A graphical method of estimating bed shear from measured velocity profiles is presented as an alternative to logarithmic law approach. In the present approach the entire velocity profile is considered as per binary law of velocity distribution i.e., logarithmic law in the wall region and parabolic law in the outer region. The validity of this method has been demonstrated for a typical velocity profile. An analysis has been also made in case of an erroneous measurement of bed level. and Práca obsahuje grafickú metódu určenia charakteristík trenia na dne koryta z meraných profilov rýchlosti ako alternatívu k používanému prístupu vychádzajúcemu z logaritmického zákona rozdelenia rýchlostí prúdenia. Predložený prístup charakterizuje profil rýchlosti ako binárny, t.j. zložený z logaritmického rozdelenia v oblasti steny a z parabolického rozdelenia mimo túto oblasť. Vhodnosť tohto prístupu bola demonštrovaná pre typický rýchlostný profil. Bola vykonaná analýza aj pre nepresné meranie úrovne dna koryta.
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. and 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.
This paper presents the results of a laboratory study on the flow characteristics of sharp-crested weirs, broad-crested weirs, and labyrinth weirs. The variation of the maximum bubble penetration depth for different weir types is investigated depending on overfall jet expansion, discharge, and drop height. Moreover, most efficient depth, length and width of the downstream receiving pool in an open channel system are studied by considering the penetration depth, overfall jet expansion, jet trajectory and the bubble zone. The results show that overfall jet expansion at the labyrinth weirs is significantly wider than the rectangular sharp-crested weirs and the trapezoidal sharp-crested weir. It is demonstrated that the labyrinth weirs have the lowest values of bubble penetration depth among the weirs tested. Furthermore, it is found that the rectangular and the trapezoidal weirs are observed to have the highest bubble penetration depth among all weirs. Consequently, empirical equations are obtained for predicting the maximum penetration depth of bubbles, trajectory of free overfall nappe, jet expansion of free overfall nappe, and the length of the bubble zone. and Príspevok prezentuje výsledky laboratórneho výskumu charakteristík prúdenia cez ostrohranné priepady, cez priepady so širokou hranou a cez labyrintové priepady. Bola študovaná variácia maximálnej hĺbky prieniku vzduchových bublín pre rozdielne typy priepadov v závislosti od rozšírenia prúdu, prietoku a výšky priepadu. Okrem toho bola analyzovaná efektívna hĺbka, šírka a dĺžka vývaru v systéme otvorených kanálov s uvážením rozšírenia prúdu, prietoku a výšky priepadu a oblasti so vzduchovými bublinami. Z výsledkov vyplýva, že rozšírenie prúdu pri labyrintových priepadoch je výrazne väčšie, ako pri pravouhlých a lichobežníkových ostrohranných priepadoch. Bolo ukázané, že labyrintové priepady majú najmenšiu hĺbku prieniku vzduchových bublín spomedzi všetkých testovaných priepadov. Zistilo sa však, že pravouhlé a lichobežníkové priepady majú najväčšie hĺbky prieniku vzduchových bublín spomedzi všetkých testovaných priepadov. Tieto výsledky výskumu viedli k empirickým rovniciam, umožňujúcim výpočet maximálnej hĺbky prieniku vzduchových bublín, trajektórií prepadového lúča, rozšírenia prúdu a dĺžky prevzdušnenej oblasti.
The paper by Jarušková and Hanek (2006) advocated application of the peaks over threshold method (POT method) for estimating the probability that a precipitation or discharges series exceeds a chosen high level. If daily precipitation amounts or average discharges are obtained at several stations one might be interested in estimating the probability that in the same time all variables of interest, e.g. precipitation amounts measured at several stations, exceed some chosen high levels. The paper explains how the method based on the point process approach may be used to get good estimates of such probabilities. Moreover, it presents some useful parametric models that were successfully applied by the author to some precipitation and discharges series of northern Moravia. and Článek navazuje na práci Jarušková, Hanek (2006), kde autoři doporučovali používání metody špiček nad prahem k odhadu pravděpodobností, s jakou srážková nebo průtoková řada překročí danou vysokou úroveň. V případě, že se denní srážková či průtoková řada měří ve více stanicích, může nás zajímat, s jakou pravděpodobností současně (to znamená ve stejný den) všechny studované řady, to je například srážkové řady měřené v několika stanicích, překročí nějaké předem stanovené vysoké úrovně. Článek vysvětluje, jak lze k odhadu takových pravděpodobností použít metodu založenou na bodovém procesu. Zároveň uvádí některé parametrické modely, které byly úspěšně použity autorkou článku pro odhady pravděpodobností překročení pro srážkové a průtokové řady na severní Moravě.
