Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    Galilean invariant lattice Boltzmann scheme for natural convection on square and rectangular lattices
    Sman, R.G.M. van der - \ 2006
    Physical Review. E, Statistical nonlinear, and soft matter physics 74 (2006)2. - ISSN 1539-3755 - 17 p.
    hydrodynamics - simulations - diffusion - relaxation - dispersion - models - cavity - number - flow
    In this paper we present lattice Boltzmann (LB) schemes for convection diffusion coupled to fluid flow on two-dimensional rectangular lattices. Via inverse Chapman-Enskog analysis of LB schemes including source terms, we show that for consistency with physics it is required that the moments of the equilibrium distributions equal those of the Maxwell-Boltzmann distribution. These constraints can be satisfied for the rectangular D2Q9 lattice for only fluid flow in the weakly compressible regime. The analysis of source terms shows that fluxes are really defined on the boundaries of the Wigner-Seitz cells, and not on the lattice sites where the densities are defined¿which is quite similar to the staggered grid finite-volume schemes. Our theoretical findings are confirmed by numerical solutions of benchmark problems for convection diffusion and natural convection. The lattice Boltzmann scheme shows remarkably good performance for convection diffusion, showing little to non-numerical diffusion or numerical dispersion, even at high grid Peclet numbers
    A method for measuring effects of bioturbation and consolidation on erosion resistance of aquatic sediments
    Zambrano, L. ; Beijer, J.A.J. ; Roozen, F.C.J.M. ; Scheffer, M. - \ 2005
    Archiv für Hydrobiologie 162 (2005)3. - ISSN 0003-9136 - p. 327 - 337.
    sediment - hydrodynamica - geologische sedimentatie - erosie - zoet water - waterstroming - aquatische ecosystemen - waterbodems - sediment - hydrodynamics - geological sedimentation - erosion - fresh water - water flow - aquatic ecosystems - water bottoms - wind-induced resuspension - shallow lake
    Sediment erosion by water movement affects turbidity and thus benthic communities in numerous aquatic systems. This aspect has been widely studied in coastal habitats and estuaries, but less studied in freshwater systems such as shallow lakes. Here we present a simple device to study the effects of biota on the resistance of aquatic sediments to erosion by water movement. Circular 75 l tanks are used to incubate selected sediments with microbial communities. The tank size allows addition of organisms such as small fish, invertebrates and aquatic plants. Effects are studied by gradually increasing water movement by means of a rotor and continuously monitoring the increase of suspended solids. The water speed needed for resuspension is a measure of sediment erosion resistance. With this device we found a linear increment of erosion resistance over time if sediments are left undisturbed, and a significant reduction of erosion resistance with small holes punched randomly in the top layer of sediment (to mimic the effect of benthivorous fish foraging behaviour). Fish biotic perturbation was indicated by a reduction of sediment resistance associated with benthivorous fish presence. However, three spined stickleback did not create the same effect. Measurements with this simple device are reasonably precise and suggest that the set-up can be used to study effects of numerous factors that may affect sediment erosion resistance. For example, sediment consolidation associated with light, temperature, and microbial and plant colonization, along with sediment perturbation related to big invertebrates and fish behaviour.
    Uitspoelingsgevoelige gronden op de kaart; werkwijze en resultaten
    Kekem, A.J. van; Hoogland, T. ; Horst, J.B.F. van der - \ 2005
    Wageningen : Alterra (Alterra-rapport 1080) - 89
    bodemwater - grondwaterstand - uitspoelen - nitraten - cartografie - bodemeigenschappen - hydrodynamica - bodemwaterbeweging - veengronden - dierlijke meststoffen - overheidsbeleid - nederland - bodemkarteringen - kaarten - geostatistiek - soil water - groundwater level - leaching - nitrates - mapping - soil properties - hydrodynamics - soil water movement - peat soils - animal manures - government policy - netherlands - soil surveys - maps - geostatistics
    Voor de uitvoering van het mestbeleid in Nederland is het van belang om de uitspoelingsgevoeligheid voor nitraat van de bodems in Nederland zo goed mogelijk te kennen. Deze uitspoelingsgevoeligheid hangt o.a. af van de grondsoort en de grondwaterstand om hiervan een inschatting te maken dienen basisbestanden van de bodem en de grondwaterstanden voldoende nauwkeurig en actueel dienen te zijn. Uit een quick scan bleek dat 47% van de oppervlakte veengronden in Oost-Nederland is gedeformeerd naar een ander bodemtype, met name zandgronden. Voor de zand- en lössgronden van Nederland is met een geostatistische methode de grondwaterdynamiek geactualiseerd en er is een methodiek ontwikkeld om op basis hiervan de landbouwpercelen op zand- en lössgronden te classificeren naar uitspoelingsgevoeligheid. Deze berekeningen zijn uitgevoerd voor verschillende scenario's waarin is gevarieerd met de GHG grens, de areaal fractie per perceel en een kanscriterium. In het gewijzigd beleid is ervoor gekozen om niet op perceelsniveau uitspoelingsgevoelige gronden aan te wijzen. Daarom is het areaal uitspoelingsgevoelige grond ook voor pixels van 25x25 meter berekend. Voor de zandgronden bedraagt het areaal uitspoelingsgevoelige gronden met een GHG ≥ 70 cm en een GLG ≥ 120, ongeveer 335000 ha, 36% van het landbouw areaal op zandgronden
