L'hydroélectricité est la première des énergies renouvelables électriques. Sa production repose en partie sur des centrales au fil de l'eau dont les capacités de modulation sont encore faiblement exploitées. Les capacités d'ajustement des centrales hydrauliques sont d'autant plus essentielles aujourd'hui que la pénétration d'énergies intermittentes dans un mix énergétique décarboné est indispensable.Dans cette thèse, nous nous intéressons aux centrales au fil de l'eau turbinant le débit de cours d'eau aux marnages limités. Les enjeux de sûreté, notamment liés au multi-usage de l'eau, ainsi que la perspective de moduler les débits turbinés nous ont amenés à considérer le problème de la modélisation des écoulements dans les canaux reliant les centrales au fil de l'eau. Les équations de Saint-Venant sont les plus pertinentes pour ce type de modélisation. Nous avons proposé plusieurs approches à partir de ces dernières pour caractériser analytiquement la dynamique de l'écoulement à des variations de débits turbinés. Nous avons considéré la dynamique du système autour d'un régime fluvial stationnaire non-uniforme caractéristique des configurations hydroélectriques. La première approche est basée sur une approximation basses fréquences. La seconde approche est basée sur une méthode de réduction de modèle avec une paramétrisation selon le débit support. Une troisième approche est proposée en considérant explicitement la recherche d'une solution approximée des équations de Saint-Venant linéarisées autour d'une configuration hydroélectrique. Un critère spatio-fréquentiel est alors introduit, l'existence d'un biais en basses fréquences nous conduit à proposer un modèle d'ordre réduit dont la dynamique basses fréquences est imposée selon les résultats de la première approche. La solution exprimée sous forme de fonctions de transfert, comme pour les deux précédentes approches, met en évidence explicitement la présence de modes de résonance/anti-résonance. Finalement, nous illustrons les résultats vis à vis de simulations non-linéaires et de données réelles et proposons une régulation de niveau basée sur cette dernière approche. / New challenges arise from energy transition toward a more sustainable energy mix. Hydropower is already the main source of renewable electricity. In order to integrate a massive increase in generation of renewable intermitent energies, improving the flexibility of run-of-the-river hydropower plants becomes essential. In this thesis, we focus on run-of-the river power plants facing water level constraints. Safety issues, partly due to the multiple uses of water, and the opportunity to modulate turbined flow rates have led us to adress the problem of flow modelisation in open channels that connect run-of-the rivers facilities with each others. An accurate model is provided by the Saint-Venant equations. From these latters, we have proposed different approaches to characterize analytically the flow dynamics in response to turbined flow variations. The system dynamics have been considered around a subcritical stationary non-uniform regime typical of hydroelectric configuration. The first approach is based on a low frequency approximation. The second approach is based on a parametric model reduction technique. By seeking explicitly an approximate solution to the linearized Saint-Venant equations around an hydroelectric configuration, we have proposed a third approach. A space-frequency criterion is introduced, which shows a bias in low frequency. Results of the first approach are then used to propose a reduced order model asymptotically exact in low frequency. As for the two other approaches, the solution takes the shape of parametric transfer functions. Resonance/anti-resonance modes explicitly appear. Finally, comparisons with non-linear simulations taking into account actual real data are discussed and a water level controller is developed based on the last approach.

