Resilience of River Deltas in the Anthropocene
Hoitink, A.J.F. ; Nittrouer, J.A. ; Passalacqua, P. ; Shaw, J.B. ; Langendoen, E.J. ; Huismans, Y. ; Maren, D.S. van - \ 2020
Journal of Geophysical Research: Earth Surface 125 (2020)3. - ISSN 2169-9003
deltas - morphodynamics - resilience - rivers - sea level rise - sediment transport
At a global scale, delta morphologies are subject to rapid change as a result of direct and indirect effects of human activity. This jeopardizes the ecosystem services of deltas, including protection against flood hazards, facilitation of navigation, and biodiversity. Direct manifestations of delta morphological instability include river bank failure, which may lead to avulsion, persistent channel incision or aggregation, and a change of the sedimentary regime to hyperturbid conditions. Notwithstanding the in-depth knowledge developed over the past decades about those topics, existing understanding is fragmented, and the predictive capacity of morphodynamic models is limited. The advancement of potential resilience analysis tools may proceed from improved models, continuous observations, and the application of novel analysis techniques. Progress will benefit from synergy between approaches. Empirical and numerical models are built using field observations, and, in turn, model simulations can inform observationists about where to measure. Information theory offers a systematic approach to test the realism of alternative model concepts. Once the key mechanism responsible for a morphodynamic instability phenomenon is understood, concepts from dynamic system theory can be employed to develop early warning indicators. In the development of reliable tools to design resilient deltas, one of the first challenges is to close the sediment balance at multiple scales, such that morphodynamic model predictions match with fully independent measurements. Such a high ambition level is rarely adopted and is urgently needed to address the ongoing global changes causing sea level rise and reduced sediment input by reservoir building.
Flow and Suspended Sediment Division at Two Highly Asymmetric Bifurcations in a River Delta: Implications for Channel Stability
Kästner, K. ; Hoitink, A.J.F. - \ 2019
Journal of Geophysical Research: Earth Surface 124 (2019)10. - ISSN 2169-9003 - p. 2358 - 2380.
ADCP - Indonesia - river bifurcation - river delta - sediment transport - tidal hydrodynamics
The division of sediment at river bifurcations results from the complex interaction between three-dimensional flow, planform, and channel bed morphology, as well as the heterogeneity of the bed material. Sediment division processes cannot be incorporated in their full complexity in scale experiments and are difficult to reproduce with numerical models. Field measurements are thus necessary to advance our understanding of those processes in river deltas. However, such measurements are rare. We present measurements of the flow and sediment division at two tidally influenced bifurcations of the Kapuas River, a large sand-bedded suspended load-dominated river in West Kalimantan, Indonesia. At both bifurcations, a smaller channel branches off from the side of the main river, which makes the planform strongly asymmetric. The planform of both bifurcations has been stable at least since the end of the nineteenth century when the region was mapped for the first time. Based on our measurements, we explore possible factors that stabilize the bifurcations. We measure the flow velocities with a boat-mounted acoustic velocity profiler and determine the sediment concentration from acoustic backscatter, calibrated against water samples. The side branch of the first bifurcation receives a proportionally lower fraction of sediment than water. In contrast, the side branch at the second bifurcation receives a proportionally higher fraction of sediment than water. A comparison of flow velocity and suspended sand concentration indicates that the bed material sorting strongly influences the division of sediment, in particular at one of the bifurcations, which is situated in a meander bend.
Supporting Information for: Scale-dependent evanescence of river dunes during discharge extremes
Naqshband, Suleyman ; Hoitink, Ton - \ 2019
Wageningen University & Research
river dunes - sediment transport - upper stage plane bed
Data contains dune slipface angles (steepest part of the dune lee-face) for different experimental conditions as shown in figure 4 of the submitted manuscript. The slipface angles are derived using a widely used bedform tracking tool.
