDC) is widely used in hydrology to assess streamflow in a river basin. In this study, a simple FDC model is developed for monthly streamflow data. The model consists of several steps including the nondimensionalization and then normalization in case the monthly streamflow data do not fit the normal probability distribution function. The normalized quantiles are calculated after which a back transformation is applied to the normalized quantiles to return back to the original dimensional streamflow data. In order to calculate annual streamflow of the river basin, an empirical regression equation is proposed using the drainage area and the annual total precipitation only as the input. As the final step of the model, dimensional quantiles of FDC are calculated. Ceyhan River basin in southern Turkey is chosen for the case study. Forty-two streamflow gauging stations are considered; two thirds of the gauging stations are used for the model calibration, and one third for validation. The modeled FDCs are compared to the observation and assessed with a number of performance metrics. They are found similar to the observed ones with a relatively good performance; they are good in the mid and high flow parts particularly while the low flow part of FDCs might require further detailed analysis.

ACS Style

Halil Ibrahim Burgan; Hafzullah Aksoy. Monthly Flow Duration Curve Model for Ungauged River Basins. Water 2020, 12, 338 .

AMA Style

Halil Ibrahim Burgan, Hafzullah Aksoy. Monthly Flow Duration Curve Model for Ungauged River Basins. Water. 2020; 12 (2):338.

Chicago/Turabian Style

Halil Ibrahim Burgan; Hafzullah Aksoy. 2020. "Monthly Flow Duration Curve Model for Ungauged River Basins." Water 12, no. 2: 338.

Journal article
Published: 02 December 2019 in Journal of Hydrology
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Prediction 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.

ACS Style

Hafzullah Aksoy; Abdullah Gedikli; Murat Yilmaz; Ebru Eris; N. Erdem Unal; Jaeyoung Yoon; M. Levent Kavvas; Gokmen Tayfur. Soil erosion model tested on experimental data of a laboratory flume with a pre-existing rill. Journal of Hydrology 2019, 581, 124391 .

AMA Style

Hafzullah Aksoy, Abdullah Gedikli, Murat Yilmaz, Ebru Eris, N. Erdem Unal, Jaeyoung Yoon, M. Levent Kavvas, Gokmen Tayfur. Soil erosion model tested on experimental data of a laboratory flume with a pre-existing rill. Journal of Hydrology. 2019; 581 ():124391.

Chicago/Turabian Style

Hafzullah Aksoy; Abdullah Gedikli; Murat Yilmaz; Ebru Eris; N. Erdem Unal; Jaeyoung Yoon; M. Levent Kavvas; Gokmen Tayfur. 2019. "Soil erosion model tested on experimental data of a laboratory flume with a pre-existing rill." Journal of Hydrology 581, no. : 124391.

Journal article
Published: 06 November 2019 in Journal of Hydrology
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Drought is one of the most disastrous natural phenomena that causes scarcity and lack of water in hydrological basins and affects seriously the majority of the population in many ways such as economical, social and environmental. Therefore, drought plays a significant role in the risk management of water resources systems. The purpose of this study is to develop the severity/intensity–duration-frequency curves based on precipitation deficit and provide a comprehensive characterization of droughts by using Standardized Precipitation Index (SPI) which considers precipitation data only. Instead of using SPI directly, the severity and intensity were calculated in the duration-frequency curves. On the other hand, SPI is a technical tool and thus difficult to understand at first glance by end-users and decision-makers. Precipitation deficit is therefore more useful and physically meaningful to the users. In this study, drought with the largest severity in each year is defined as the critical drought of the year. Frequency analysis is applied on the critical drought severity to determine the best-fit probability distribution function by using the total probability theorem. Results show that the 2 year-return period drought severity/intensity–duration-frequency curve is well lower than and separated clearly from the curves at higher return periods of 5–100 years although it has the same tendency with the longer return period curves, and also that almost no difference is observed between the precipitation deficit of the droughts of 25 years or longer return periods. With the precipitation deficit and such newly introduced concepts as critical drought severity, singular drought and within-period drought, the proposed methodology gains a novelty. It is expected that the destructive and irreversible effects of meteorological, agricultural and hydrological droughts can be realized in a more physical sense with the use of precipitation deficit.

ACS Style

Yonca Cavus; Hafzullah Aksoy. Critical drought severity/intensity-duration-frequency curves based on precipitation deficit. Journal of Hydrology 2019, 584, 124312 .