Flow modelling in a compound channel is a complex matter. Indeed, due to the smaller velocities in the floodplains than in the main channel, shear layers develop at the interfaces between these subsections, and the channel conveyance is affected by a momentum transfer corresponding to this shear layer, but also to possible geometrical changes in a non-prismatic reach. In this work, a one-dimensional approach, the Exchange Discharge Model (EDM), is proposed for such flows. The EDM accounts for the momentum transfer between channel subsections, estimated as proportional to the velocity gradient and to the discharges exchanged through the interface; where two main processes are identified : (1) the turbulent exchange, due to the shear-layer development; and (2) the geometrical transfer, due to cross-sectional changes. The EDM is successfully validated for discharge prediction, but also for water-profile computation, through comparison with existing laboratory and field measurements. The momentum transfer due to turbulent exchanges is then studied experimentally, theoretically and numerically. At first, new experimental data, obtained by using Particle Tracking Velocimetry techniques, are presented : the periodical vortex structures that develop in the shear layer are clearly identified and characterised. Secondly, a hydrodynamic linear stability analysis enables to predict quite successfully the wave length of some observed vortices. Lastly, an Unsteady-RANS numerical method is used to simulate the perturbation development. The estimated vortex wave lengths agree again with the measurements and the theoretical predictions, although vortices merging occurs in the simulation results, which was actually not observed experimentally. The velocity-profile prediction is found improved when the effect of vortices is considered, thanks to the corresponding additional shearing. The geometrical transfer is also investigated experimentally and numerically. Novel experiments are designed, with the measurements of the flow in a compound channel with symmetrically narrowing floodplains. The mass transfer and the evolution of the flow distribution along the channel length are clearly observed. A significant additional head loss due to this transfer is measured, in accordance with the EDM hypothesis. Measured water profiles are finally compared successfully with the EDM predictions. In addition to the EDM development and validation, the so-called Lateral Distribution Method (LDM) is also investigated and the significance of the secondary-currents models proposed by previous authors for this method is discussed. When considering the velocity-profile prediction, the effect of these helical secondary currents is again clearly highlighted, by using dispersion terms in the Saint-Venant equations. However, the actual physical meaning of the related dispersion coefficients remains uncertain. In addition, an extended LDM is also proposed and discussed for non-prismatic flow modelling, using the new narrowing-channel data set./La modélisation des écoulements dans les rivières à plaines inondables est particulièrement complexe. En effet, la vitesse de l'eau étant plus faible sur la plaine d'inondation que dans le lit mineur, une couche de cisaillement se développe à l'interface entre ces sous-sections. La débitance totale de la rivière est dés lors réduite, à cause du transfert de quantité de mouvement qu'occasionne la présence de la couche de cisaillement, mais aussi de part les changements de géométrie qui peuvent se produire dans un lit non-prismatique. La présente thèse propose, pour la représentation de tels écoulements, une nouvelle approche uni-dimensionnelle dénommée Modèle des Débits d'Echange ("Exchange Discharge Model" – EDM). Le transfert de quantité de mouvement entre les soussections de la rivière est pris en compte par l'EDM comme étant proportionnel au gradient de vitesse entre celles-ci et aux débits échangés à travers leur interface. A cette interface, deux phénomènes sont essentiellement présents : (1) un échange turbulent, dû au développement de la couche de cisaillement; et (2) un transfert géométrique, correspondant aux changements de section. L'EDM est validé avec succès pour la prédiction du débit et pour le calcul de lignes d'eau, par comparaison avec des données existantes de laboratoire et de terrain. Le transfert de quantité de mouvement dû à l'échange turbulent est ensuite étudié expérimentalement, théoriquement et numériquement. De nouvelles mesures sont obtenues, au moyen d'une technique de vélocimétrie par suivi de particules. Les structures périodiques qui se développent dans la couche de cisaillement sont clairement identifiées et caractérisées. Deuxièmement, une analyse linéaire de stabilité hydrodynamique permet de prédire théoriquement les longueurs d'onde de quelques tourbillons qui ont été observés expérimentalement, et ce avec succès. Enfin, un modèle numérique, de type "Unsteady-RANS", est utilisé pour simuler la croissance des tourbillons dans la couche de cisaillement. Encore une fois, les longueurs d'onde obtenues correspondent relativement bien avec les valeurs mesurées et prédites théoriquement; bien que les coalescences de tourbillons qui se produisent numériquement n'aient pas été observées expérimentalement. La prédiction des profils de vitesse est améliorée, lorsque l'effet des tourbillons est considéré, grâce à la contrainte de cisaillement additionnelle que ceux-ci génèrent. Les transferts géométriques sont également explorés expérimentalement et numériquement. Une nouvelle campagne expérimentale a été réalisée, en considérant l'écoulement dans un lit composé symétrique, dont les plaines d'inondation se rétrécissent progressivement. Le transfert de masse entre sous-sections et la redistribution des débits qui lui est associée sont clairement observés au long du canal. Une importante perte de charge additionnelle due à ce transfert est mesurée, en concordance avec les hypothèses de l'EDM. Finalement, les lignes d'eau mesurées sont reproduites avec succès par un calcul utilisant l'EDM. En complément au développement et à la validation de l'EDM, la "Lateral Distribution Method" (LDM) est également utilisée, avec pour objectif la clarification du rôle des termes de courants secondaires proposés par différents auteurs. Par rapport à la prédiction du profil de vitesse, l'effet de ces courants secondaires est très marqué. Il est ici reproduit en utilisant des termes de dispersion dans les équations de Saint-Venant. Cependant, le sens physique des valeurs des coefficients de dispersion qui doivent être utilisés est discutable. Par ailleurs, une LDM étendue, pour les écoulement en lits nonprismatiques, est proposée et commentée, en utilisant le nouveau jeu de données pour le canal convergent.

