The peaks over threshold method (POT method) is an alternative to the block-maxima method for estimating return levels (these are the levels that are exceeded by a daily precipitation, resp. by a daily average discharge, only with a given small probability; in statistical language they are called high quantiles) when the studied series are not long enough. The paper compares both methods for precipitation and discharges series of Northern Moravia. It is shown how to overcome problems in the POT method caused by autocorrelation and seasonality. and Metoda špiček nad prahem může sloužit při odhadování vysokých kvantilů (to znamená takových hodnot, že je denní úhrnná srážka, respektive denní průměrný průtok, překročí jen s malou předem danou pravděpodobností). Jedná se o alternativu k metodě blokových maxim, a to zvláště tam, kde studované řady nejsou příliš dlouhé. Článek porovnává výsledky obou metod na příkladech srážkových a průtokových dat ze severní Moravy. Ukazuje dále, jak lze v metodě POT překonat problémy spojené s autokorelací a sezónností řad.
Deposition of solid particles in the stormwater sewers reduces the discharging capacity, causing inundation. A sediment invert trap (SIT) is an option that can be installed at the bottom of the stormwater sewer drain to intercept the flowing solid particles. In the present study performance of rectangular SIT were analyzed experimentally and computationally. Variation of particle trapping efficiency of rectangular SIT fitted at the bottom of the open channel flume has been studied under the interpretation of invert trap depth, flow depth, particle size, particle shape, and slot width. To predict the flow field and trap efficiency of a rectangular invert trap, 2D-VOF-DPM-CFD modelling has been carried out using ANSYS Fluent 2020 R1 software. For velocity field determination, the volume of fluid (VOF) model was used along with realizable k-є turbulence model. To predict particle trap efficiency, stochastic discrete phase model (DPM) was utilized. From experimental study and CFD modeling, it has been found that the particle trap efficiency of rectangular invert trap varied with change in the depth of invert trap, sediment size, shape factor, depth of flow and slot width. Consideration of particle shape in terms of shape factor in the modeling of solid-phase through DPM validated the CFD predicted results with those obtained experimentally with mean absolute percent error (MAPE) of 2.68%, 3.99% and 6.6% for sewer solid size ranges SS1, SS2, and SS3 respectively at all flow depths for both slot widths considered in this study.
Detailed data on the long-term performance of bioretention cells (BC) for stormwater management are sparse. This research aimed at setting up and testing an infrastructure that will provide the data on hydrologic and chemical performance of BC. Two identical experimental BC’s were built. The monitoring methodology monitoring was developed and tested during a first growing season with the first BC supplied with natural rainfall, while the second BC was used for ponding experiments. Key layer of the BCs, a biofilter, was composed of sand, compost and topsoil. Both BCs are equipped with sensors monitoring the components of water balance and the water potential of the biofilter. High levels of total suspended solids were detected in the outflow. The runoff coefficient for the entire period of the growing season was 0.72 in the first BC and 0.86 in the second BC, while the peak outflow reduction for individual rainfall episodes ranged between 75% to 95% for the first BC and 19% to 30% for the second BC. Saturated hydraulic conductivity of the biofilter in the first BC decreased by two orders of magnitudes after the first year of operation. Retention curves of the biofilter changed due to material consolidation.
The recently advanced approach of wavelet transforms is applied to the analysis of lake levels. The aim of this study is to investigate the variability of lake levels in four lakes in the Great Lakes region where the method of continuous wavelet transform and global spectra are used. The analysis of lake-level variations in the time-scale domain incorporates the method of continuous wavelet transform and the global spectrum. Four lake levels, Lake Erie, Lake Michigan, Lake Ontario, and Lake Superior in the Great Lakes region were selected for the analysis. Monthly lake level records at selected locations were analyzed by wavelet transform for the period 1919 to 2004. The periodic structures of the Great Lakes levels revealed a spectrum between the 1-year and 43- year scale level. It is found that major lake levels periodicities are generally the annual cycle. Lake Michigan levels show different periodicities from Lake Erie and Lake Superior and Lake Ontario levels. Lake Michigan showed generally long-term (more than 10 years) periodicities. It was shown that the Michigan Lake shows much stronger influences of inter-annual atmospheric variability than the other three lakes. The other result was that some interesting correlations between global spectrums of the lake levels from the same climatic region were found. and Nedávno zdokonalená metóda vlnovej transformácie je aplikovaná na analýzu úrovne hladín jazier. Táto práca obsahuje výsledky štúdia variability úrovne hladín štyroch jazier v regióne Veľkých jazier, s využitím metódy kontinuálnej vlnovej transformácie a globálneho spektra. Boli študované variácie hladín vybraných Veľkých jazier v závislosti od času. Na analýzu úrovne hladín boli vybrané štyri jazerá: Lake Erie, Lake Michigan, Lake Ontario, a Lake Superior v regióne Great Lakes. Mesačné chody úrovne hladín za obdobie rokov 1919 až 2004 boli študované vlnovou analýzou. Periodická štruktúra hladín Great Lakes bola zistená v spektre medzi 1 a 43 rokmi. Bolo zistené, že hlavnou periódou úrovne hladín je ročný cyklus. Na rozdiel od jazier Lake Erie, Lake Superior a Lake Ontario úrovne hladín Lake Michigan majú inú periodicitu. Lake Michigan má vo všeobecnosti dlhodobú (viac ako 10-ročnú) periodicitu. Je ukázané, že jazero Michigan reaguje na medziročnú variabilitu vlastností atmosféry výraznejšie ako ostatné tri jazerá. Ďalšími výsledkami analýzy sú niektoré zaujímavé korelácie medzi všeobecným spektrom úrovne hladín jazier z identického klimatického regiónu.