AMA Style

Yonca Cavus, Hafzullah Aksoy. Critical drought severity/intensity-duration-frequency curves based on precipitation deficit. Journal of Hydrology. 2019; 584 ():124312.

Chicago/Turabian Style

Yonca Cavus; Hafzullah Aksoy. 2019. "Critical drought severity/intensity-duration-frequency curves based on precipitation deficit." Journal of Hydrology 584, no. : 124312.

Article
Published: 21 August 2019 in Water Resources Management
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Frequency domain analysis using an additive decomposition method is proposed to reconstruct the missing hydrometeorological data of selected sites in Lake Urmia basin in Iran. Precipitation, evaporation, streamflow and groundwater time series are used for this aim. Trends, within- and multi-year cycles, and randomness are taken into account to reconstruct each of the time series for which models are developed, calibrated and validated separately. Statistical similarity between the observed and reconstructed time series is checked. Statistical characteristics including the average, standard deviation, skewness, and the first-order autocorrelation coefficient are well preserved at the reconstructed time series. A conceptual water budget model is also established to check for the consistency between the reconstructed and the observed datasets. The water budget model is taken as a quantitative way to confirm that the frequency domain analysis using the additive decomposition is an effective method for the reconstruction of the missing hydrometeorological data based on the case study performed for the Lake Urmia basin in Iran.

ACS Style

Babak Vaheddoost; Hafzullah Aksoy. Reconstruction of Hydrometeorological Data in Lake Urmia Basin by Frequency Domain Analysis Using Additive Decomposition. Water Resources Management 2019, 33, 3899 -3911.

AMA Style

Babak Vaheddoost, Hafzullah Aksoy. Reconstruction of Hydrometeorological Data in Lake Urmia Basin by Frequency Domain Analysis Using Additive Decomposition. Water Resources Management. 2019; 33 (11):3899-3911.

Chicago/Turabian Style

Babak Vaheddoost; Hafzullah Aksoy. 2019. "Reconstruction of Hydrometeorological Data in Lake Urmia Basin by Frequency Domain Analysis Using Additive Decomposition." Water Resources Management 33, no. 11: 3899-3911.

Editorial
Published: 12 August 2019 in Water
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Climate and anthropogenic changes impact on the erosion and sediment transport processes in rivers. Rainfall variability and, in many places, the increase of rainfall intensity have a direct impact on rainfall erosivity. Increasing changes in demography have led to the acceleration of land cover changes from natural areas to cultivated areas, and then from degraded areas to desertification. Such areas, under the effect of anthropogenic activities, are more sensitive to erosion, and are therefore prone to erosion. On the other hand, with an increase in the number of dams in watersheds, a great portion of sediment fluxes is trapped in the reservoirs, which do not reach the sea in the same amount nor at the same quality, and thus have consequences for coastal geomorphodynamics. The Special Issue “Modeling and Practice of Erosion and Sediment Transport under Change” is focused on a number of keywords: erosion and sediment transport, model and practice, and change. The keywords are briefly discussed with respect to the relevant literature. The papers in this Special Issue address observations and models based on laboratory and field data, allowing researchers to make use of such resources in practice under changing conditions.

ACS Style

Hafzullah Aksoy; Gil Mahe; Mohamed Meddi. Modeling and Practice of Erosion and Sediment Transport under Change. Water 2019, 11, 1665 .

AMA Style

Hafzullah Aksoy, Gil Mahe, Mohamed Meddi. Modeling and Practice of Erosion and Sediment Transport under Change. Water. 2019; 11 (8):1665.

Chicago/Turabian Style

Hafzullah Aksoy; Gil Mahe; Mohamed Meddi. 2019. "Modeling and Practice of Erosion and Sediment Transport under Change." Water 11, no. 8: 1665.