    Multistress van verontreiniging en hydrodynamiek op populaties van Oligochaeta in de uiterwaarden; een onderzoek in de Afferdensche en Deestsche Waarden
    Ma, W.C. ; Vliet, P.W. van; Bodt, J.M. - \ 2004
    Wageningen : Alterra (Alterra-rapport 877) - 107
    oligochaeta - annelida - verontreiniging - stress - hydrodynamica - populatie-ecologie - biodiversiteit - bodem - nederland - gelderland - land van maas en waal - uiterwaarden - oligochaeta - annelida - pollution - stress - hydrodynamics - population ecology - biodiversity - soil - netherlands - gelderland - land van maas en waal - river forelands
    Dit rapport beschrijft een onderzoek naar de populatie-ecologie van regenwormen (Oligochaeta, Lumbricidae) in de Afferdensche en Deestsche Waarden (ADW), een uiterwaarde van de rivier de Waal. Ondanks het feit dat de bodem in dit gebied is verontreinigd en elk jaar overstromingen plaatsvinden komen regenwormen er in een grote soortsdiversiteit en in grote aantalsdichtheden voor. Afhankelijk van de bodemgesteldheid omvat de totale gemiddelde populatie een biomassa van 1500 kg per hectare. De uiterwaarden vormen hiermee een belangrijk voedselzoekgebied voor vermivore (wormenetende) faunasoorten en dragen als zodanig bij aan de totale biodiversiteit van de natuur in Nederland. Om de ecologische betekenis van multipele stress in beeld te brengen is onderzoek verricht naar de invloed van potentieel sturende omgevingsfactoren, waaronder hoogteligging, textuur en verontreiniging van de bodem, nutriëntengehalten en bodemvocht. Uit (multivariate) statistische analyse bleek dat de hydrodynamiek van het gebied en het bodemvochtgehalte belangrijke sturende variabelen vormden voor de soortsdiversiteit en populatiedichtheden, terwijl de aanwezige metaalverontreiniging in dit opzicht van mindere betekenis was. Vanuit het oogpunt van praktische toepasbaarheid leveren de resultaten belangrijke aanknopingspunten op voor het bodem- en natuurbeheer van de uiterwaarden in Nederland.
    Actualisatie grondwaterdynamiek waterschap De Dommel
    Hoogland, T. ; Hoogerwerf, M.R. ; Kekem, A.J. van - \ 2004
    Wageningen : Alterra (Alterra-rapport 1008) - 44
    bodemwater - grondwaterstand - cartografie - monitoring - hydrodynamica - bodemwaterbeweging - uitspoelen - nederland - noord-brabant - soil water - groundwater level - mapping - monitoring - hydrodynamics - soil water movement - leaching - netherlands - noord-brabant
    Omdat de provinciale kartering van de grondwaterdynamiek (Gd) volgens het waterschap de Dommel vooral in de beekdalen te droog gekarteerde waarden liet zien, zijn in opdracht van het waterschap geactualiseerde ruimtelijke bestanden gemaakt van de gemiddelde hoogste, voorjaars- en laagste grondwaterstand (GHG, GVG en GLG) en van de grondwatertrap (Gt). Als basisinformatie zijn hierbij aanvullende incidentele metingen en tijdreeksen van grondwaterstanden gebruikt. Door toepassing van technieken uit de tijdreeksmodellering en regressietechnieken is een uniforme set puntschattingen van GHG, GVG en GLG verkregen. Deze gegevens zijn, gewogen naar kwaliteit, gebruikt om relaties met recent verzamelde hoogte-gegevens (het AHN) te leggen. Door gebiedsdekkende toepassing van deze relaties en een statistische foutencorrectie zijn gedetaileerde ruimtelijkebestanden verkregen met de resolutie van het AHN waarin GHG, GVG en GLG en hun voorspelfout worden weergegeven. De geactualiseerde Gd-kaart geeft vooral in de beekdalen een natter beeld dan de provinciale kartering en levert een groter nauwkeurigheid in de gekarteerde grondwaterdynamiek.
    Meetschotten Bargerveen. Ontwerp, constructie en ijking
    Boiten, W. ; Dommerholt, A. ; Romelingh, J.C.F. - \ 2004
    Wageningen : Sectie Waterhuishouding (Rapport / Sectie Waterhuishouding 120) - 29
    veengronden - natuurreservaten - hydrologie - meting - monitoring - hydrodynamica - afvoer - drenthe - peat soils - nature reserves - hydrology - measurement - monitoring - hydrodynamics - discharge - drenthe
    Delen van het Bargerveen zijn gespaard gebleven voor grootschalige vervening. In 1968 kocht het rijk de eerste hectares natuurreservaat in het Bargerveen. In 1995 werd de inrichting van het inmiddels 2000 ha grote natuurreservaat voltooid. Deze inrichting heeft vooral als doel, uiteindelijk weer een levend hoogveen te krijgen dat uit zichzelf aangroeit. Dat kan alleen onder natte omstandigheden. Daartoe heeft Staatsbosbeheer in de periode 1970-1998 veertig kilometer dammen van het ondoorlatend zwartveen aangelegd om zoveel mogelijk regenwater vast te houden.
