Hafzullah Aksoy

Effect of catalyst on the pyrolysis of used oil carried out in a fractionating pyrolysis reactor

Conversion of used sunflower oil was carried out thermal and in the presence of different catalysts (Na2 CO3, silica- alumina, and HZSM- 5) in a reactor (#316 SS tubing, 210 mm long, 45mm i.d.) equipped with thermocouples, inert gas connection and packed fractionating column (#316 SS tubing, 540mm, 45mm i.d., packed with ceramic rings having 7mm i.d.). The products consisted of gaseous and liquid hydrocarbons, carboxylic acids, CO, CO2, H2, water, coke, and residual oil. Highest conversion of oil (73.2%) and the maximum amount of the liquid hydrocarbon product (32.8%) were obtained at 420 °C with Na2 CO3 as catalyst. The liquid hydrocarbon products consisted mainly of hydrocarbons in the gasoline boiling range.

Using wavelets for data generation

Wavelets are proposed as a non-parametric data generation tool. The idea behind the suggested method is decomposition of data into its details and later reconstruction by summation of the details randomly to generate new data. A Haar wavelet is used because of its simplicity. The method is applied to annual and monthly streamflow series taken from Turkey and USA. It is found to give good results for non-skewed data, as well as in the presence of auto-correlation.

Nonlinear baseflow recession analysis in watersheds with intermittent streamflow

Abstract Discharge in most rivers consists mainly of baseflow exfiltrating from shallow groundwater reservoirs, while surface or other direct flows cease soon after rain storms or snowmelt. Analysis of observed baseflow recessions of two rivers in Turkey with intermittent flows and different geographical and climatic characteristics yielded nonlinear storage–outflow relationships of the highly seasonal aquifers. Baseflow separation was carried out using a nonlinear reservoir algorithm. Baseflow seasonality is related to the hydro-climatic conditions influencing groundwater recharge and evapotranspiration of groundwater. As intermittent streams generally have zero flows in the dry season, calibration of recession parameters is in many cases a complicated task. Citation Aksoy, H. & Wittenberg, H. (2011) Nonlinear baseflow recession analysis in watersheds with intermittent streamflow. Hydrol. Sci. J. 56(2), 226–237.

Markov chain-based modeling techniques for stochastic generation of daily intermittent streamflows

This study is an attempt to generate synthetic daily streamflow data for intermittent streams. The method followed in the study is based on the Markov chain. Two two-state Markov chains or alternatively one three-state Markov chain is proposed for determination of the state of the stream. Ascension curve of the hydrograph is simulated by the two-parameter gamma distribution. Recession curve of the hydrograph is assumed to decay exponentially. Comparison of the statistics of the generated and observed streamflow series shows the applicability of the techniques. Not only long-term statistics such as mean, variance, skewness, and correlation but also short-term features such as the non-invertible shape of the daily streamflow hydrograph are preserved.

Panta Rhei 2013–2015: global perspectives on hydrology, society and change

ABSTRACT In 2013, the International Association of Hydrological Sciences (IAHS) launched the hydrological decade 2013–2022 with the theme “Panta Rhei: Change in Hydrology and Society”. The decade recognizes the urgency of hydrological research to understand and predict the interactions of society and water, to support sustainable water resource use under changing climatic and environmental conditions. This paper reports on the first Panta Rhei biennium 2013–2015, providing a comprehensive resource that describes the scope and direction of Panta Rhei. We bring together the knowledge of all the Panta Rhei working groups, to summarize the most pressing research questions and how the hydrological community is progressing towards those goals. We draw out interconnections between different strands of research, and reflect on the need to take a global view on hydrology in the current era of human impacts and environmental change. Finally, we look back to the six driving science questions identified at the outset of Panta Rhei, to quantify progress towards those aims. Editor D. Koutsoyiannis; Associate editor not assigned

Nonparametric streamflow simulation by wavelet or Fourier analysis

Abstract Wavelet or Fourier analysis is proposed as an alternative nonparametric method to simulate streamflows. An observed series is decomposed into its components at various resolutions and then recombined randomly to generate synthetic series. The mean and standard deviation are perfectly reproduced and coefficient of skewness tends to zero as the number of simulations increases. Normalizing transforms can be used for skewed series. Autocorrelation coefficients and the dependence structure are better preserved when Fourier analysis is used, but the mean and variance remain constant when the simulated and observed series have the same length. Monthly as well as annual flows can be simulated by this technique as illustrated on some examples. Wavelet analysis should be preferred as it generates flow series that exhibit a wider range of required reservoir capacities.

Probabilistic approach to modelling of recession curves

Abstract Recession curves of daily streamflow hydrographs are analysed by a probabilistic approach. Flow of a day on a recession curve is calculated by multiplying the previous days flow with a value of K smaller than one; K, defined as the ratio of the flows of successive days on the recession curve, was determined from observed daily flow time series. The range of K is divided into three class intervals. A procedure using the concept of gradually increasing values of K is adopted. For this, transition probabilities and average values of K are determined for each class interval and each month of the year. A recession curve can be generated, once the peak flow is known, by the probabilistic approach. The procedure allows nonlinear, seasonal and stochastic effects in flow recession of a river to be considered.

Groundwater intrusion into leaky sewer systems

Vast volumes of groundwater are drained by urban sewer systems. This unwanted flow component intrudes into sewer systems through leaky joints or connected house drains. However, unlike urban storm drainage, it has a high seasonal variation corresponding to groundwater storage and long slow recessions similar to baseflow in rivers also fed by shallow groundwater exfiltrating into the surface waters. By applying the nonlinear reservoir algorithm as used for baseflow separation from total flow in a river, groundwater flow is separated from daily measured influents to treatment plants in Lower Saxony and Baden-Württemberg, Germany and in the Terkos Lake watershed near Istanbul, Turkey. While waste water flows vary only moderately within a year, separated intruded groundwater flows show recessions and seasonal variations correlated to baseflow in neighbouring rivers. It is possible to conclude that recession characteristics of treatment plant influents allow quantification and prediction of groundwater intrusion into sewer systems.

Evaluation of overland flow model for a hillslope using laboratory flume data.

Comprehensive modelling of overland flow requires models for both rill and interrill area overland flow. Evaluation of a physically based mathematical model for simulating overland flow generated on rill and interrill areas of hillslope was done using a data set gathered from a laboratory experimental setup. A rainfall simulator has been constructed together with a 6.50 m × 1.36 m erosion flume that can be given adjustable slopes in both longitudinal and lateral directions. The model was calibrated and validated using the experimental results from the setup of the flume having 5% lateral and 10% longitudinal slopes where rainfall intensities of 105 and 45 mm/hr were induced with the use of nozzles. Results show that for the given slope combination, the model was capable of simulating the flow coming from the rill and interrill areas for the two different rainfall intensities. It was found that significantly more of the flow occurred in the form of the rill flow. The model studied here can be used for the better prediction of overland flow and can also be used as a building block for an associated erosion and sediment transport model.

Laboratory experiments of sediment transport from bare soil with a rill

Abstract Mathematical 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%. Editor Z.W. Kundzewicz; Associate editor G. Mahé Citation Aksoy, H., Unal, N.E., Cokgor, S., Gedikli, A., Yoon, J., Koca, K., Inci, S.B., Eris, E., and Pak, G., 2013. Laboratory experiments of sediment transport from bare soil with a rill. Hydrological Sciences Journal, 58 (7), 1505–1518.