General rights Copyright and moral rights for the publications made accessible in the public port... more General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal Take down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.
west. Our study offers a local framework, but its Pleistocene landscape record has regional signi... more west. Our study offers a local framework, but its Pleistocene landscape record has regional significance. Most of all, it forms a much-needed basis for future, detailed studies on the build-up of the hominin site of Trinil, its fossil assemblages and numerical ages.
ABSTRACT This chapter aims to demonstrate how uncertainty in digital elevation model (DEM) attrib... more ABSTRACT This chapter aims to demonstrate how uncertainty in digital elevation model (DEM) attributes can be quantified using geostatistical methods and to show how the propagation of errors to DEM derived products may be computed. To attribute errors DEMs may have positional errors like a shift along one or both coordinate axes, rotational errors, scaling errors, projection errors, or a combination of these. In this chapter, only attribute errors are considered. It describe how propagation of attribute errors in spatial modeling can be computed using the Monte-Carlo method. This method is the most often used error propagation method because it is generic, flexible, and intuitively appealing. In order of increasing complexity, the chapter considers the propagation of error from DEMs to three derivatives, namely slope (a local land-surface parameter), topographic wetness index (a regional land-surface parameter), and soil redistribution resulting from water erosion (a complex model). It also describes the uncertainty propagation analysis in detail.
Landscape evolution modeling can make the consequences of landscape evolution hypotheses explicit... more Landscape evolution modeling can make the consequences of landscape evolution hypotheses explicit and theoretically allows for their falsification and improvement. Ideally, landscape evolution models (LEMs) combine the results of all relevant landscape forming processes into an ever-adapting digital landscape (e.g. DEM). These processes may act on different spatial and temporal scales. LAPSUS is such a LEM. Processes that have in different studies been included in LAPSUS are water erosion and deposition, landslide activity, creep, solifluction, weathering, tectonics and tillage. Process descriptions are as simple and generic as possible, ensuring wide applicability. Vegetation-effects can be included. Interactions between processes are turn-based: volumes of one process are calculated and used to update the DEM before another process starts. LAPSUS uses multiple flow techniques to model flows of water and sediment over the landscape. Though computationally costly, this gives a more natural result than steepest descent methods. In addition, the combination of different processes may create sinks during modelling. Since these sinks are not spurious, the model has been adapted to deal with them in natural ways. This is crucial for several purposes, for instance when studying damming of valleys by landslides, and subsequent infilling of the resulting lake with sediments from upstream.
Until recently, NW Iberia was assumed to be tectonically quiescent (stable). However, a combinati... more Until recently, NW Iberia was assumed to be tectonically quiescent (stable). However, a combination of tectono-morphological analyses demonstrates that neotectonic movements do occur, which are in agreement with recent findings by other workers. We use a DEM-based tectono-geomorphic approach in combination with field work to assess the presence and nature of neotectonics in the Lower Miño catchment in NW Iberia.
Spatial multi-scale analyses of actual land use system performance as determined by spatial yield... more Spatial multi-scale analyses of actual land use system performance as determined by spatial yield variability reveals the need for landscape research in agronomy. Main`drivers' of spatial yield variability for ®ve different crops in Honduras, Costa Rica and Ecuador were identi®ed. It is demonstrated how they vary with spatial scales and that landscape-related factors often play a large and signi®cant role in when the variability in yield is determined. These results indicate that landscape experiments in agronomy are relevant. Apart from empirical analysis, spatial±temporal explicit modeling of landscape process dynamics such as water and soil redistribution within a landscape can give insight in the performance of agronomic systems within a dynamic landscape context. For a case study in the South of Spain it is demonstrated how within a landscape this type of research can determine the on-and off-site effects of water and soil redistribution in agro-ecosystems. Only after a spatially explicit multi-scale system analysis and explorative landscape process modeling is completed, relevant agronomic landscape experiments can be designed.
In this paper the use of topographical attributes for the analysis of the spatial distribution an... more In this paper the use of topographical attributes for the analysis of the spatial distribution and ecological cycle of kauri (Agathis australis), a canopy emergent conifer tree from northern New Zealand, is studied. Several primary and secondary topographical attributes are derived from a Digital Elevation Model (DEM) for a study area in the Waitakere Ranges. The contribution of these variables in explaining presence or absence of mature kauri is assessed with logistic regression and Receiver Operating Characteristic (ROC) plots. A topographically based landslide hazard index, calculated by combining a steady state hydrologic model with the infinite slope stability equation, appears to be very useful in explaining the occurrence and ecological dynamics of kauri. It is shown that the combination of topographical, soil physical and hydrological parameters in the calculation of this single landslide hazard index, performs better in explaining presence of mature kauri than using topographical attributes calculated from the DEM alone. Moreover, this study demonstrates the possibilities of using terrain attributes for representing geomorphological processes and disturbance mechanisms, often indispensable in explaining a species' ecological cycle. The results of this analysis support the 'temporal stand replacement model', involving disturbance as a dominant ecological process in forest regeneration, as an interpretation of the community dynamics of kauri. Furthermore a threshold maturity stage, in which trees become able to stabilize landslide prone sites and postpone a possible disturbance, together with great longevity are seen as major factors making kauri a 'landscape engineer'.
