Kadri Yürekli

Stochastic Modeling of Annual Maximum and Minimum Streamflow of Kelkit Stream

Abstract The aim of this study is to determine whether the daily extreme streamflows could be generated by stochastic models. For the study, a linear stochastic model known as either Box-Jenkins or ARIMA was used. A Mann-Kendal nonparametric test was applied to the daily extreme data sequences to examine the existence of trends. This test showed that there was no trend in the daily data sequences. The ARIMA model is referred as ARMA since there was no trend in the data sequences and thus, the non-seasonal differencing operator is equal to zero. By using the graphs of ACF and PACF, alternative ARMA models were determined. The plots of the ACF show that there was no linear dependence between the daily maximum streamflows, whereas a linear dependence was observed between the daily minimum streamflows. Therefore, modeling of daily maximum data sequences was discarded. There are four ARMA models that fulfilled all the diagnostic checks among selected models from the graphs of ACF and PACF for the daily minimum data sequences. But ARMA (1, 0) with a constant was chosen as the best model by considering Schwarz Bayesian Criterion (SBC). In addition, error estimates were also shown that ARMA (1, 0) with a constant was the best model.

Debideki değişimin Yeşilırmak Nehri su kalitesi parametrelerine etkisi

In this study, streamflow and water quality variables including specific conductivity (EC), water temperature, Na+, K+, Ca2++Mg2+, CO32-, HCO3-, Cl-, SO42- B, sodium adsorption rate (SAR), hardness and total salt (TS), relationships and hysteresis diagrams were investigated to determine the major processes affecting water quality in the Yesilirmak River. The base-flow water discharge was observed between July and February whereas March April and May represent a peak as a result of seasonal rainfall, snowmelt and run-off. The results indicate that most variables exhibit clockwise hysteresis with high values during the base-flow and lower values during the high discharge. There is a negative relationship between discharge and water quality variables including EC, Na+, K+, Ca2++Mg2+, HCO3-, Cl-, SO42-, SAR, hardness and TS. However, no relationship was obtained between discharge and water temperature, pH, CO32- and B. Among the water quality variables EC, Ca2++Mg2+, HCO3-, SO42-, hardness and TS exhibit an open clockwise loop whereas pH, Na+, K+, Cl- CO32-, SAR and B exhibit a complex loop. Water temperature was the only variable that exhibits counterclockwise loop.

Tersakan Çayı Havzasında Taşkına Neden Olan Günlük En Büyük Akımların Tekrarlanma Sürelerinin Saptanması

The main purpose of this study was to determine the recurrence intervals of Tersakan stream’s daily maximum flows. For this purpose, the daily flow values measured from 1967 to 1987 in the flow station numbered 47 and controlled by General Directorate of State Water works (DSi) were used. The daily maximum flows among daily flows for every year were selected. Since reserving water by Yedikir dam built on Tersakan stream had been started after 1987, the daily flows that came after this date are not suitable for homogeneity and were not taken into account, it was determined that the Tersakan stream’s daily maximum flows was homogen according to homogeneity test. In the study, plotting positions {Hazen, Weibull, Chegodayev, Tukey, Gringorten) and probability distributions (normal, log normal, three parameter log normal, two parameter gama, Pearson type III, log Pearson type III, extreme value type I) were used to determine the recurrence intervals of Tersakan stream’s daily maximum flows. The plotting position formulas including Hazen, Weibull, Chegodayev, Tukey and Gringorten can be used to obtain daily maximum flows, if expected periods are smaller than observation period. In addition, one of the considered probability distribution can be used to determine the flows which have smaller return periods than 10-year. The three parameter log normal probability distribution can be suggested for the recurrence intervals of the daily maximum flows.