Thickened tailings production and disposal continue to grow in importance in the mining industry. In particular, the transport of oil sands tailings is of interest in this study. These tailings must be in a homogeneous state (non-segregating) during pipeline flow and subsequent discharge. Tailings are often transported in an open channel or flume. Slurries containing both clay and coarse sand particles typically exhibit non-Newtonian rheological behaviour. The prediction of the flow behaviour of these slurries is complicated by the limited research activity in this area. As a result, the underlying mechanisms of solids transport in these slurries are not well understood. To address this deficiency, experimental studies were conducted with kaolin clay slurries containing coarse sand in an open circular channel.<p> A numerical model has been developed to predict the behaviour of coarse solid particles in laminar, open channel, non-Newtonian flows. The model involves the simultaneous solution of the Navier-Stokes equations and a scalar concentration equation describing the behaviour of coarse particles within the flow. The model uses the theory of shear-induced particle diffusion (Phillips et al., 1992) to provide a number of relationships to describe the diffusive flux of coarse particles within laminar flows. A sedimentation flux has been developed and incorporated into the Phillips et al. (1992) model to account for gravitational flux of particles within the flow. Previous researchers (Gillies et al., 1999) have shown that this is a significant mechanism of particle migration.<p> The momentum and concentration partial differential equations have been solved numerically by applying the finite volume method. The differential equations are non-linear, stiff and tightly coupled which requires a novel means of analysis. Specific no-flux, no-slip and no-shear boundary conditions have been applied to the channel walls and free surface to produce simulated velocity and concentration distributions. The results show that the model is capable of predicting coarse particle settling in laminar, non-Newtonian, open channel flows. The results of the numerical simulations have been compared to the experimental results obtained in this study, as well as the experimental results of previous studies in the literature.

Thickened tailings production and disposal continue to grow in importance in the mining industry. In particular, the transport of oil sands tailings is of interest in this study. These tailings must be in a homogeneous state (non-segregating) during pipeline flow and subsequent discharge. Tailings are often transported in an open channel or flume. Slurries containing both clay and coarse sand particles typically exhibit non-Newtonian rheological behaviour. The prediction of the flow behaviour of these slurries is complicated by the limited research activity in this area. As a result, the underlying mechanisms of solids transport in these slurries are not well understood. To address this deficiency, experimental studies were conducted with kaolin clay slurries containing coarse sand in an open circular channel.<p> A numerical model has been developed to predict the behaviour of coarse solid particles in laminar, open channel, non-Newtonian flows. The model involves the simultaneous solution of the Navier-Stokes equations and a scalar concentration equation describing the behaviour of coarse particles within the flow. The model uses the theory of shear-induced particle diffusion (Phillips et al., 1992) to provide a number of relationships to describe the diffusive flux of coarse particles within laminar flows. A sedimentation flux has been developed and incorporated into the Phillips et al. (1992) model to account for gravitational flux of particles within the flow. Previous researchers (Gillies et al., 1999) have shown that this is a significant mechanism of particle migration.<p> The momentum and concentration partial differential equations have been solved numerically by applying the finite volume method. The differential equations are non-linear, stiff and tightly coupled which requires a novel means of analysis. Specific no-flux, no-slip and no-shear boundary conditions have been applied to the channel walls and free surface to produce simulated velocity and concentration distributions. The results show that the model is capable of predicting coarse particle settling in laminar, non-Newtonian, open channel flows. The results of the numerical simulations have been compared to the experimental results obtained in this study, as well as the experimental results of previous studies in the literature.