LAPSUS climate change Monte Carlo method uncertainty analysis South Africa In the light of increa... more LAPSUS climate change Monte Carlo method uncertainty analysis South Africa In the light of increasing societal interest in the effects of climate change, geomorphologists face the task of discriminating between natural landscape changes and landscape changes that result from human-induced climate change. Landscape Evolution Models (LEMs) are available for this purpose, but their application for prediction of future landscapes is problematic. Calibration of LEMs on a sufficiently long palaeo-record of landscape change solves some of these problems, but large uncertainties in input (e.g. climate) records and process descriptions remain. Using one of the few existing ka-scale LEM studies as starting point, this paper explores how uncertainty in the LEM LAPSUS (LandscApe ProcesS modelling at mUlti dimensions and scaleS, [Schoorl, J.M., Veldkamp, A. and Bouma, J., 2002. Modeling water and soil redistribution in a dynamic landscape context. Soil Science Society of America Journal, 66(5): 1610-1619]) affects its ability to discriminate future one-thousand year landscape change under stable climate from that under human-induced changed climate. Okhombe Valley in South Africa is used as a case study area. LEM uncertainty is characterized by different levels of parameter uncertainty. Results indicate that even under high levels of parameter uncertainty, LEM LAPSUS discriminates between responses to stable and changed climates for some zones in the landscape. Although confidence in model predictions remains limited, some explorative and relative conclusions about the effects of changed climate on future landscape evolution of Okhombe Valley are drawn. Finally, some possibilities and limitations of future studies on landscape evolution under changing climate are discussed.
In this study we propose a model to assess the location of shallow landslides and their impact on... more In this study we propose a model to assess the location of shallow landslides and their impact on landscape development within a timeframe of years to decades. Processes that need to be incorporated in the model are reviewed then followed by the proposed modelling framework. The capabilities of the model are explored through an application for a forested 17 km 2 study catchment in Northern New Zealand for which digital elevation data are available with a grid resolution of 25 × 25 m. The model predicts the spatial pattern of landslide susceptibility within the simulated catchment and subsequently applies a spatial algorithm for the redistribution of failed material by effectively changing the corresponding digital elevation data after each timestep on the basis of a scenario of triggering rainfall events, relative landslide hazard and trajectories with runout criteria for failed slope material. The resulting model will form a landslide module within the dynamic landscape evolution model LAPSUS. The model forms a spatially explicit method to address the effects of shallow landslide erosion and sedimentation because digital elevation data are adapted between timesteps and on-and off-site effects over the years can be simulated in this way. By visualization of the modelling results in a GIS environment, the shifting pattern of upslope and downslope (in) stability, triggering of new landslides and the resulting slope retreat by soil material redistribution due to former mass movements can be simulated and assessed.
