Jan Pekar

Spatial and temporal runoff oscillation analysis of the main rivers of the world during the 19th -20th centuries

The annual discharge time series of selected large rivers in the world were tested for wet and dry periods. The 28 – 29-years cycle, as well as 20 – 22-years cycle of extremes occurrence were identified. From the trend analysis it follows that the hydrological characteristics of the rivers must be stated at least for one 28-year period. If we want to identify any trend uninfluenced by the 28-year periodicity of the discharge time series, we must determine the trend during a single or multiple curve cycle, starting and terminating by either minima (e.g. 1861 –1946 in West/Central Europe) or maxima (e.g. 1847 –1930 or 1931– 1984 in West/Central Europe). Trends determined for other periods are influenced by the periodicity of the series and depend on the position of the starting point on the increasing or recession curve. Long-term trends during the period 1860– 1990 have not been detected for the West/Central European runoff. Further, the temporal shift in the discharge extremes occurrence (both, maxima and minima) was shown to depend on the longitude and latitude. The time shift between Neva and Amur discharge time series is about four years, between Amur and St Lawrence is about 16 years, and between St. Lawrence and Neva is about nine years. The time shift between Congo and Amazon is about seven years. q 2003 Elsevier Science B.V. All rights reserved.

The impact of land use on stream water quality in Slovakia

In the first part of this paper, the impact of forestry, agriculture and urban activities on the quality of surface water is analysed. Daily data from 15 forest and agricultural experimental catchments of the Institute of Hydrology, Slovak Academy of Sciences are used. It is shown, that the nitrate concentrations in surface water have decreased in Slovakia since 1989 as a result of decreased use of inorganic nitrogen fertilisers (lower intensity of agricultural production in Slovakia owing to recent economic changes). The annual nitrate specific load varies from 5.90 to 110 kg ha−1 year−1, the annual sulphate load varied from 29.16 to 509.60 kg ha−1 year−1 and the annual phosphate load varied from 0.0098 to 0.0224 kg ha−1 year−1 during 1990–1992. In the second part, a two-step method of three-component hydrograph separation of rain-, soil- and groundwater is proposed. The method is used in the Manelo-Gribov microbasin (O.95 km2) in Eastern Slovakia. The annual contribution of surface runoff in total runoff volume was 57.5%, the contribution of interflow runoff was 21.1%, and the contribution of groundwater was 21.4%, during the period from 1 August to 31 July 1992. A deterministic regression model for predicting daily nitrate concentrations from values of stream daily discharge and flow component data was developed. A set of 1421 modelled NO3−1 data was compared with the set of measured data.

Is the Water Temperature of the Danube River at Bratislava, Slovakia, Rising?

This paper aims to reveal the annual regime, time series, and long-term water temperature trends of the Danube River at Bratislava, Slovakia, between the years 1926 and 2005. First, the main factors affecting the river’s water temperature were identified. Using multiple regression techniques, an empirical relationship is derived between monthly water temperatures and monthly atmospheric temperatures at Vienna (Hohe Warte), Austria, monthly discharge of the Danube, and some other factors as well. In the second part of the study, the long-term trends in the annual time series of water temperature were identified. The following series were evaluated: 1) The average annual water temperature (To) (determined as an arithmetic average of daily temperatures in the Danube at Bratislava), 2) the weighted annual average temperature values (To) (determined from the daily temperatures weighted by the daily discharge rates at Bratislava), and 3) the average heat load (Zt) at the Bratislava station. In the long run, the To series is rising; however, the trend of the weighted long-term average temperature values, To, is near zero. This result indicates that the average heat load of the Danube water did not change during the selected period of 80 yr. What did change is the interannual distribution of the average monthly discharge. Over the past 25 yr, an elevated runoff of “cold” water (increase of the December–April runoff) and a lower runoff of “warm” water (decrease of the river runoff during the summer months of June–August) were observed.