Η παρούσα Διατριβή Μεταπτυχιακού Διπλώματος Ειδίκευσης, πραγματεύεται την ανάλυση της τυρβώδους ροής σε ανοικτούς αγωγούς στον πυθμένα των οποίων ενυπάρχουν σχηματισμοί μορφής θινών (dunes). Μελετήθηκε η περίπτωση 5 θινών οι οποίες τοποθετήθηκαν στον πυθμένα ενός καναλιού βάθους d θεωρώντας μόνιμη ροή. Για την επίλυση χρησιμοποιήθηκαν οι εξισώσεις RANS, ενώ για το κλείσιμο της τύρβης χρησιμοποιήθηκαν τα μοντέλα μιας εξίσωσης Spalart-Allmaras και δύο εξισώσεων k-ε. Η διαχείριση της ελεύθερης επιφάνειας έγινε με την μέθοδο VOF, ενώ η αριθμητική επίλυση βασίστηκε στην μέθοδο των πεπερασμένων όγκων και πραγματοποιήθηκε με τον εμπορικό κώδικα FLUENT 6.1.2. Για την ροή στον ανοικτό αγωγό, στον πυθμένα του οποίου ενυπήρχαν οι σχηματισμοί, θεωρήθηκε αριθμός Reynolds , κλίση πυθμένα και συντελεστή Manning , ο οποίος αντιστοιχεί σε ισοδύναμο ύψος τραχύτητας τοιχωμάτων . Προκειμένου να επαληθευθεί η ακρίβεια της αριθμητικής μεθόδου, επιλύθηκε η περίπτωση του επίπεδου πυθμένα και τα αποτελέσματα συγκρίθηκαν με γνωστά πειραματικά αποτελέσματα καθώς και αποτελέσματα τα οποία προέκυψαν από την μονοδιάστατη ανάλυση της ροής πάνω από επίπεδο πυθμένα. Τα αποτελέσματα βρέθηκαν σε καλή συμφωνία, κυρίως για την κατανομή της ταχύτητας, ενώ για την τύρβη υπήρχε πολύ καλή συμφωνία κυρίως πλησίον του πυθμένα. Για το πρόβλημα των θινών εξετάσθηκαν: (α) τρεις περιπτώσεις με σταθερό άνοιγμα θίνης προς βάθος ροής και διαφορετικά ύψη θινών , 0.25 και (β) τρεις περιπτώσεις με σταθερή αναλογία ανοίγματος προς ύψος και ύψη θινών όπως στην περίπτωση (α). Η ανάλυση έδειξε ότι το μέσο προφίλ της ελεύθερης επιφάνειας μειώνεται στην διεύθυνση της ροής, ενώ πάνω από κάθε θίνη το πλάτος της ανύψωσης της ελεύθερης επιφάνειας αυξάνει με την αύξηση του ύψους και του ανοίγματος των θινών. Η κατανομή των διατμητικών τάσεων παρουσιάζει κυματοειδή μορφή υπεράνω των θινών και αυξάνει αυξανομένου του ύψους τους και με την μείωση του ανοίγματός τους. Πίσω από κάθε θίνη δημιουργείται θύλακας ανακυκλοφορίας της ροής και ο λόγος της απόστασης του σημείου επανακόλλησης προς το ύψος της θίνης είναι . / The spatial development of the turbulent open channel flow over bottom with five dunes is studied. The steady-state flow is described by the RANS equations utilizing either the or the Spalart-Allmaras turbulence models. The free-surface treatment is based on the VOF formulation, while the numerical solution is based on a finite-volume, unstructured-grid discretization. Lengths are rendered dimensionless by the inflow channel depth, while velocities by the mean inflow velocity. The inflow Reynolds number is , the channel slope is and the Manning coefficient is , which results to a roughness height . In order to verify the numerical methods, the flat bottom case is considered and the numerical predictions are compared to known experimental data. We get very good agreement for the velocity distributions, while for turbulence the results are very good close to the bottom and poor close to the free surface. Then, we consider: (a) three cases with constant dune length and differing dune heights 0.15, 0.25, 0.35, and (b) three cases with constant ratio and dune heights as in (a). The spatial development of the free-surface elevation over the dunes presents a negative mean slope for all cases. Locally over each dune, the amplitude of the free-surface elevation increases with increasing dune height and increasing dune length. The spatial development of the wall shear stress presents a wave-like behavior and its amplitude increases with increasing dune height and decreasing dune length. On every dune crest the streamwise velocity profile is steeper than the universal logarithmic profile similar to the behavior in a favorable pressure gradient boundary layer. The detachment at each dune crest is followed by a recirculation region and reattachment at a distance from the dune trough.

