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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Can pore-clogging by ash explain post-fire runoff?
Stoof, Cathelijne R. ; Gevaert, Anouk I. ; Baver, Christine ; Hassanpour, Bahareh ; Morales, Verónica L. ; Zhang, Wei ; Martin, Deborah ; Giri, Shree K. ; Steenhuis, Tammo S. - \ 2016
International Journal of Wildland Fire 25 (2016)3. - ISSN 1049-8001 - p. 294 - 305.
hydraulic conductivity - infiltration - wildland fire ash

Ash plays an important role in controlling runoff and erosion processes after wildfire and has frequently been hypothesised to clog soil pores and reduce infiltration. Yet evidence for clogging is incomplete, as research has focussed on identifying the presence of ash in soil; the actual flow processes remain unknown. We conducted laboratory infiltration experiments coupled with microscope observations in pure sands, saturated hydraulic conductivity analysis, and interaction energy calculations, to test whether ash can clog pores (i.e. block pores such that infiltration is hampered and ponding occurs). Although results confirmed previous observations of ash washing into pores, clogging was not observed in the pure sands tested, nor were conditions found for which this does occur. Clogging by means of strong attachment of ash to sand was deemed unlikely given the negative surface charge of the two materials. Ponding due to washing in of ash was also considered improbable given the high saturated conductivity of pure ash and ash-sand mixtures. This first mechanistic step towards analysing ash transport and attachment processes in field soils therefore suggests that pore clogging by ash is unlikely to occur in sands. Discussion is provided on other mechanisms by which ash can affect post-fire hydrology. Journal compilation

Watermanagement: oppervlakkige afspoeling aanpakken
Noij, I.G.A.M. - \ 2015
Nieuwsbrief Koeien & Kansen (2015)43. - p. 2 - 2.
oppervlakkige afvoer - oppervlaktewater - nutriëntenuitspoeling - infiltratie - waterbeheer - bodemstructuur - runoff - surface water - nutrient leaching - infiltration - water management - soil structure
Oppervlakkige afspoeling zorgt voor nutriëntenverlies. Het is een hele specifieke emissie route, die slechts beperkt wordt aangepakt via de bekende maatregelen rondom mest manage ment. De waterschappen zijn erg geïnteresseerd in dit onderwerp, om de belasting van het oppervlaktewater terug te dringen. Flinke verbeteringen zijn nodig én mogelijk.
Hydrologische en landbouwkundige effecten toepassing onderwaterdrains in polder Zeevang : vervolgonderzoek gericht op de toepassing van een zomer- en winterpeil
Hoving, I.E. ; Massop, H.T.L. ; Houwelingen, K.M. van; Akker, J.J.H. van den; Kollen, J. - \ 2015
Wageningen : Wageningen UR Livestock Research (Rapport / Wageningen UR Livestock Research 875) - 87
graslanden - grondwaterstand - peilbeheer - veengronden - broeikasgassen - landgebruik - drainage - infiltratie - noord-holland - grasslands - groundwater level - water level management - peat soils - greenhouse gases - land use - infiltration
In polder Zeevang is een veldonderzoek uitgevoerd naar de toepassing van onderwaterdrains op veengrond bij drie slootpeilregimes. De drains verlaagden de variatie in grondwaterstanden significant. Dit betekent dat het grondwaterstandverloop vlakker was dan in de ongedraineerde situatie. De drains, die onder slootpeil liggen, hadden zowel een drainerend effect (extra waterafvoer) als een infiltrerend effect (extra water aanvoer). Het toepassen van een zomer- en winterpeil is gunstig voor het verminderen van maaivelddaling, maar tijdens natte perioden in het groeiseizoen leveren onderwaterdrains bij een peil van 40 cm –maaiveld geen extra afvoercapaciteit op. Het belang van melkveehouders, namelijk het vergroten van de gebruiksmogelijkheden van het grasland, wordt daardoor onvoldoende gediend. Een meer flexibelere invulling van de perioden, waarop de slootpeilen volgens de beleidsregels omhoog en omlaag gezet moeten worden, is gewenst.
