The Surface Water Department of the Czech Hydrometeorological Institute in 2006 selected a new period for the evaluation of hydrological characteristics of mean daily discharge series. Initially, two fortyyear long periods were considered: 1961-2000 and 1966-2005 and the period of 1961-2005 was finally accepted. Comparison of the still used 1931-1980 period with the new one was carried out using the data from 50 Czech gauging stations that had continuous data time series. The mean long-term runoff of Czech rivers changed very little from 1931-1980 to 1961-2005. Comparison of the variation coefficients brought similar results. However, among specific M-day discharges the low flow values (e.g. Q355d) showed a significant increase. This might reflect not only natural causes but could suggest anthropogenic factors as well. Trend analyses started with testing mean annual runoff at 65 Czech gauging stations that were not influenced by human activity. 34 stations showed an increasing trend and 31 a decreasing trend. However, the trend was statistically significant only at one station. Trends of individual months dramatically differentiate. In January through March the increasing trends prevail. March trends show the highest number of stations with a significant increase. The three following months are complete opposites in which decreasing trends dominate. In May and June, not a single increase was recorded and many decreases were statistically significant. Almost no significant trends were examined in the months of the second half of the year. and V posledních měsících se oddělení povrchových vod ČHMÚ zabývalo výběrem období pro výpočet nových hydrologických charakteristik M-denních průtoků na českých tocích. Uvažována byla čtyřicetiletí 1961-2000 a 1966-2005, nakonec však bylo přijato období 1961-2005. Na datech z 50 vodoměrných stanic, které měly nepřerušené řady pozorování, bylo uskutečněno první srovnání statistických charakteristik období 1931-1980 (doposud používané) a 1961-2005. U nového období byly u neovlivněných stanic vyhodnoceny trendy průměrných ročních průtoků a průtoků jednotlivých měsíců.
Forecasting the river flow level and volumes are essential to making the most efficient use of rivers and in minimizing damages to flood. A relationship between the released discharges from Mosul dam and river levels in Mosul station is predicted with high correlation coefficient for the two periods within the year (rainy and non-rainy months). A time series technique analysis for predicting the best relevant statistical model for future forecasting of Tigris River levels within the river reach between Mosul dam and Mosul city was applied. Deterministic prediction of the water levels of Tigris River within the reach between Mosul dam and Mosul city will help to avoid the increasing of the water level within the river reach to minimize the damages which may occur due to inundation areas. The average monthly Tigris River stages of Mosul station for the two periods before and after Mosul dam construction are constant with a reduction in the average value of the maximum water stages and increasing the average value of the minimum water stages after Mosul dam construction. Through the statistical analysis of the time series of the available river stages data at Mosul station, a repetition in the annual cycle in the water stages before Mosul dam construction and a decreasing trend through this period was observed. Winter model is the most suitable time series model to forecast the Tigris River stages or any missing data in the future in the Tigris River reach between Mosul dam and Mosul city. and Predpoveď vodných stavov a prietokov vodných tokov je podstatná pre ich efektívne využitie a minimalizáciu povodňových škôd. Závislosť medzi výtokom z priehrady Mosul a stavom vody v rieke v stanici v Mosule bola určená s vysokou hodnotou súčiniteľa korelácie pre dve obdobia roka (zrážkové a bezzrážkové obdobie). Na analýzu časových radov sme použili najvhodnejší štatistický model, ktorý umožnil predpoveď vodných stavov Tigrisu medzi priehradou Mosul a mestom Mosul. Deterministická predpoveď vodných stavov Tigrisu môže pomôcť minimalizovať škody v záplavovom území. Priemerné mesačné stavy vody v hydrologickej stanici v Mosule na rieke Tigris pre dve obdobia - pred vybudovaním priehrady Mosul a po ňom - sa nemenia, ale priemerné hodnoty maximálnych stavov vody po vybudovaní priehrady v Mosule sa znížili, naopak minimálne hodnoty vodných stavov sa zvyšujú. Štatistickou analýzou časových radov dostupných vodných stavov v stanici Mosul sa zistila nemennosť vodných stavov počas ich ročného cyklu pred vybudovaním priehrady Mosul a po jej vybudovaní. Najvhodnejším modelom časových radov pre predpoveď vodných stavov v rieke Tigris, alebo pre predpoveď chýbajúcich hodnôt vodných stavov v úseku rieky medzi priehradou a mestom Mosul, sa ukázal zimný model.
An analytical solution for the creeping flow of an inelastic fluid past a solid sphere has been obtained using an empirical 3-parameter fluid model. The governing equations of motion have been solved aproximately using a perturbation approach. Expressions have been obtained for the Stokes stream function and the drag experienced by the stationary sphere. It is shown that the drag for the non-Newtonian fluid is greater than the one predicted by the classical Stokes formula. and Použitím trojparametrického empirického modelu tekutiny sme získali analytické riešenie pomalého prúdenia neelastickej tekutiny okolo pevnej gule. Pohybové rovnice boli riešené približne metódou malých rozruchov. Získali sme vzťahy pre výpočet Stokesovej prúdovej funkcie a pre odpor stojacej gule. Bolo ukázané, že tento odpor z obtekania je pre nenewtonskú tekutinu väčší, ako vyplýva z klasického vzťahu Stokesa pre newtonskú tekutinu.