Investigations into the turbulent flows in uniform and nonuniform open channels by previous researchers have demonstrated the requirement and importance of understanding the turbulence structures and energy losses due to irregularity in non- uniform open channels. Responding to this requirement, the turbulent flow in one special non-uniform open channel has been studied both experimentally and numerically. This non-uniform open channel was designed so that its width and bed level vary while its cross-sectional area below the water surface keeps constant. An upstream uniforzn open channel is attached to the non-uniform open channel to establish fully developed turbulent flow conditions. A downstream uniform channel is also attached for control of water depth and downstream flow condition. The experimental study consisted of measurements of turbulent velocity field with a LDV (Laser Doppler Velocimetry) and measurements of boundary shear stress (BSS) with Roving Preston tubes in the experimental channel. Turbulent velocity components in the longitudinal and vertical directions were measured with the LDV in forward scattering mode and the laser beams were focused from the channel side wall into the water. Turbulent velocity components in the longitudinal and transverse directions were measured with the LDV in back scattering mode and the laser beams are focused from above the water surface into the water. Both the forward scattering mode measurements and the back scattering mode measurements were taken at two cross sections in the upstream uniform open-channel and at twelve cross sections in the nonuniform open channel. Obtained data include mean longitudinal velocity U, transverse velocity V, vertical velocity W, turbulence intensities u^2, v^2, w^2, and Reynolds shear stresses -uv and -uw. The chief results of these measurements are: 1) There is no separation of flow in the nonuniform open channel. 2) As flow passes from wider and shallower section to narrower and deeper section, it responds as though it experiences contraction in horizontal planes and expansion in vertical planes. The reverse occurs as flow passes from narrower and deeper section to wider and shallower section; 3) The secondary currents in the nonuniform open channel are combinations of the effects of pure contraction and expansion of channel boundaries and the effects of the vortex kind secondary currents; 4) Turbulence intensities in the non-uniform open channel show similar distribution patterns to that in the uniform open-channel but their magnitudes change due to the change of channel shape; 5) Negative values of the Reynolds shear stresses, -uw, appear at the free surface and may extend to a large depth below the free surface in the nonuniform open channel. Boundary shear stresses in the experimental channel were measured with Roving Preston tubes. The use of the Roving Preston tubes was preceded with calibrations of themselves in air pipe flow and calibrations of a special pressure transducer in air and in water. Delicate measurement procedures were designed for measurements of BSS in the nonuniform open channel. The BSS were measured at one cross section in the uniform open-channel and at twelve cross sections in the nonuniform open channel. The chief results of these measurements are: 1) The irregularity of the nonuniform open channel significantly affects the distribution of the BSS but the total shear force has little change; 2) The effect of the secondary currents on the BSS is very similar to the effect of secondary currents on the ESS in uniform open channel; 3) The irregularity in the non-uniform open channel does not cause extra energy loss since there is no flow separation. The numerical study made use of a FEM (finite element method) commercial package FIDAP to simulate the turbulent flows in the experimental channel. These simulations are carried out with Speziale's eddy-viscosity anisotropic k-E model, the standard k-E model, and the RNG model. With each model, simulations were undertaken for four consecutive uniform channels of 5 m length so that fully developed turbulent flow conditions were established before entering into the simulation of flow in the non- uniform channel. In all simulations the free surfaces were fixed. Simulation results include U, V, W, k, and E. For turbulent flow in the uniform channel, only Speziale's model is capable of predicting qualitatively correct secondary currents. For turbulent flow in the non-uniform open channel, all three models gave similar simulation results. The calculated distribution patterns of U and W are in agreement with measurements except near the free surface but differences exist in magnitude. None of the three models was capable of modelling the transverse velocity V in the nonuniform open channel correctly. Further simulations are necessary with movable free surface and better boundary condition for the energy dissipation rate s in order to achieve better agreement with the experimental values, especially near the free surface.