Prediction of water quality in the Danube River under extreme hydrological and temperature conditions

Prediction of Water Quality in the Danube River Under extreme Hydrological and Temperature Conditions One of the requirements imposed by the Water Framework Directive (WFD, 2000/60/EC) is to analyze and predict how quality of surface waters will evolve in the future. In assessing the development of a streams pollution one must consider all sources of pollution and understand how water quality evolves over time. Flow and water temperature regime of a stream or river are the main factors controlling the extent to which deterioration of a streams water quality can propagate under constant input from pollution sources. In addition, there is ever increasing public concern about the state of the aquatic environment. Decision makers and scientists involved in water management call for studies proposing simulation models of water quality under extreme natural hydrologic and climatic scenarios. Also, human impact on water resources remain an issue for discussion, especially when it comes to sustainability of water resources with respect to water quality and ecosystem health. In the present study we investigate the long-term trends in water quality variables of the Danube River at Bratislava, Slovakia (Chl-a, Ca, EC, SO2-, Cl-, O2, BOD5, N-tot, PO4-P, NO3-N, NO2-N, etc.), for the period 1991-2005. Several SARIMA models were tested for the long-term prediction of selected pollutant concentrations under various flow and water temperature conditions. In order to create scenarios of selected water quality variables with prediction for 12 months ahead, three types of possible hydrologic and water temperature conditions were defined: i) average conditions - median flows and water temperature; ii) low flows and high water temperature; and iii) high flows and low water temperature. These conditions were derived for each month using daily observations of water temperature and daily discharge readings taken in the Danube at Bratislava over the period 1931-2005 in the form of percentiles (1th-percentile, median, 99th-percentile). Once having derived these extreme-case scenarios, we used selected Box-Jenkins models (with two regressors - discharge and water temperature) to simulate the extreme monthly water quality variables. The impact of natural and man-made changes in a streams hydrology on water quality can be readily well simulated by means of autoregressive models. Predpoveď Vybraných Ukazovateľov Kvality Vody V Dunaji Za Extrémnych Hydrologických A Teplotných Podmienok Jednou z požiadaviek Rámcovej smernice o vode (WFD, 2000/60/EC) je analýza trendov a dlhodobá predpoveď vývoja znečistenia povrchových tokov. Pri odhade vývoja znečistenia toku je potrebné brať do úvahy nielen možné zdroje znečistenia, ale je potrebné uvažovať aj s vývojom množstva vody v tokoch a so zvyšovaním teploty tokov v dôsledku očakávanej klimatickej zmeny a zmeny vo využívaní vodných zdrojov. V príspevku je analyzovaný vývoj mesačných koncentrácií vybraných ukazovateľov kvality vody v toku Dunaja v stanici Bratislava (napr. Chl-a, Ca, EC, SO2-, Cl-, O2, BSK5, N-celk, PO4-P, NO3-N, NO2-N a pod.) za obdobie r. 1991-2005. Za účelom dlhodobej predpovede koncentrácií každého ukazovateľa kvality vody sme na základe štatistických testov vybrali najlepší autoregresný Box-Jenkinsov model s dvoma regresormi: 1. prietokmi a 2. teplotami vody. Scenáre pre mesačné prietoky a mesačné teploty vody boli vytvorené pre tri stavy: i) priemerné podmienky - medián prietokov a teploty vody; ii) nízke prietoky a vysoké teploty vody; a iii) vysoké prietoky a nízke teploty vody. Tieto scenárové podmienky boli vypočítané z denných údajov z obdobia 1931-2005 ako percentily (1. percentil, medián, 99. percentil). Použijúc tieto scenáre sme vybranými Box-Jenkinsovými modelmi s dvoma regresormi simulovali extrémne mesačné hodnoty vybraných ukazovateľom kvality vody v Dunaji pre extrémne hydrologické a teplotné podmienky.