Data underlying “Multi-Scale monitoring and modelling of the Kapuas River Delta”
Kästner, K. ; Vermeulen, B. ; Hoitink, A.J.F. ; Geertsema, T.J. - \ 2019
hydrodynamics - morphodynamics - sand-bedded rivers - sediment transport - tropics
unprocessed raw data: - water level (pressure gauge) - velocity (boat mounted VADCP and HADCP) - turbulence (bottom mounted coupled VADCP) - bathymetry (single beam) - side scan sonar - bed material grain size - water samples (suspended sediment concentration) - particle size (lisst casts) - salinity (gauged)
The Importance of Combined Tidal and Meteorological Forces for the Flow and Sediment Transport on Intertidal Shoals
de Vet, P.L.M. ; van Prooijen, B.C. ; Schrijvershof, R.A. ; van der Werf, J.J. ; Ysebaert, T. ; Schrijver, M.C. ; Wang, Z.B. - \ 2018
Journal of Geophysical Research: Earth Surface 123 (2018)10. - ISSN 2169-9003 - p. 2464 - 2480.
hydrodynamics - intertidal area - morphology - numerical model - sediment transport - wind
Estuarine intertidal areas are shaped by combined astronomical and meteorological forces. This paper reveals the relative importance of tide, surge, wind, and waves for the flow and sediment transport on large intertidal shoals. Results of an intensive field campaign have been used to validate a numerical model of the Roggenplaat intertidal shoal in the Eastern Scheldt Estuary, the Netherlands, in order to identify and quantify the importance of each of the processes over time and space. We show that its main tidal creeks are not the cause for the dominant direction of the net flow on the shoal. The tidal flow over the shoal is steered by the water level differences between the surrounding channels. Also during wind events, the tidal flow (enhanced by surge) is dominant in the creeks. In contrast, wind speeds of order 40 times the typical tidal flow velocity are sufficient to completely alter the flow direction and magnitude on an intertidal shoal. This has significant consequences for the sediment transport patterns. Apart from this wind-driven flow dominance during these events, the wind also increases the bed shear stress by waves. For the largest intertidal part of the Roggenplaat, only ∼1–10% of the yearly transport results from the 50% least windy tides, even if the shoal is artificially lowered half the tidal range. This dominance of energetic meteorological conditions in the transports matches with field observations, in which the migration of the creeks and high parts of the shoal are in line with the predominant wind direction.
Flow and bed morphology response to the introduction of large wood for sediment
Poelman, Judith - \ 2018
Wageningen University & Research
bed morphology - conveyance capacity - flow patterns - physical scale model - sedimant management - sediment transport - submerges vanes
Submerged vanes alter sediment transport by inducing a secondary circulation without significantly compromising the conveyance capacity of the river. Similarly, large trunks of wood may be implemented in rivers as a means of sediment management, with the additional benefit of improving bio-diversity. A laboratory study is conducted to investigate the effects of large wood (LW) on flow patterns and bed morphology. The effectivity of a traditional vane field is compared to a set-up with screens composed of a stacked pile of wooden cylinders, and a set-up with an array of large individual trunks. Results from experiments with a fixed bed indicate that a reduction of streamwise velocity occurs for all configurations, and is markedly larger for the set-up with an array individual trunks. The trunks are least effective in inducing a secondary circulation and cause higher turbulence and drag. Increased porosity does not significantly influence the effectivity of the sediment management structures. In experiments with a mobile sediment bed, all three experimental set-ups have increased bed elevation conform expectations, but for different reasons. A field of trunks acts as a sediment trap because of strong reduction of the streamwise velocity, without producing a strong secondary flow such as dominant in the other configurations. Screens of large wood may be successfully implemented in rivers, as they are only slightly less effective than traditional vanes. The risk of piping underneath structures and the associated development of scour are points of concern. This dataset contains the ADV data, processed ADV data and bed elevation data measured with a line laser scanner and 3D camera.
Modelling fine-grained sediment transport in the Mahakam land-sea continuum, Indonesia
Phan, Van, C. ; Gourgue, O. ; Sassi, M. ; Hoitink, A.J.F. ; Deleersnijder, Eric ; Soares-Frazão, Sandra - \ 2016
Journal of Hydro-environment Research 13 (2016). - ISSN 1570-6443 - p. 103 - 120.
fine-grained - Indonesia - sediment transport - Mahakam
SLIM is an unstructured mesh, finite element model of environmental and geophysical fluid flows, which is being improved to simulate fine-grained sediment transport in riverine and marine water systems. A 2D depth-averaged version of the model is applied to the Mahakam Delta (Borneo, Indonesia), the adjacent ocean, and three lakes in the central part of the Mahakam River catchment. The 2D code is coupled to a 1D section-averaged model for the Mahakam River and four tributaries. The coupled 2D/1D model is mainly aimed at simulating fine-grained sediment transport in the riverine and marine water continuum of the Mahakam River system. Using the observations of suspended sediment concentration (SSC) at five locations in the computational domain, the modelling parameters are first determined in a calibration step, for a given period of time. A validation step is then performed using data related to another period of time. It is concluded that the coupled 2D/1D model reproduces very well the observed suspended sediment distribution within the delta. The spatial distribution of sediment concentration in the delta and its temporal variation are also discussed.