A sediment record is used, in combination with shallow landslide soil redistribution and sediment... more A sediment record is used, in combination with shallow landslide soil redistribution and sediment-yield modelling, to reconstruct the incidence of high-magnitude/low-frequency landslide events in the upper part of a catchment and the history of a wetland in the lower part. Eleven sediment cores were obtained from a dune-impounded wetland at Te Henga, west Auckland, northern New Zealand. Sediment stratigraphy and chronology were interpreted by radiocarbon dating, foraminiferal analysis, and provisional tephrochronology. Gradual impoundment of the wetland began c. 6000 cal yr BP, coinciding with the start of a gentle sea-level fall, but complete damming and initial sedimentation did not begin until c. 1000 cal yr BP. After damming, four well-defined sediment pulses occurred and these are preserved in the form of distinct clay layers in most of the sediment cores. For interpreting the sediment pulses, a physically based landslide model was used to determine spatially distributed relative landslide hazard, applicable at the catchment scale. An empirical landslide-soil redistribution component was added and proved able to determine the volumes and spatial pattern of eroded and deposited soil material, sediment delivery ratio and the impact on total catchment sediment yield. Sediment volumes were calculated from the wetland cores and corresponding landslide scenarios are defined through back-analysis of modelled sediment yield output. In general, at least four major high-magnitude landslide events, both natural and intensified by forest clearance activities, occurred in the catchment upstream of Te Henga Wetland during the last c. 1000 years. The spatial distribution of modelled critical rainfall values for the catchment can be interpreted as an expression of shallow landslide hazard. The magnitude of the sediment
In semi-arid areas vegetation is scarce and often dominated by individual shrubs on raised mounds... more In semi-arid areas vegetation is scarce and often dominated by individual shrubs on raised mounds. The processes of formation of these mounds are diverse and still debated. Often, shrub mound formation is directly related to the formation of vegetation patterns, thereby assuming that shrub mound formation is driven by biological interactions. We hypothesize that water-related erosion and sedimentation are also important drivers of shrub mound formation in the Northern Negev Desert of Israel. We test this hypothesis by combining field observations with model simulations. We studied shrub mounds in the semi-arid catchment of Sayeret Shaked in the Northern Negev Desert (200 mm annual precipitation). Height and diameter of shrub-canopy and shrub mounds were measured and micro-morphological techniques were used to reconstruct the formation of the shrub mounds. We used landscape evolution model LAPSUS to simulate shrub mound formation at short (single precipitation event) and longer (100 years) timescales at different slope angles. Both field and model results indicate that shrub mounds in Sayeret Shaked are at least partly formed by redeposition of eroded material below the shrubs, and by erosion and lowering of the surrounding crust. Additional model simulations suggest that mounds are formed most under low shrub density and large shrub-canopy diameter. Shrub mound formation increases with slope. In dryer and wetter climates than the studied 200 mm rainfall semi-arid climate zone, shrub mound formation is less likely.
Landscape evolution models (LEMs) quantitatively simulate processes of sedimentation and erosion ... more Landscape evolution models (LEMs) quantitatively simulate processes of sedimentation and erosion on millennial timescales. An important aspect of human impact on erosion is sediment redistribution due to agriculture, referred to herein as tillage erosion. In this study we aim to analyse the potential contribution of tillage erosion to landscape development using LEM LAPSUS. The model is calibrated separately for a water erosion process (i) without tillage and (ii) with tillage. The model is applied to thẽ 250 km 2 Torrealvilla case study catchment, SE Spain. We were able to simulate alternating sequences of incision and aggradation, that are important on longer (millennial) timescales. Generally, model results show that tillage erosion adds to deposition in the lower floodplain area, but neither water erosion alone nor water with tillage erosion together could exactly reproduce the observed amounts of erosion and sedimentation for the case study area. In addition, scale effects are apparent. On hillslopes, tillage may contribute importantly to erosion and may fill local depressions. If assessed on the catchment scale, sediments from tillage erosion eventually reach the lower floodplain area where they contribute to deposition. However, water erosion was observed in the model simulations to be the most important process on the catchment scale. This is the first time that tillage erosion has been explicitly included in a landscape evolution model at a millennial timescale and large catchment scale.
In this paper we analyse the effects of digital elevation model (DEM) resolution on the results o... more In this paper we analyse the effects of digital elevation model (DEM) resolution on the results of a model that simulates spatially explicit relative shallow landslide hazard and soil redistribution patterns and quantities. We analyse distributions of slope, specific catchment area and relative hazard for shallow landsliding for four different DEM resolutions (grid sizes of 10, 25, 50 and 100 m) of a 12 km2 study area in northern New Zealand. The effect of DEM resolution is especially pronounced for the boundary conditions determining a valid hazard calculation. For coarse resolutions, the smoothing effect results in a larger area becoming classified as unconditionally stable or unstable. We apply simple empirical soil redistribution algorithms for scenarios in which all sites with a certain landslide hazard fail and generate debris flow. The lower initial number of failing cells but also the inclusion of slope (limit) in those algorithms becomes apparent with coarser resolutions. F...
Depressions in landscapes function as buffers for water and sediment. A landscape with depression... more Depressions in landscapes function as buffers for water and sediment. A landscape with depressions has less runoff, less erosion and more sedimentation than a landscape without depressions. Sinks in digital elevation models (DEMs) can be existing features that correctly represent depressions in actual landscapes or spurious features that result from errors in DEM creation. In many erosion, landscape and hydrological models, all sinks are considered spurious features and, as a result, these models do not deal with sinks that do represent real depressions. Consequently, erosion is overestimated and sedimentation is underestimated. Dynamic geomorphological models that simulate soil redistribution in modelled landscapes in multiple timesteps have this problem in every timestep. A method that allows these models to deal with depressions in a realistic way is needed. This paper presents an algorithm that allows models in general, and dynamic geomorphological model LAPSUS in particular, to deal with sinks in a DEM and, thus, with depressions in a landscape. An application is presented where LAPSUS runs with the new algorithm are compared to the conventional runs. Results indicate that the new algorithm can realistically model the sediment buffer function of depressions. The inclusion of the new depression algorithm allows modelling landscape processes that can result in depressions, like landsliding, glacial processes and tectonics. It is also demonstrated that static models, running only once with a DEM without sinks, display effects from the filling of the sinks before running.
