Einstein-Barbarossa velocity or resistance equation (1952) is widely used to find resistance to flow in alluvial channel. In order to validate the equation in all ranges (smooth to rough); they introduced a correction factor based on the Nikuradse measurement. This correction factor is determined from the graphical method, which can be erroneous. Present work reanalyzes the Nikuradse measurements and gives an analytical formulation for the correction factor. and Einsteinova-Barbarossova rovnica (1952) sa často používa na určenie odporu voči prúdeniu v kanáloch. Autori do nej zaviedli korekčný faktor, založený na meraniach Nikuradzeho, aby overili platnosť rovnice v celom rozsahu drsností (od hladkých stien po drsné). Tento korekčný faktor sa určuje grafickou metódou, ktorá môže viesť k chybným výsledkom. V tejto práci sa znova analyzujú výsledky Nikuradzeho meraní a je navrhnutá analytická formulácia na výpočet korekčného faktora.
This study shows a comprehensive simulation of water and sediment fluxes from the catchment to the reach scale. We describe the application of a modelling cascade in a well researched study catchment through connecting stateof-the-art public domain models in ArcGIS. Three models are used consecutively: (1) the hydrological model SWAT to evaluate water balances, sediment input from fields and tile drains as a function of catchment characteristics; (2) the onedimensional hydraulic model HEC-RAS to depict channel erosion and sedimentation along a 9 km channel onedimensionally; and (3) the two-dimensional hydraulic model AdH for simulating detailed substrate changes in a 230 m long reach section over the course of one year. Model performance for the water fluxes is very good, sediment fluxes and substrate changes are simulated with good agreement to observed data. Improvement of tile drain sediment load, simulation of different substrate deposition events and carrying out data sensitivity tests are suggested as future work. Main advantages that can be deduced from this study are separate representation of field, drain and bank erosion processes; shown adaptability to lowland catchments and transferability to other catchments; usability of the model’s output for habitat assessments.
Twelve predictive bedload sediment transport equations are rated against 14 sets of gravel-bed river field data collected by handheld bedload sampler in Narmab River, northeastern Iran. To evaluate these formulas two types of grain size namely bedload and bed material were used. The results show that the equations of Engelund and Hansen, Van Rijn and Einstein perform well with bed material grain size, while Shocklitsch, Meyer-Peter and Mueller, and Frijlink yield the best results using the bedload grain size.
This paper presents the results of an experimental study to quantify the effects of bed slope and relative submergence on incipient motion of sediment under decelerating flows. Experiments were conducted in an experimental tilting-flume of 8 m long 0.4 m wide and 0.6 m deep with glass-walls. Three uniform sediments with median grain sizes of 0.95, 1.8 and 3.8 mm and three bed slopes of 0.0075, 0.0125 and 0.015 were used under decelerating flow. The main conclusion is that the Shields diagram, which is commonly used to evaluate the critical shear stress, is not suitable to predict the critical shear stress under decelerating flows.
In Tunisia especially in the Medjerda watershed the recurring of floods becoming more remarkable. In order to limit this risk, several studies were performed to examine the Medjerda hydrodynamic. The analysis of results showed that the recurrences of floods at the Medjerda watershed is strongly related to the sediment transport phenomena. Initially, a one dimensional modelling was conducted in order to determine the sediment transport rate, and to visualize the river morphological changes during major floods. In continuity of this work, we will consider a two-dimensional model for predicting the amounts of materials transported by the Medjerda River. The goal is to visualize the Medjerda behaviour during extreme events and morphological changes occurred following the passage of the spectacular flood of January 2003. As a conclusion for this study, a comparative analysis was performed between 1D and 2D models results. The objective of these comparisons is to visualize the benefits and limitations of tested models. The analysis of the results demonstrate that 2D model is able to calculate the flow variation, sediment transport rates, and river morphological changes during extreme events for complicated natural domains with high accuracy comparing with 1D Model.
