Landscape Evolution

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Gregory E. Tucker - One of the best experts on this subject based on the ideXlab platform.

  • Developing and exploring a theory for the lateral erosion of bedrock channels for use in Landscape Evolution models
    Earth Surface Dynamics, 2018
    Co-Authors: Abigail L. Langston, Gregory E. Tucker
    Abstract:

    Abstract. Understanding how a bedrock river erodes its banks laterally is a frontier in geomorphology. Theories for the vertical incision of bedrock channels are widely implemented in the current generation of Landscape Evolution models. However, in general existing models do not seek to implement the lateral migration of bedrock channel walls. This is problematic, as modeling geomorphic processes such as terrace formation and hillslope–channel coupling depends on the accurate simulation of valley widening. We have developed and implemented a theory for the lateral migration of bedrock channel walls in a catchment-scale Landscape Evolution model. Two model formulations are presented, one representing the slow process of widening a bedrock canyon and the other representing undercutting, slumping, and rapid downstream sediment transport that occurs in softer bedrock. Model experiments were run with a range of values for bedrock erodibility and tendency towards transport- or detachment-limited behavior and varying magnitudes of sediment flux and water discharge in order to determine the role that each plays in the development of wide bedrock valleys. The results show that this simple, physics-based theory for the lateral erosion of bedrock channels produces bedrock valleys that are many times wider than the grid discretization scale. This theory for the lateral erosion of bedrock channel walls and the numerical implementation of the theory in a catchment-scale Landscape Evolution model is a significant first step towards understanding the factors that control the rates and spatial extent of wide bedrock valleys.

  • Developing and evaluating a theory for the lateral erosion of bedrock channels for use in Landscape Evolution models
    2017
    Co-Authors: Abigail L. Langston, Gregory E. Tucker
    Abstract:

    Abstract. Understanding how a bedrock river erodes its banks laterally is a frontier in geomorphology. Theory for the vertical incision of bedrock channels is widely implemented in the current generation of Landscape Evolution models. However, in general existing models do not seek to implement the lateral migration of bedrock channel walls. This is problematic, as modeling geomorphic processes such as terrace formation and hillslope-channel coupling depends on accurate simulation of valley widening. We have developed and implemented a theory for the lateral migration of bedrock channel walls in a catchment-scale Landscape Evolution model. Two model formulations are presented, one representing the slow process of widening a bedrock canyon, the other representing undercutting, slumping, and rapid downstream sediment transport that occurs in softer bedrock. Model experiments were run with a range of values for bedrock erodibility and tendency towards transport- or detachment-limited behavior and varying magnitudes of sediment flux and water discharge in order to determine the role each plays in the development of wide bedrock valleys. Results show that this simple, physics-based theory for the lateral erosion of bedrock channels produces bedrock valleys that are many times wider than the grid discretization scale. This theory for the lateral erosion of bedrock channel walls and the numerical implementation of the theory in a catchment-scale Landscape Evolution model is a significant first step towards understanding the factors that control the rates and spatial extent of wide bedrock valleys.

  • Modelling Landscape Evolution
    Earth Surface Processes and Landforms, 2010
    Co-Authors: Gregory E. Tucker, G.r. Hancock
    Abstract:

    Geomorphology is currently in a period of resurgence as we seek to explain the diversity, origins and dynamics of terrain on the Earth and other planets in an era of increased environmental awareness. Yet there is a great deal we still do not know about the physics and chemistry of the processes that weaken rock and transport mass across a planet's surface. Discovering and refining the relevant geomorphic transport functions requires a combination of careful field measurements, lab experiments, and use of longer-term natural experiments to test current theory and develop new understandings. Landscape Evolution models have an important role to play in sharpening our thinking, guiding us toward the right observables, and mapping out the logical consequences of transport laws, both alone and in combination with other salient processes. Improved quantitative characterization of terrain and process, and an ever-improving theory that describes the continual modification of topography by the many and varied processes that shape it, together with improved observation and qualitative and quantitative modelling of geology, vegetation and erosion processes, will provide insights into the mechanisms that control catchment form and function. This paper reviews Landscape theory – in the form of numerical models of drainage basin Evolution and the current knowledge gaps and future computing challenges that exist. Copyright © 2010 John Wiley & Sons, Ltd.