Landscapes in Southeastern Spain have developed in response to tectonics, climatic fluctuations a... more Landscapes in Southeastern Spain have developed in response to tectonics, climatic fluctuations and, more recently, to human action. In the valleys, fluvial and colluvial sediments are found in the form of river terraces, pediments and slope deposits. We studied these sediments to evaluate landscape dynamics and the processes of sedimentation and erosion in the semi-arid region of the Guadalentín Basin, Murcia Province, SE Spain. The objective of the study is to deduce controls on Late Quaternary and Holocene landscape development. Fieldwork was carried out on the reach of the Upper Guadalentin, upstream of the city of Lorca, and two of its tributaries (Rio Velez and Rambla de Torrealvilla). River terrace levels were mapped using GPS and presence of gravel layers in outcrops. For the Rambla de Torrealvilla, more detailed sediment descriptions show their build-up. Charcoal was found and dated (14C) on ten locations, while 15 samples for Optically Stimulated Luminescence (OSL) dating were taken to have an age-control on processes of sedimentation and erosion. While the OSL dating measurements and analysis are still in process at this time, some preliminary results are given. Several terrace levels are identified along the Rio Guadalentin and the Rio Velez. These have formed in response to regional and/or global changes in climate. However, local mechanisms have played an important role in the area, overruling regional dynamics. From finely layered sediments, it is deduced that a lake existed during some time in the area, caused by a blockage of the valley. This lake was filled in with sediments and a delta was build at its end, interfering with terrace levels. When the blockage was broken through, lake sediments have been removed and after incision, younger terraces have developed. The Torrealvilla tributary is draining the Lorca Basin, and sediments seem to be younger than those along the Guadalentin and Velez rivers. Infilling of the basin and incomplete removal has shaped this valley. Outcrops in the gully sidewall show stacked layers of large to fine gravels and fine sediments with smaller gravel layers in between. We will present a conceptual model of landscape development since the Late Quaternary based on the age control (14C and OSL) and field observations. This reconstruction is correlated to climatic fluctuations and rates of sedimentation and erosion are approximated on a millennial timescale. Following this approach of longer-term geomorphological investigation of landscape development, we can ultimately put the relative contribution of human actions in the context of natural erosion and sedimentation processes.
Calibration of landscape evolution models (LEMs) needs long term input data on climate and soil r... more Calibration of landscape evolution models (LEMs) needs long term input data on climate and soil redistribution. Rainfall data over the last decades can often be estimated from field stations and interpolation. A decadal estimate of soil redistribution can be derived from analysing the spatial variation of the Caesium-137 inventory in the soil. The objective of this case study is to calibrate LEM LAPSUS for a small watershed in Taiwan, using historical rainfall records and Caesium-137 derived soil redistribution estimates. In general, the point location soil redistribution estimates from the Caesium-137 activity can be modelled with LAPSUS within a certain margin of error. However, the LAPSUS soil redistribution maps can differ considerably from the point-interpolation derived maps. This is mainly due to the process based LAPSUS methodology, where the DEM and water flow routing are the main driving factors.
Rivers tend to develop towards an equilibrium length profile, independently of exogenous factors.... more Rivers tend to develop towards an equilibrium length profile, independently of exogenous factors. In general, although still under debate, this so-called self-organisation is assumed to be caused by simple feedbacks between sedimentation and erosion. Erosion correlates positively with gradient and discharge and sedimentation negatively. With the LAPSUS model, which was run for the catchment of the Sabinal, a small river in the South of Spain, this interplay of erosion and sedimentation results in sediment pulses (sequences of incision and sedimentation through time). These pulses are visualised in a short movie (see http://www.youtube.com/watch?v=V5LDUMvYZxU). In this case the LAPSUS model run did not take climate, base level nor tectonics into account. Therefore, these pulses can be considered independent of them. Furthermore, different scenarios show that the existence of the pulses is independent of precipitation, erodibility and sedimentation rate, although they control the number and shape of the pulses. A fieldwork check showed the plausibility of the occurrence of these sediment pulses. We conclude that the pulses as modelled with LAPSUS are indeed the consequence of the feedbacks between erosion and sedimentation and are not depending on exogenous factors.