Lumped surface and sub- surface runoff for erosion modeling within a small hilly watershed in northern Vietnam
Bui, Y.T. ; Orange, D. ; Visser, S.M. ; Hoanh, C.T. ; Laissus, M. ; Poortinga, A. ; Tran, D.T. ; Stroosnijder, L. - \ 2014
Hydrological Processes 28 (2014)6. - ISSN 0885-6087 - p. 2961 - 2974.
land-use changes - soil-erosion - sediment transport - steep slopes - sensitivity-analysis - scale - infiltration - catchments - framework - thailand
Developing models to predict on-site soil erosion and off-site sediment transport at the agricultural watershed scale represent an on-going challenge in research today. This study attempts to simulate the daily discharge and sediment loss using a distributed model that combines surface and sub-surface runoffs in a small hilly watershed (<1km(2)). The semi-quantitative model, Predict and Localize Erosion and Runoff (PLER), integrates the Manning-Strickler equation to simulate runoff and the Griffith University Erosion System Template equation to simulate soil detachment, sediment storage and soil loss based on a map resolution of 30m x 30m and over a daily time interval. By using a basic input data set and only two calibration coefficients based, respectively, on water velocity and soil detachment, the PLER model is easily applicable to different agricultural scenarios. The results indicate appropriate model performance and a high correlation between measured and predicted data with both Nash-Sutcliffe efficiency (Ef) and correlation coefficient (r(2)) having values>0.9. With the simple input data needs, PLER model is a useful tool for daily runoff and soil erosion modeling in small hilly watersheds in humid tropical areas.
Methode voor het selecteren van lokale zoetwateroplossingen en het afwegen van hun effecten "Fresh Water Options Optimizer"
Hoogvliet, M. ; Stuyt, L.C.P.M. ; Bakel, J. van; Velstra, J. ; Louw, P. de; Massop, H.T.L. ; Tolk, L. ; Kempen, C. van; Nikkels, M. - \ 2014
Utrecht : Programmabureau Kennis voor Klimaat (Rapport / KvK 141/014) - 177
zoet water - watervoorziening - drainage - infiltratie - wateropslag - inventarisaties - fresh water - water supply - infiltration - water storage - inventories
Binnen Kennis voor Klimaat worden kleinschalige oplossingen ontwikkeld om de zoetwatervoorziening te verbeteren. In deze studie zijn de mogelijkheden voor opschaling onderzocht. Het gaat om de oplossingen (1) drains2buffer (D2B), (2) regelbare en klimaatadaptieve drainage (RD/KAD), (3) kreekruginfiltratie (KRI), (4) freshmaker (FM), (5) verticale ASR (VASR), (6) waterconservering door stuwen (WCST) en (7) waterconservering door slootbodemverhoging (WCSB).
Root zone salinity and sodicity under seasonal rainfall due to feedback of decreasing hydraulic conductivity
Zee, S.E.A.T.M. van der; Shah, S.H.H. ; Vervoort, R.W. - \ 2014
Water Resources Research 50 (2014)12. - ISSN 0043-1397 - p. 9432 - 9446.
soil-moisture dynamics - irrigation - infiltration - variability - management - california - transport - quality - systems - sodium
Soil sodicity, where the soil cation exchange complex is occupied for a significant fraction by Na+, may lead to vulnerability to soil structure deterioration. With a root zone flow and salt transport model, we modeled the feedback effects of salt concentration (C) and exchangeable sodium percentage (ESP) on saturated hydraulic conductivity Ks(C, ESP) for different groundwater depths and climates, using the functional approach of McNeal (1968). We assume that a decrease of Ks is practically irreversible at a time scale of decades. Representing climate with a Poisson rainfall process, the feedback hardly affects salt and sodium accumulation compared with the case that feedback is ignored. However, if salinity decreases, the much more buffered ESP stays at elevated values, while Ks decreases. This situation may develop if rainfall has a seasonal pattern where drought periods with accumulation of salts in the root zone alternate with wet rainfall periods in which salts are leached. Feedback that affects both drainage/leaching and capillary upward flow from groundwater, or only drainage, leads to opposing effects. If both fluxes are affected by sodicity-induced degradation, this leads to reduced salinity (C) and sodicity (ESP), which suggests that the system dynamics and feedback oppose further degradation. Experiences in the field point in the same direction.