    Veranderende draagkracht van de Oosterschelde voor kokkels
    Geurts van Kessel, A.J.M. ; Kater, B.J. ; Prins, T.C. - \ 2003
    IJmuiden [etc,] : RIVO (RIVO rapport C062/03) - 128
    schaal- en schelpdierenvisserij - kokkels - hydrodynamica - habitats - crassostrea gigas - visbestand - milieueffect - voedingsgedrag - concurrentie tussen dieren - biomassa productie - draagkracht - nederland - oosterschelde - aquatische ecosystemen - stormvloedkeringen - visserijbiologie - shellfish fisheries - clams - hydrodynamics - habitats - crassostrea gigas - fishery resources - environmental impact - feeding behaviour - animal competition - biomass production - carrying capacity - netherlands - eastern scheldt - aquatic ecosystems - storm surge barriers - fishery biology
    Effecten van veranderingen in hydrodynamiek en morfologie door de Deltawerken op de habitatgeschiktheid voor kokkels. Rapportage uit het lange termijn onderzoeksprogramma voedselreservering Oosterschelde, in het kader van de tweede evaluatie Nederlands schelpdiervisserijbeleid (EVA II)
    Gas and liquid distribution in the monolith film flow reactor
    Heibel, A.K. ; Vergeldt, F.J. ; As, H. van - \ 2003
    AIChE Journal 49 (2003)12. - ISSN 0001-1541 - p. 3007 - 3017.
    mass-transfer - porous-media - packed-columns - maldistribution - hydrodynamics - performance - dispersion - scale
    The gas-liquid distribution in a monolith film flow reactor is investigated in the scope of this work. Magnetic resonance imaging (MRI) and a customized liquid collection method hate been successfully applied to determine the liquid distribution over the monolith cross-section. Using a well-positioned spray nozzle liquid distributor, very uniform distributions are found which address the needs for applications that require high single-pass conversions. Due to the lack of radial convective flow in monoliths, the initial distribution propagates through the reactor. With a correct positioned spray nozzle distributor, a far more uniform distribution than the natural one for trickle beds is obtained. MRI, applied to study the local gas-liquid distribution in a monolith channel, clearly shows the accumulation of the liquid in the corners of the individual channel with an arc-shaped gas-liquid interface. Differences in local liquid holdup over the channel corners were found, which is described as channel scale nonuniformities. The experimental results are in good agreement with a fundamental hydrodynamic model based on the Navier-Stokes equations. The average liquid saturation is conveniently described with an engineering correlation ßL = 6.6 . (Fr2Ls/ReLs)0.46, as a function of the liquid phase Reynolds and Froude number
    Hydrodynamics of a liquid-liquid-solid fluidized-bed bioreactor
    Zessen, E. van - \ 2003
    Wageningen University. Promotor(en): Hans Tramper, co-promotor(en): Arjen Rinzema; Rik Beeftink. - [S.l.] : S.n. - ISBN 9789058088758 - 199
    bioreactoren - hydrodynamica - wervelbedden - fermentatie - biotechnologie - bioreactors - hydrodynamics - fluidized beds - fermentation - biotechnology
    If a batchwise bioconversion and subsequent ( i.e. serial) downstream processing are adopted as a standard production strategy, a low overall productivity may result for certain types of biotransformations (substrate- or product-inhibited fermentations). An alternative to sequential processing would be the integration of bioconversion and downstream processing by controlled supply of substrate to the reaction in situ , or by controlled removal of product from the reaction in situ . Such integration involves a multi-phase reactor in which a helper phase may serve as substrate reservoir or as product sink. A new type of multi-phase bioreactor was developed, containing a continuous liquid phase, a dispersed liquid phase, and a dispersed solid phase; it may be conceived of as a 3-phase liquid-liquid-solid fluidized bed. This thesis focuses on the hydrodynamic aspects of such a 3-phase fluidized bed; a general design strategy was developed. Within this 3-phase system, a liquid-solid fluidized bed consisting of biocatalytic gel beads in a continuous medium phase, and a liquid-liquid extraction column or spray column, consisting of organic droplets in a continuous medium phase can be discerned. The hydrodynamic characteristics of these constituent 2-phase systems were studied as well. At the end this thesis reviews the current status of the newly developed 3-phase liquid-liquid-solid fluidized-bed bioreactor; it outlines additional research to be performed for a full understanding of its hydrodynamicbehavior. Additional steps that have to be taken for practical implementation of the 3-phase fluidized bed as a new type of bioreactor are emphasized.