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.
A Mixed Modeling Approach to Predict the Effect of Environmental Modification on Species Distributions
Cozzoli, F. ; Eelkema, M. ; Bouma, T.J. ; Ysebaert, T. ; Escaravage, V. ; Herman, P.M.J. - \ 2014
PLoS ONE 9 (2014)2. - ISSN 1932-6203
cockles cerastoderma-edule - natural animal assemblages - quantile regression - lanice-conchilega - body-size - ecosystem engineers - sediment transport - hydrobia-ulvae - abundance - oosterschelde
Human infrastructures can modify ecosystems, thereby affecting the occurrence and spatial distribution of organisms, as well as ecosystem functionality. Sustainable development requires the ability to predict responses of species to anthropogenic pressures. We investigated the large scale, long term effect of important human alterations of benthic habitats with an integrated approach combining engineering and ecological modelling. We focused our analysis on the Oosterschelde basin (The Netherlands), which was partially embanked by a storm surge barrier (Oosterscheldekering, 1986). We made use of 1) a prognostic (numerical) environmental (hydrodynamic) model and 2) a novel application of quantile regression to Species Distribution Modeling (SDM) to simulate both the realized and potential (habitat suitability) abundance of four macrozoobenthic species: Scoloplos armiger, Peringia ulvae, Cerastoderma edule and Lanice conchilega. The analysis shows that part of the fluctuations in macrozoobenthic biomass stocks during the last decades is related to the effect of the coastal defense infrastructures on the basin morphology and hydrodynamics. The methodological framework we propose is particularly suitable for the analysis of large abundance datasets combined with high-resolution environmental data. Our analysis provides useful information on future changes in ecosystem functionality induced by human activities.
River scale model of an training dam using lightweight granulates
Vermeulen, B. ; Boersema, M.P. ; Hoitink, A.J.F. ; Sieben, J. ; Sloff, C.J. ; Wal, M.F. van der - \ 2014
Journal of Hydro-environment Research 8 (2014). - ISSN 1570-6443 - p. 88 - 94.
sediment transport - spur dikes - bed
Replacing existing river groynes with longitudinal training dams is considered as a promising flood mitigation measure in the main Dutch rivers, which can also serve to guarantee navigability during low flows and to create conditions favourable for ecological development. Whereas the bed response in the streamwise uniform part of a river trained by a longitudinal dam can be readily predicted, the bed response at the transition zones is unclear. In the present study, we investigate the local morphological effects resulting at the intake section of a longitudinal training dam, where the flow is distributed over the main channel and a side channel in between the dam and the river shore. A sediment recirculating model with a nearly undistorted geometry with respect to the prototype was setup. Lightweight polystyrene granulates were used as a surrogate for sediment, to properly scale the Shields parameter without compromising Froude scaling, and reach dynamical similarity. A laser scanner allowed collecting high-resolution bed elevation data. Results obtained under typical low flow and high flow conditions show a general deepening of the bed in the area adjacent to the training dam, in response to narrowing of the main channel. Scour at an upstream river groyne embedded in the model showed a scour hole which was deeper than realistic. Throughout the entire domain, bedforms developed featuring geometrical properties that reproduced the prototype conditions appropriately. Based on a comparison with characteristics from the River Waal, regarded as the prototype without a longitudinal dam, lightweight sediments were considered to be a proper choice for this study, in which bedload is the main sediment transport mode. The main conclusion regards the absence of significant morphodynamic developments at the intake section, both during the high flow experiment and during the low flow experiment, which can be attributed to the alignment of the dam with the local streamlines.