Plassen op het land : een landsdekkende kaart van potentiële risicolocaties voor oppervlakkige afspoeling
Massop, H.T.L. ; Clement, J. ; Schuiling, C. - \ 2014
Wageningen : Alterra, Wageningen-UR (Alterra-rapport 2546) - 85
landbouwgrond - bodemtypen - oppervlakkige afvoer - bodemwater - infiltratie - perceelsvorm (landbouwkundig) - monitoring - agricultural land - soil types - runoff - soil water - infiltration - field shape
Oppervlakkige afstroming over maaiveld draagt bij aan de belasting van het oppervlaktewater met nutriënten en gewasbeschermingsmiddelen. De beschikbaarheid van een hoogtekaart met een hoge resolutie geeft de mogelijkheid potentiele risicolocaties op landbouwpercelen in kaart te brengen. Gebieden met het hoogste risico voor oppervlakkige afspoeling zijn de kleigebieden van Friesland en Groningen, het rivierengebied en de veengebieden, zoals het Utrechts-Hollands en het Friese veengebied.
Effect onderwaterdrainage op bodemkwaliteit veenweiden
Deru, J.G.C. ; Lenssinck, F.A.J. ; Hoving, I.E. ; Akker, J.J.H. van den; Bloem, J. ; Eekeren, N.J.M. van - \ 2014
V-focus 11 (2014)3. - ISSN 1574-1575 - p. 27 - 29.
bodemdaling - grondwaterstand - drainagesystemen - veenweiden - peilbeheer - infiltratie - subsidence - groundwater level - drainage systems - peat grasslands - water level management - infiltration
Veenweidegebieden hebben te maken met bodemdaling en uitstoot van broeikasgassen als gevolg van veenoxidatie. Dit proces wordt versterkt door aerobe omstandigheden in de bodem bij lage slootwater- en grondwaterpeilen, vooral in de zomer. Het gebruik van onderwaterdrains kan bodemdaling verminderen door een verhoogde infiltratie van water uit de sloot naar de veenweidebodem, waardoor grondwaterstanden
Methode voor het bepalen van de potentie voor het toepassen van lokale zoetwateroplossingen : Fresh Water Options Optimizer - fase 1
Bakel, J. van; Louw, P. de; Stuyt, L.C.P.M. ; Tolk, L. ; Velstra, J. ; Hoogvliet, M. - \ 2014
Utrecht : Programmabureau Kennis voor Klimaat (Rapport / STOWA 2014-16) - ISBN 9789490070847 - 82
zoet water - watervoorziening - drainage - infiltratie - sloten - wateropslag - watervoerende lagen - maatregelen - inventarisaties - fresh water - water supply - infiltration - ditches - water storage - aquifers - measures - inventories
Binnen Kennis voor Klimaat worden kleinschalige maatregelen ontwikkeld om de zoetwatervoorziening te verbeteren. In deze studie zijn methoden ontwikkeld waarmee de potentie van dergelijke maatregelen op het schaalniveau van een groter gebied, voor hoog en laag Nederland, kan worden verkend. In deze studie zijn de opschalingsmogelijkheden bekeken voor de volgende lokale zoetwateroplossingen: (1) drains2buffer, (2) regelbare en klimaatadaptieve drainage, (3) kreekruginfiltratie, (4) Freshmaker, (5) verticale ASR, (6) waterconservering door stuwen en (7) waterconservering door slootbodemverhoging.
Comparison of two methods to assess heterogeneity of water flow in soils
Lichner, L. ; Dusek, J. ; Dekker, L.W. ; Zhukova, N. ; Fasko, P. ; Holko, L. ; Sir, M. - \ 2013
Journal of Hydrology and Hydromechanics 61 (2013)4. - ISSN 0042-790X - p. 299 - 304.
preferential flow - sandy soil - hydrophysical parameters - field experiment - loam - infiltration - movement
The heterogeneity of water flow and solute transport was assessed during radioactive tracer infiltration experiment in a black clay loam soil using modified methods to estimate the effective cross section (ECS) and the degree of preferential flow (DPF). The results of field and numerical experiments showed that these parameters characterized the heterogeneity of water flow in the soils unequivocally. The ECS decreases non-linearly and the DPF increases linearly with an increase of the bypassing ratio (ratio of macropore flow rate to total flow rate). The ECS decreased and the DPF increased with depth, which suggests an increase in the heterogeneity of water flow with depth. The plot of the DPF against ECS values calculated from the tracer experiment data was consistent with the relationship obtained by the numerical simulation assuming preferential flow in the neighbourhood of three probes.
