One of the basic questions related to the safety of dikes and river levees is the size of the freeboard. One of the important parameters for freeboard design is the height of waves and wave run-up on levee slopes. Routine and standardised calculations of wave run-up deal with the freeboards of dams where wind waves originate on the still water of the reservoir. In the case of running water in streams (thereinafter only ''currents'') the effect of wave and current interaction on wave run-up is usually not taken into account due to the lack of reliable knowledge regarding the phenomenon. In the Czech Republic this question is topical in the case of large rivers such as the Elbe, the Vltava and the Morava. Within the framework of the projects Hydralab III and NAZV QI 92A139, hydraulic research and further analysis focused on wave run-up as a result of the combination of current and wind wave parameters were performed. The laboratory research was carried out in a hydraulic flume with a wavemaker on the right bank and a levee with a slope of 1:3 installed on the left bank opposite the wavemaker. Waves were generated both perpendicular and oblique to the levee axis; the angle of oblique wave attack varied within the range of ± 30°. The aim of this paper is to compare the results of the mentioned research with recommendations mentioned in the Czech National Standard CSN 75 0255 Calculation of wave effects on water structures and to quantify the effect of current on the wave run-up height. and Jednou ze základních otázek spojených s bezpečností hráze je návrh převýšení její koruny nad maximální hladinou vzdouvané vody. Důležitým parametrem ovlivňujícím návrh převýšení je výška vln vybíhajících po svahu hráze. Běžné postupy výpočtu výšky výběhu vlny na svah jsou realizovány za předpokladu, že vlny vznikají na stojatých vodách. Vliv proudění se obvykle vzhledem k nízké úrovni znalostí tohoto jevu na tekoucích vodách zanedbává. V podmínkách České Republiky je otázka vlivu proudění na výšku výběhu relevantní zejména na velkých tocích jako Labe, Vltava nebo Morava. V rámci projektů Hydralab III a NAZV QI 92A139 byl uskutečněn hydraulický výzkum a analýza dat se speciálním zaměřením na výšku výběhu větrových vln při započtení vlivu proudění. Výzkum byl realizován na modelu hráze se sklonem svahu 1 : 3, který byl umístěn ve zkušební nádrži osazené vlnoproduktorem vedeným rovnoběžně s modelem hráze. Vlny zde byly generovány jednak kolmo vzhledem k podélné ose hráze, jednak šikmo v rozsahu úhlů ± 30°. Výsledky výzkumu byly porovnány s doporučeními uvedenými v České státní normě ČSN 75 0255 Výpočet účinků vln na stavby na vodních nádržích a zdržích.
Influence of the pattern of effective rainfall on modeled hydrograph was investigated in the study. The modelling was performed with the U.S. Army Corps of Engineers hydrograph package HEC-HMS 3.2 and calibrated and validated on measured hydrographs of Glinscica watershed. Six different models of rainfall loss were applied and their effect on modeled hydrograph was evaluated. Peak discharge, time of peak discharge and runoff volume were compared. The best results with the lowest RMSE in the study was obtained with the SCS curve number loss method. Also synthetic hyetographs of different probability and duration were used. Three positions of the maximum rainfall intensity at 25, 50 and 75 % of the rainfall duration were applied. The results showed essential differences in simulated time to peak and also differences in peak discharge. The differences in time to peak increases considerably with the increasing of the rainfall duration. Finally, the results of constant intensity distribution of rainfall of different durations were compared with those obtained with typical rainfall distribution with the position of the maximum intensity at 50 %. Results showed considerable differences in peak discharge and time to peak by longer durations of the rainfall. and Práca obsahuje výsledky výskumu vplyvu efektívnych zrážok na modelovaný hydrograf. Odtok bol modelovaný pomocou nástroja U.S. Army Corps of Engineers hydrograph package HEC-HMS 3.2, potom kalibrovaný a verifikovaný na meraných hydrografoch povodia Glinscica. Vplyv zrážok na modelovaný hydrograf bol vypočítaný pre šesť rôznych modelov priebehu zrážok. Porovnali sme maximálne prietoky, časy ich trvania a odtečené množstvá. Najlepšie výsledky s najnižším RMSE sme získali s SCS modelom odtoku. Použili sme tiež syntetické hyetografy rozdielnej pravdepodobnosti a trvania. Použili sa tri polohy maximálnych intenzít zrážok; pre 25, 50 a 75 % ich trvania. Výsledky ukázali zásadný rozdiel v simulovaných časoch maximálneho prietoku a tiež rozdiely v maximálnych prietokoch. Rozdiely v časoch dosiahnutia maximálnych odtokov sa výrazne zvyšovali s časom trvania zrážky. Nakoniec sme porovnali výsledky výpočtov s konštantnými intenzitami rozdelenia s rôznym trvaním zrážky s tými, ktoré boli vypočítané s použitím typických rozdelení, s polohou maximálnej intenzity zrážok pri 50 % ich trvania. Výsledky ukazujú významné rozdiely v maximálnych prietokoch a v časoch ich dosiahnutia v závislosti od trvania zrážky.