Journal article
Published: 27 June 2019 in Water
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Drought is a natural phenomenon that has great impacts on the economy, society and environment. Therefore, the determination, monitoring and characterization of droughts are of great significance in water resources planning and management. The purpose of this study is to investigate the spatial drought characterizations of Seyhan River basin in the Eastern Mediterranean region of Turkey. The standardized precipitation index (SPI) was calculated from monthly precipitation data at 12-month time scale for 19 meteorological stations scattered over the river basin. Drought with the largest severity in each year is defined as the critical drought of the year. Frequency analysis was applied on the critical drought to determine the best-fit probability distribution function by utilizing the total probability theorem. The sole frequency analysis is insufficient in drought studies unless it is numerically related to other factors such as the severity, duration and intensity. Also, SPI is a technical tool and thus difficult to understand at first glance by end-users and decision-makers. Precipitation deficit defined as the difference between precipitation threshold at SPI = 0 and critical precipitation is therefore more preferable due to its usefulness and for being physically more meaningful to the users. Precipitation deficit is calculated and mapped for 1-, 3-, 6- and 12-month drought durations and 2-, 5-, 10-, 25-, 50- and 100-year return periods at 12-month time scale from the frequency analysis of the critical drought severity. The inverse distance weighted (IDW) interpolation technique is used for the spatial distribution of precipitation deficit over the Seyhan River basin. The spatial and temporal characteristics of drought suggest that the Seyhan River Basin in the Eastern Mediterranean region of Turkey experiences quite mild and severe droughts in terms of precipitation deficit. The spatial distribution would alter greatly with increasing return period and drought duration. While the coastal part of the basin is vulnerable to droughts at all return periods and drought durations, the northern part of the basin would be expected to be less affected by the drought. Another result reached in this study is that it could be common for one point in the basin to suffer dry conditions, whilst surrounding points in the same basin experience normal or even humid conditions. This reinforces the importance of spatial analysis over the basin under investigation instead of the point-scale temporal analysis made in each of the meteorological stations. With the use of spatial mapping of drought, it is expected that the destructive and irreversible effects of hydrological droughts can be realized in a more physical sense.

ACS Style

Yonca Cavus; Hafzullah Aksoy. Spatial Drought Characterization for Seyhan River Basin in the Mediterranean Region of Turkey. Water 2019, 11, 1331 .

AMA Style

Yonca Cavus, Hafzullah Aksoy. Spatial Drought Characterization for Seyhan River Basin in the Mediterranean Region of Turkey. Water. 2019; 11 (7):1331.

Chicago/Turabian Style

Yonca Cavus; Hafzullah Aksoy. 2019. "Spatial Drought Characterization for Seyhan River Basin in the Mediterranean Region of Turkey." Water 11, no. 7: 1331.

Chapter
Published: 05 June 2019 in Water Resources of Turkey
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Turkey is a country with considerable water resources in a region where water is a strategic element due to its scarcity. With the increase in the population and demand, water scarcity has accelerated, making water a more vital element. Due to the considerably large size of the country and to the spatial and temporal uneven distribution of water resources, water demand in some regions exceeds the available water for a period of time that creates a water shortage. Surface water hydrology in Turkey is a great challenging problem as it has the greatest share (80%) in the water potential of the country. The total annual surface flow is 186.6 billion m3, almost all born from the river basins within the territory of Turkey and harvested with the rainfall-runoff coefficient of 0.37 from the 574.0 mm annual rainfall. Surface water resources of Turkey are divided between 25 river basins; most stay within the country. There are also transboundary river basins where Turkey is either the upstream country or the downstream country. Among the river basins, the Euphrates-Tigris has the highest contribution, which is almost 1/3 of the surface water potential of Turkey. The northeastern part of Turkey receives the highest precipitation while the least amount of rainfall falls on Central Anatolia. A quite high number of hydrometric gauges have been established to record the quantity and quality of water; however, more are emerging, considering the topographical and geographical diversity in Turkey, to observe such hydrometeorological variables as streamflow, precipitation, evaporation, snow depth, etc. Due to the great spatial variability in the hydrometeorological conditions, some regions in Turkey are flood-prone while others can be affected by extreme droughts. Trend analysis has shown that extremes in the streamflow become more pronounced with larger maxima and lower minima than before. Also, lakes are important fresh water bodies for domestic use as well as irrigation, farming, industry, fisheries, etc. Water level in many lakes however decreases so that the availability of water in the lakes are under risk. Integrated water resources development strategies are needed at country-scale to balance the demand with the available water, considering also the decreasing trend in water availability and the increasing trend in the demand.

ACS Style

Hafzullah Aksoy. Surface Water. Water Resources of Turkey 2019, 127 -158.

AMA Style

Hafzullah Aksoy. Surface Water. Water Resources of Turkey. 2019; ():127-158.

Chicago/Turabian Style

Hafzullah Aksoy. 2019. "Surface Water." Water Resources of Turkey , no. : 127-158.