Measurement uncertainties in quantifying aeolian mass flux: evidence from wind tunnel and field site data
Poortinga, A. ; Keijsers, J.G.S. ; Maroulis, J. ; Visser, S.M. - \ 2014
PeerJ 2 (2014). - ISSN 2167-8359
dr.-nicholas-kraus - issue no. 59 - sand transport - vertical-distribution - sediment transport - coastal research - eroded sediment - water erosion - pp. 280-290 - p. eds.
Aeolian sediment traps are widely used to estimate the total volume of wind-driven sediment transport, but also to study the vertical mass distribution of a saltating sand cloud. The reliability of sediment flux estimations from such measurements are dependent upon the specific configuration of the measurement compartments and the analysis approach used. In this study, we analyse the uncertainty of these measurements by investigating the vertical cumulative distribution and relative sediment flux derived from both wind tunnel and field studies. Vertical flux data was examined using existing data in combination with a newly acquired dataset; comprising meteorological data and sediment fluxes from six different events, using three customized catchers at Ameland beaches in northern Netherlands. Fast-temporal data collected in a wind tunnel shows that the median transport height has a scattered pattern between impact and fluid threshold, that increases linearly with shear velocities above the fluid threshold. For finer sediment, a larger proportion was transported closer to the surface compared to coarser sediment fractions. It was also shown that errors originating from the distribution of sampling compartments, specifically the location of the lowest sediment trap relative to the surface, can be identified using the relative sediment flux. In the field, surface conditions such as surface moisture, surface crusts or frozen surfaces have a more pronounced but localized effect than shear velocity. Uncertainty in aeolian mass flux estimates can be reduced by placing multiple compartments in closer proximity to the surface.
Evaluating competing hypotheses for the origin and dynamics of river anastomosis
Kleinhans, M.G. ; Haas, T. de; Lavooi, E. ; Makaske, B. - \ 2012
Earth Surface Processes and Landforms 37 (2012)12. - ISSN 0197-9337 - p. 1337 - 1351.
rhine-meuse delta - upper columbia river - british-columbia - sediment transport - channel - netherlands - avulsion - canada - classification - bifurcation
Anastomosing rivers have multiple interconnected channels that enclose flood basins. Various theories potentially explain this pattern, including an increased discharge conveyance and sediment transport capacity of multiple channels, deltaic branching, avulsion forced by base-level rise, or a tendency to avulse due to upstream sediment overloading. The former two imply a stable anabranching channel pattern, whereas the latter two imply disequilibrium and evolution towards a single-channel pattern in the absence of avulsion. Our objective is to test these hypotheses on morphodynamic scenario modelling and data of a well-documented case study: the upper Columbia River. Proportions of channel and floodplain sediments along the river valley were derived from surface mapping. Initial and boundary conditions for the modelling were derived from field data. A 1D network model was built based on gradually varied flow equations, sediment transport prediction, mass conservation, transverse slope and spiral meander flow effects at the bifurcations. The number of channels and crevasse splays decreases in a downstream direction. Also, measured sediment transport is higher at the upstream boundary than downstream. These observations concur with bed sediment overloading from upstream, which can have caused channel aggradation above the surrounding floodplain and subsequent avulsion. The modelling also indicates that avulsion was likely caused by upstream overloading. In the model, multi-channel systems inevitably evolve towards single-channel systems within centuries. The reasons are that symmetric channel bifurcations are inherently unstable, while confluenced channels have relatively less friction than two parallel channels, so that more discharge is conveyed through the path with more confluences and less friction. Furthermore, the present longitudinal profile curvature of the valley could only be reproduced in the model by temporary overfeeding.
Downstream hydraulic geometry of a tidally influenced river delta
Sassi, M.G. ; Hoitink, A.J.F. ; Brye, B. de; Deleersnijder, E. - \ 2012
Journal of Geophysical Research: Earth Surface 117 (2012). - ISSN 2169-9003 - 13 p.