    Actualisatie van de grondwaterdynamiek; volledige herkartering of beperkte actualisatie?
    Bierkens, M.F.P. ; Hoogland, T. - \ 2002
    Wageningen : Alterra (Alterra-rapport 602) - 39
    bodemwater - grondwaterspiegel - cartografie - nederland - monitoring - hydrodynamica - geo-informatie - geostatistiek - grondwaterstand - hydrologie kartering - soil water - water table - mapping - monitoring - netherlands - hydrodynamics
    Het maken van grondwaterdynamiekkaarten (Gd-kaarten) is betrekkelijk duur, met name vanwege het vele veldwerk. Het is dus van belang om na te gaan of bij een hernieuwde kartering het gebruik van de oude kaart en informatie over ingrepen sinds de vorige kartering kan leiden tot kostenbesparing. In dit onderzoek zijn vier alternatieven getoetst op nauwkeurigheid en kosten: grondwaterdynamiekkartering zonder gebruik te maken van een bestaande Gd-kaart; volledige herkartering gebruikmakend van een bestaande Gd-kaart en informatie over ingrepen; herkartering met geringe dichtheid van veldwaarnemingen gebruikmakend van een bestaande Gd-kaart en informatie over ingrepen; herkartering met reguliere dichtheid zich beperkend tot de zone waar wordt vermoed datingrepen effect hebben gehad en gebruikmakend van een bestaande Gd-kaart. Bij de toesting is gebruik gemaakt van een numeriek laboratorium om de "werkelijke" Gd-kaart te construeren. De belangrijkste aanbeveling uit dit onderzoek is om een Gd-herkartering te beperken tot gebieden waar ingrepen hebben plaatsgevonden en in deze gebieden een grotere waarnemingsdichtheid dan normaal (> 1 per kmr) te hanteren.
    Water measurement with flumes and weirs
    Clemmens, A.J. ; Wahl, T.L. ; Bos, M.G. ; Replogle, J.A. - \ 2001
    International Institute for Land Reclamation and Improvement/ILRI (ILRI publication 58) - 382
    stuwen - overlaten - hydrodynamica - afvoer - ontwerp - monitoring - hydrologie - meetinstrumenten - simulatiemodel - waterbeheer - weirs - spillways - hydrodynamics - discharge - design - monitoring
    Inrichting debietmeetnet Vallei en Eem : vooronderzoek, richtingsadvies en ontwerp van een lange overlaat achter de Grebbesluis
    Boiten, W. - \ 2001
    Wageningen : Wageningen Universiteit (Rapport / Wageningen Universiteit, Omgevingswetenschappen, Sectie Waterhuishouding 102) - 17
    hydrodynamica - afvoer - waterstroming - doorstroommeters - sluizen - overlaten - utrecht - gelderse vallei - hydrodynamics - discharge - water flow - flow meters - sluices - spillways - utrecht - gelderse vallei
    Debietmetingen Gelderse Vallei
    Statistical Analysis of Daily Discharge Data of the River Meuse and its Tributaries (1968-1998): Assessment of Drought Sensitivity
    Uijlenhoet, R. ; Wit, M.J.M. de; Warmerdam, P.M.M. ; Torfs, P.J.J.F. - \ 2001
    Wageningen : Sub-department Water Resources (Rapport 100) - 40
    hydrologie van stroomgebieden - neerslag - watersystemen - klimaatverandering - hydrodynamica - maas - frankrijk - belgië - limburg - catchment hydrology - precipitation - water systems - climatic change - hydrodynamics - river meuse - france - belgium - limburg
    The rivers Rhine and Meuse fulfill important functions in the water supply of The Netherlands. Global climate change may affect the hydrological behaviour of these rivers and consequently the availability of water for a variety of purposes. The possible effects of global climate change on the discharge regime of the river Rhine system has been studied extensively during recent years. The Meuse, however, has received significantly less attention.
    Debietmeetstations in het gebied Halkenbroek
    Boiten, W. - \ 2000
    Wageningen : Landbouwuniversiteit Wageningen (Rapport / Sectie Waterhuishouding, [Departement] Omgevingswetenschappen, Wageningen Universiteit 93)
    hydrodynamica - afvoer - monitoring - hydrodynamics - discharge - monitoring
    Levering drie Rossum-stuwen Schouwen West
    Boiten, W. - \ 1998
    Wageningen : Landbouwuniversiteit Wageningen (Rapport / Landbouwuniversiteit Wageningen, Afdeling Waterhuishouding 76) - 5
    hydrodynamica - vloeistoffen (liquids) - vloeistoffen (fluids) - stroming - kanalen - kanalen, klein - meting - snelheid - nederland - zeeland - zeeuwse eilanden - hydrodynamics - liquids - fluids - flow - canals - channels - measurement - velocity - netherlands - zeeland - zeeuwse eilanden
    Sediment transport in irrigation canals
    Mendez V., N.J. - \ 1998
    Agricultural University. Promotor(en): E. Schultz; L.C. van Rijn. - Rotterdam etc. : Balkema - ISBN 9789054104131 - 285
    irrigatiewater - transport - waterverdeling - hydrodynamica - hydraulica - suspensies - sediment - irrigation water - transport - water distribution - hydrodynamics - hydraulics - suspensions - sediment