Journal article
Published: 27 February 2019 in Journal of Hydrology
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Groundwater recharge by precipitation is often assumed by practitioners as well as scientists to be a slow process of filtration through layers of uniform texture analogous to Darcy’s law. In most basins, however, rainwater also finds its way through macropores and preferential pathways to the shallow unconfined aquifers within hours of falling. Recharge phases may extend over several days, increasing groundwater levels, stored volume and hence baseflows into adjoining rivers. In this study, groundwater recharge and storage are computed from baseflow as separated with a nonlinear reservoir algorithm from time series of daily flows at gauging stations in northern Germany. Results are compared to groundwater level fluctuation in the catchments and to daily seepage rates measured in a lysimeter station. Peak times of the fast transfer of rain water through the vadose zone are generally the same. However, while recharge from baseflow ends when baseflow assumes its typical recession, the attenuation of lysimeter seepage may last much longer. The volume of lysimeter seepage is generally higher than the recharge in catchments due not only to different vegetation but also to rim effects impeding direct runoff. Furthermore, the lysimeter walls allow vertical fluxes only. Without further evidence or improved devices, lysimeter seepage should therefore not be indicated as groundwater recharge for the site or catchment. Findings also indicate that the shape of derived recharge unit responses is practically time invariant but with a strong seasonal variation in the recharge-rainfall ratio of precipitation events.

ACS Style

Hartmut Wittenberg; Hafzullah Aksoy; Konrad Miegel. Fast response of groundwater to heavy rainfall. Journal of Hydrology 2019, 571, 837 -842.

AMA Style

Hartmut Wittenberg, Hafzullah Aksoy, Konrad Miegel. Fast response of groundwater to heavy rainfall. Journal of Hydrology. 2019; 571 ():837-842.

Chicago/Turabian Style

Hartmut Wittenberg; Hafzullah Aksoy; Konrad Miegel. 2019. "Fast response of groundwater to heavy rainfall." Journal of Hydrology 571, no. : 837-842.

Research article
Published: 12 September 2018 in Hydrological Processes
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Being a large hyper‐saline water body, Lake Urmia in northwestern Iran deals with a gradual decline in its water level. Most of the studies on Lake Urmia have neglected the groundwater issue. In this study, as a direct approach, the interaction between the groundwater level and the lake water level is investigated both in time and space by analyzing the groundwater data compiled from observation wells surrounding the lake. Baseflow separation is considered as an indirect approach to understand the groundwater contribution to the river network flowing into the lake. It is determined that about 70% of runoff in the rivers draining into the lake is born in the form of baseflow. An interaction between the lake and the groundwater storage is clearly seen from the analysis to conclude that groundwater has a potential to recharge the lake. Thus, the shrinkage of water level in Lake Urmia could be expected to accelerate with the drastic use of groundwater which will be a disaster with no‐return.

ACS Style

Babak Vaheddoost; Hafzullah Aksoy. Interaction of groundwater with Lake Urmia in Iran. Hydrological Processes 2018, 1 .

AMA Style

Babak Vaheddoost, Hafzullah Aksoy. Interaction of groundwater with Lake Urmia in Iran. Hydrological Processes. 2018; ():1.

Chicago/Turabian Style

Babak Vaheddoost; Hafzullah Aksoy. 2018. "Interaction of groundwater with Lake Urmia in Iran." Hydrological Processes , no. : 1.

Journal article
Published: 01 July 2018 in Journal of Hydrology
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For forecasting monthly precipitation in an arid region, the feed forward back-propagation, radial basis function and generalized regression artificial neural networks (ANNs) are used in this study. The ANN models are improved after incorporation of a Markov chain-based algorithm (MC-ANNs) with which the percentage of dry months is forecasted perfectly, thus generation of any non-physical negative precipitation is eliminated. Due to the fact that recorded precipitation time series are usually shorter than the length needed for a proper calibration of ANN models, synthetic monthly precipitation data are generated by Thomas-Fiering model to further improve the performance of forecasting. For case studies from Jordan, it is seen that only a slightly better performance is achieved with the use of MC and synthetic data. A conditional statement is, therefore, established and imbedded into the ANN models after the incorporation of MC and support of synthetic data, to substantially improve the ability of the models for forecasting monthly precipitation in arid regions.

ACS Style

Hafzullah Aksoy; Ahmad Dahamsheh. Markov chain-incorporated and synthetic data-supported conditional artificial neural network models for forecasting monthly precipitation in arid regions. Journal of Hydrology 2018, 562, 758 -779.