  • modeling fluvial incision and transient Landscape Evolution influence of dynamic channel adjustment
    Journal of Geophysical Research, 2008
    Co-Authors: Mikael Attal, Gregory E. Tucker, Alexander C Whittaker, P A Cowie, Gerald P Roberts
    Abstract:

    [1] Channel geometry exerts a fundamental control on fluvial processes. Recent work has shown that bedrock channel width depends on a number of parameters, including channel slope, and is not solely a function of drainage area as is commonly assumed. The present work represents the first attempt to investigate the consequences of dynamic, gradient-sensitive channel adjustment for drainage-basin Evolution. We use the Channel-Hillslope Integrated Landscape Development (CHILD) model to analyze the response of a catchment to a given tectonic perturbation, using, as a template, the topography of a well-documented catchment in the footwall of an active normal fault in the Apennines (Italy) that is known to be undergoing a transient response to tectonic forcing. We show that the observed transient response can be reproduced to first order with a simple detachment-limited fluvial incision law. Transient Landscape is characterized by gentler gradients and a shorter response time when dynamic channel adjustment is allowed. The differences in predicted channel geometry between the static case (width dependent solely on upstream area) and dynamic case (width dependent on both drainage area and channel slope) lead to contrasting Landscape morphologies when integrated at the scale of a whole catchment, particularly in presence of strong tilting and/or pronounced slip-rate acceleration. Our results emphasize the importance of channel width in controlling fluvial processes and Landscape Evolution. They stress the need for using a dynamic hydraulic scaling law when modeling Landscape Evolution, particularly when the relative uplift field is nonuniform.

  • implications of sediment flux dependent river incision models for Landscape Evolution
    Journal of Geophysical Research, 2002
    Co-Authors: Kelin X Whipple, Gregory E. Tucker
    Abstract:

    [1] Developing a quantitative understanding of the factors that control the rate of river incision into bedrock is critical to studies of Landscape Evolution and the linkages between climate, erosion, and tectonics. Current models of long-term river network incision differ significantly in their treatment of the role of sediment flux. We analyze the implications of various sediment-flux-dependent incision models for large-scale topography, in an attempt (1) to identify quantifiable and diagnostic differences between models that could be detected from topographic data or from the transient responses of perturbed systems and (2) to explain the apparent ubiquity of mixed bedrock-alluvial channels in active orogens. Although certain forms of the various models can be discarded as inconsistent with morphological data, we find that the relative intrinsic concavity indices of detachment- and transport-limited systems (defined herein) largely dictate whether the various models can be tied to distinctive steady state morphologies. Preliminary data suggest that no such diagnostic differences may exist, and other methods must be developed to test models. Accordingly, we develop and explore differences in the scaling behavior of topographic relief and the extent of detachment- versus transport-limited channels as a function of rock uplift rate that may allow discrimination among various models. Further, we explore potentially diagnostic differences in the rates and patterns of transient channel response to changes in rock uplift rate. In addition to general differences between detachment- and transport-limited systems our analysis identifies an interesting hysteresis in Landscape Evolution: “hybrid” channels at the threshold between detachment- and transport-limited conditions are expected to act as detachment-limited systems in response to an increase in rock uplift rate (or base level fall) and as transport-limited systems in response to a decrease in rock uplift rate, especially during postorogenic topographic decline. The analyses presented set the stage for field studies designed to test quantitatively the various river incision models that have been proposed.

Jean Braun - One of the best experts on this subject based on the ideXlab platform.

  • HyLands 1.0: a hybrid Landscape Evolution model to simulate the impact of landslides and landslide-derived sediment on Landscape Evolution
    2020
    Co-Authors: Benjamin Campforts, Charles M. Shobe, Philippe Steer, Matthias Vanmaercke, Dimitri Lague, Jean Braun
    Abstract:

    Abstract. Landslides are the main source of sediment in most mountain ranges. Rivers then act as conveyor belts, evacuating landslide-derived sediment. Sediment dynamics are known to influence Landscape Evolution through interactions among landslide sediment delivery, fluvial transport, and river incision into bedrock. Sediment delivery and its interaction with river incision therefore control the pace of Landscape Evolution and mediate relationships among tectonics, climate, and erosion. Numerical Landscape Evolution models (LEMs) are well suited to study the interaction among these earth surface processes. They enable evaluation of a range of hypotheses at varying temporal and spatial scales. While many models have been used to study the dynamic interplay between tectonics, erosion and climate, the role of interactions between landslide-derived sediment and river incision has received much less attention. Here, we present HyLands, a hybrid Landscape Evolution model integrated within the Topo Toolbox Landscape Evolution Model (TTLEM) framework. The hybrid nature of the model lies in its capacity to simulate both erosion and deposition at any place in the Landscape due to fluvial bedrock incision, sediment transport and rapid, stochastic mass wasting through landsliding. Fluvial sediment transport and bedrock incision are calculated using the recently developed Stream Power with Alluvium Conservation and Entrainment (SPACE) model. Therefore, rivers in HyLands can dynamically transition from detachment-limited to transport-limited, and from bedrock to bedrock-alluvial to fully alluviated states. Erosion and sediment production by landsliding is calculated using a Mohr-Coulomb stability analysis while landslide-derived sediment is routed and deposited using a multiple flow direction, non-linear deposition method. We describe and evaluate the HyLands 1.0 model using analytical solutions and observations. We first illustrate the functionality of HyLands to capture river dynamics ranging from detachment-limited to transport-limited configurations. Second, we apply the model to a portion of the Namche-Barwa massif in Eastern Tibet and compare simulated and observed landslide magnitude-frequency and area-volume scaling relationships. Finally, we illustrate the relevance of explicitly simulating landsliding and sediment dynamics over longer timescales for Landscape Evolution in general and river dynamics in particular. With HyLands we provide a new tool to understand both the long and short-term coupling between stochastic hillslope processes, river incision, and source-to-sink sediment dynamics.

  • The FastScape software stack: reusable tools for Landscape Evolution modelling
    2020
    Co-Authors: Benoît Bovy, Jean Braun, Guillaume Cordonnier, Raphael Lange, Xiaoping Yuan
    Abstract:

    <div> <div> <div> <div> <p>The name “FastScape” has been used to describe a Landscape Evolution model as well as a set of efficient algorithms to simulate various processes of erosion, transport and deposition (e.g., fluvial, hillslope and marine). We also use this name for a set of software components (https://github.com/fastscape-lem) aimed at making those models and algorithms readily accessible to a wide range of users, from experts in Landscape Evolution modelling to scientists, researchers and teachers in the broader Earth science community. Those software components are organised as a stack where each level has a distinct scope. At the bottom of this stack, “fastscapelib-fortran” is the original, full-featured implementation of the FastScape model, which provides a Fortran API as well as Python bindings. Its successor “fastscapelib” is a library written in modem C++ that directly exposes the FastScape algorithms (e.g., flow-routing, depression-resolving, channel erosion, hillslope diffusion) through basic APIs in C++, Python and potentially other languages such as R or Julia in the future. Built on top of those core libraries, “fastscape” is a high-level yet flexible tool that helps anyone who wants to quickly build, extend or simply run FastScape model variants in a user-friendly, interactive environment. Through its xarray-centric interface, it is deeply integrated with the rest of the Python scientific ecosystem, therefore offering great capabilities at user’s fingertips for pre/post-processing, visualisation and simulation management. One of our primary concern is following good practices (API design, testing, documentation, distribution...) while developing each of these tools. We show through a gallery of examples how the FastScape software stack has been used in research and outreach projects. We plan to provide better integration with other tools for topographic analysis/modelling (e.g., Landlab, LSDTopotools) in the future and we also greatly encourage contributions from the broader community.</p> </div> </div> </div> </div>

  • Constraining 90 Ma Landscape Evolution model of Madagascar using erosional and sedimentary data
    2018
    Co-Authors: Ruohong Jiao, Jean Braun, Antoine Delaunay
    Abstract:

    Madagascar has its own geological and geomorphic histories since its separation from India at ~90 Ma. Since then despite the lack of intense tectonic activity, the island has undergone two phases of topographic uplift, which were driven by 1) flexural rebound due to sediment loading along the west coast and erosional unloading on the high plateau during the Late Cretaceous, and 2) dynamic doming supported by the convective upwelling of the sub-lithosphere mantle during the Late Cenozoic. The temporal and spatial variations of the uplift shaped the fluvial network, e.g. by modifying channel gradients and flow directions. The Evolution of the drainage basins played an important role in creating the complex topography, which has been causally linked to the island's high-level of biodiversity and biotic endemism. Therefore, reconstructing the long-term Landscape Evolution and drainage network history is a key step in revealing the potential link between the Malagasy Landscape and its biogeographic Evolution. We attempt to reproduce the Landscape Evolution of Madagascar by combining a wide range of observational constraints and using a numerical Landscape Evolution model, in which the surface Evolution is predicted as a consequence of uplift, fluvial incision and hillslope procesess. Since the Early Cretaceous, several erosional surfaces were created by planation, but the ages of their formation are not well dated. We use the vertical offsets between the remnants of these surfaces as proxies for uplift magnitudes, and use an inversion approach (Neighbourhood Algorithm) to estimate the ages of the uplift as well as the uncertainties on these estimates. Simultaneously, parameters in the fluvial erosion and hillslope diffusion equations are inverted. Sediment flux data from the Morondava Basin along the west coast is used to constrain the inversion, assuming a general balance between the sediment volume preserved in the basin and the eroded mass from the source area. Other model constraints include the present topography and catchment geometry. Our current best-fit model shows that although the Cenozoic uplift started from ~30 Ma, most of the current elevation of the island was gained over the last ~10 Ma, during which period the drainage system of the island has been dynamically reorganized.

  • Role of erosion and isostasy in the Cordillera Blanca uplift: Insights from Landscape Evolution modeling (northern Peru, Andes)
    Tectonophysics, 2018
    Co-Authors: Audrey Margirier, Jean Braun, Xavier Robert, Laurence Audin
    Abstract:

    Abstract The processes driving uplift and exhumation of the highest Peruvian peaks (the Cordillera Blanca) are not well understood. Uplift and exhumation seem closely linked to the formation and movement on the Cordillera Blanca normal fault (CBNF) that delimits and shapes the western flank of the Cordillera Blanca. Several models have been proposed to explain the presence of this major normal fault in a compressional setting, but the CBNF and the Cordillera Blanca recent rapid uplift remain enigmatic. Whereas the Cordillera Blanca morphology demonstrates important erosion and thus a significant mass of rocks removal, the impact of erosion and isostasy on the Evolution of the Cordillera Blanca uplift rates has never been explored. We address the role of erosion and associated flexural rebound in the uplift and exhumation of the Cordillera Blanca with numerical modeling of Landscape Evolution. We perform inversions of the broad features of the present-day topography, total exhumation and thermochronological data using a Landscape Evolution model (FastScape) to provide constraints on the erosion efficiency factor, the uplift rate and the temperature gradient. Our results evidence the not negligible contribution of erosion and associated flexural rebound to the uplift of the Cordillera Blanca and allow us to question the models previously proposed for the formation of the CBNF.

  • Eocene to mid-Pliocene Landscape Evolution in Scandinavia inferred from offshore sediment volumes and pre-glacial topography using inverse modelling
    Geomorphology, 2018
    Co-Authors: Vivi Kathrine Pedersen, Jean Braun, Ritske S. Huismans
    Abstract:

    Abstract The origin of high topography in Scandinavia is highly debated, both in terms of its age and the underlying mechanism for its formation. Traditionally, the current high topography is assumed to have formed by several Cenozoic (mainly Neogene) phases of surface uplift and dissection of an old peneplain surface. These same surface uplift events are suggested to explain the increased deposition observed in adjacent offshore basins on the Norwegian shelf and in the North Sea. However, more recently it has been suggested that erosion and isostatic rock uplift of existing topography may also explain the recent Evolution of topography in Scandinavia. For this latter view, the increased sedimentation towards the present is assumed to be a consequence of a climate related increase in erosion. In this study we explore whether inverse modelling of Landscape Evolution can give new insight into Eocene to mid-Pliocene (54–4 Ma) Landscape Evolution in the Scandinavian region. We do this by combining a highly efficient forward-in-time Landscape Evolution model (FastScape) with an optimization scheme suitable for non-linear inverse problems (the neighbourhood algorithm – NA). To limit our approach to the fluvial regime, we exclude the most recent mid-Pliocene-Quaternary time period where glacial erosion processes are expected to dominate Landscape Evolution. The “goodness” of our Landscape Evolution models is evaluated using i) sediment fluxes based on decompacted offshore sediment volumes and ii) maximum pre-glacial topography from a mid-Pliocene Landscape, reconstructed using geophysical relief and offshore sediment volumes from the mid-Pliocene-Quaternary. We find several tested scenarios consistent with the offshore sediment record and the maximum elevation for our reconstructed pre-glacial (mid-Pliocene) Landscape reconstruction, including: I) substantial initial topography (~ 2 km) at 54 Ma and no induced tectonic rock uplift, II) the combination of some initial topography (~ 1.1 km) at 54 Ma and minor continued rock uplift ( Our preferred model for Eocene to mid-Pliocene Landscape Evolution in Scandinavia is therefore one where high topography (~ 2 km) has existed throughout the time interval from 54 to 4 Ma. We do not find several phases of peneplain surface uplift necessary to explain offshore sediment volumes and large-scale topographic patterns. On the contrary, extensive peneplain dissection seems inconsistent with the low rates of erosion we infer based on the offshore sediment volumes.