sediment transport - mahakam delta - flow - estuaries - discharge - model - tides - propagation - channels - bifurcations
Channel geometry in tidally influenced river deltas can show a mixed scaling behavior between that of river and tidal channel networks, as the channel forming discharge is both of river and tidal origin. We present a method of analysis to quantify the tidal signature on delta morphology, by extending the hydraulic geometry concept originally developed for river channel networks to distributary channels subject to tides. Based on results from bathymetric surveys, a systematic analysis is made of the distributary channels in the Mahakam Delta (East Kalimantan, Indonesia). Results from a finite element numerical model are used to analyze the spatial variation of river and tidal discharges throughout the delta. The channel geometry of the fluvial distributary network scales with bifurcation order, until about halfway the radial distance from the delta apex to the sea. In the seaward part of the delta, distributary channels resemble funnel shaped estuarine channels. The break in morphology, which splits the delta into river- and tide-dominated parts, coincides with a break in the ratio between tidal to fluvial discharges. Downstream hydraulic geometry exponents of the cross-sectional area show a transition from the landward part to the seaward part of the delta. The numerical simulations show that the tidal impact on river discharge division at bifurcations increases with the bifurcation order, and that the variation of river discharge throughout the network is largely affected by the tides. The tidal influence is reflected by the systematic variation of downstream hydraulic geometry exponents.
Field experiments for understanding and quantification of rill erosion processes
Wirtz, S. ; Seeger, K.M. ; Ries, J.B. - \ 2012
Catena 91 (2012)April. - ISSN 0341-8162 - p. 21 - 34.
concentrated flow erosion - ephemeral gully erosion - soil-erosion - sediment transport - interrill erosion - rainfall simulation - water erosion - slope length - shallow flow - detachment
Despite many efforts over the last decades to understand rill erosion processes, they remain unclear. This paper presents the results of rill experiments accomplished in Andalusia in September 2008 using a novel experimental set up. 72 L of water are introduced with an intensity of 9 L min(-1) into a rill. Rill cross sections, slope values, flow velocities and sediment concentrations were measured and these values were used to calculate sediment detachment and transport. Each experiment was repeated once within 15 min. With this new experimental setup it is possible to calculate several hydraulic parameters like hydraulic radius, wetted perimeter, flow cross section, transport rate and transport capacity which are usually estimated from coarse flow and rill parameters. In rill experiments, four different natural rills were flooded with the same experimental setup. Several processes like transport of loose material, erosion, bank failure and knickpoint retreat and the runoff effectiveness showed different and variable intensities. The sediment concentrations ranged between 5.2 and 438 g L-1. most cases, detachment rates are close to the transport capacity and, in some cases, the transport capacity is even exceeded. This can be explained by the occurrence of different erosion processes within a rill (e.g. detachment, bank failure, and headcut retreat) which are not all explained by the given equations. The results suggest that the existing soil erosion equations based on shear forces exerted by the flowing water are not able to describe rill erosion processes satisfactory. Too many different processes with a high spatial and temporal variability are responsible for rill development. (C) 2010 Elsevier B.V. All rights reserved.
Tidal impact on the division of river discharge and distributary channels in the Mahakam Delta
Sassi, M.G. ; Hoitink, A.J.F. ; Brye, B. de; Vermeulen, B. ; Deleersnijder, E. - \ 2011
Ocean Dynamics 61 (2011)12. - ISSN 1616-7341 - p. 2211 - 2228.
doppler current profiler - sediment transport - multiscale model - flow - propagation - tides - bifurcations - friction
Bifurcations in tidally influenced deltas distribute river discharge over downstream channels, asserting a strong control over terrestrial runoff to the coastal ocean. Whereas the mechanics of river bifurcations is well-understood, junctions in tidal channels have received comparatively little attention in the literature. This paper aims to quantify the tidal impact on subtidal discharge distribution at the bifurcations in the Mahakam Delta, East Kalimantan, Indonesia. The Mahakam Delta is a regular fan-shaped delta, composed of a quasi-symmetric network of rectilinear distributaries and sinuous tidal channels. A depth-averaged version of the unstructured-mesh, finite-element model second-generation Louvain-la-Neuve Ice-ocean Model has been used to simulate the hydrodynamics driven by river discharge and tides in the delta channel network. The model was forced with tides at open sea boundaries and with measured and modeled river discharge at upstream locations. Calibration was performed with water level time series and flow measurements, both spanning a simulation period. Validation was performed by comparing the model results with discharge measurements at the two principal bifurcations in the delta. Results indicate that within 10 to 15 km from the delta apex, the tides alter the river discharge division by about 10% in all bifurcations. The tidal impact increases seaward, with a maximum value of the order of 30%. In general, the effect of tides is to hamper the discharge division that would occur in the case without tides
Discharge estimation from H-ADCP measurements in a tidal river subject to sidewall effects and a mobile bed
Sassi, M.G. ; Hoitink, A.J.F. ; Vermeulen, B. ; Hidayat, H. - \ 2011
Water Resources Research 47 (2011). - ISSN 0043-1397 - 14 p.