Pilot onderwaterdrains Krimpenerwaard
Akker, J.J.H. van den; Hendriks, R.F.A. ; Hoving, I.E. ; Meerkerk, B. ; Houwelingen, K.M. van; Kleef, J. van; Pleijter, M. ; Toorn, A. van den - \ 2013
Wageningen : Alterra, Wageningen-UR (Alterra-rapport 2466) - 114
veenweiden - infiltratie - drainage - bodemdaling - melkveehouderij - economische evaluatie - krimpenerwaard - waterkwaliteit - modellen - peat grasslands - infiltration - subsidence - dairy farming - economic evaluation - water quality - models
Dit rapport beschrijft het onderzoek in 2011 en 2012 naar de pilot onderwaterdrains Krimpenerwaard, waarin voornamelijk het effect van onderwaterdrains op de waterkwantiteit (debieten) en de waterkwaliteit is onderzocht. De meetresultaten zijn uitgewerkt en geëvalueerd met de modellen SWAP en ANIMO. Daarnaast zijn de economische en bedrijfsmatige aspecten van onderwaterdrains voor de veehouderij onderzocht. Een overzicht van eerder en lopend onderzoek naar maaivelddaling, waterkwantiteit, waterkwaliteit, bedrijfseconomische aspecten en effect op weidevogels is gegeven en betrokken in de conclusies. In de conclusies zijn ook de resultaten van pilots in de Keulevaart en Demmeriksekade betrokken (gerapporteerd in een volgend Alterra-rapport). De hoeveelheden in en uit te pompen water blijken in het algemeen toe te nemen. Het effect op de waterkwaliteit is in het algemeen neutraal of gunstig. Melkveehouders zijn in het algemeen positief over de effecten van onderwaterdrains.
Regelbare drainage als schakel in toekomstbestendig waterbeheer : bundeling van resultaten van onderzoek, ervaringen en indrukken, opgedaan in binnen- en buitenland
Stuyt, L.C.P.M. - \ 2013
Wageningen [etc.] : Alterra [etc.] (Alterra-rapport 2370) - 4188
drainage - ontwateren - grondwaterstand - agrarische bedrijfsvoering - peilbeheer - klimaatadaptatie - nutriëntenuitspoeling - infiltratie - natuurgebieden - dewatering - groundwater level - farm management - water level management - climate adaptation - nutrient leaching - infiltration - natural areas
De sinds 1950 ontwikkelde kennis over de functionaliteit van (samengestelde) regelbare drainagesystemen, uitgedrukt in effecten op de gewasopbrengst en de lokale en regionale water- en stoffenbalans, wordt gerapporteerd, met de nadruk op enkele recente Nederlandse projecten.
A spatially distributed model of pesticide movement in Dutch macroporous soils
Tiktak, A. ; Hendriks, R.F.A. ; Boesten, J.J.T.I. ; Linden, A.M.A. van der - \ 2012
Journal of Hydrology 470-471 (2012)november. - ISSN 0022-1694 - p. 316 - 327.
clay soil - preferential flow - solute transport - hydraulic conductivity - unsaturated soils - water-flow - infiltration - simulation - rainfall - bromide
In the Netherlands, a spatially distributed version of the pesticide fate model PEARL is routinely used to assess the leaching potential of pesticides to groundwater. Recently, the model was modified to simulate the movement of pesticides to surface water. The peak concentration is considered to be the most important exposure endpoint for the ecotoxicological effect assessment for aquatic organisms. Macropore flow is an important driver for the peak concentration, so the leaching model PEARL was extended with a macropore module. Macropore parameters were derived from generally available soil data such as organic matter content and clay content using newly developed pedotransfer functions. These pedotransfer functions were constructed using a wide range of Dutch clayey soils. Results indicate a good correlation between these variables and soil structural parameters, which is due to the homogeneous mineralogical composition of Dutch clayey soils. Results of the spatially distributed modelling indicate that due to rapid transport through macropores, the concentration of pesticides in drainage water is generally higher in clayey soils than in light textured soils. In clayey soils, the boundary hydraulic conductivity and organic matter content were the most important drivers for the concentration in drainage water. Results further indicate that the concentration of pesticide in drainage water increases with increasing half-life and decreases with increasing sorption coefficient. However, the effect of these parameters is much less than obtained with the convection–dispersion equation because due to preferential flow most of the reactive part of the soil profile is bypassed.