AMA Style

Hafzullah Aksoy, Ahmad Dahamsheh. Markov chain-incorporated and synthetic data-supported conditional artificial neural network models for forecasting monthly precipitation in arid regions. Journal of Hydrology. 2018; 562 ():758-779.

Chicago/Turabian Style

Hafzullah Aksoy; Ahmad Dahamsheh. 2018. "Markov chain-incorporated and synthetic data-supported conditional artificial neural network models for forecasting monthly precipitation in arid regions." Journal of Hydrology 562, no. : 758-779.

Journal article
Published: 12 February 2018 in Water Policy
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A flow duration curve (FDC) plots the percentage of time that flow in a stream is equal to or exceeding a given value. In a gauged basin, it is obtained by sorting the observed flow from the largest to the smallest, and plotting against the corresponding exceedance probability. At ungauged basins where no data exist, the need for developing empirical methods emerges. This study aims at developing an FDC model for ungauged basins. The model is based on the normalized nondimensional annual mean flow quantiles. The annual mean flow is empirically calculated by a regression equation that takes drainage area and annual precipitation as input. Slope of the channel is additionally considered in the regression, however no better performance is achieved. Seyhan and Ceyhan basins in the Mediterranean region in southern Turkey are chosen as the study area. Data from 109 gauging stations are used for the calibration and validation of the model. Gauging stations on the tributaries are studied with a view to limiting anthropogenic activities on the rivers. Results of the application are found so promising that the model can be considered a good foundation for the development of FDCs at ungauged basins.

ACS Style

Halil Ibrahim Burgan; Hafzullah Aksoy. Annual flow duration curve model for ungauged basins. Water Policy 2018, 49, 1684 -1695.

AMA Style

Halil Ibrahim Burgan, Hafzullah Aksoy. Annual flow duration curve model for ungauged basins. Water Policy. 2018; 49 (5):1684-1695.

Chicago/Turabian Style

Halil Ibrahim Burgan; Hafzullah Aksoy. 2018. "Annual flow duration curve model for ungauged basins." Water Policy 49, no. 5: 1684-1695.

Original article
Published: 23 October 2017 in Environmental Fluid Mechanics
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Incipient motion of sediment is one of the main aspects of the sedimentation process. Determination of the minimum shear stress or velocity required to initiate the motion of sediment particles is a crucial task in the rigid boundary drainage system design. This study investigates incipient motion through laboratory experiments conducted in trapezoidal, rectangular, circular, U-shape and V-bottom cross-section smooth channels using four different size-sands. Experimental data are analyzed using the shear stress and velocity approaches. Shields method is used in the shear stress approach while formulation proposed by Novak and Nalluri is used as the velocity approach. New relationships are proposed for computing shear stress and velocity required for incipient motion in each of the channels. Results are compared with the corresponding models available in the literature. Data collected in this study are found in an acceptable agreement with the existing models. Channel cross-section shape plays an important role in incipient motion of sediment. Among the channels, the rectangular and V-bottom channels require the lowest and the highest shear stress and velocity for the initiation of sediment motion, respectively.

ACS Style

Mir Jafar Sadegh Safari; Hafzullah Aksoy; Necati Erdem Unal; Mirali Mohammadi. Experimental analysis of sediment incipient motion in rigid boundary open channels. Environmental Fluid Mechanics 2017, 17, 1281 -1298.

AMA Style

Mir Jafar Sadegh Safari, Hafzullah Aksoy, Necati Erdem Unal, Mirali Mohammadi. Experimental analysis of sediment incipient motion in rigid boundary open channels. Environmental Fluid Mechanics. 2017; 17 (6):1281-1298.

Chicago/Turabian Style

Mir Jafar Sadegh Safari; Hafzullah Aksoy; Necati Erdem Unal; Mirali Mohammadi. 2017. "Experimental analysis of sediment incipient motion in rigid boundary open channels." Environmental Fluid Mechanics 17, no. 6: 1281-1298.