The need for continuous recording rain gauges makes it difficult to determine the rainfall erosivity factor (Rfactor) of the Universal Soil Loss Equation in regions without good spatial and temporal data coverage. In particular, the R-factor is only known at 16 rain gauge stations in the Madrid Region (Spain). The objectives of this study were to identify a readily available estimate of the R-factor for the Madrid Region and to evaluate the effect of rainfall record length on estimate precision and accuracy. Five estimators based on monthly precipitation were considered: total annual rainfall (P), Fournier index (F), modified Fournier index (MFI), precipitation concentration index (PCI) and a regression equation provided by the Spanish Nature Conservation Institute (RICONA). Regression results from 8 calibration stations showed that MFI was the best estimator in terms of coefficient of determination and root mean squared error, closely followed by P. Analysis of the effect of record length indicated that little improvement was obtained for MFI and P over 5- year intervals. Finally, validation in 8 additional stations supported that the equation R = 1.05·MFI computed for a record length of 5 years provided a simple, precise and accurate estimate of the R-factor in the Madrid Region.
Beerkan infiltration runs could provide an incomplete description of infiltration with reference to either the near steady-state or the transient stages. In particular, the process could still be in the transient stage at the end of the run or some transient infiltration data might be loss. The Wu1 method and the BEST-steady algorithm can be applied to derive soil hydrodynamic parameters even under these circumstances. Therefore, a soil dataset could be developed using two different data analysis methods. The hypothesis that the Wu1 method and BEST-steady yield similar predictions of the soil parameters when they are applied to the same infiltration curve was tested in this investigation. For a sandy-loam soil, BEST-steady yielded higher saturated soil hydraulic conductivity, Ks, microscopic pore radius, λm, and depth of the wetting front at the end of the run, dwf, and lower macroscopic capillary length, λc, as compared with the Wu1 method. Two corresponding means differed by 1.2–1.4 times, depending on the variable, and the differences appeared overall from moderate to relatively appreciable, that is neither too high nor negligible in any circumstance, according to some literature suggestions. Two estimates of Ks were similar (difference by < 25%) when the gravity-driven vertical flow and the lateral capillary components represented the 71–89% of total infiltration. In conclusion, the two methods of data analysis do not generally yield the same predictions of soil hydrodynamic parameters when they are applied to the same infiltration curve. However, it seems possible to establish what are the conditions making the two methods similar.
The Sacramento soil moisture-accounting model has been used to simulate the discharges of a major catchment (Pra river basin) in southern Ghana. Through the simulation it was possible to assess the temporal variability of evapotranspiratio, base flow proportions and groundwater in storage, as well as the average groundwater recharge to the weathered aquifers. Groundwater recharge was estimated by considering the measured discharge of groundwater across the boundary of the basin over periods of equivalent storage, to be equal to the net recharge inside the catchment. The direct groundwater recharge rate over the basin of area 22,836 km2 amounted to an annual average of 50 mm. This represented 4 % of mean annual rainfall of 1300 mm, giving natural groundwater resources potential of 1.6 l s-1 km-2. For regional groundwater resources assessment, the results obtained could be applied to other river basins in southwest Ghana. and Použitím SAC-SMA modelu byly simulovány odtoky z povodí řeky Pra v jižní části Ghany. Tímto bylo možno odhadnout časové tměny evapotranspirace, podzemního odtoku a zásoby podzemní vody, i průměrné doplňování podzemní vody do zvětralé zóny hydrogeologických kolektorů. Doplňování podzemní vody bylo stanoveno s uvážením měřených odtoků podzemní vody přes hranice povodí tak, aby se v obdobích stejné zásoby rovnaly výslednému doplňování uvnitř infiltrační oblasti. Roční průměr přirozeného doplňování podzemní vody v povodí s plochou 22 836 km2 činilo 50 mm. To odpovídá 4 % ročního průměru srážky (1300 mm) a 1,61 s-1 km-2 specifického odtoku podzemní vody. Dosažené výsledky mohou být aplikovány na další povodí v jihozápadní Ghaně pro regionální odhad zásoby podzemní vody.