Vegetation is commonly modelled as emergent arrays of rigid, circular cylinders. However, the drag coefficient (CD) of real stems or trunks is closer to that of cylinders with a square cross-section. In this thesis, vegetation has been idealised as square cylinders in laboratory experiments with a turbulence intensity of the order of 10% which is similar to that of typical river flows. These cylinders may also represent other obstacles such as architectural structures. This research has determined CD of an isolated cylinder and cylinder pairs as a function of position as well as the average drag coefficient (CDv) of larger arrays. A strain gauge was used to measure CD whilst CDv was computed with a momentum balance which was validated by strain gauge measurements for a regularly spaced array. The velocity and turbulence intensity surrounding a pair of cylinders arranged one behind the other with respect to mean flow (in tandem) were also measured with an Acoustic Doppler Velocimeter. The isolated cylinder CD was found to be 2.11 in close agreement with other researchers. Under fixed flow conditions CD for a cylinder in a pair was found to be as low as -0.40 and as high as 3.46 depending on their relative positioning. For arrays, CDv was influenced more by the distribution of cylinders than the flow conditions over the range of conditions tested. Mean values of CDv for each array were found to be between 1.52 and 3.06. This new insight therefore suggests that CDv for vegetation in bulk may actually be much higher than the typical value of 1 which is often assumed to apply in practice. If little other information is available, a crude estimate of CDv = 2 would be reasonable for many practical applications. The validity of a 2D realizable k-epsilon turbulence model for predicting the flow around square cylinders was evaluated. The model was successful in predicting CD for an isolated cylinder. In this regard the model performed as well as Large Eddy Simulations by other authors with a significant increase in computational efficiency. However, the numerical model underestimates CD of downstream cylinders in tandem pairs and overestimates velocities in their wake. This suggests it may be necessary to expand the model to three-dimensions when attempting to simulate the flow around two or more bluff obstacles with sharp edges.

<p>U radu su prikazani razvoj, testiranje, kalibracija i verifikacija linijskog modela neustaljenog tečenja vode i transporta nanosa u mreži prirodnih vodotoka.<br />Hidraulički model se zasniva na St. Venant -ovim jednačinama koje su diskretizovane primenom Preissmann-ove &scaron;eme. Za modelisanje transporta nanosa i deformacije korita je usvojen koncept koji daje mogućnost da se obuhvate oba vida<br />kretanja nanosa (suspendovanog i vučenog). Primenom pristupa aktivnog sloja su<br />definisani procesi razmene materijala između nanosa u suspenziji i nanosa u aktivnom sloju. Osnovne jednačine transporta nanosa i deformacije korita su rečene<br />primenom metode etapnog re&scaron;avanja čija primena rezultuje u dva uzastopna koraka, advektivnom i difuzionom koraku. Jednaˇcine advektivnog koraka su ređavane<br />metodom karakteristika, dok se za jednačine difuzionog koraka primenila CrankNicholson-ova &scaron;ema metode konaˇcnih razlika. Dobijene jednačine su dopunjene<br />sa dodatnim jednačinama kako bi se omogućilo modelisanje opisanih procesa u<br />granatoj mrezi otvorenih tokova. Izvedene jednacine su primenjene za formiranje<br />numerickog modela koji jeđvalitativno testiran na &scaron;ematskim primerima, a kvantitativni testovi su urađeni na realnom primeru. Za realan primer je izabrana deonica Dunava u Srbiji sa glavnim pritokama Savom i Tisom. Kako bi se definisala oblast koja će se koristiti za verifikaciju modela napravljen je detaljan pregled i sistematizacija postojećih merenja morfologije korita, nivoa, proticaja i koncentracija suspendovanog nanosa. Na osnovu ovog pregleda je definisana morfologija modelisane mreže tokova. Pri kalibraciji hidrauličkog modela su razmotrena dva pristupa,<br />kalibracija putem Manning-ovog koeficijenta zadatog kao funkcije od proticaja, i<br />kalibracija zadavanjem apsolutne hrapavosti, dok je verifikacija modela urađena<br />pu&scaron;tanjem simulacije od godinu dana i poređenjem rezultata proračuna sa merenjima. Kalibracija modela transporta je sprovedena za duži vremenski period kako bi se &scaron;to bolje opisale godi&scaron;nje varijacije koncentracije suspendovanog nanosa, a za verifikaciju modela je odabran petogodiˇsnji period tokom kojeg su upoređeni rezultati proracuna sa merenjima, čime je pokazano da razvijen model moze pouzdano da simulira procese strujanja vode i transprta nanosa u mreži otvorenih tokova.