Journal article
Published: 19 July 2017 in Water Science and Technology
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Drainage systems must be designed in a way to minimize undesired problems such as decrease in hydraulic capacity of the channel, blockage and transport of pollutants due to deposition of sediment. Channel design considering self-cleansing criteria are used to solve the sedimentation problem. Incipient deposition is one of the non-deposition self-cleansing design criteria that can be used as a conservative method for channel design. Experimental studies have been carried out in five different cross-section channels, namely trapezoidal, rectangular, circular, U-shape and V-bottom. Experiments were performed in a tilting flume using four different sizes of sands as sediment in nine different channel bed slopes. Two well-known methods, namely the Novak & Nalluri and Yang methods are considered for the analysis of sediment motion. Equations developed using experimental data are found to be in agreement with the literature. It is concluded that the design velocity depends on the shape of the channel cross-section. Rectangular and V-bottom channels need lower and higher incipient deposition velocities, respectively, in comparison with other channels.

ACS Style

Hafzullah Aksoy; Mir Jafar Sadegh Safari; Necati Erdem Unal; Mirali Mohammadi. Velocity-based analysis of sediment incipient deposition in rigid boundary open channels. Water Science and Technology 2017, 76, 2535 -2543.

AMA Style

Hafzullah Aksoy, Mir Jafar Sadegh Safari, Necati Erdem Unal, Mirali Mohammadi. Velocity-based analysis of sediment incipient deposition in rigid boundary open channels. Water Science and Technology. 2017; 76 (9):2535-2543.

Chicago/Turabian Style

Hafzullah Aksoy; Mir Jafar Sadegh Safari; Necati Erdem Unal; Mirali Mohammadi. 2017. "Velocity-based analysis of sediment incipient deposition in rigid boundary open channels." Water Science and Technology 76, no. 9: 2535-2543.

Conference paper
Published: 18 May 2017 in World Environmental and Water Resources Congress 2017
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ACS Style

H. I. Burgan; B. Vaheddoost; H. Aksoy; Christopher N. Dunn; Brian Van Weele. Frequency Analysis of Monthly Runoff in Intermittent Rivers. World Environmental and Water Resources Congress 2017 2017, 327 -334.

AMA Style

H. I. Burgan, B. Vaheddoost, H. Aksoy, Christopher N. Dunn, Brian Van Weele. Frequency Analysis of Monthly Runoff in Intermittent Rivers. World Environmental and Water Resources Congress 2017. 2017; ():327-334.

Chicago/Turabian Style

H. I. Burgan; B. Vaheddoost; H. Aksoy; Christopher N. Dunn; Brian Van Weele. 2017. "Frequency Analysis of Monthly Runoff in Intermittent Rivers." World Environmental and Water Resources Congress 2017 , no. : 327-334.

Journal article
Published: 01 March 2017 in Journal of Hydro-environment Research
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Self-cleansing is a substantial aspect of the drainage systems in which it is desired to minimize the sediment deposition that can cause channel blockage and surcharge early overflows. In the conventional self-cleansing design criteria of drainage systems, a single value of velocity or shear stress is used based on experience. In the recent decades rather than using a single value, non-deposition design concept has been further modified to develop self-cleansing models based on higher number of parameters considering flow, fluid, sediment and channel characteristics. However, non-deposition self-cleansing models have been mostly developed for circular channels, and none of the models considers yet the effect of channel cross-section although some models take into account the pipe diameter, hydraulic radius and cross-section area as independent variables. In this study, a self-cleansing model considering the effect of cross-section by a shape factor available in the literature is developed to determine the non-deposition particle Froude number for bed load sediment transport. The model is developed using experimental data of circular, rectangular and U-shape channel cross-sections from the literature; and data of trapezoidal channel cross-section from experiments carried out in this study. For validation of the model, data collected in this study is used together with four different sources of data taken from the literature. Validation of the model for each cross-section data shows its wide range applicability in terms of different channel cross-sections.

ACS Style

Mir-Jafar-Sadegh Safari; Hafzullah Aksoy; Necati Erdem Unal; Mirali Mohammadi. Non-deposition self-cleansing design criteria for drainage systems. Journal of Hydro-environment Research 2017, 14, 76 -84.

AMA Style

Mir-Jafar-Sadegh Safari, Hafzullah Aksoy, Necati Erdem Unal, Mirali Mohammadi. Non-deposition self-cleansing design criteria for drainage systems. Journal of Hydro-environment Research. 2017; 14 ():76-84.

Chicago/Turabian Style

Mir-Jafar-Sadegh Safari; Hafzullah Aksoy; Necati Erdem Unal; Mirali Mohammadi. 2017. "Non-deposition self-cleansing design criteria for drainage systems." Journal of Hydro-environment Research 14, no. : 76-84.