Real time prediction of return periods of flood events that might occur in the course of anticipated dangerous meteorological situations at a catchment could be useful as additional information for decision makers involved in flood warning. Such a method is proposed in the paper for the Torysa basin in the western part of East Slovakia for rainfall-induced floods. A conceptual rainfall-runoff model with a daily time step was adopted for modelling of the runoff. The study of the relationship between the modelled basin’s soil moisture index at the beginning of the annual maximum floods and the flood-causing precipitation totals showed no dependence between these two quantities. Based on that finding, several scenarios involving the independent joint occurrence of synthetic extreme precipitation and antecedent basin saturation indexes were constructed. Using event-based flood simulations, synthetic flood waves were generated for these scenarios with the rainfall-runoff model. The relationships between the return periods of the synthetic precipitation and the return periods of the simulated floods were analysed, and the effect of antecedent basin saturation index on the extremity of the floods was quantified. Critical values of the basin saturation index leading to floods with higher return periods than the return period of flood-causing precipitation were suggested. A simple method of implementing such critical values into real time flood risk warnings in a hydrological forecasting and warning system in the Torysa basin was outlined. and Predpovedanie N-ročnosti povodní v reálnom čase pri výskyte kritických meteorologických situácií na povodiach je dôležité ako dodatočná informácia z hľadiska rozhodovacieho procesu v protipovodňovom varovnom systéme a následných opatreniach na povodiach. Táto štúdia bola preto zameraná na posudzovanie vzájomného pôsobenia extrémnych príčinných tekutých zrážok a rôznych stavov predchádzajúceho nasýtenia na pilotnom povodí Torysy po Prešov. Pre modelovanie odtoku na povodí bol použitý koncepčný zrážkovo-odtokový model s denným krokom. Pri výbere počiatočných podmienok vzniku povodní sme posudzovali rôzne stavy nasýtenia povodia pred vznikom najväčších ročných povodní, ktoré sa vyskytli na uvedenom povodí v minulosti. Na základe kombinácií modelových extrémnych príčinných zrážok s rôznymi stavmi predchádzajúceho nasýtenia povodia sme hydrologickým modelovaním simulovali odtok z povodia. Analyzoval sa vzťah medzi dobou opakovania modelových zrážok a simulovaných povodní a následne sa kvantifikoval vplyv predchádzajúceho nasýtenia povodia na extremitu odtoku. Určili sa kritické hodnoty nasýtenia povodia, kedy doba opakovania povodní prevyšuje hodnotu doby opakovania príčinných zrážok. Záverom bola navrhnutá jednoduchá metóda implementácie týchto kritických hodnôt pri predpovedaní povodní v reálnom čase na povodí Torysy.
A large single-ring infiltrometer test was performed in order to characterize the saturated hydraulic conductivity
below an infiltration basin in the well field of Lyon (France). Two kinds of data are recorded during the experiment:
the volume of water infiltrated over time and the extension of the moisture stain around the ring. Then numerical
analysis was performed to determine the saturated hydraulic conductivity of the soil by calibration.
Considering an isotropic hydraulic conductivity, the saturated hydraulic conductivity of the alluvial deposits is estimated
at 3.8 10–6 m s–1. However, with this assumption, we are not able to represent accurately the extension of the moisture
stain around the ring. When anisotropy of hydraulic conductivity is introduced, experimental data and simulation results
are in good agreement, both for the volume of water infiltrated over time and the extension of the moisture stain.
The vertical saturated hydraulic conductivity in the anisotropic configuration is 4.75 times smaller than in the isotropic
configuration (8.0 10–7 m s–1), and the horizontal saturated hydraulic conductivity is 125 times higher than the vertical
saturated hydraulic conductivity (1.0 10–4 m s–1).
An estimation procedure for suspended sediment concentrations based on the intensity of backscattered sound of acoustic Doppler current profilers (ADCP) is introduced in this paper. Based on detailed moving and fixed boat ADCP measurements with concurrent sediment sampling, we have successfully calibrated the estimation method for a reach of River Danube in Hungary, characterized by significant suspended sediment transport. The effect of measurement uncertainty and various data filtering on sediment load determination is also analyzed and quantified. Some of the physical model parameters describing the propagation of sound in water are estimated based on known empirical formulas, while other parameters are derived from measured. Regression analysis is used to obtain a relationship between the intensity of backscattered sound and sediment concentrations. The empirical relationship has been then used to estimate the suspended sediment concentrations from the ADCP data collected in fixed and moving boat measurement operation mode, along verticals and path-lines, respectively. We show that while some measurement uncertainty is inherent to the acoustic Doppler principle, it is further enhanced by the complexity of the near-bottom sediment-laden flow. This uncertainty has then a significant effect on the local sediment load estimation. In turn, reasonable smoothing of raw velocity and backscatter intensity data shows insignificant impact on cross-sectional sediment load estimation.