Effecten van onderwaterdrains op de waterkwaliteit in veenweiden : modelberekeningen met SWAP-ANIMO voor veenweide-eenheden naar veranderingen van de fosfor-, stikstof- en sulfaatbelasting van het oppervlaktewater bij toepassing van onderwaterdrains in het westelijke veenweidegebied
Hendriks, R.F.A. ; Akker, J.J.H. van den - \ 2012
Wageningen : Alterra, Wageningen-UR (Alterra-rapport 2354) - 201
veenweiden - drainage - infiltratie - eutrofiëring - fosfor - waterkwaliteit - modellen - peat grasslands - infiltration - eutrophication - phosphorus - water quality - models
Dit rapport beschrijft een modelstudie naar de effecten van onderwaterdrains op de nutriëntenbelasting van het oppervlaktewater in veenweiden in West-Nederland. Met SWAP-ANIMO zijn zeventien representatieve veenweide-eenheden doorgerekend. Veenweideeenheden zijn gedefinieerd voor vijf kenmerken: veensoort, veendikte, voorkomen van een kleidek, onderrand (kwel/wegzijging) en nutriëntenconcentraties in het infiltratiewater. De effecten van onderwaterdrains op de belasting van het slootwater met fosfor, stikstof en sulfaat zijn onderzocht door modelresultaten van varianten met en zonder drains te vergelijken. Hiertoe is de sulfaathuishouding ingebouwd in ANIMO. Onderwaterdrains geven meestal een (aanzienlijke) vermindering van de nutriëntenbelasting van het oppervlaktewater. Dit geldt het sterkst voor fosfor en het minst voor sulfaat. Sulfaat is erg gevoelig voor de drooglegging. Voor elk nutriënt is er voor alle veenweide-eenheden een drooglegging waarbij de belasting niet toeneemt door drains. Voor sulfaat is die drooglegging consequent 40 cm, de kleinste doorgerekende drooglegging.
Microtopography as a driving mechnism for ecohydrological processes in shallow groundwater systems
Ploeg, M.J. van der; Appels, W.M. ; Cirkel, D.G. ; Oosterwoud, M.R. ; Witte, J.P.M. ; Zee, S.E.A.T.M. van der - \ 2012
Vadose Zone Journal 11 (2012)3. - ISSN 1539-1663
acrotelm-catotelm model - peat bog growth - hydraulic conductivity - blanket peat - surface-water - micro-topography - flow - vegetation - runoff - infiltration
Microtopography can have a large effect on flow processes at the soil surface and the composition of soil water. Microtopography is often represented by a roughness parameter in hydrological models. In areas without a strong topographical gradient, microtopography may be underestimated when accumulated in a single parameter, especially in shallow groundwater systems. This study reviews the intricate relationships between microtopography, surface runoff, and ecohydrology in systems featuring shallow water tables. We specifically focus on relations between microtopography and runoff, impact of microtopography on response times of shallow groundwater ecosystems, and microtopography and spatial distribution of groundwater quality parameters and site factors. We advocate the use of microtopography in modeling approaches by examples that feature typical ecosystems with shallow groundwater under influence of microtopography. With a simple modeling approach, we show how microtopography could add flexibility to the acrotelm–catotelm concept in raised bog hydrology. The classic acrotelm–catotelm concept hinders progress in understanding small scale hydrological variations and other ecohydrological relations. Furthermore, we illustrate possible self-organization properties of wetlands. Finally, we show how microtopography and surface runoff affect the mixing of water with different chemical signatures, resulting in variations of the occurrence of plant species.