The present study focuses on the possible influence of large-scale climatic patterns on precipitation, temperature, and discharge in two distinct river basins in the Czech Republic. The first one is a flat lowland basin of the Cidlina River and the second one represents a more mountainous type of climate (the Blanice River). The large-scale climatic patterns used comprise monthly averages of teleconnection patterns, sea level pressure values, and two geopotential heights (850 hPa and 500 hPa). The correlations for corresponding months and also up to a three months lead time were investigated. The relations concerning the corresponding months proved to be most reliable in the winter period of the year. The behaviour of both selected river basins with respect to these predictors is rather similar in character. However, higher values of correlation coefficients are reached in the case of the Cidlina River basin. Considering the prediction abilities with a certain lead time, the results seem to be more promising for the winter and spring periods in both basins. In the Cidlina River basin, they are likely to be beneficial also for the late summer and autumn period.
Substantial evidence shows that the frequency of hydrological extremes has been changing and is likely to continue to change in the near future. Non-stationary models for flood frequency analyses are one method of accounting for these changes in estimating design values. The objective of the present study is to compare four models in terms of goodness of fit, their uncertainties, the parameter estimation methods and the implications for estimating flood quantiles. Stationary and non-stationary models using the GEV distribution were considered, with parameters dependent on time and on annual precipitation. Furthermore, in order to study the influence of the parameter estimation approach on the results, the maximum likelihood (MLE) and Bayesian Monte Carlo Markov chain (MCMC) methods were compared. The methods were tested for two gauging stations in Slovenia that exhibit significantly increasing trends in annual maximum (AM) discharge series. The comparison of the models suggests that the stationary model tends to underestimate flood quantiles relative to the non-stationary models in recent years. The model with annual precipitation as a covariate exhibits the best goodness-of-fit performance. For a 10% increase in annual precipitation, the 10-year flood increases by 8%. Use of the model for design purposes requires scenarios of future annual precipitation. It is argued that these may be obtained more reliably than scenarios of extreme event precipitation which makes the proposed model more practically useful than alternative models.
Longwave radiation, as part of the radiation balance, is one of the factors needed to estimate potential evapotranspiration (PET). Since the longwave radiation balance is rarely measured, many computational methods have been designed. In this study, we report on the difference between the observed longwave radiation balance and modelling results obtained using the two main procedures outlined in FAO24 (relying on the measured sunshine duration) and FAO56 (based on the measured solar radiation) manuals. The performance of these equations was evaluated in the April–October period over eight years at the Liz experimental catchment and grass surface in the Bohemian Forest (Czech Republic). The coefficients of both methods, which describe the influence of cloudiness factor and atmospheric emissivity of the air, were calibrated. The Penman-Monteith method was used to calculate the PET. The use of default coefficient values gave errors of 40–100 mm (FAO56) and 0–20 mm (FAO24) for the seasonal PET estimates (the PET was usually overestimated). Parameter calibration decreased the FAO56 error to less than 20 mm per season (FAO24 remained unaffected by the calibration). The FAO56 approach with calibrated coefficients proved to be more suitable for estimation of the longwave radiation balance.