open-channel flows - shear-stress - sediment transport - secondary currents - velocity - roughness - sand
Horizontal acoustic Doppler current profilers (H-ADCPs) can be employed to estimate river discharge based on water level measurements and flow velocity array data across a river transect. A new method is presented that accounts for the dip in velocity near the water surface, which is caused by sidewall effects that decrease with the width to depth ratio of a channel. A boundary layer model is introduced to convert single-depth velocity data from the H-ADCP to specific discharge. The parameters of the model include the local roughness length and a dip correction factor, which accounts for the sidewall effects. A regression model is employed to translate specific discharge to total discharge. The method was tested in the River Mahakam, representing a large river of complex bathymetry, where part of the flow is intrinsically three-dimensional and discharge rates exceed 8000 m3 s-1. Results from five moving boat ADCP campaigns covering separate semidiurnal tidal cycles are presented, three of which are used for calibration purposes, whereas the remaining two served for validation of the method. The dip correction factor showed a significant correlation with distance to the wall and bears a strong relation to secondary currents. The sidewall effects appeared to remain relatively constant throughout the tidal cycles under study. Bed roughness length is estimated at periods of maximum velocity, showing more variation at subtidal than at intratidal time scales. Intratidal variations were particularly obvious during bidirectional flow conditions, which occurred only during conditions of low river discharge. The new method was shown to outperform the widely used index velocity method by systematically reducing the relative error in the discharge estimates
The rill experiment as a method to approach a quantification of rill erosion process activity
Wirtz, S. ; Seeger, K.M. ; Ries, J.B. - \ 2010
Zeitschrift für Geomorphologie 54 (2010)1. - ISSN 0372-8854 - p. 47 - 64.
concentrated flow erosion - ephemeral gully erosion - sediment transport - resistance - areas - mine - soil
Within this paper a standardized method to quantify sediment transport and runoff in natural rills is described. In order to achieve this, several rill experiments (RE) were accomplished in March 2007 in the Arnás catchment in the Spanish Pyrenees. Both, anthropogenically initiated and naturally developed rills were flushed with a total water quantity of 72 l in 8 minutes (equivalent to 9 l min-1). For the characterisation of the rill, slope is measured and micromorphological features like scours are registered. The experiments are characterised by the flow velocities along the whole flushed rill, sediment concentrations at different points and different times during the experiment. Runoff is measured after 25 m continuously. With this data, a set of characteristic variables is generated, which reflects the infiltration and flow behaviour along the rill. By means of rainfall simulations within the rills catchments, their contributing runoff was estimated also. The tested rills were developed on average slopes oscillating between 7.6° and 11.3°, the steepest slope reached 16°. The sediment concentrations reached average values between 0.69 and 2.21 g l-1, the maximum values ranged between 1.59 and 6.31 g l-1. Comparing the sediment concentrations measured in the rills to the sediment concentrations in the runoff of the river Arnás, it can be stated that the concentrations in the rills are usually higher. Though, the runoff was to low to cause erosion. Accordingly, the runoff amount that can be produced within the rills catchments was found to be about 10-25 times higher. By means of the developed rill experiments, for which easy to handle devices were built and are described in detail, it becomes possible to assess the effectivity of individual rills in a catchment and to evaluate their hydraulic functioning as well as their geomorphodynamic activity
Multi-process Late Quaternary landscape evolution modelling reveals lags in climate response over small spatial scales
Temme, A.J.A.M. ; Veldkamp, A. - \ 2009
Earth Surface Processes and Landforms 34 (2009)4. - ISSN 0197-9337 - p. 573 - 589.
