J.M. Schoorl

Three‐dimensional landscape process modelling: the effect of DEM resolution

Many landscape models have been developed over the past decades; however, relatively little is known about handling the effects of changing spatial and temporal resolutions. Therefore, resolution effects remain a factor of uncertainty in many hydrological and geomorphological modelling approaches. In this paper we present an experimental multi-scale study of landscape process modelling. Emphasis was laid on quantifying the effect of changing the spatial resolution upon modelling the processes of erosion and sedimentation. A simple single process model was constructed and equal boundary conditions were created. Using artificial digital elevation models (DEMs) eliminated effects of landscape representation. The only variable factors were DEM resolution and the method of flow routing, both steepest descent and multiple flow directions. Our experiments revealed an important dependency of modelled erosion and sedimentation rates on these main variables. The general trend is an increase of erosion predictions with coarser resolutions. An artificial mathematical overestimation of erosion and a realistic natural modelling effect of underestimating resedimentation cause this. Increasing the spatial extent eliminates the artificial effect while at the same time the realistic effect is enhanced. Both effects can be quantified and are expected to increase within natural landscapes. The modelling of landscape processes will benefit from integrating these types of results at different resolutions

Linking land use and landscape process modelling: a case study for the Álora region (south Spain)

Changing land use is increasingly known to affect on-site landscape properties, nevertheless off-site effects are often neglected. A single process landscape evolution model (LandscApe ProcesS modelling at mUlti dimensions and scaleS (LAPSUS)) is used to explore the impacts of land use changes on landscape and soil properties. Examples are shown for both on-site as well as off-site effects of land use change and the influence of different pathways of change. A case study area near Alora, in the province of Malaga, south Spain is selected. In this area the main land use consists of citrus, olive/almond, wheat, semi-natural vegetation and a rest group (bare, river beds, urban). For a period of 10 years LAPSUS calculates soil redistribution (erosion and sedimentation) for different scenarios of input parameters. These inputs are a digital elevation model (e.g. slope lengths and angles), precipitation, soil erodibility, and land use related infiltration. For each scenario, different assumptions are made on direction and rate of land use change. As an example, effects of abandonment of olive orchards are demonstrated, simulating both a fast and gradual change for a period of 10 years. Each scenario produces different spatial and temporal patterns of total amounts of erosion and sedimentation throughout the landscape. As a result, potential land use related parameters like soil depth, infiltration and flooding risk change significantly too. The scenario of an abrupt change produces the highest erosion rates compared to the gradual change scenario and the baseline scenario. However, because of the multi-dimensional characteristics of the landscape, not only the area suffering from land use changes is affected. Increasing erosion and run-off rates from upstream-located olive orchards have an impact on down slope local run-on, erosion and sedimentation rates. In this case, the citrus orchards situated in the valley bottom locally suffer damages from re-sedimentation events but benefit from the increase in run-on water and nutrients. Concluding, off-site effects from an exogenous driven change in land use (EC subsidies) can trigger endogenous land use changes in adjacent areas.

Multi-scale system approaches in agronomic research at the landscape level

Abstract 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 five different crops in Honduras, Costa Rica and Ecuador were identified. It is demonstrated how they vary with spatial scales and that landscape-related factors often play a large and significant 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.

Algorithm for dealing with depressions in dynamic landscape evolution models

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.

Modeling longitudinal-profile development in response to Late Quaternary tectonics, climate and sea-level changes: the River Meuse

Abstract We present a forward-modelling case study for the development of the longitudinal profile of a basin–marginal fluvial system (River Meuse, NW Europe) responding to Late Quaternary tectonics, climate and sea-level changes. Modelling results show that river reaches in different tectonic domains will respond differently to isochronous events of climate and sea-level change. Climatic change dominates river–valley development in the long-term uplifting upper and middle Meuse reaches (NE Paris Basin, Ardennes, terrace flight area). An alternation of stadial depositional and interstadial erosional phases causes net aggradation of the river valley during glacials, but the river valley considerably degrades during interglacials. The long-term trend in these upper and middle reaches is river–valley degradation. Continuous aggradation leads to long-term deposition during glacials in the subsiding lower Meuse reaches, including the greater part of the Venlo-Block area, the western Roer Valley Graben and the southern part of the West Netherlands Basin. However, decreasing sediment supply combined with increasing discharges at the start of interglacials favours discharge-controlled (kinetic) incision in these net-depositional areas. Post-glacial sea-level rise and the subsequent interglacial highstand strongly influence the subsiding graben areas and the southern West Netherlands Basin. Rising sea level generates a zone of gradient-backfilling that migrates upstream with time. Consequently, the terrace intersection migrates upstream too and a coastal prism is built up during the interglacial highstand. The present case study indicates that the Meuse terrace intersection may migrate to at least 113 km upstream from the modelled coastline. The model also suggests post-interglacial incision of the Eemian highstand coastal prism during the subsequent relative sea-level fall in the Early Weichselian.