    The world population is rapidly increasing and is expected to double to about 10 billion by the year 2050. To support an increasing population in terms of food sufficiency, more and more water will be required. Irrigation is the most critical component of the modern package of inputs to effect high crop production. Irrigation has been the largest recipient of public agricultural investment in the developing world. Hence, continued investment in irrigation along with reforms in institutional arrangements for management of water are very much necessary to ensure adequate supply of food. Simultaneously, water requirements for other purposes, domestic, industrial and hydropower will steadily increase as well. Under this competing situation irrigation will have to become increasingly more efficient in the future.

    Improved management and operation activities must be implemented to prevent recurring degradation of irrigation projects. Clogging of turnouts and reduction of the conveyance capacity of canals by siltation are problems frequently met in irrigation systems. Annually, high investments are required for rehabilitation of irrigation systems in order to keep them suitable for their purposes. New development of irrigation projects or upgrading of existing schemes will require a better understanding of the sediment transport process under the prevailing flow conditions in irrigation canals. Applicability of the existing sediment transport relationships on irrigation canals has to be better understood. In this way predictions on sediment deposition in irrigation canals will be more reliable.

    The present study is focused on sediment transport in irrigation canals which may have a serious impact on the operation and maintenance activities. The design of the canal system either should be based on the transport of all the in the water present sediment to the fields or to places in the canal system, where the deposition can be removed with least costs. Sedimentation should be prevented in canals and near structures, as it will hamper and endanger a proper irrigation management. In the design and operation of irrigation canals with sediment-laden water several aspects related to irrigation criteria and sediment transport must be taken into consideration. The need for conveying different discharges at a required water level to meet the irrigation requirement and at the same time to convey the sediment load with a minimum deposition and/or erosion in the canal system should be the main criteria for the canal design. Irrigation canals are generally designed upon the assumption of uniform and steady flow.

    It is also assumed that there exists an equilibrium situation where the sediments entering into the irrigation canals will be transported without settling or erosion. However, uniform and steady flow are seldom found in reality. In the operation of an irrigation system the flow is predominantly non-uniform. While the sediment transport is highly dependent on the flow conditions it is obvious that the sediment transport capacity of the canals varies as well.

    Development on sediment transport in open channels have been mainly focused on river engineering. Even though certain similarities between rivers and irrigation canals are present, these concepts are not fully applicable to irrigation canals. A description and analysis of the sediment transport concepts under the specific conditions of irrigation canals will contribute to improve the understanding of these concepts and will help to decide on the applicability of them on simulation of the sediment transport processes for particular conditions of water flow and sediment inputs. A mathematical model which includes sediment transport concepts for the specific conditions of irrigation canals will become an important and timely tool for designers and managers of those systems.

    The aim of this research is to present a detailed analysis of the sediment transport processes, a physical and mathematical description of the behaviour of sediment transport under flow conditions encountered in irrigation canals and to develop a model to predict sediment transport and the deposition or entrainment rate for various flow conditions and sediment inputs.

    Sediment transport processes

    Sediment transport and water flow are interrelated and cannot be separated. From a mathematical point of view the interrelation can be described for a one-dimensional phenomenon without changes in the shape of the cross section by the following equations:

    • governing water flow equations : continuity and dynamic equations;
    • governing sediment equations : resistance to flow, sediment transport equations, continuity equation for sediment mass.

    Water flow equations : although one-dimensional flow hardly can be found in nature, water flow in an irrigation canal will be considered to be one-dimensional. Under this assumption, the general equations for one dimensional flow can be described by the Saint Venant equations. The amount of water flowing into irrigation canals during the irrigation season and moreover during the life time of irrigation canals is not constant. For the time depending changes in the bottom of the canal the water flow can be easily schematized as quasi-steady which means that the time depending factors in the Saint Venant equations can be neglected.

    Resistance to flow : the resistance to flow in open channels is affected by several factors, among which the development of bed forms play an important role. Determination of the friction factor of a movable bed is a complex problem that requires knowledge of an implicit process of flow conditions and bed form development. In order to predict the type of bed forms in irrigation canals the theories developed by Liu, Simons and Richardsons, Bogardi and van Rijn were compared to a selected set of laboratory and field data. Also a comparison of the most widely used methods to predict the resistance to flow with field and flume data has contributed to select an appropriate method for similar situations. The selected methods for predicting the resistance to flow were: White, Bettes and Paris (1979), Brownlie (1983) and van Rijn (1984c).The objective was to find the appropriate theories to describe the bed form and to estimate the resistance to flow (friction factor) in irrigation canals.

    From the performance of each predictor of bed form type and friction factor method when compared with selected field and laboratory data some conclusions can be drawn:

    • the theories of van Rijn and Simons and Richardson behave as the best to predict the bed form in irrigation canals;
    • all the bed forms described for the lower regime (ripples, mega-ripples and dunes) can be expected in irrigation canals;
    • the prediction of the friction factor by using the previously described methods takes only into account the bottom friction;
    • the van Rijn method for predicting the friction factor shows the best results when compared with the selected data.