General rights Copyright and moral rights for the publications made accessible in the public port... more General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal Take down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.
west. Our study offers a local framework, but its Pleistocene landscape record has regional signi... more west. Our study offers a local framework, but its Pleistocene landscape record has regional significance. Most of all, it forms a much-needed basis for future, detailed studies on the build-up of the hominin site of Trinil, its fossil assemblages and numerical ages.
ABSTRACT This chapter aims to demonstrate how uncertainty in digital elevation model (DEM) attrib... more ABSTRACT This chapter aims to demonstrate how uncertainty in digital elevation model (DEM) attributes can be quantified using geostatistical methods and to show how the propagation of errors to DEM derived products may be computed. To attribute errors DEMs may have positional errors like a shift along one or both coordinate axes, rotational errors, scaling errors, projection errors, or a combination of these. In this chapter, only attribute errors are considered. It describe how propagation of attribute errors in spatial modeling can be computed using the Monte-Carlo method. This method is the most often used error propagation method because it is generic, flexible, and intuitively appealing. In order of increasing complexity, the chapter considers the propagation of error from DEMs to three derivatives, namely slope (a local land-surface parameter), topographic wetness index (a regional land-surface parameter), and soil redistribution resulting from water erosion (a complex model). It also describes the uncertainty propagation analysis in detail.
Landscape evolution modeling can make the consequences of landscape evolution hypotheses explicit... more Landscape evolution modeling can make the consequences of landscape evolution hypotheses explicit and theoretically allows for their falsification and improvement. Ideally, landscape evolution models (LEMs) combine the results of all relevant landscape forming processes into an ever-adapting digital landscape (e.g. DEM). These processes may act on different spatial and temporal scales. LAPSUS is such a LEM. Processes that have in different studies been included in LAPSUS are water erosion and deposition, landslide activity, creep, solifluction, weathering, tectonics and tillage. Process descriptions are as simple and generic as possible, ensuring wide applicability. Vegetation-effects can be included. Interactions between processes are turn-based: volumes of one process are calculated and used to update the DEM before another process starts. LAPSUS uses multiple flow techniques to model flows of water and sediment over the landscape. Though computationally costly, this gives a more natural result than steepest descent methods. In addition, the combination of different processes may create sinks during modelling. Since these sinks are not spurious, the model has been adapted to deal with them in natural ways. This is crucial for several purposes, for instance when studying damming of valleys by landslides, and subsequent infilling of the resulting lake with sediments from upstream.
Until recently, NW Iberia was assumed to be tectonically quiescent (stable). However, a combinati... more Until recently, NW Iberia was assumed to be tectonically quiescent (stable). However, a combination of tectono-morphological analyses demonstrates that neotectonic movements do occur, which are in agreement with recent findings by other workers. We use a DEM-based tectono-geomorphic approach in combination with field work to assess the presence and nature of neotectonics in the Lower Miño catchment in NW Iberia.
Spatial multi-scale analyses of actual land use system performance as determined by spatial yield... more Spatial multi-scale analyses of actual land use system performance as determined by spatial yield variability reveals the need for landscape research in agronomy. Main`drivers' of spatial yield variability for ®ve different crops in Honduras, Costa Rica and Ecuador were identi®ed. It is demonstrated how they vary with spatial scales and that landscape-related factors often play a large and signi®cant role in when the variability in yield is determined. These results indicate that landscape experiments in agronomy are relevant. Apart from empirical analysis, spatial±temporal explicit modeling of landscape process dynamics such as water and soil redistribution within a landscape can give insight in the performance of agronomic systems within a dynamic landscape context. For a case study in the South of Spain it is demonstrated how within a landscape this type of research can determine the on-and off-site effects of water and soil redistribution in agro-ecosystems. Only after a spatially explicit multi-scale system analysis and explorative landscape process modeling is completed, relevant agronomic landscape experiments can be designed.
In this paper the use of topographical attributes for the analysis of the spatial distribution an... more In this paper the use of topographical attributes for the analysis of the spatial distribution and ecological cycle of kauri (Agathis australis), a canopy emergent conifer tree from northern New Zealand, is studied. Several primary and secondary topographical attributes are derived from a Digital Elevation Model (DEM) for a study area in the Waitakere Ranges. The contribution of these variables in explaining presence or absence of mature kauri is assessed with logistic regression and Receiver Operating Characteristic (ROC) plots. A topographically based landslide hazard index, calculated by combining a steady state hydrologic model with the infinite slope stability equation, appears to be very useful in explaining the occurrence and ecological dynamics of kauri. It is shown that the combination of topographical, soil physical and hydrological parameters in the calculation of this single landslide hazard index, performs better in explaining presence of mature kauri than using topographical attributes calculated from the DEM alone. Moreover, this study demonstrates the possibilities of using terrain attributes for representing geomorphological processes and disturbance mechanisms, often indispensable in explaining a species' ecological cycle. The results of this analysis support the 'temporal stand replacement model', involving disturbance as a dominant ecological process in forest regeneration, as an interpretation of the community dynamics of kauri. Furthermore a threshold maturity stage, in which trees become able to stabilize landslide prone sites and postpone a possible disturbance, together with great longevity are seen as major factors making kauri a 'landscape engineer'.