<br />&nbsp;</p> / <p>This work presents the development, evaluation, calibration and verification of a<br />one dimensional unsteady flow, sediment transport and bed evolution looped river<br />network model. The hydraulic model is based on the St. Venant&rsquo;s equations discretized using the Preissmann&rsquo;s scheme. The sediment transport and bed evolution<br />model implements a concept that differentiates sediment particles moving in the<br />form of suspended sediment, and near bed and bed sediment. Applying the active<br />layer concept the developed model includes definitions of the exchange mechanisms<br />between the suspended sediment and active layer material. The governing transport equations were solved using the split operator approach that resulted in two<br />successive steps, the advection and diffusion step. The advection step equations<br />were solved using the characteristics method, whereas the diffusion step equations<br />are discretized using the Crank-Nicholson&rsquo;s scheme. The obtained system of the<br />developed equations was complemented with additional equations in order to allow<br />sediment transport and bed evolution simulation in a looped river network. The<br />derived equations were applied to develop an open channel flow, sediment transport and bed evolution numerical model that was subjected to a series of schematic<br />tests and a real life situation simulation. The model&rsquo;s evaluation was conducted<br />by comparison of the simulation results with the available measurements. The presented work was complemented with an comprehensive overview of the existing<br />bathymetry, water level, discharge and suspended sediment concentration measurements in order to define the model&rsquo;s domain, initial and boundary conditions. The calibration of the hydraulic model was done by assigning the Manning&rsquo;s coefficient<br />as a function of the discharge. As a result of the exhausting requirements of this<br />approach, a second approach was considered, where the calibration is conducted by<br />changing the absolute roughness. The verification of the hydraulic model was done<br />by comparing the computed results of a one year flow simulation with the available<br />measurements. Since the agrement between the two was satisfying, the sediment<br />transport and bed evolution model was calibrated using a longer time interval in<br />order to better capture the annual variations of the suspended sediment. The calibrated model was employed for a long term sediment transport and bed evolution<br />simulation. The simulation results were compared with the existing measurements<br />confirming the developed model&rsquo;s reliability.</p>

It is important for practical and legal reasons that water and sediments in disturbed areas around the mining operation should be controlled. The construction of a well-designed drainage system that controls erosion and thus restores the proper hydraulic function of the surface is one of the most important post-disturbance features which should be done as part of the mining activities. However, even with the best planning and design, unless proper construction practices are adapted; both the disturbed and reclaimed areas are very much likely to be susceptible to erosion, sedimentation and stability problems. In order to tackle the problem, guidelines on how to design and construct the drainage system should be well prepared. The main objective of this study was to prepare guidelines for the proper design, construction and monitoring of the water drainage management system in the study areas (Kankberg, Maurliden and Renström-Petiknäs). This report has analysed the results from the outcome of HEC-RAS software for the case study of the new ditch around the Maurliden mine site and integrated with different guidelines. Based on the results of the HEC-RAS, the most common problems in the drainage system have been identified. Moreover the thesis project identified important physical parameters such as cross-sections and slopes of the representative ditch which affect the function of the ditch in the study areas. Hydraulic parameters such as velocity which is very important for designing the type of lining and also Froude number which is very important in identifying the type of flow whether it is super-critical, critical or sub-critical were identified. The latter helps to select the type of guideline to be used between steep slope and mild slope.

L’État haïtien, pour faire face à l’insécurité alimentaire que connaît sa population (à croissance rapide et à faible revenu), s’appuie particulièrement sur la Vallée du département de l’Artibonite qui constitue depuis toujours le véritable grenier agricole du pays, en fournissant, à elle seule, plus de 80% de la production rizicole nationale. Cette production agricole assure non seulement les besoins alimentaires de la population locale, mais également ceux particuliers des départements voisins (Ouest, Nord et Centre).L’irrigation de cette vaste plaine agricole (32400 ha de terres agricoles irrigables) est garantie, à plus de 75%, par le réseau d’irrigation établi en rive Gauche de l'ouvrage-partiteur de Canneau, alimenté par un Canal principal (CMRG) ayant un débit nominal de 40 m3/s.Néanmoins, ce Partiteur, source d’approvisionnement exclusive du CMRG, est lui-même régulé par le Barrage-réservoir de Péligre qui se trouve à 70 km plus en amont sur le fleuve de l’Artibonite. En termes hydrauliques, nos travaux ont d'abord examiné la situation du