    Another important feature related to the resistance of water flow in irrigation canals is the estimation of the friction factor of a irrigation canal with composite hydraulic roughness. The development of bed forms on the bottom, different material on the bottom and side of the canal or vegetated side banks are typical situations for the composite roughness conditions in irrigation canals. The most common cross sections in irrigation canals are the trapezoidal and rectangular cross section with a relatively small value for the bottom width-water depth ratio. In these cross-sections the velocity distribution is strongly affected by the varying water depth on the side slope and the boundary condition imposed to the velocity at the side wall. A method to estimate the effective roughness in a trapezoidal canal with composite roughness along the wetted perimeter which uses the theoretical velocity distribution in the cross section, is proposed.

    In order to predict the effective roughness in irrigation canals with composite roughness, the existing methods for predicting the effective roughness and the proposed method in this study have been compared with a selected set of laboratory data, which has been collected in the hydraulic laboratory of the Wageningen Agricultural University. The aim of the experiments has been to investigate the friction factor in a trapezoidal canal having varying roughness on side and bottom and to find an appropriate method to estimate the friction factor in a non-wide canal with different roughness along the wetted perimeter. From the comparison the main conclusion can be drawn that the proposed method gives better results than the other methods.

    For rectangular cross sections with composite roughness the existing methods for estimating the effective roughness can not explicitly be used. Therefor it is proposed to estimate the composite roughness in rectangular cross sections by the same principle as used for the side wall correction. The procedure to estimate the effective roughness in rectangular cross sections has been tested with a selected set of laboratory data used by Krüger. The proposed method predicts more than 95% of the measured values of the composite roughness within a range of error of 15%.

    Sediment transport equations : sediment transport equations are related to the way in which the sediment is transported: namely in equilibrium and non-equilibrium condition.

    Sediment transport predictors for equilibrium conditions have been established for different conditions. The use of those equations should be restricted to the conditions for which they were developed. However a comparison of the different equations under similar flow and sediment characteristics, both in irrigation canals and from field and laboratory data will be a useful tool to evaluate the suitability of each equation under these particular flow conditions. In this study, five of the most widely used equations to compute sediment transport have been compared, namely the Ackers and White, Brownlie, Engelund and Hansen, van Rijn and Yang equations. These equations have been compared with field and laboratory data. The objective was to find more reliable predictors of the sediment transport capacity under the flow conditions prevailing in irrigation canals. From that evaluation some remarks can be drawn:

    • prediction of the sediment transport in irrigation canals within an error factor less than 2 is hardly possible;
    • based on an overall evaluation of all performance criteria for each equation, the Ackers and White and Brownlie equations seem to be the best to predict the sediment transport rate in irrigation canals.

    Sediment transport theories have been developed for wide, open channels. Most of the man-made irrigation canals are not considered as wide canals. Recommended values for the ratio of bottom width and water depth (B/h) in those canals are smaller than 8. Existing methods for calculating the total sediment transport capacity for the entire cross section of a non-wide canal do not take into account the velocity distribution over the cross section. A new method to compute the total sediment transport by using a cross section integrated method is proposed, which is based on the assumption of a quasi two-dimensional model. The objective is to consider the effect of the side banks on the distribution of velocities and to adapt the sediment transport predictors for computing the sediment transport for the entire cross section of a non-wide canal. The existing methods and the proposed method to compute the total sediment transport in non-wide canals were compared with a selected set of laboratory data. Based on the overall comparison the proposed method gives better results than the existing methods for computing the sediment transport capacity for the whole cross section.

    An interesting phenomenon of the non-equilibrium sediment transport in irrigation canals is the adjustment of the actual sediment transport to the sediment transport capacity of the irrigation canal. To simulate the sediment transport under non-equilibrium conditions, the Gallapatti's depth integrated model for adaptation of the suspended load has been used. It has been assumed that the adaptation length for bed load is the same adaptation length for suspended load. Therefore the Gallapatti's depth integrated model can be used to describe the approach of the total sediment concentration to the transport capacity of the irrigation canal.

    Application of mathematical modelling of sediment transport in irrigation canals

    In order to simulate the sediment transport in irrigation canals, a computer program (SETRIC) has been developed. The computer program can simulate water flow, sediment transport and changes of bottom level in a network composed by a main canal and several laterals with/without tertiary outlets. Also some hydraulics structures are included in the program: overflow and undershot type, submerged culverts and inverted siphons, flumes and drops.

    The computer program is based on a sub-critical, quasi-steady, uniform or non-uniform flow (gradually varied flow). The water flow can be simulated in open channels, with a rectangular or trapezoidal cross section with single or composite roughness. Only friction losses are considered. No local losses due to changes in the bottom level, cross section or discharges are taken into account. However, changes in the bottom level are included.

    Sediment characteristics are defined by the sediment concentration at the head of the canal and sediment size is characterized by the mean diameter d 50 . The range of values is 0.05 mm≤d 50 ≤0.5 mm. A uniform sediment size distribution has been assumed.