This article presents the numerical modelling of hydrodynamics and sediment transport processes in the seasonal Pathri Rao River, which flows in the Northern part of India. Modelling is made by the coupled application of the hydrodynamic model called TELEMAC-2D and the morphodynamic model called SediMorph. The hydrodynamic model results are validated with the observed data and it has been found that the present model provides reasonable predictions. Likewise, the validation of the morphodynamic model is also presented. For this purpose, the suspended and bed load transport modules are validated separately for four runoff events observed during the investigations. The validation of the former is approached by comparing the depth-averaged suspended transport concentrations against experimental measurements made at the make-shift gauging station and subsequent comparison against experimental measurements. On the other hand, due to non-availability of the observed values on bed load sediment transport, the bed load sediment transport and bed evolution numerical results could not be validated quantitatively and was approached only on qualitative basis. In general, both validations present an acceptable agreement with measurements and scientific facts. Further, this study demonstrates that the coupled TELEMAC-2D/SediMorph system could be used with confidence for practical applications in the Pathri Rao River. and Príspevok obsahuje výsledky numerického modelovania hydrodynamických javov a transportu sedimentov v občasnom toku Pathri Rao, v severnej časti Indie. Procesy boli modelované zdvojenou aplikáciou hydrodynamického modelu TELEMAC-2D a morfodynamického modelu SediMorph. Výsledky modelovania hydrodynamickým modelom boli verifikované s využitím pozorovaných hodnôt; bolo zistené, že model dáva akceptovateľné výsledky. Prezentuje sa tiež verifikácia morfodynamického modelu. Počas epizód odtoku bol transport suspendovaných častíc a častíc transportovaných po dne toku verifikovaný osobitne. Verifikácia transportu suspendovaných častíc bola uskutočnená porovnaním hĺbkovo spriemerovanými koncentráciami suspendovaných častíc s meranými hodnotami na prietokomerných staniciach. Pre nedostatok pozorovaných údajov o dnovom transporte, údaje o ňom a o zmenách morfológie toku mohli byť verifikované len kvalitatívne. Záverom, obe verifikácie dali akceptovateľnú zhodu s výsledkami meraní a existujúcimi vedeckými poznatkami. Okrem toho výsledky štúdie demonštrujú schopnosť zdvojených modelov TELEMAC-2D/SediMorph získavať spoľahlivé výsledky pri aplikácii na rieke Pathri Rao.
The focus of this paper is on the analysis of the influence of near-bed turbulence structures with the inclusion of existing coherent structures on the entrainment of saltating particles in a water stream from the Lagrangian perspective. The interactions between turbulence structures and initiation of particles movement is the key for better understanding of the physics of sediment transport and particles behaviour. These aims are addressed by use of a 3D relevant model of spherical saltating particles, in which a special procedure has been designed to produce coherent structures. In this method, the spectra of turbulent kinetic energy, consisting of four ranges, are used to generate the time series of turbulent velocities in the streamwise, vertical and transversal directions. Numerical results suggest that the initiation of sediment movement is strongly correlated to positive streamwise velocity fluctuations and as such, supports earlier laboratory experimental and field observations, showing that the sweeps and outward interactions play a crucial role in the initiation of saltating particles’ movement.