The use of environmentally-friendly materials in hydraulic engineering (e.g. the stone lining of weirs at levees) calls for the more accurate estimation of the discharge coefficient for broad-crested weirs with a rough crest surface. However, in the available literature sources the discharge coefficient of broad-crested weirs is usually expressed for a smooth crest. The authors of this paper have summarized the theoretical knowledge related to the effect of weir crest surface roughness on the discharge coefficient. The method of determination of the head-discharge relation for broad-crested weirs with a rough crest surface is proposed based on known discharge coefficient values for smooth surfaces and on the roughness parameters of the weir. For selected scenarios the theoretical results were compared with experimental research carried out at the Laboratory of Water Management Research, Faculty of Civil Engineering (FCE), Brno University of Technology (BUT). and Používání přírodě blízkých materiálů ve vodním hospodářství (např. kamenná opevnění povrchu přelivů v ochranných hrázích) vyvolává požadavek přesnějšího stanovení součinitele průtoku pro přelivy se širokou a hydraulicky drsnou korunou. V dostupných literárních pramenech je součinitel průtoku přelivů se širokou korunou obvykle vyjádřen pouze pro hladký povrch koruny přelivu. Autoři článku shrnuli teoretické poznatky týkající se vlivu drsnosti povrchu koruny přelivu na součinitel průtoku a navrhli metodu pro stanovení způsobu hydraulického výpočtu konzumční křivky přepadu přes přeliv se širokou a drsnou korunou. Postup vychází ze znalosti součinitele průtoku přelivu s hladkou korunou a charakteristik drsnosti. Pro vybrané scénáře byly teoreticky vypočítané hodnoty porovnány s výsledky experimentálního výzkumu uskutečněného v Laboratoři vodohospodářského výzkumu Ústavu vodních staveb, Fakulty stavební, Vysokého učení technického v Brně.
Stony soils are composed of two fractions (rock fragments and fine soil) with different hydrophysical characteristics. Although stony soils are abundant in many catchments, their properties are still not well understood. This manuscript presents an application of the simple methodology for deriving water retention properties of stony soils, taking into account a correction for the soil stoniness. Variations in the water retention of the fine soil fraction and its impact on both the soil water storage and the bottom boundary fluxes are studied as well. The deterministic water flow model HYDRUS-1D is used in the study. The results indicate that the presence of rock fragments in a moderate-to-high stony soil can decrease the soil water storage by 23% or more and affect the soil water dynamics. Simulated bottom fluxes increased or decreased faster, and their maxima during the wet period were larger in the stony soil compared to the non-stony one.
In normal practice, during the estimation of reservoir storage uncertainties affecting the values of mean monthly discharge series are not normally considered, and usually no estimates of these are known. Therefore, the question arises as to whether the results of the estimation of the capacity of storage reservoirs may be affected by uncertainties in the discharge series. The aim of this article is the suggestion of a possible approach to estimating the level of uncertainties affecting the elements of mean monthly discharge series. These discharge series are subsequently integrated into water reservoir storage capacity calculations, and the significance of the proposed approach is explored. and Nejistoty členů řad průměrných měsíčních průtoků nejsou v běžné praxi udávány, není ani znám odhad jejích velikostí. Otázkou rovněž je, zda nejistotami zatížené průtokové řady mohou ovlivnit výsledky vodohospodářského řešení zásobní funkce vodní nádrže. Cílem článku je naznačení možného postupu odhadu míry nejistot zatěžujících členy průtokové řady průměrných měsíčních průtoků a následné začlenění uvedené řady do výpočtů zásobního objemu vodní nádrže a posouzení významu uvedeného postupu.