Contribution of Topographically Based Landslide Hazard Modelling to the Analysis of the Spatial Distribution and Ecology of Kauri (Agathis australis)

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’.

Late Cenozoic landscape development and its tectonic implications for the Guadalhorce valley near Álora (Southern Spain)

Abstract Landscape evolution is the result of a variety of geomorphological processes and their controls in time. In southern Spain tectonics, climate and sea-level fluctuations have been some of the main variables controlling long-term (Late Cenozoic) landscape evolution. In the Guadalhorce valley, Malaga, geomorphological reconstructions can be undertaken using sedimentary evidence from marine and fluvial deposits as well as erosional evidence such as terrain form and longitudinal profile analysis. Data are obtained and analysed from the Upper Miocene to present. These allow reconstructions which add information and constraints to the uplift history and landscape development of the area. Main sedimentation phases are the Late Tortonian, Early Pliocene and Pleistocene. Important erosional hiatus are found for the Middle Miocene, Messinian and Late Pliocene to Early Pleistocene. These phases of erosion and sedimentation resulted in a relative large and elongated Tortonian marine valley filled with complex sedimentary structures. Next, a prolonged stage of erosion of these deposits and incision of the major valley system took place during the Messinian. In the Pliocene, a short palaeo-Guadalhorce, in a narrow and much smaller valley existed. This valley was partly filled with marine sediments and prograding fan delta complexes. During the Pleistocene, a wider and larger incising river system resulted in rearrangements of the drainage network. Evaluating the uplift history of the area, we found that rates of tectonic activity were higher during the Tortonian–Messinian and Upper Pleistocene, while tectonic activity was lower during the Pliocene. Relative uplift rates for the study area range for the Messinian between 160 and 276 m Ma−1, for the Pliocene between 10 and 15 m Ma−1 and for the Pleistocene between 40 and 100 m Ma−1.

Chapter 5 Geostatistical Simulation and Error Propagation in Geomorphometry

Publisher Summary 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.

Developing, choosing and using landscape evolution models to inform field-based landscape reconstruction studies: Developing, choosing and using landscape evolution models

Landscape evolution models (LEMs) are an increasingly popular resource for geomorphologists as they can operate as virtual laboratories where the implications of hypotheses about processes over human to geological timescales can be visualized at spatial scales from catchments to mountain ranges. Hypothetical studies for idealized landscapes have dominated, although model testing in real landscapes has also been undertaken. So far however, numerical landscape evolution models have rarely been used to aid field-based reconstructions of the geomorphic evolution of actual landscapes. To help make this use more common, we review numerical landscape evolution models from the point of view of model use in field reconstruction studies. We first give a broad overview of the main assumptions and choices made in many LEMs to help prospective users select models appropriate to their field situation. We then summarize for various timescales which data are typically available and which models are appropriate. Finally, we provide guidance on how to set up a model study as a function of available data and the type of research question. Copyright

Fluvial terraces of the northwest Iberian lower Miño River

A new fluvial terrace map with a tectonic framework for the northwest Iberian lower Miño River is presented. It is the first integrated map to cover the entire lower, 67-km reach of the Miño River, and to cover both the Spanish and Portuguese side of the river. The map is presented at a scale of 1:200,000, although its features were mapped at a scale of 1:5000. Various map layers can be viewed, such as a digital elevation model (DEM), fluvial sediment thickness layers, a palaeoflow direction layer, a lineament and fault layer, and two terrace and tectonic basin layers, showing up to 10 fluvial terraces and a floodplain level. Interpretation of the map shows that next to regional tectonic uplift and glacioeustacy, local basin subsidence and small-scale block movement are very important for the fluvial network, localised fluvial terrace formation, and preservation.