Donald M. Fisher - One of the best experts on this subject based on the ideXlab platform.

  • Landscape Evolution within a retreating volcanic arc, Costa Rica,
    2003
    Co-Authors: Jeffrey S. Marshall, Bruce D. Idleman, Thomas W. Gardner, Donald M. Fisher
    Abstract:

    Subduction of hotspot-thickened seafloor profoundly affects convergent margin tectonics, strongly affecting upper plate structure, volcanism, and Landscape Evolution. In southern Central America, low-angle subduction of the Cocos Ridge and seamount domain largely controls Landscape Evolution in the volcanic arc. Field mapping, stratigraphic correlation, and 40 Ar/ 39 Ar geochronology for late Cenozoic volcanic rocks of central Costa Rica provide new insights into the geomorphic response of volcanic arc Landscapes to changes in subduction parameters (slab thickness, roughness, dip). Late Neogene volcanism was focused primarily along the now-extinct Cordillera de Aguacate. Quaternary migration of the magmatic front shifted volcanism northeastward to the Caribbean slope, creating a new topographic divide and forming the Valle Central basin. Stream capture across the paleo‐Aguacate divide led to drainage reversal toward the Pacific slope and deep incision of reorganized fluvial networks. Pleistocene caldera activity generated silicic

  • Landscape Evolution within a retreating volcanic arc, Costa Rica, Central America
    Geology, 2003
    Co-Authors: Jeffrey S. Marshall, Bruce D. Idleman, Thomas W. Gardner, Donald M. Fisher
    Abstract:

    Subduction of hotspot-thickened seafloor profoundly affects convergent margin tectonics, strongly affecting upper plate structure, volcanism, and Landscape Evolution. In southern Central America, low-angle subduction of the Cocos Ridge and seamount domain largely controls Landscape Evolution in the volcanic arc. Field mapping, stratigraphic correlation, and 4 0 Ar/ 3 9 Ar geochronology for late Cenozoic volcanic rocks of central Costa Rica provide new insights into the geomorphic response of volcanic arc Landscapes to changes in subduction parameters (slab thickness, roughness, dip). Late Neogene volcanism was focused primarily along the now-extinct Cordillera de Aguacate. Quaternary migration of the magmatic front shifted volcanism northeastward to the Caribbean slope, creating a new topographic divide and forming the Valle Central basin. Stream capture across the paleo-Aguacate divide led to drainage reversal toward the Pacific slope and deep incision of reorganized fluvial networks. Pleistocene caldera activity generated silicic ash flows that buried the Valle Central and descended the Tarcoles gorge to the Orotina debris fan at the coast. Growth of the modern Cordillera Central accentuated relief along the new divide, establishing the Valle Central as a Pacific slope drainage basin. Arc migration, relocation of the Pacific-Caribbean drainage divide, and formation of the Valle Central basin resulted from slab shallowing as irregular, hotspot-thickened crust entered the subduction zone. The geomorphic Evolution of volcanic arc Landscapes is thus highly sensitive to changes in subducting plate character.

Greg Hancock - One of the best experts on this subject based on the ideXlab platform.