This study tested the hypothesis that the changes in hydrophysical parameters and heterogeneity of water flow in an aeolian sandy soil have the same trend as the process of succession. Three sub-sites were demarcated at the area of about 50 m x 50 m. The first sub-site was located at the pine-forest glade covered with a biological soil crust and represented the initial stage of succession. The second sub-site was located at the grassland and represented more advanced stage of succession. The third sub-site was located at the pine forest with 30-year old Scots pines and represented advanced stage (close to climax) of succession. The sandy soil at the surface was compared to the soil at the pine-forest glade at 50 cm depth, which served as a control because it had a similar texture but limited impact of vegetation or organic matter. It was found that any type of vegetation cover studied had a strong influence on hydrophysical parameters and heterogeneity of water flow in an aeolian sandy soil during hot and dry spells. The changes in some hydrophysical parameters (WDPT, R, k(-2 cm), Sw(-2 cm), ECS and DPF) and heterogeneity of water flow in an aeolian sandy soil had the same trend as the process of succession, but it was not so in the case of Ks and Se(-2 cm), probably due to the higher content of smaller soil particles in grassland soil in comparison with that content at other sub-sites. Both the persistence and index of water repellency of pure sand differed significantly from those of grassland, glade and forest soils. The highest repellency parameter values in forest soil resulted in the lowest value of both the water sorptivity and hydraulic conductivity in this soil in comparison with other soils studied. The highest value of ethanol sorptivity and the lowest value of saturated hydraulic conductivity in the grassland soil in comparison with other soils studied were due to the higher content of fine-grained (silt and clay) particles in the grassland soil. The effective cross section and the degree of preferential flow of pure sand differed significantly from those of grassland, glade and forest soils. The change in soil hydrophysical parameters due to soil water repellency resulted in preferential flow in the grassland, glade and forest soils, while the wetting front in pure sand area exhibited a form typical of that for stable flow. The latter shape of the wetting front can be expected in the studied soils in spring, when soil water repellency is alleviated substantially., The columnar shape of the wetting front, which can be met during heavy rains following long dry and hot spells, was attributed to redistribution of applied water on the surface to a series of micro-catchments, which acted as runon and runoff zones., V príspevku sa testovala hypotéza, že zmeny hydrofyzikálnych parametrov a heterogenita prúdenia vody v piesočnatej pôde majú rovnaký trend ako proces sukcesie. Na ploche asi 50 m x 50 m sa vytýčili tri parcely. Prvá parcela sa nachádzala na čistine pokrytej biologickým pôdnym pokryvom a reprezentovala počiatočné štádium sukcesie. Druhá parcela sa nachádzala na zatrávnenej ploche a reprezentovala rozvinutejšie štádium sukcesie. Tretia parcela sa nachádzala v borovicovom lese a reprezentovala rozvinuté štádium sukcesie (blízke ku klimaxovej vegetácii). Piesočnatá pôda na povrchu parciel sa porovnávala s pôdou z čistiny v hĺbke 50 cm, ktorá slúžila ako kontrola, pretože mala skoro rovnakú textúru, avšak veľmi malý vplyv vegetácie alebo organickej hmoty. Zistili sme, že akýkoľvek typ študovaného vegetačného pokryvu mal veľký vplyv na hydrofyzikálne parametre a heterogenitu prúdenia vody v piesočnatej pôde počas horúcich a suchých období. Zmeny niektorých hydrofyzikálnych parametrov (WDPT, R, k(-2 cm), Sw(-2 cm), ECS a DPF) a heterogenity prúdenia vody v piesočnatej pôde mali rovnaký trend ako proces sukcesie, neplatilo to však v prípade Ks a Se(-2 cm), pravdepodobne v dôsledku vyššieho obsahu malých pôdnych častíc v pôde s trávnatým pokryvom v porovnaní s inými parcelami. Stálosť aj index vodoodpudivosti čistého piesku sa štatisticky významne líšili od hodnôt týchto parametrov v pôde pod trávou, biologickým pôdnym pokryvom a borovicami. Najvyššie hodnoty parametrov vodoodpudivosti v tráve pod borovicami mali za následok najnižšie hodnoty sorptivity pre vodu a hydraulickej vodivosti v tejto pôde v porovnaní s