LAPSUS climate change Monte Carlo method uncertainty analysis South Africa In the light of increa... more LAPSUS climate change Monte Carlo method uncertainty analysis South Africa In the light of increasing societal interest in the effects of climate change, geomorphologists face the task of discriminating between natural landscape changes and landscape changes that result from human-induced climate change. Landscape Evolution Models (LEMs) are available for this purpose, but their application for prediction of future landscapes is problematic. Calibration of LEMs on a sufficiently long palaeo-record of landscape change solves some of these problems, but large uncertainties in input (e.g. climate) records and process descriptions remain. Using one of the few existing ka-scale LEM studies as starting point, this paper explores how uncertainty in the LEM LAPSUS (LandscApe ProcesS modelling at mUlti dimensions and scaleS, [Schoorl, J.M., Veldkamp, A. and Bouma, J., 2002. Modeling water and soil redistribution in a dynamic landscape context. Soil Science Society of America Journal, 66(5): 1610-1619]) affects its ability to discriminate future one-thousand year landscape change under stable climate from that under human-induced changed climate. Okhombe Valley in South Africa is used as a case study area. LEM uncertainty is characterized by different levels of parameter uncertainty. Results indicate that even under high levels of parameter uncertainty, LEM LAPSUS discriminates between responses to stable and changed climates for some zones in the landscape. Although confidence in model predictions remains limited, some explorative and relative conclusions about the effects of changed climate on future landscape evolution of Okhombe Valley are drawn. Finally, some possibilities and limitations of future studies on landscape evolution under changing climate are discussed.
In this study we propose a model to assess the location of shallow landslides and their impact on... more In this study we propose a model to assess the location of shallow landslides and their impact on landscape development within a timeframe of years to decades. Processes that need to be incorporated in the model are reviewed then followed by the proposed modelling framework. The capabilities of the model are explored through an application for a forested 17 km 2 study catchment in Northern New Zealand for which digital elevation data are available with a grid resolution of 25 × 25 m. The model predicts the spatial pattern of landslide susceptibility within the simulated catchment and subsequently applies a spatial algorithm for the redistribution of failed material by effectively changing the corresponding digital elevation data after each timestep on the basis of a scenario of triggering rainfall events, relative landslide hazard and trajectories with runout criteria for failed slope material. The resulting model will form a landslide module within the dynamic landscape evolution model LAPSUS. The model forms a spatially explicit method to address the effects of shallow landslide erosion and sedimentation because digital elevation data are adapted between timesteps and on-and off-site effects over the years can be simulated in this way. By visualization of the modelling results in a GIS environment, the shifting pattern of upslope and downslope (in) stability, triggering of new landslides and the resulting slope retreat by soil material redistribution due to former mass movements can be simulated and assessed.