  • Global Sensitivity Analysis of Parameter Uncertainty in Landscape Evolution Models
    2017
    Co-Authors: Christopher J. Skinner, Tom J. Coulthard, Wolfgang Schwanghart, Marco J. Van De Wiel, Greg Hancock
    Abstract:

    Abstract. Landscape Evolution Models have a long history of use as exploratory models, providing greater understanding of the role large scale processes have on the long-term development of the Earth’s surface. As computational power has advanced so has the development and sophistication of these models. This has seen them applied at increasingly smaller scale and shorter-term simulations at greater detail. However, this has not gone hand-in-hand with more rigorous verifications that are commonplace in the applications of other types of environmental models- for example Sensitivity Analyses. This can be attributed to a paucity of data and methods available in order to calibrate, validate and verify the models, and also to the extra complexity Landscape Evolution Models represent – without these it is not possible to produce a reliable Objective Function against which model performance can be judged. To overcome this deficiency, we present a set of Model Functions – each representing an aspect of model behaviour – and use these to assess the relative sensitivity of a Landscape Evolution Model (CAESAR-Lisflood) to a large set of parameters via a global Sensitivity Analysis using the Morris Method. This novel combination of behavioural Model Functions and the Morris Method provides insight into which parameters are the greatest source of uncertainty in the model, and which have the greatest influence over different model behaviours. The method was repeated over two different catchments, showing that across both catchments and across most model behaviours the choice of Sediment Transport formula was the dominate source of uncertainty in the CAESAR-Lisflood model, although there were some differences between the two catchments. Crucially, different parameters influenced the model behaviours in different ways, with Model Functions related to internal geomorphic changes responding in different ways to those related to sediment yields from the catchment outlet. This method of behavioural sensitivity analysis provides a useful method of assessing the performance of Landscape Evolution Models in the absence of data and methods for an Objective Function approach.

  • Surface armour and erosion – impacts on long‐term Landscape Evolution
    Land Degradation & Development, 2017
    Co-Authors: Greg Hancock, John Lowry, M. J. Saynor
    Abstract:

    The parameterisation of Landscape Evolution models is key to their reliable use. To determine reliable parameter sets, data collected from many events over a number of years are required. However, for many recently disturbed, degraded and/or rehabilitated sites, this data may not represent the long-term behaviour of the surface as armouring, weathering, together with vegetation establishment change the erodibility of the surface. Here, we evaluate a new armouring sub-model within the SIBERIA Landscape Evolution model. The calibration of the armour model is conducted using 6 years of field data from four plots, each composed of different surface materials and vegetation characteristics. The calibrated model is then tested on an area of the proposed rehabilitated landform of the Ranger Uranium Mine in the Northern Territory, Australia. The SIBERIA model was then run for a simulated period of 100,000 years using parameters representing (i) a surface constructed of fresh waste rock; (ii) a vegetated surface; and (iii) the calibrated armour sub-model. The results demonstrate that the different parameter sets produce catchments that are unique despite the same starting surface. Surface material properties exert a first-order control on Landscape Evolution. Therefore making predictions for the Evolution of a Landscape requires a reliable understanding of the material properties. This requires a knowledge of what material will be placed where in the catchment. Copyright © 2017 John Wiley & Sons, Ltd.

  • Early Landscape Evolution — A field and modelling assessment for a post-mining landform
    CATENA, 2016
    Co-Authors: Greg Hancock, John Lowry, M. J. Saynor
    Abstract:

    Data from field plots describing how new surfaces evolve in the first few years post-construction are scarce in the literature. Here we examine sediment output from four similar 30 m by 30 m plots on a rehabilitated mine site over a six year period. Field measurements from the trial plots found that there is an initial high pulse of sediment over the first three years which rapidly reduces to rates similar to that expected for a natural or undisturbed surface. At 6 years the sediment output is equivalent to that expected from the surrounding undisturbed Landscape. This plot data was compared to predictions from a calibrated Landscape Evolution model. The Landscape Evolution model used two sets of parameters, one derived from bare waste rock and one derived from an older vegetated surface. The simulations using bare waste parameters produced sediment output that matched the plot data in the first few years while the vegetated parameters produced sediment output which compared well with the field plot data at times > 3 years. The results demonstrate that when correctly calibrated the Landscape Evolution model is able to reliably predict sediment output from these field plots. These results suggest that there is the potential to employ the bare waste rock dump parameters for the first 3-4 years then switch to vegetated parameters for the longer term modelling. Both the field plots and Landscape Evolution model simulations displayed considerable annual variability in total load. This variability is the result of different surface structure from imposed surface roughness (ripping by a bulldozer) and their unique topographic structure. Both initial DEM and model parameters have a large influence on predicted sediment load. The results here support the reliability of the model at the sub-metre grid scale