rudimentary mechanistic model - south-africa - soil redistribution - sediment transport - elevation models - dem resolution - erosion - dynamics - topography - vegetation
Landscapes evolve in complex, non-linear ways over Quaternary timespans. Integrated geomorphological field studies usually yield plausible hypotheses about timing and impact of process activity. Landscape Evolution Models (LEMs) have the potential to test and falsify these landscape evolution hypotheses. Despite this potential, LEMs have mainly been used with hypothetical data and rarely to simulate the evolution of an actual landscape. In this paper, we use a LEM (LAPSUS: LandscApe ProcesS modelling at mUlti dimensions and scaleS) to explore if it is possible to test and falsify conclusions of an earlier field study on 50 ka landscape evolution in Okhombe Valley, KwaZulu Natal, South Africa. In this LEM, five landscape processes interact without supervision: water driven erosion and deposition, creep, solifluction, biological weathering and frost weathering. Calibration matched model results to three types of qualitative fieldwork observations: individual process activity over time, relative process activity over time and net landscape changes over time. Results demonstrate that landscape evolution of the Okhombe valley can be plausibly simulated. A particularly interesting and persistent feature of model results are erosional and depositional phases that lag climatic drivers both by decades, and by several ka within a few hundred meters. The longer lag has not been reported for this spatial scale before and may be an effect of slow landscape-soil-vegetation feedbacks. The combined modelling and fieldwork results allow a more complete understanding of these responses to climate change and can fill in hiatuses in the stratigraphical record. Suggestions are made for methodological adaptations for future LEM studies.
Sand transport dynamics after a foredune breach: a case study from Schoorl, the Netherlands
Meerkerk, A. ; Arens, B. ; Lammeren, R.J.A. van; Stuiver, H.J. - \ 2007
Geomorphology 86 (2007)1-2. - ISSN 0169-555X - p. 52 - 60.
sediment transport - aeolian processes - transverse dunes - natural tracers - profile - models - desert - island - inlet - wind
Near Schoorl in The Netherlands a gap was created in the foredunes during a nature development project in 1997. This resulted in considerable aeolian sand transport and allowed the sea to enter the swale valley behind the foredunes during storm events. From 1997 to 2002 a monitoring program was carried out and various data sets were collected. This study used a part of those data to investigate the effects of a foredune breach on sand transport dynamics. The main focus was on the aeolian transport of sediment through the gap in the dunes. After the breach calcareous beach sand was transported into the swale valley where exclusively decalcified sand was present. This enabled a study of the spatial aspects of transport based on six data sets of carbonate content that were collected during the 1997¿2002 period. Grids of carbonate content were interpolated and analysed together with data on geomorphology, topography and wind characteristics. The results provided insight on the displacement speed of the deposition front of calcareous sand, the influence of transport barriers and the correlation of transport directions with wind data. In addition, the study led to the observation that the trend of increase of available digital data during the last two decades is significant in facilitating the study of sand transport at the landscape scale. This is encouraging given the fact that the practical use of existing sand transport models in this context remains limited.
Suitability of transport equations in modelling soil erosion for a small Loess Plateau catchment
Hessel, R. ; Jetten, V.G. - \ 2007
Engineering Geology 91 (2007)1. - ISSN 0013-7952 - p. 56 - 71.
interrill overland-flow - sediment transport - rough surfaces - capacity - lisem
Erosion models have not often been applied to very steep terrain such as the gully catchments of the Chinese Loess Plateau. The purpose of this research was to evaluate the suitability of a number of transport equations for use in erosion modelling under Loess Plateau conditions. To do this the equations were programmed into the LISEM model, which was applied to the 3.5 km2 Danangou catchment in the rolling hills region of the Loess Plateau. Previous evaluations of transport equations used either flume tests or river sections, and did no spatial modelling. The results show that some equations predicted physically impossible concentrations (defined as above 1060 g/l). The results were evaluated by using two methods: 1) by comparing predicted and measured sedigraphs and sediment yield at the catchment outlet, and 2) by comparing the fraction of the catchment in which physically impossible transport capacities occurred. The results indicated that for the small grain sizes, high density flows and steep slopes of the gully catchments on the Loess Plateau the Shields parameter attained very high values. Furthermore, the transport threshold can usually be neglected in the equations. Most of the resulting equations were too sensitive to slope angle (Abrahams, Schoklitsch, Yalin, Bagnold, Low and Rickenmann), so that transport rates were overpredicted for steep slopes and underpredicted for gentle slopes. The Yang equation appeared to be too sensitive to grainsize. The Govers equation performed best, mainly because of its low slope dependency, and is therefore recommended for erosion models that simulate sediment transport by flowing water in conditions with small grain sizes and steep slopes.