    The simulation periods take into account the variation of the irrigation water requirement during the growing season. The growing season is divided into four stages depending on the crop development and climate conditions. The program assumes a maximum of four different periods in which the discharges along the system can be varied.

    Maintenance activities can also be included into the program. Those maintenance activities are referred to the obstruction degree due to weed growth on the banks and by its effect on the roughness condition of the canal. From that point of view three types of maintenance are included in the program: ideal maintenance, well maintained and poor maintained.

    Some applications of the model to simulate sediment transport in irrigation canals are shown. The results can not be generalized so that they can only be applied for the local flow conditions and sediment characteristics of each application. The applications are meant to show the applicability of the model and to improve the understanding of the sediment transport process for situations usually encountered in irrigation systems. The sediment deposition in an irrigation canal during a certain period will be simulated for each of the different applications. The sediment transport capacity of the irrigation canal is computed according to the Ackers and White's predictor method. The adjustment towards the sediment transport capacity is according to the Gallapatti's depth integrated model. A sediment mass balance in each reach of the canal will give either the net deposition or net entrainment between the two boundaries of a specific canal reach. From the application cases some conclusions are drawn:

    Changes of discharges : during the simulations for reductions of discharge to 80% of the design value (equilibrium condition), more than 40% of the incoming sediment load was deposited.

    Changes in the incoming sediment load : the effect of changes in the incoming sediment load on the sediment transport include the effect of variations in the incoming sediment concentration and in the median sediment size during the irrigation season and/or the lifetime of an irrigation canal. For 100% of variation in the incoming sediment concentration about 30% of the incoming sediment load is expected to settle into the canal. A similar behaviour is observed for the case of changes in the design value of the median size of the incoming sediment. For instance a total of about 45% of the incoming sediment during the simulation period is deposited when the sediment size deviates 100% from the equilibrium size.

    Controlled sediment deposition : two scenarios to concentrate the sediment deposition at the head reach of a canal were simulated. They can be described as: widening (scenario 1) and deepening (scenario 2). No additional considerations for optimizing economical cost and sediment deposition were done. For the specific flow and sediment transport conditions scenario 2 trapped 4 times more sediment than an irrigation canal without control and 1.3 times more than scenario 1.

    Sediment transport predictor : large differences in the computed sediment deposition were observed among the sediment transport predictors. The hydraulic conditions during the simulation period gave a low sediment transport capacity for the Engelund and Hansen predictor and larger for Brownlie and Ackers and White predictors. By using the Engelund and Hansen's predictor the sediment deposition was 2 and 3 times more that the Brownlie and Ackers and White's predictors respectively.

    Flow control structures : two types of flow control structures were compared: overflow type and undershot type. The observed total deposition in both cases is rather similar. A larger difference was observed in the distribution of the sediment deposition along the canal. That difference was mainly concentrated in the upstream part of the structure.

    Maintenance activities : maintenance was related to weed infestation and it was simulated by assuming optimal maintenance and no maintenance at all during the irrigation season. No direct effect of the growth of the weed on the sediment transport is considered. More sediment deposition was observed in the ideally maintained canal than the non-maintained canal. Due to the constant water level at the downstream side of the irrigation canal the flow condition within the canal behaved as: in the ideally maintained canal a gradually varied flow (backwater curve) remained constant during the simulation period. A continuous deposition was observed during all the time along the irrigation canal. In the non-maintained canal the initial flow condition changed in time from a backwater curve to a drawdown curve due to the constant water level at the downstream end and due to the variation of the water level within the canal imposed by the variation of the roughness condition. A sediment deposition period followed by an entrainment period was observed during the irrigation season.

    Operation activities : for simulating the effect of the operation procedures on the sediment deposition in the main canal four scenarios were investigated. The four scenarios are: scenario 1 (continuous flow); scenario 2 (rotational flow by hour); scenario 3 (rotational flow by day); scenario 4 (rotational flow by week). From the comparison the following conclusions can be drawn:

    • the largest total sediment deposition was observed in scenario 1. Total sediment deposition in scenarios 2, 3 and 4 was rather similar;
    • large differences were observed in the distribution of the sediment deposition within the reaches of the main canal.

    By considering the results of the applications of the mathematical modelling, it can be concluded that model is a useful tool for assessing the sediment deposition within irrigation canals under different flow conditions and sediment characteristics. Nevertheless, the mathematical model's performance can most probably be improved when it is applied in more situations. Monitoring of the sediment deposition in irrigation networks is required to evaluate the model under specific conditions and to investigate the response in time and space of the bottom level to determined water flows and sediment characteristics. Influences of the type and operation of flow control structures, geometrical characteristics of the canals, water flow and incoming sediment characteristics on the deposition, which the mathematical model predicts, will contribute to a better understanding of the sediment transport processes in irrigation canals.

