Milan Onderka

Retrieval of suspended particulate matter concentrations in the Danube River from Landsat ETM data.

Alternations in river channel morphology result in a disturbed natural transport of suspended particulate matter (SPM). Suspended particulate matter serves as a transport medium for various pollutants, e.g. heavy metals. It is therefore important to understand how artificial obstructions alter the natural transport of suspended matter. Measurements of SPM in rivers are traditionally carried out during in situ sampling campaigns, which can provide only a limited view of the actual spatial distribution of suspended matter over large distances. Several authors have studied how space-borne remote sensing could be used for mapping of water quality in standing waters, but with only little attention paid to rivers. This paper describes the methodology how a Landsat ETM image was used to map the spatial patterns of SPM in the Slovak portion of the Danube River. Results of our investigation reveal that the Danube River in Slovakia exhibits gradual longitudinal decrease in concentrations of SPM. Based on a strong relationship between the Landsat near-infrared band (TM4) and field measurements, we developed a map of suspended particulate matter in the Danube River with a standard error (SE) of 2.92 mg/L. This study aims to show how archived satellite data and historical water quality data can be used for monitoring of SPM in large rivers. A methodology describing the minimum samples required for sufficiently accurate results is discussed in this paper also.

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.

Analysis of extreme hydrological Events on THE danube using the Peak Over Threshold method

Analysis of extreme hydrological Events on THE danube using the Peak Over Threshold method The Peak Over Threshold Method (POT) was used as an alternative technique to the traditional analysis of annual discharge maxima of the Danube River. The POT method was applied to a time-series of daily discharge values covering a period of 60 years (1931-1990) at the following gauge stations: Achleiten, Kienstock, Wien, Bratislava and Nagymaros. The first part of the paper presents the use of the POT method and how it was applied to daily discharges. All mean daily discharges exceeding a defined threshold were considered in the POT analysis. Based on the POT waves independence criteria the maximum daily discharge data were selected. Two theoretical log-normal (LN) and Log-Pearson III (LP3) distributions were used to calculate the probability of exceeding annual maximum discharges. Performance of the POT method was compared to the theoretical distributions (LN, LP3). The influence of the data series length on the estimation of the N-year discharges by POT method was carried out too. Therefore, with regard to later regulations along the Danube channel bank the 40, 20 and 10-year time data series were chosen in early of the 60-year period and second analysed time data series were selected from the end of the 60-year period. Our results suggest that the POT method can provide adequate and comparable estimates of N-year discharges for more stations with short temporal coverage. Analýza extrémnych hydrologických situácií na dunaji využitím metódy POT Príspevok sa zaoberá analýzou extrémnych hydrologických udalostí na Dunaji metódou Peak Over Threshold (POT). Metóda POT sa používa ako alternatíva určovania N-ročných prietokov k metóde ročných maxím pri analýzach extrémnych hydrologických udalostí. Pre výskyt vrcholových prietokov sa zvyčajne predpokladá Poissonova distribúcia. Základnými vstupnými údajmi pre štatistickú analýzu sú 60-ročné časové rady priemerných denných prietokov a 60-ročné rady maximálnych ročných prietokov v nami zvolených staniciach: Achleiten, Kienstock, Viedeň, Bratislava a Nagymaros - za obdobie 1931-1990. Extrémne hydrologické udalosti na Dunaji boli analyzované metódou POT, ktorá zahŕňa všetky maximálne denné prietoky povodní za dané obdobie, presahujúce zvolenú prahovú hodnotu. Na zostavenie teoretickej čiary prekročenia boli vybrané dve teoretické rozdelenia pravdepodobnosti: logaritmicko-normálne rozdelenie (LN) a Pearsonovo rozdelenie III. typu (LP III). Druhým cieľom príspevku bolo analyzovať vplyv zmeny dĺžky časového radu na odhad N-ročných prietokov. V práci boli 60-ročné časové rady údajov skrátené na 40, 20 a 10-ročné rady. V závere sme porovnali a zhodnotili získané výsledky štatistických odhadov N-ročných prietokov vo zvolených staniciach. Z výsledkov analýzy vyplýva, že metóda POT dáva pomerne dobré odhady N-ročných prietokov aj pre krátke časové rady údajov.