Emissie door oppervlakkige afspoeling : relevantie en preventie : tussenrapportage 2011
Evenhuis, A. ; Beltman, W.H.J. ; Weide, R.Y. van der; Zeeland, M.G. van; Schepers, H.T.A.M. ; Deneer, J.W. - \ 2012
Wageningen : Praktijkonderzoek Plant & Omgeving B.V. - 68
oppervlakkige afvoer - landbouwgronden - oppervlaktewater - emissie - pesticiden - pesticidenresiduen - gewasbescherming - neerslag - infiltratie - meteorologische waarnemingen - runoff - agricultural soils - surface water - emission - pesticides - pesticide residues - plant protection - precipitation - infiltration - meteorological observations
De doelstelling van het rapportage-project was: - Op basis van bestaande kennis uit binnen- en buitenland (metingen, modelstudies) inzichtelijk maken in hoeverre oppervlakkige afspoeling van (vrijwel) vlakke percelen verantwoordelijk kan zijn voor (piek) belasting van oppervlaktewater; - Inzichtelijk maken in hoeverre een vergelijking met andere emissieroutes mogelijk is en, zo mogelijk, deze vergelijking inzichtelijk maken; - Verkenning van de mate van overeenstemming tussen de uitgangspunten van de modelmatige berekening van afspoeling en de situatie op representatieve praktijksituaties in Nederland. Wanneer relevante afwijkingen verwacht worden, deze benoemen; - Vaststellen of er zicht is op effectieve maatregelen om oppervlakkige afspoeling tegen te gaan. Dit kunnen bestaande of nieuwe maatregelen zijn. Hiervoor is een korte internationale literatuurscan uitgevoerd naast een verkenning om te bepalen hoe vaak afspoeling van water kan optreden op landbouwgronden in het vlakke deel van Nederland. Voor dit laatste onderdeel zijn neerslaggegevens van 30 jaar geanalyseerd op de frequentie van optreden van buien voor 3 meteostations en zijn zand- en kleigronden gekarakteriseerd met hun infiltratiesnelheid.
Simulation of movement of pesticides towards drains with a preferential flow version of PEARL
Tiktak, A. ; Hendriks, R.F.A. ; Boesten, J.J.T.I. - \ 2012
Pest Management Science 68 (2012)2. - ISSN 1526-498X - p. 290 - 302.
dutch clay soil - unsaturated soils - solute transport - macropore flow - water-flow - sandy soil - model - infiltration - rainfall - bromide
Background: As part of the Dutch authorisation procedure for pesticides, an assessment of the effects on aquatic organisms in surface waters adjacent to agricultural fields is required. The peak concentration is considered to be the most important exposure endpoint for the ecotoxicological effect assessment. Macropore flow is an important driver for the peak concentration, so the leaching model PEARL was extended with a macropore module. The new model has two macropore domains: a bypass domain and an internal catchment domain. The model was tested against data from a field leaching study on a cracking clay soil in the Netherlands.Results: Most parameters of the model could be obtained from site-specific measurements, pedotransfer functions and general soil structural knowledge; only three macropore-flow-related parameters needed calibration. The flow-related macropore parameters could not be calibrated without using the concentration in drain water. Sequential calibration strategies, in which firstly the water flow model and then the pesticide fate model are calibrated, may therefore be less suitable for preferential flow models.Conclusion: After calibration, PEARL could simulate well the observed rapid movement towards drains of two pesticides with contrasting sorption and degradation rate properties. The calibrated value for the fraction of the internal catchment domain was high (90%). This means that a large fraction of water entering the macropores infiltrates into the soil matrix, thus reducing the fraction of rapid flow.
Hydropedological insights when considering catchment classification
Bouma, J. ; Droogers, P. ; Sonneveld, M.P.W. ; Ritsema, C.J. ; Hunink, J.E. ; Immerzeel, W.W. ; Kauffman, S. - \ 2011
Hydrology and Earth System Sciences 15 (2011). - ISSN 1027-5606 - p. 1909 - 1919.
simulate preferential flow - repellent porous-media - remotely-sensed data - land-use history - sandy soil - modeling approach - water repellency - loess plateau - clay soil - infiltration
Soil classification systems are analysed to explore the potential of developing classification systems for catchments. Soil classifications are useful to create systematic order in the overwhelming quantity of different soils in the world and to extrapolate data available for a given soil type to soils elsewhere with identical classifications. This principle also applies to catchments. However, to be useful, soil classifications have to be based on permanent characteristics as formed by the soil forming factors over often very long periods of time. When defining permanent catchment characteristics, discharge data would therefore appear to be less suitable. But permanent soil characteristics do not necessarily match with characteristics and parameters needed for functional soil characterization focusing, for example, on catchment hydrology. Hydropedology has made contributions towards the required functional characterization of soils as is illustrated for three recent hydrological catchment studies. However, much still needs to be learned about the physical behaviour of anisotropic, heterogeneous soils with varying soil structures during the year and about spatial and temporal variability. The suggestion is made therefore to first focus on improving simulation of catchment hydrology, possibly incorporating hydropedological expertise, before embarking on a catchment classification effort which involves major input of time and involves the risk of distraction. In doing so, we suggest to also define other characteristics for catchment performance than the traditionally measured discharge rates. Such characteristics may well be derived from societal issues being studied, as is illustrated for the Green Water Credits program.