  • Transient Landscapes: gully development and Evolution using a Landscape Evolution model
    Stochastic Environmental Research and Risk Assessment, 2013
    Co-Authors: Greg Hancock, Garry Willgoose, John Lowry
    Abstract:

    Gullies are a common feature of many landforms and play a significant role in Landscape Evolution. They are transient Landscape features that move along a drainage line incising into soil, alluvium or colluvium disturbing the catchment both headwards and along its banks. It is important to understand gully initiation, development and Evolution as while they are transient features they are drivers of Landscape change and erode and transport considerable volumes of sediment through the channel network. There has been considerable research into understanding gully development with many numerical predictive models developed. Here a computer-based Landscape Evolution model (SIBERIA) is examined for its ability to predict gully development in a catchment undisturbed by European agricultural practices. The simulations demonstrate that the SIBERIA model is able to produce gullies in the same position that are qualitatively and quantitatively morphologically similar to field data. The modelling suggests that the whole catchment is at risk of gullying and is in accordance with the field data which demonstrated that the presence of gullies was extensive throughout the catchment. The model also produces erosion rates within that of independently measured field data.

  • Ecohydrological controls on soil erosion and Landscape Evolution
    Ecohydrology, 2011
    Co-Authors: Greg Hancock, Ken G. Evans, Jeffrey J. Mcdonnell, Luisa Hopp
    Abstract:

    The ecohydrological controls on soil erosion and Landscape Evolution are difficult to quantify and poorly understood. In many parts of the world, cyclone-induced tree throw is a major source of disturbance. Tree throw may increase sediment transport by exposing a mound of fresh soil as well as providing a pit which may act as a knickpoint triggering gully erosion. Alternatively, while tree throw provides characteristic pit–mound topography, the amount of soil disturbed or exposed in a mound is relatively small on the hillslope and catchment scale and the effects may be minimal. The April 2006 tropical cyclone Monica that impacted the coast of northern Australia with winds' speeds > 100 m s−1 uprooted approximately 50% of the trees in the study catchment. We use a Landscape Evolution model with repeated occurrence of the cyclone over a 1000-year simulated period to quantify the effect of pit–mound topography distributions on both sediment transport and Landscape Evolution by including the fallen trees into the digital elevation model both as a pit–mound and also as a pit–mound and tree trunk. The results show that the inclusion of pit–mound topography substantially reduced erosion for the first 10–15 years of its introduction and adding pit–mound–trunk topography reduced erosion rates even further. The pit–mound and pit–mound–trunk acted as sediment traps, capturing sediment from upslope and storing it in debris dams reducing hillslope connectivity. Model simulations predict average denudation rates for the catchment approximating field measured data. These findings suggest that any tree throw is unlikely to result in Landscape instability

Tom J. Coulthard - One of the best experts on this subject based on the ideXlab platform.

  • Global Sensitivity Analysis of Parameter Uncertainty in Landscape Evolution Models
    2017
    Co-Authors: Christopher J. Skinner, Tom J. Coulthard, Wolfgang Schwanghart, Marco J. Van De Wiel, Greg Hancock
    Abstract:

    Abstract. Landscape Evolution Models have a long history of use as exploratory models, providing greater understanding of the role large scale processes have on the long-term development of the Earth’s surface. As computational power has advanced so has the development and sophistication of these models. This has seen them applied at increasingly smaller scale and shorter-term simulations at greater detail. However, this has not gone hand-in-hand with more rigorous verifications that are commonplace in the applications of other types of environmental models- for example Sensitivity Analyses. This can be attributed to a paucity of data and methods available in order to calibrate, validate and verify the models, and also to the extra complexity Landscape Evolution Models represent – without these it is not possible to produce a reliable Objective Function against which model performance can be judged. To overcome this deficiency, we present a set of Model Functions – each representing an aspect of model behaviour – and use these to assess the relative sensitivity of a Landscape Evolution Model (CAESAR-Lisflood) to a large set of parameters via a global Sensitivity Analysis using the Morris Method. This novel combination of behavioural Model Functions and the Morris Method provides insight into which parameters are the greatest source of uncertainty in the model, and which have the greatest influence over different model behaviours. The method was repeated over two different catchments, showing that across both catchments and across most model behaviours the choice of Sediment Transport formula was the dominate source of uncertainty in the CAESAR-Lisflood model, although there were some differences between the two catchments. Crucially, different parameters influenced the model behaviours in different ways, with Model Functions related to internal geomorphic changes responding in different ways to those related to sediment yields from the catchment outlet. This method of behavioural sensitivity analysis provides a useful method of assessing the performance of Landscape Evolution Models in the absence of data and methods for an Objective Function approach.