A sediment record is used, in combination with shallow landslide soil redistribution and sediment... more A sediment record is used, in combination with shallow landslide soil redistribution and sediment-yield modelling, to reconstruct the incidence of high-magnitude/low-frequency landslide events in the upper part of a catchment and the history of a wetland in the lower part. Eleven sediment cores were obtained from a dune-impounded wetland at Te Henga, west Auckland, northern New Zealand. Sediment stratigraphy and chronology were interpreted by radiocarbon dating, foraminiferal analysis, and provisional tephrochronology. Gradual impoundment of the wetland began c. 6000 cal yr BP, coinciding with the start of a gentle sea-level fall, but complete damming and initial sedimentation did not begin until c. 1000 cal yr BP. After damming, four well-defined sediment pulses occurred and these are preserved in the form of distinct clay layers in most of the sediment cores. For interpreting the sediment pulses, a physically based landslide model was used to determine spatially distributed relative landslide hazard, applicable at the catchment scale. An empirical landslide-soil redistribution component was added and proved able to determine the volumes and spatial pattern of eroded and deposited soil material, sediment delivery ratio and the impact on total catchment sediment yield. Sediment volumes were calculated from the wetland cores and corresponding landslide scenarios are defined through back-analysis of modelled sediment yield output. In general, at least four major high-magnitude landslide events, both natural and intensified by forest clearance activities, occurred in the catchment upstream of Te Henga Wetland during the last c. 1000 years. The spatial distribution of modelled critical rainfall values for the catchment can be interpreted as an expression of shallow landslide hazard. The magnitude of the sediment
In semi-arid areas vegetation is scarce and often dominated by individual shrubs on raised mounds... more In semi-arid areas vegetation is scarce and often dominated by individual shrubs on raised mounds. The processes of formation of these mounds are diverse and still debated. Often, shrub mound formation is directly related to the formation of vegetation patterns, thereby assuming that shrub mound formation is driven by biological interactions. We hypothesize that water-related erosion and sedimentation are also important drivers of shrub mound formation in the Northern Negev Desert of Israel. We test this hypothesis by combining field observations with model simulations. We studied shrub mounds in the semi-arid catchment of Sayeret Shaked in the Northern Negev Desert (200 mm annual precipitation). Height and diameter of shrub-canopy and shrub mounds were measured and micro-morphological techniques were used to reconstruct the formation of the shrub mounds. We used landscape evolution model LAPSUS to simulate shrub mound formation at short (single precipitation event) and longer (100 years) timescales at different slope angles. Both field and model results indicate that shrub mounds in Sayeret Shaked are at least partly formed by redeposition of eroded material below the shrubs, and by erosion and lowering of the surrounding crust. Additional model simulations suggest that mounds are formed most under low shrub density and large shrub-canopy diameter. Shrub mound formation increases with slope. In dryer and wetter climates than the studied 200 mm rainfall semi-arid climate zone, shrub mound formation is less likely.
Landscape evolution models (LEMs) quantitatively simulate processes of sedimentation and erosion ... more Landscape evolution models (LEMs) quantitatively simulate processes of sedimentation and erosion on millennial timescales. An important aspect of human impact on erosion is sediment redistribution due to agriculture, referred to herein as tillage erosion. In this study we aim to analyse the potential contribution of tillage erosion to landscape development using LEM LAPSUS. The model is calibrated separately for a water erosion process (i) without tillage and (ii) with tillage. The model is applied to thẽ 250 km 2 Torrealvilla case study catchment, SE Spain. We were able to simulate alternating sequences of incision and aggradation, that are important on longer (millennial) timescales. Generally, model results show that tillage erosion adds to deposition in the lower floodplain area, but neither water erosion alone nor water with tillage erosion together could exactly reproduce the observed amounts of erosion and sedimentation for the case study area. In addition, scale effects are apparent. On hillslopes, tillage may contribute importantly to erosion and may fill local depressions. If assessed on the catchment scale, sediments from tillage erosion eventually reach the lower floodplain area where they contribute to deposition. However, water erosion was observed in the model simulations to be the most important process on the catchment scale. This is the first time that tillage erosion has been explicitly included in a landscape evolution model at a millennial timescale and large catchment scale.
In this paper we analyse the effects of digital elevation model (DEM) resolution on the results o... more In this paper we analyse the effects of digital elevation model (DEM) resolution on the results of a model that simulates spatially explicit relative shallow landslide hazard and soil redistribution patterns and quantities. We analyse distributions of slope, specific catchment area and relative hazard for shallow landsliding for four different DEM resolutions (grid sizes of 10, 25, 50 and 100 m) of a 12 km2 study area in northern New Zealand. The effect of DEM resolution is especially pronounced for the boundary conditions determining a valid hazard calculation. For coarse resolutions, the smoothing effect results in a larger area becoming classified as unconditionally stable or unstable. We apply simple empirical soil redistribution algorithms for scenarios in which all sites with a certain landslide hazard fail and generate debris flow. The lower initial number of failing cells but also the inclusion of slope (limit) in those algorithms becomes apparent with coarser resolutions. F...
Depressions in landscapes function as buffers for water and sediment. A landscape with depression... more Depressions in landscapes function as buffers for water and sediment. A landscape with depressions has less runoff, less erosion and more sedimentation than a landscape without depressions. Sinks in digital elevation models (DEMs) can be existing features that correctly represent depressions in actual landscapes or spurious features that result from errors in DEM creation. In many erosion, landscape and hydrological models, all sinks are considered spurious features and, as a result, these models do not deal with sinks that do represent real depressions. Consequently, erosion is overestimated and sedimentation is underestimated. Dynamic geomorphological models that simulate soil redistribution in modelled landscapes in multiple timesteps have this problem in every timestep. A method that allows these models to deal with depressions in a realistic way is needed. This paper presents an algorithm that allows models in general, and dynamic geomorphological model LAPSUS in particular, to deal with sinks in a DEM and, thus, with depressions in a landscape. An application is presented where LAPSUS runs with the new algorithm are compared to the conventional runs. Results indicate that the new algorithm can realistically model the sediment buffer function of depressions. The inclusion of the new depression algorithm allows modelling landscape processes that can result in depressions, like landsliding, glacial processes and tectonics. It is also demonstrated that static models, running only once with a DEM without sinks, display effects from the filling of the sinks before running.