The friction conditions at the top of a mobile bed are discussed for flows in the upper-plane-bed regime, i.e. for the flows with values of the bed Shields parameter larger than approximately 0.6. A special attention is devoted to flows of the bed Shields parameter bigger than 2. Experimental data for flows at high bed shear are collected from literature and new data are added from own measurements of flows of a 1.36-mm sand slurry in the 100-mm pipe loop of the Institute of Hydrodynamics. The database represents flows of very different solids and covers friction conditions within a broad range of Shields parameters up to the maximum value of about 23. The paper analyses the data in order to evaluate a relationship among the equivalent roughness of the top of the bed and other relevant parameters. A semi-empirical formula is proposed that relates the equivalent roughness to the bed Shields parameter, the ratio of flow velocity and particle settling velocity, and the ratio of flow hydraulic radius and particle diameter. The formula is applicable primarily to flows of combined load (contact- and suspended loads together). and Příspěvek se zabývá mechanismem tření na povrchu erodovatelného dna za podmínek horního režimu pohybu splavenin nad plochým dnem, to jest při hodnotách Shieldsova parametru větších než přibližně 0,6. Zvláštní pozornost je věnována proudění při Shieldsově parametru větším než 2. Z literatury byla sebrána experimentální data pro proudění za vysokých smykových napětí, ke kterým byla přidána nová data z vlastních měření s pískem velikosti středního zrna 1,36 mm v potrubí průměru 100 mm trubního okruhu Ústavu pro hydrodynamiku AV ČR. Databáze obsahuje výsledky měření pro částice různých vlastností v širokém rozsahu hodnot Shieldsova parametru až do hodnoty okolo 23. Příspěvek analyzuje data za účelem stanovení závislosti hydraulické drsnosti povrchu sedliny na ostatních parametrech proudění. Je navržen semiempirický vztah, který předpokládá závislost hydraulické drsnosti na Shieldsově parametru, poměru rychlosti proudění k usazovací rychlosti částic a poměru hydraulického poloměru průtočného profilu k velikosti částic. Tento vztah se doporučuje především pro proudění nesoucí jak dnové splaveniny, tak suspendované částice.
Incipient motion is the critical condition at which bed particles begin to move. Existing relationships for incipient motion prediction do not consider the effect of seepage. Incipient motion design of an alluvial channel affected from seepage requires the information about five basic parameters, i.e., particle size d, water depth y, energy slope Sf, seepage velocity vs and average velocity u. As the process is extremely complex, getting deterministic or analytical form of process phenomena is too difficult. Data mining technique, which is particularly useful in modeling processes about which adequate knowledge of the physics is limited, is presented here as a tool complimentary to model the incipient motion condition of alluvial channel at seepage. This article describes the radial basis function (RBF) network to predict the seepage velocity vs and average velocity u based on experimental data of incipient condition. The prediction capability of model has been found satisfactory and methodology to use the model is also presented. It has been found that model predicts the phenomena very well. With the help of the RBF network, design curves have been presented for designing the alluvial channel when it is affected by seepage. and Návrh aluviálneho kanála s ohľadom na iniciáciu pohybu dna koryta, ovplyvneného priesakom vyžaduje informáciu o piatich základných parametroch: veľkosti častice d, hĺbke vody y, sklone čiary energie Sf, rýchlosti priesaku vs a priemernej rýchlosti prúdenia u. Pretože proces je extrémne zložitý, získať deterministickú alebo analytickú formu riešenia je ťažké. Príspevok opisuje získavanie údajov (data mining technique), bežne používané pri modelovaní. Opisuje aj sieť tzv. ''radial basis function (RBF)'' na prognózu rýchlosti priesaku vs a priemernej rýchlosti u; výpočet je založený na experimentálnych hodnotách v štádiu začínajúceho sa pohybu častíc v koryte. Bola konštatovaná dobrá schopnosť modelu prognózovať začínajúci pohyb; je uvedená tiež metodológia používania modelu. Bolo zistené, že model predpovedá uvedené javy veľmi dobre. Je tu opísaný návrh aluviálneho kanála ovplyvneného priesakom pomocou návrhových kriviek vytvorených pomocou siete RBF.
The paper describes results of validation of authors' recently proposed formulae for sediment transport and bed friction in the upper plane bed regime using laboratory experiments in a pressurized pipe. Flows of mixture of water and fine to medium ballotini (d50 = 0.18 mm) were observed in a rectangular pipe (51 x 51 mm) with a deposit at the bottom of the pipe. A comparison of test results with transport-formula predictions shows a satisfactory match confirming a good prediction ability of the proposed transport formula at high bed shear. A prediction ability of the friction formulae appears to be less convincing but still reasonable. A joint use of the formulae for transport and friction predicts the delivered concentration of transported sediment within the accuracy range of ± 40 per cent for flows in which transported sediments strongly affect the bed friction, i.e. for flows with delivered concentration of sediment higher than say 3 per cent.