ostatnými študovanými pôdami. Najvyššie hodnoty sorptivity pre etanol a najnižšie hodnoty nasýtenej hydraulickej vodivosti v pôde pod trávou v porovnaní s inými pôdami boli pravdepodobne spôsobené vyšším obsahom malých pôdnych častíc v tejto pôde. Efektívny prierez (ECS) a stupeň preferovaného prúdenia (DPF) čistého piesku sa štatisticky významne líšili od hodnôt týchto parametrov v pôde pod trávou, biologickým pôdnym pokryvom a borovicami. Zmeny hydrofyzikálnych parametrov pôdy v dôsledku jej vodoodpudivosti mala za následok preferované prúdenie v pôde pod trávou, biologickým pôdnym pokryvom a borovicami, zatiaľ čo čelo omáčania v čistom piesku malo tvar typický pre stabilné prúdenie. Takýto tvar čela omáčania možno vo všetkých študovaných pôdach očakávať na jar, keď je vodoodpudivosť pôdy podstatne znížená v dôsledku jej zvýšenej vlhkosti., and Čelo omáčania v tvare prstov, ktoré možno očakávať počas prívalových dažďov nasledujúcich po dlhých suchých a horúcich obdobiach, možno pričítať redistribúcii vody na povrchu pôdy do viacerých mikropovodí, ktoré sa správali ako vtokové a odtokové oblasti
Water erosion is an important degradation agent not only on the agricultural land but it also shows up on the forested soil. It is associated with the progress of forest mechanisation and with changing forest cover and it occurs especially on the Flysch substratum under exceptional hydrometerological situations. Research of water erosion has been organized by the Department of Physical Geography and Geoecology of the Ostrava university since 1976 till 2000 in the central part of the Moravskoslezske Beskydy Mts. (NE part of the Czech Republic). The article shows main results of analysis of suspended load regime. Suspended load as a transition part of the erosional products is an evidence of the intensity of erosional processes in the observed catchments. and Vodní eroze je důležitým degradačním činitelem nejen na zemědělské půdě, ale také na půdě lesní. Vodní eroze je spojená s rozvojem mechanizace lesních prací a se změnou skladby lesních porostů, a to zvláště ve flyšovém podloží při výjimečných hydrometeorologických situacích. Výzkum vodní eroze lesní půdy byl organizován Katedrou fyzické geografie a geoekologie Ostravské univerzity od roku 1976 do roku 2000 ve střední části Moravskoslezských Beskdyd (severovýchodní část České republiky). Studie obsahuje hlavní výsledky analýzy plaveninového režimu, který jako transportní část erozních produktů svědčí o intenzitě erozních procesů ve sledovaných povodích.
The project was aimed at comparing suspended load in four model river basins which are about of the same area and where each of them represents different geographical environment within the territory of the Czech Republic. We have chosen the Blšanka River basin, and basins of the rivers of Lužická Nisa, Loučka and Olšava as model territories. We have developed a model of the erosion risk for these basins. The model is based on a multi-criterion scale evaluation of chief erosion factors so that we can compare the potential of river basins for the sediment transport and define the chief risky areas. The sediment transport was evaluated for closing profiles of model river basins. We defined basic types of run-off situations to characterise the relationship between the content of sediments and the water flow. Mains trends in the development of erosion processes and suspended load are discussed in conclusion. and Hlavním cílem projektu bylo porovnat transport plavenin ve čtyřech modelových povodích, která jsou navzájem porovnatelná svojí plochou a zároveň reprezentují odlišné geografické prostředí území České republiky. Jako modelová území byla zvolena povodí Blšanky, Lužické Nisy, Loučky a Olšavy. Pro sledovaná povodí byl vytvořen model erozní ohroženosti založený na multikriteriálním bodovém hodnocení hlavních erozních faktorů s cílem porovnat potenciál povodí pro transport plavenin a vymezit hlavní rizikové oblasti. Transport plavenin byl vyhodnocen pro uzávěrové profily modelových povodí. Pro bližší charakteristiku vztahu mezi obsahem plavenin a průtokem vody byly vymezeny základní typy odtokových situací. V závěru jsou diskutovány trendy ve vývoji erozních procesů a transportu plavenin.
editoři Stanislava Fedrová, Jan Hejk, Alice Jedličková., Obsahuje bibliografie a bibliografické odkazy, and Část. německý a slovenský text, anglická resumé