We consider a special dilatant fluid model for which the apparent viscosity can be expressed as a polynomial in the second scalar invariant of the rate of strain tensor. The model has been used to investigate the steady plane Couette flow of a non-Newtonian fluid through a channel with suction, assumed small, at the lower porous wall. The introduction of a similarity transformation in the perturbed governing partial differential equations of the flow leads to a system of coupled non-linear ordinary differential equations. The solutions of these equations have been obtained analytically as a power series in the suction parameter . The combined effects of the non-Newtonian and the suction parameters on the longitudinal and transverse velocity profiles as well as the skin friction, have been discussed. The validity of the analytical solutions has also been checked with the corresponding numerical solutions for small values of the governing parameters. and Štúdia sa zaoberá sa špeciálnym modelom nenewtonskej tekutiny, pre ktorú sa môže skutočná viskozita vyjadriť vo forme polynomickej závislosti na druhom skalárnom invariante tenzora rýchlosti deformácie. Model bol využitý na štúdium ustáleného Couetteho rovinného prúdenia nenewtonskej tekutiny v kanáli so saním cez porézne steny. Zavedenie transformácie podobnosti do lineanizovaných parciálnych diferenciálnych rovníc vedie k systému obyčajných nelineárnych diferenciálnych rovníc. Ich riešenie sme získali vo forme potenčného radu od sacieho parametra λ. Analyzovali sme vplyv rozťažnosti tekutiny a sacieho parametra na pozdĺžny a priečny rýchlostny profil, ako aj na povrchové trenie. Platnosť analytického riešenia sme porovnali s numerickým riešením pre malé hodnoty použitých parametrov.
Water resource has become a guarantee for sustainable development on both local and global scales. Exploiting water resources involves development of hydrological models for water management planning. In this paper we present a new stochastic model for generation of mean annul flows. The model is based on historical characteristics of time series of annual flows and consists of the trend component, long-term periodic component and stochastic component. The rest of specified components are model errors which are represented as a random time series. The random time series is generated by the single bootstrap model (SBM). Stochastic ensemble of error terms at the single hydrological station is formed using the SBM method. The ultimate stochastic model gives solutions of annual flows and presents a useful tool for integrated river basin planning and water management studies. The model is applied for ten large European rivers with long observed period. Validation of model results suggests that the stochastic flows simulated by the model can be used for hydrological simulations in river basins.
In the context of discussed global climate change the emphasis is placed mainly on the adaptability of the water management methodology at present time. Therefore a questionnaire inquiry oriented to the perception of the climate change impact and current state of adaptation strategies implementation was carried out and evaluated. The research was realised among the water management experts in six large transboundary basins: Elbe, Rhine, Guadiana, Amudaria, Orange and Nile. The questionnaire was divided into six parts concerning for example: expected climate change impacts, adaptation measures, drivers for development of adaptation strategy, adaptation barriers etc. Responses were evaluated with rating and the dominant answers and lists of priority were established. Results were evaluated looking for overall conclusions in all or almost all regions, as well as conclusions for each region. The main benefit of the research lies in the evaluation based principally on the opinions of policy makers, stakeholders and water managers in the river basins not on the climate scenarios. The outcomes have proved understanding of the climate change impact issue over all six basins, only the approach to adaptation is partly different. The historical development of water management in the basin influences the perception as well. and V současnosti se v souvislosti s diskutovanou globální změnou klimatu stále zvyšuje důraz na požadavek adaptability metodik uplatňovaných ve vodním hospodářství. Z tohoto důvodu byl v šesti vybraných světových povodích uskutečněn a vyhodnocen dotazníkový průzkum mezi oslovenými experty se zaměřením na chápání důsledků klimatické změny a na zjištění aktuálního stavu implementace adaptačních opatření v povodí. Šlo o povodí Labe, Rýna, Guadiany, Amudarji, Orange a Nilu. Dotazník byl rozdělen do několika sekcí týkající se např. očekávaných dopadů klimatické změny, adaptačních opatření, podnětů pro návrh strategie adaptace, bariér adaptace atd. Dotazníky byly vyhodnocovány pomocí bodování a stanoveny vždy dominantní odpovědi a seznamy priorit. Výsledky byly vyhodnoceny vždy z obecného hlediska i v rámci konkrétního povodí a vzájemně porovnány. Významným přínosem bylo, že průzkum byl založen na závěrech a zkušenostech expertů, nikoli na klimatických scénářích. Ukázalo se, že ve všech povodích bylo dosaženo pochopení problému dopadu klimatické změny, jen přístup k vlastní adaptaci je částečně odlišný. Záleží rovněž na historickém vývoji vodního hospodářství v daném regionu
The local scour around bridge piers influences their stabilities and plays a key role in the bridge failures. The estimation of the maximum possible scour depth around bridge piers is an important step in the design of the bridge pier foundations. In this study, the temporal evolution of local scour depths as well as the equilibrium scour depths were analyzed.
The experiments were carried out in a rectangular flume by using uniform sediment with median diameter of 3.5 mm and geometric standard deviation of 1.4. The diameters of the tested circular bridge piers were 40 mm, 80 mm, 150 mm and 200 mm. The flow and scour depths were determined by ultrasonic sensors. The experiments were realized in clear water conditions with various constant flow rates.
The experimental findings were compared with those calculated from some empirical equations existing in the literature. A new empirical relation involving the flow intensity, the relative water depth and the dimensionless time is also introduced. The advantage of this proposed relation is that the only parameter requiring the calculation is the critical velocity, other parameters being known geometric and hydraulic parameters. The performance of this relation was tested by using experimental data available in the literature, and a satisfactory compatibility was revealed between the experimental and numerical results.