réservoir de Péligre. Alors qu'au moment de la construction il était initialement prévu d’y stocker 607 Mm3, il ne reste plus aujourd'hui qu'à peine 40% de cette capacité utile, en raison des dépôts sédimentaires qui se sont constitués année après année derrière le barrage.Cette sédimentation spectaculaire (due à l’érosion des bassins versants amont fort dégradés), combinée aux déficits pluviométriques, provoque en période d’étiage une rareté d’eau, des lâchers insuffisants et donc des déficits en eau utile envoyée en amont de ce Partiteur de Canneau. Cela impacte significativement le réseau d’irrigation aval, dont le CMRG. Nos travaux ont montré que la situation est d'autant plus critique que les débits eux-mêmes, en amont comme en aval du Partiteur, sont en fait très mal connus et devraient faire l'objet d'approches méthodologiques plus rigoureuses que celles déployées sur site actuellement.Aussi, face à ces constats, de nouvelles règles de distribution de l’eau s’imposent, pour continuer à irriguer et espérer obtenir un rendement agricole acceptable (souhaitable).Notre travail s'est ainsi donné pour objectif de contribuer à la mise en place des nouvelles règles de gestion de l’eau (répartition) au sein du réseau d’irrigation alimenté par le CMRG, pour continuer à fournir l’eau à l’irrigant en quantité acceptable (et connue). Cette amélioration de gestion a été envisagée à la fois en amont et en aval de ce réseau d’irrigation, particulièrement en ses différents nœuds-clés (Canal principal et Canal secondaire).La démarche méthodologique adoptée pour relever ce défi majeur s’appuie notamment sur un système d’information hydro-morpho-sédimentaire actualisé et de qualité. Il s’agit d’une base de données, riche en observations de hauteurs d’eau (lues aux stations limnimétriques), vitesses de surface au flotteur, champs de vitesse explorés au moyen d’un courantomètre et en données bathymétriques et granulométriques des tronçons des canaux étudiés, appréciées respectivement au moyen d’un GPS différentiel et du tamisage à sec.Les résultats fort encourageants obtenus permettent d'acquérir une meilleure compréhension du système et une amélioration particulière du réseau d’irrigation en rive gauche du Partiteur de Canneau. En s’appuyant sur les historiques de sédimentation du Lac-réservoir de Péligre (de 1960 à 2016), nous présentons un document de synthèse sur la sédimentation du Lac-réservoir de Péligre. Ce document met notamment en exergue le taux de sédimentation sévère de ce dernier (5.47 Mm3/an), qui continue d’augmenter encore aujourd’hui, ainsi que les conséquences de celui-ci sur les débits turbinés et la disponibilité de l’eau en amont du Partiteur de Canneau.Nous mettons également en évidence les formes irrégulières (Lit-non prismatique) des tronçons des canaux étudiés, via une vue axonométrique des profils en travers (issus de l’étude bathymétrique) des canaux d’irrigation en terre battue étudiés. Puis, nous présentons de manière détaillée le caractère très hétérogène des dépôts sédimentaires de ces derniers, à partir d’une analyse des représentations en Log-Probit des résultats du tamisage, construites au moyen du logiciel GrandPlots.En nous appuyant sur les mesures expérimentales des contraintes de Reynolds et des profils instantanés de vitesse (pris à intervalle de 64 ms), tirés de la base de données EPFL, nous avons montré qu’il faut absolument travailler dans les 18% inférieurs de la colonne d’eau (z/h<0.18) et en mode déficitaire, dans un écoulement turbulent comme celui-là, pour extraire de façon représentative et pertinente une pente expérimentale u*/, comme indicateur de u*.À l’issue d’un examen détaillé de la distribution verticale de la vitesse au canal secondaire FNE, nous validons un DMLWL (Dip-Modified-log-wake-law) à la fois en amont et en aval du réseau. Nous montrons que ceci permet de modéliser le Dip-phenomenon observé systématiquement au sein des profils explorés in situ. Nous proposons une relation entre le coefficient d’inégale répartition de la vitesse à la verticale αv (de Prony) et l’aspect ratio (W/h) pour tout le réseau d’irrigation étudié ;ceci afin d’obtenir une vitesse débitante (Ū), simplement à partir d’une prise de vitesse au flotteur, dans l’axe central d’écoulement.À partir des débits quantifiés à la section de référence du CMRG, via l’équation de continuité (Q=AŪ), nous fournissons un Abaque, diagramme à 3 entrées (débit (Qp), charge amont (H0) et ouverture de vanne (hv)), permettant aux vanniers de connaitre les débits au pont de fer correspondant aux différentes ouvertures de vanne et celui pour lequel le trop-plein (retour des eaux excédentaires vers le fleuve de l’Artibonite) commence à fonctionner.À l’égard des opérateurs locaux et gestionnaires du système, nous mettons enfin à disposition, des méthodes/outils simples et efficaces leur permettant de quantifier finement le débit au Canal principal en amont ainsi qu’au canal secondaire en aval, simplement à partir d’une mesure de hauteur d’eau (h) et de vitesse de surface au flotteur (Us). / Doctorat en Sciences agronomiques et ingénierie biologique / info:eu-repo/semantics/nonPublished