Historic flood marks and flood frequency analysis of the Danube River at Bratislava, Slovakia

Abstract In this paper we focused on the history of floods and extreme flood frequency analysis of the upper Danube River at Bratislava. Firstly, we briefly describe the flood marks found on the Danube River in the region of Bratislava, Slovakia, and provide an account of the floods’ consequences. Secondly, we analyzed the annual maximum discharge series for the period 1876-2012, including the most recent flood of June 2013. Thirdly, we compare the values of T-year design discharge computed with and without incorporating the historic floods (floods of the years 1501, 1682, and 1787 into the 138-year series of annual discharge peaks). There are unfortunately only a few historic flood marks preserved in Bratislava, but there are very important and old marks in neighbouring Hainburg and other Austrian cities upstream to Passau. The calculated T-year maximum discharge of the Danube at Bratislava for the period 1876-2010 without and with historic flood values have been compared. Our analysis showed that without incorporating the historic floods from the years 1501, 1682, and 1787 the 1000-year discharge calculated only with data from the instrumented period 1876- 2013 is 14,188 m3 s-1, and it is lower compared to the 1000-year discharge of 14,803 m3 s-1 when the three historic floods are included. In general, the T-year discharge is higher throughout the whole spectrum of T-year discharges (10, 20, 50, 100, 200, 500-year discharge) when the three historic floods are included. Incorporating historic floods into a time series of maximum annual discharge seems to exert a significant effect on the estimates of low probability floods. This has important implications for flood managements and estimation of flood design discharge.

Global drivers effect in multi-annual variability of runoff

Abstract Changes in runoff parameters are very important for Slovakia, where stream-flow discharges, being supplied by precipitation and groundwater runoff, are preferentially influenced by climatic conditions. Therefore, teleconnections between runoff parameters, climate parameters and global atmospheric drivers such as North Atlantic Oscillation, Southern Pacific Oscillation, Quasi-biennial oscillation and solar activity were studied in the Nitra River Basin, Slovakia. Research was mostly based on records of 80 years (1931-2010) for discharges and baseflow, and 34 years for groundwater heads. Methods of autocorrelation, spectral analysis, cross-correlation and coherence function were used. Results of auto- correllograms for discharges, groundwater heads and base flow values showed a very distinct 11-year and 21-year periodicity. Spectrogram analysis documented the 11-year, 7.8-year, 3.6-year and 2.4-year periods in the discharge, precipitation and air temperature time series. The same cycles except of 11-years were also identified in the long-term series of the North Atlantic Oscillation and Southern Pacific Oscillation indices. The cycle from approximately 2.3 to 2.4-years is most likely connected with Quasi-biennial oscillation. The close negative correlation between the North Atlantic Oscillation winter index and the hydrological surface and groundwater parameters can be used for their prediction within the same year and also for one year in advance.

ESTIMATING FLASH FLOOD PEAK DISCHARGE IN GIDRA AND PARNÁ BASIN: CASE STUDY FOR THE 7-8 JUNE 2011 FLOOD

Estimating Flash Flood Peak Discharge in Gidra and Parná Basin: Case Study for the 7-8 June 2011 Flood We analyzed the runoff and its temporal distribution during the catastrophic flood events on river Gidra (32.9 km2) and Parná (37.86 km2) of the 7th June 2011. The catchments are located in the Small Carpathian Mountains, western Slovakia. Direct measurements and evaluation of the peak discharge values after such extreme events are emphasized in the paper including exceedance probabilities of peak flows and of their causal flash rainfall events. In the second part of the paper, plausible modeling mode is presented, using the NLC (Non Linear Cascade) rainfall-runoff model. Several hypothetical extreme flood events were simulated by the NLC model for both rivers. Also the flood runoff volumes are evaluated as basic information on the natural or artificial catchment storage. Odhad Vrcholových Prietokov v Povodí Gidry a Parnej - Prípadová Štúdia Povodne Zo 7.-8. Júna 2011 Predložený príspevok analyzuje tvorbu a priebeh odtoku počas katastrofickej povodňovej situácie na Gidre (32,9 km2) a na Parnej (37,86 km2) dňa 7. 6. 2011. Povodia týchto tokov sa nachádzajú v Malých Karpatoch na západnom Slovensku. V príspevku sa kladie dôraz na priame zameranie a vyhodnotenie kulminačných prietokov po výskyte takýchto povodní. Diskutujú sa problémy vyjadrenia pravdepodobnosti prekročenia kulminačných prietokov a dažďov, ktoré ich spôsobili. V druhej časti príspevku je prezentovaný možný spôsob modelovania povodne jednoduchým zrážkovo-odtokovým modelom NLC. Daným modelom NLC sú následne simulované prietoky Gidry v stanici Píla a Parná v stanici Horné Orešany za extrémnej hypotetickej zrážkovej udalosti. Hodnotené sú objemy odtoku počas povodní, ako základný údaj pre reálny odhad ich prirodzeného alebo umelého zadržania.