Dynamics of storm-driven suspended sediments in a headwater catchment described by multivariable modeling

PurposePrevious research has shown that the rate at which suspended sediment is transported in watercourses depends primarily on discharge (Q) as the first-order control, but additional factors are thought to affect suspended sediment concentrations (SSC) as well. Among these, antecedent hydrological and meteorological conditions (e.g., rainfall depth and intensity, discharge prior to a runoff event and the duration of runoff events) may represent significant transport controlling mechanisms. Univariate models using Q–SSC rating curves often produce large scatter and nonlinearity, because many of the hydrological and biotic processes affecting the dynamics of sediment are non-linear and exhibit threshold behavior. The simulation of such highly non-linear processes is therefore an elusive task requiring consideration of several interrelated controlling variables. The aim of this study was to identify the major hydrological and meteorological controls determining the dynamics of SSC during storm-runoff events and the magnitude of SSC in a headwater catchment in Luxembourg.Materials and methodsA parsimonious data-driven model (M5′ modular trees) was used to simulate SSC in response to the identified controlling variables. Antecedent hydro-meteorological variables (e.g., antecedent precipitation depths, antecedent precipitation indices, and a suit of hydrological data) were used as input variables.Results and discussionTwenty-four-hour antecedent runoff volumes were determined as the major control explaining sediment depletion effects during high-flow periods, and a gradual decline of SSC as a runoff event progresses. The modeling results obtained by M5′ trees were then compared to conventional power-law rating curves. The M5′ model outperformed the rating-curve by being successful in describing the shape and magnitude of the analyzed sedigraphs. Therefore, we propose that incorporating antecedent hydro-meteorological data into SSC prediction models may strongly enhance the accuracy of export coefficients. Two splitting criteria identified by the M5′ model tree (Q and antecedent runoff volume) were found and are discussed as possible thresholds responsible for the greatest nonlinearity in the Q–SSC relationship.ConclusionsOur study highlights the dominant antecedent hydro-meteorological conditions acting as the major controls on the magnitude of SSC during episodic events in the headwater Huewelerbach catchment in Luxembourg. For future application, it would be interesting to extend and test the data-mining approach presented in this paper to other catchments, where other controls on sediment transport may be identified.

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.

Water balance comparison of two small experimental basins with different vegetation cover

In a river, the flow directly affects the physical and chemical properties of its water, with further consequences for aquatic biota. Land use practices and vegetation cover play a significant role in the water cycle. The wide-spread perception of forest cover, in terms of hydrology is that forests may reduce water runoff: although in rare instances the contrary has been reported. Water runoff varies seasonally and depends on the forest tree species. By no means can it be considered constant over large expanses of area or for various rainfall patterns. In this paper, the results of a long-term hydrological survey conducted in two experimental microbasins (operated by the Institute of Hydrology SAS, IH SAS) with different land use practices are presented. The Rybárik microbasin (0.119 km2) is dominated by row crop production. The basin was 70% cultivated by the state farm and 30% by a private farm. The Lesný microbasin (0.086 km2) is covered by a deciduous hornbeam regrowth forest (Carpinus betulus). The analysis revealed that the difference in the runoff from the forest and the agricultural land increases with increasing precipitation; however, at some point (extreme precipitations with low probability) the runoff from these basins is nearly equal.

Analyzing temporal changes in maximum runoff volume series of the Danube River

Several hypotheses claim that more extremes in climatic and hydrologic phenomena are anticipated. In order to verify such hypotheses it is inevitable to examine the past periods by thoroughly analyzing historical data. In the present study, the annual maximum runoff volumes with t-day durations were calculated for a 130-year series of mean daily discharge of Danube River at Bratislava gauge (Slovakia). Statistical methods were used to clarify how the maximum runoff volumes of the Danube River changed over two historical periods (1876-1940 and 1941-2005). The conclusion is that the runoff volume regime during floods has not changed significantly during the last 130 years.