Landscapes in Southeastern Spain have developed in response to tectonics, climatic fluctuations a... more Landscapes in Southeastern Spain have developed in response to tectonics, climatic fluctuations and, more recently, to human action. In the valleys, fluvial and colluvial sediments are found in the form of river terraces, pediments and slope deposits. We studied these sediments to evaluate landscape dynamics and the processes of sedimentation and erosion in the semi-arid region of the Guadalentín Basin, Murcia Province, SE Spain. The objective of the study is to deduce controls on Late Quaternary and Holocene landscape development. Fieldwork was carried out on the reach of the Upper Guadalentin, upstream of the city of Lorca, and two of its tributaries (Rio Velez and Rambla de Torrealvilla). River terrace levels were mapped using GPS and presence of gravel layers in outcrops. For the Rambla de Torrealvilla, more detailed sediment descriptions show their build-up. Charcoal was found and dated (14C) on ten locations, while 15 samples for Optically Stimulated Luminescence (OSL) dating were taken to have an age-control on processes of sedimentation and erosion. While the OSL dating measurements and analysis are still in process at this time, some preliminary results are given. Several terrace levels are identified along the Rio Guadalentin and the Rio Velez. These have formed in response to regional and/or global changes in climate. However, local mechanisms have played an important role in the area, overruling regional dynamics. From finely layered sediments, it is deduced that a lake existed during some time in the area, caused by a blockage of the valley. This lake was filled in with sediments and a delta was build at its end, interfering with terrace levels. When the blockage was broken through, lake sediments have been removed and after incision, younger terraces have developed. The Torrealvilla tributary is draining the Lorca Basin, and sediments seem to be younger than those along the Guadalentin and Velez rivers. Infilling of the basin and incomplete removal has shaped this valley. Outcrops in the gully sidewall show stacked layers of large to fine gravels and fine sediments with smaller gravel layers in between. We will present a conceptual model of landscape development since the Late Quaternary based on the age control (14C and OSL) and field observations. This reconstruction is correlated to climatic fluctuations and rates of sedimentation and erosion are approximated on a millennial timescale. Following this approach of longer-term geomorphological investigation of landscape development, we can ultimately put the relative contribution of human actions in the context of natural erosion and sedimentation processes.
Calibration of landscape evolution models (LEMs) needs long term input data on climate and soil r... more Calibration of landscape evolution models (LEMs) needs long term input data on climate and soil redistribution. Rainfall data over the last decades can often be estimated from field stations and interpolation. A decadal estimate of soil redistribution can be derived from analysing the spatial variation of the Caesium-137 inventory in the soil. The objective of this case study is to calibrate LEM LAPSUS for a small watershed in Taiwan, using historical rainfall records and Caesium-137 derived soil redistribution estimates. In general, the point location soil redistribution estimates from the Caesium-137 activity can be modelled with LAPSUS within a certain margin of error. However, the LAPSUS soil redistribution maps can differ considerably from the point-interpolation derived maps. This is mainly due to the process based LAPSUS methodology, where the DEM and water flow routing are the main driving factors.
Rivers tend to develop towards an equilibrium length profile, independently of exogenous factors.... more Rivers tend to develop towards an equilibrium length profile, independently of exogenous factors. In general, although still under debate, this so-called self-organisation is assumed to be caused by simple feedbacks between sedimentation and erosion. Erosion correlates positively with gradient and discharge and sedimentation negatively. With the LAPSUS model, which was run for the catchment of the Sabinal, a small river in the South of Spain, this interplay of erosion and sedimentation results in sediment pulses (sequences of incision and sedimentation through time). These pulses are visualised in a short movie (see http://www.youtube.com/watch?v=V5LDUMvYZxU). In this case the LAPSUS model run did not take climate, base level nor tectonics into account. Therefore, these pulses can be considered independent of them. Furthermore, different scenarios show that the existence of the pulses is independent of precipitation, erodibility and sedimentation rate, although they control the number and shape of the pulses. A fieldwork check showed the plausibility of the occurrence of these sediment pulses. We conclude that the pulses as modelled with LAPSUS are indeed the consequence of the feedbacks between erosion and sedimentation and are not depending on exogenous factors.
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Papers by J. Schoorl