A new method for estimating soil water repellency index

Abstract The soil water repellency index, R, is calculated from the ethanol sorptivity, Se, and water sorptivity, Sw, using an equation: R = 1.95 Se/Sw. In the older method, Se and Sw were measured in pairwise arrangements to reduce the influence of spatial heterogeneity of soil properties, and one value of R only was calculated from one pair of Se and Sw measurements. The new method to estimate R takes into account all the measured values of water and ethanol sorptivity, i.e., m × n values of R are to be calculated from m values of Sw and n values of Se. The results of the t-test revealed that there is not a statistically significant difference between the means of both samples at the 95.0% confidence level for all four studied soils. It was found using the F-test that there is not a statistically significant difference between the variances of samples estimated by the older and new methods at the 95.0% confidence level for all but one (grassland soil) studied soils. Comparison of R values taken in sandy soil under different vegetation cover in Sekule, southwest Slovakia, revealed that the average values of R estimated using the new method increased with vegetation succession, i.e., Pure sand < Glade soil < Grassland soil < Pine-forest soil, while the me|an values of R, estimated using the older method changed in the order: Pure sand < Grassland soil < Glade soil < Pine-forest soil. It seems that an increase in the number of R values processed can result in the more reliable mean values of R at the sites with high spatial heterogeneity of soil properties.

Analysis of flood propagation changes in the Kienstock—Bratislava reach of the Danube River/Analyse des changements de propagation des crues dans le tronçon Kienstock—Bratislava du Fleuve Danube

Abstract In the first part of this study, a flood wave transformation analysis for the largest historical floods in the Danube River reach Kienstock–Bratislava was carried out. For the simulation of the historical (1899 and 1954) flood propagation, the nonlinear river model NLN-Danube (calibrated on the recent river reach conditions) was used. It was shown that the simulated peak discharges were not changed significantly when compared to their historical counterparts. However, the simulated hydrographs exhibit a significant acceleration of the flood wave movement at discharges of between 5000 and 9000 m3 s-1. In the second part, the travel time-water level relationships between Kienstock and Bratislava were analysed on a dataset of the flood peak water levels for the period 1991–2002. An empirical regression routing scheme for the Danube short-term water level forecast at Bratislava station was derived. This is based on the measured water level at Kienstock gauging station.

Identification of long-term high-flow regime changes in selected stations along the Danube River

Abstract The aim of the paper is to study spatial and temporal changes in the magnitude, duration and frequency of high flows in the Danube basin. A hydrological series of the mean daily discharges from 20 gauging stations (operated minimally since 1930) were used for the analysis of changes in the daily discharges. The high flow events were classified into three classes: high flow pulses, small floods, and large floods. For each year and for each class, the means of the peak discharges, the number and duration of events, and the rate of changes of the rising and falling limbs of the waves were determined. The long-term trends of the annual time series obtained were analyzed and statistically evaluated. The long-term high flow changes were found to be different in three individual high flow classes. The duration of the category of high flow pulses is decreasing at 19 stations on the Danube and is statistically significant at the Linz, Vienna, Bratislava and Orsova stations. The frequency of the high flow pulses is increasing in all 20 stations. Also, the rising and falling rates of the high flow pulse category are increasing at the majority of the stations. The long-term trends of the selected characteristics of the small floods are very similar to the trends of the high flow pulses, i.e., the duration of small floods is decreasing, and their mean number per year is increasing. In the category of large floods the changes were not proved.