Scale effects in Hortonian surface runoff on agricultural slopes in West Africa: Field data and models
Giesen, N. van de; Stomph, T.J. ; Ajayi, A.E. ; Bagayoko, F. - \ 2011
Agriculture, Ecosystems and Environment 142 (2011)1-2. - ISSN 0167-8809 - p. 95 - 101.
soil-erosion model - overland-flow - lisem model - rainfall - length - infiltration - hillslopes - generation - management - catchments
This article provides an overview of both experimental and modeling research carried out over the past 15 years by the authors addressing scaling effects in Hortonian surface runoff. Hortonian surface runoff occurs when rainfall intensity exceeds infiltration capacity of the soil. At three sites in West Africa (Côte d’Ivoire, Ghana, and Burkina Faso) runoff was measured from plots of different lengths to assess scale effects. Consistently, longer plots showed much lower runoff percentages than shorter plots. There were large variations in runoff percentages from one rainstorm to the next but there were very good correlations between plots of equal length for each single event. This strongly suggests that temporal dynamics are the cause behind the observed scale effects. In the literature, spatial variability is often proffered as explanation for such scale effects without providing a mechanism that would cause consistent reduction in runoff percentages with increasing slope length. To further examine whether temporal dynamics can indeed provide the explanation, Hortonian runoff was simulated using models with increasing levels of complexity. The simplest model was already able to reproduce the observed scale effects. Also more complex models were used that accounted explicitly for spatial variability. The conclusions remained the same regarding the role of temporal dynamics. Finally, a dimensional analysis was developed that helps predict under which circumstances one can expect scale effects similar to the ones observed in West Africa.
Analysis of the thickness of a fresh water lens and of the transition zone
Eeman, S. ; Leijnse, A. ; Raats, P.A.C. ; Zee, S.E.A.T.M. van der - \ 2011
Advances in Water Resources 34 (2011)2. - ISSN 0309-1708 - p. 291 - 302.
geohydrologie - watervoerende lagen - zoet water - zout water - delta's - geohydrology - aquifers - fresh water - saline water - deltas - submarine groundwater discharge - porous-media - coastal aquifer - brine transport - barrier-island - interface - flow - infiltration - dispersion - intrusion
In regions with saline groundwater, fresh water lenses may develop due to rainwater infiltration. The amount of fresh water that is available for e.g. agricultural crops depends on the thickness of the lens and the extent of mixing between fresh and saline water. In this paper, we consider the mixing of fresh water and upward moving saline ground water in low-lying deltaic areas. The parameters that dominate the flow and transport problem are investigated using dimensionless groups and scaled sensitivities. We characterize the numerically simulated thicknesses of the lens and of the mixing zone by spatial moments. Rayleigh number and mass flux ratio, which is the ratio of the salt water seepage and the precipitation, determine the thickness of the fresh water lens. The local thickness of the mixing zone is mainly influenced by the dispersive/diffusive groups and the mass flux ratio. In addition, convergence of streamlines towards an outflow boundary affects the thickness, particularly in the vicinity of this boundary. Analytical and numerical steady state solutions for lens thickness are compared, taking into account upward seepage, for the two cases with and without a density difference between lens and underlying groundwater. Agreement between the numerical and analytical solutions for the lens thickness is good except when the mass flux ratio becomes small. For zero mass flux ratio, it is implicitly assumed in the analytical solution that salt water is stagnant, and that is unrealistic. Relative contributions of longitudinal and transversal hydrodynamic dispersion and diffusion to the thickness of the mixing zone are quantified numerically for different phases of lens formation. Longitudinal dispersion dominates in the early stages of lens formation, while diffusion and transversal dispersion dominate at steady state
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