    Passage of sediment through flumes and over weirs
    Bos, M.G. ; Wijbenga, J.H.A. - \ 1997
    Irrigation and Drainage Systems 11 (1997)1. - ISSN 0168-6291 - p. 29 - 39.
    stuwen - overlaten - rivieren - waterlopen - kanalen - water - geologische sedimentatie - hydrodynamica - hellingen, glijbanen - kanalen, klein - weirs - spillways - rivers - streams - canals - water - geological sedimentation - hydrodynamics - chutes - channels
    This paper reports on laboratory research on the sediment passage capability through long-throated flumes and broad-crested weirs with which the Froude number in the approach channel does not exceed 0.6 over a distance of about 20 times the water depth upstream of the structure. Design rules are given for any combination of flume or weir in combination with any channel.
    Flow resistance and hydraulic capacity of water courses with aquatic weed growth; Part 2
    Querner, E.P. - \ 1997
    Irrigation and Drainage Systems 11 (1997)2. - ISSN 0168-6291 - p. 171 - 184.
    onkruidbestrijding - kanalen - kanalen, klein - waterwegen - schadelijke waterplanten - hydrodynamica - vloeistoffen (liquids) - vloeistoffen (fluids) - stroming - rivieren - waterlopen - water - afvoer - drainage - sloten - hydrologie - modellen - analogen - weed control - canals - channels - waterways - aquatic weeds - hydrodynamics - liquids - fluids - flow - rivers - streams - water - discharge - drainage - ditches - hydrology - models - analogues
    Assessment of the effect of kinetics on colloid facilitated radionuclide transport in porous media.
    Weerd, H. van de; Leijnse, A. - \ 1997
    Journal of Contaminant Hydrology 26 (1997). - ISSN 0169-7722 - p. 245 - 256.
    grondwaterstroming - hydrodynamica - vloeistoffen (liquids) - vloeistoffen (fluids) - stroming - poreus medium - toepassingen - isotopen - straling - radioactiviteit - modellen - onderzoek - groundwater flow - hydrodynamics - liquids - fluids - flow - porous media - applications - isotopes - radiation - radioactivity - models - research
    Binding of radionuclides to natural colloids can significantly alter their transport behaviour in porous media. Dependent on the interaction between radionuclides, colloids and the solid matrix, radionuclide transport may be enhanced or retarded as a result of the presence of colloids. Often, equilibrium models are used to describe interactions between radionuclides, colloids and the solid matrix. However, experimental results indicate that kinetic processes may be important. In this paper, a model for coupled colloid and radionuclide transport in porous media is presented. Kinetic relationships are incorporated for the interaction between radionuclides, colloids and solid matrix. With this transport model, column experiments have been simulated, and modelling results are compared with experimental data reported in literature. It appears that kinetic interaction relationships are required to adequately model the experimental data.
    Hydrodynamics, sediment transport and light extinction off Cape Bolinao, Philippines
    Rivera, P.C. - \ 1997
    Agricultural University. Promotor(en): L. Lijklema; W. van Vierssen. - Rotterdam : Balkema - ISBN 9789054104087 - 244
    delta's - estuaria - hydraulica - hydrodynamica - rivieren - waterlopen - kanalen - water - geologische sedimentatie - kusten - modellen - theorie - onderzoek - oceanografie - deltas - estuaries - hydraulics - hydrodynamics - rivers - streams - canals - water - geological sedimentation - coasts - models - theory - research - oceanography

    Observational and numerical modelling studies of the hydrodynamics, sediment transport, and light extinction were undertaken in the marine environment around Cape Bolinao in the Lingayen Gulf (Northwest Philippines). Abundant with ecologically important seagrasses and benthic organisms, Cape Bolinao is presently threatened with siltation and eutrophication problems. For this reason intensive field measurements of relevant enviromnental variables which include currents, tides, temperature, salinity, total suspended solids (TSS), ash-free dry weight (AFDW), sedimentation flux, grain size distribution and organic content of bottom sediments, gilvin absorption, phytoplankton concentration, and light extinction were executed from August 1993 to June 1995. Laboratory experiments were simultaneously undertaken to determine the sedimentation and light extinction characteristics of various sediment fractions. Using time series and regression analyses, the results were analyzed and presented. A set of numerical models were developed and applied in the area around Cape Bolinao and the Lingayen Gulf. A prognostic model for the hydrodynamics, driven by realistic wind and tide forces, was developed independently for the cape (fine-resolution model) and the gulf (coarse resolution model). An operational open boundary condition based on the method of wave propagation is discussed. The hydrodynamical predictions were used, in conjunction with a diagnostic surface wave model, to force the suspended sediment transport model. The transport model, which is based on the time-dependent advection-diffusion equation, is third order accurate in space and time. For a realistic description of the suspended sediment transport process in Cape Bolinao, resuspension and sedimentation fluxes were included in the numerical model using existing parameterizations. The predicted suspended sediment concentrations were used in a diagnostic model for light extinction. This later model is based on the assumption that the contributions of the optically active components to the attenuation of the photosynthetically available radiation (PAR) are linearly additive. Calibration of the numerical models using field observations produced a set of parameter values which is deemed representative for the area of investigation. Using these parameter values, the overall model predictions were in good agreement with field observations. Finally, using the integrated model, the impact of river sediment loads (treated as a conservative tracer) in the Bolinao reef system was quantified.

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