Suspended Particulate Matter Concentrations Retrieved from Self-Calibrated Multispectral Satellite Imagery

Suspended Particulate Matter Concentrations Retrieved from Self-Calibrated Multispectral Satellite Imagery Inland waters are known to be laden with high levels of suspended particulate matter (SPM). Remotely sensed data have been shown to provide a true synoptic view of SPM over vast areas. However, as to date, there is no universal technique that would be capable of retrieving SPM concentrations without a complete reliance on time-consuming and costly ground measurements or a priori knowledge of inherent optical properties of water-borne constituents. The goal of this paper is to present a novel approach making use of the synergy found between the reflectance in the visual domain (~ 400-700 nm) with the near-infrared portion of the spectrum (~ 700-900 nm). The paper begins with a brief discourse of how the shape and spectral dependence of reflectance is determined by high concentrations of SPM. A modeled example is presented to mimic real-world conditions in fluvial systems, with specific absorption and scattering coefficients of the virtual optically active constituents taken from the literature. Using an optical model, we show that in the visual spectral domain (~ 400-700 nm) the water-leaving radiance responds to increasing SPM (0-100 g m-3) in a non-linear manner. Contrarily to the visual spectra, reflectance in the near infrared domain (~ 700-900 nm) appears to be almost linearly related to a broad range of SPM concentrations. To reduce the number of parameters, the reflectance function (optical model) was approximated with a previously experimentally verified exponential equation (Schiebe et al., 1992: Remote sensing of suspended sediments: the Lake Chicot, Arkansas project, Int. J. Remote Sensing, 13, 8, 1487-1509). The SPM term in Schiebes equation was expressed as a linear function of top-of-atmosphere reflectance. This made it possible to calibrate the reflectance in the visual domain by reflectance values from the near-IR portion of the spectrum. The possibility to retrieve SPM concentrations from only remote sensing data without any auxiliary ground mea-surements is tested on a Landsat ETM + scene acquired over a reservoir with moderately turbid water with SPM concentrations between 15-70 g m-3. The retrieved concentrations (on average) differ from in-situ measurement by ~ 10.5 g m-3. Stanovenie Koncentrácie Suspendovaných Látok Prostredníctvom Kalibrovaného Multispektrálneho Satelitného Zobrazovania Cieľom príspevku je prezentovať alternatívne spracovanie satelitných snímok na odhad koncentrácie suspendovaných sedimentov vo vodných útvaroch. Prvá časť článku sa venuje teórii a fyzikálnej podstate reflektancie a vplyvu prirodzene sa vyskytujúcich opticky aktívnych prvkov vo vode (suspendované sedimenty, pigmenty a rozpustené látky) na reflektanciu snímanú prostriedkami diaľkového prieskumu Zeme. Na modelovom príklade sme ukázali, že so zvyšovaním koncentrácie suspendovaných látok dochádza k saturácii signálu reflektancie. V druhej časti príspevku sme opísali spôsob využitia nelineárnosti vzťahu medzi reflektanciu vo viditeľnej časti (~ 400-700), a kvázi-linearitov v infračervenej časti (~ 700-900 nm) elektromegnetického spektra a koncentrácie suspendovaných sedimentov. Optimalizáciou tohto nelineárneho vzťahu sme odhadli koncentrácie suspendovaných sedimentov pre zdrž Hrušov pri Bratislave s RMSE 10.5 g m-3.

The Wavelets show it – the transit time of water varies in time

Abstract The ways how water from rain or melting snow flows over and beneath the Earth‘s surface affects the timing and intensity at which the same water leaves a catchment. Several mathematical techniques have been proposed to quantify the transit times of water by e.g. convolving the input-output tracer signals, or constructing frequency response functions. The primary assumption of these techniques is that the transit time is regarded time-invariant, i.e. it does not vary with temporarily changing e.g. soil saturation, evaporation, storage volume, climate or land use. This raises questions about how the variability of water transit time can be detected, visualized and analyzed. In this paper we present a case study to show that the transit time is a temporarily dynamic variable. Using a real-world example from the Lower Hafren catchment, Wales, UK, and applying the Continuous Wavelet Transform we show that the transit time distributions are time-variant and change with streamflow. We define the Instantaneous Transit Time Distributions as a basis for the Master Transit Time Distribution. We show that during periods of elevated runoff the transit times are exponentially distributed. A bell-shaped distribution of travel times was observed during times of lower runoff. This finding is consistent with previous investigations based on mechanistic and conceptual modeling in the study area according to which the diversity of water flow-paths during wet periods is attributable to contributing areas that shrink and expand depending on the duration of rainfall. The presented approach makes no assumptions about the shape of the transit time distribution. The mean travel time estimated from the Master Transit Time Distribution was ~54.3 weeks.