  • Developing, choosing and using Landscape Evolution models to inform field-based Landscape reconstruction studies
    Earth Surface Processes and Landforms, 2017
    Co-Authors: Arnaud J.a.m. Temme, Tom J. Coulthard, Wouter Van Gorp, John J. Armitage, Mikael Attal, Jeroen M. Schoorl
    Abstract:

    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 © 2017 John Wiley & Sons, Ltd.

  • A catchment scale evaluation of the SIBERIA and CAESAR Landscape Evolution models
    Earth Surface Processes and Landforms, 2010
    Co-Authors: G.r. Hancock, Tom J. Coulthard, Ken G. Evans, John Lowry, Dene Moliere
    Abstract:

    Landscape Evolution models provide a way to determine erosion rates and Landscape stability over times scales from tens to thousands of years. The SIBERIA and CAESAR Landscape Evolution models both have the capability to simulate catchment–wide erosion and deposition over these time scales. They are both cellular, operate over a digital elevation model of the Landscape, and represent fluvial and slope processes. However, they were initially developed to solve research questions at different time and space scales and subsequently the perspective, detail and process representation vary considerably between the models. Notably, CAESAR simulates individual events with a greater emphasis on fluvial processes whereas SIBERIA averages erosion rates across annual time scales. This paper describes how both models are applied to Tin Camp Creek, Northern Territory, Australia, where soil erosion rates have been closely monitored over the last 10 years. Results simulating 10 000 years of erosion are similar, yet also pick up subtle differences that indicate the relative strengths and weaknesses of the two models. The results from both the SIBERIA and CAESAR models compare well with independent field data determined for the site over different time scales. Representative hillslope cross-sections are very similar between the models. Geomorphologically there was little difference between the modelled catchments after 1000 years but significant differences were revealed at longer simulation times. Importantly, both models show that they are sensitive to input parameters and that hydrology and erosion parameter derivation has long-term implications for sediment transport prediction. Therefore selection of input parameters is critical. This study also provides a good example of how different models may be better suited to different applications or research questions. Copyright © 2010 John Wiley & Sons, Ltd and Commonwealth of Australia

  • Embedding reach-scale fluvial dynamics within the CAESAR cellular automaton Landscape Evolution model
    Geomorphology, 2007
    Co-Authors: Marco J. Van De Wiel, Tom J. Coulthard, Mark G. Macklin, John Lewin
    Abstract:

    Abstract We introduce a new computational model designed to simulate and investigate reach-scale alluvial dynamics within a Landscape Evolution model. The model is based on the cellular automaton concept, whereby the continued iteration of a series of local process ‘rules’ governs the behaviour of the entire system. The model is a modified version of the CAESAR Landscape Evolution model, which applies a suite of physically based rules to simulate the entrainment, transport and deposition of sediments. The CAESAR model has been altered to improve the representation of hydraulic and geomorphic processes in an alluvial environment. In-channel and overbank flow, sediment entrainment and deposition, suspended load and bed load transport, lateral erosion and bank failure have all been represented as local cellular automaton rules. Although these rules are relatively simple and straightforward, their combined and repeatedly iterated effect is such that complex, non-linear geomorphological response can be simulated within the model. Examples of such larger-scale, emergent responses include channel incision and aggradation, terrace formation, channel migration and river meandering, formation of meander cutoffs, and transitions between braided and single-thread channel patterns. In the current study, the model is illustrated on a reach of the River Teifi, near Lampeter, Wales, UK.

  • Embedding reach-scale fluvial dynamics within the CAESAR cellular automaton Landscape Evolution model
    Geomorphology, 2007
    Co-Authors: Marco J. Van De Wiel, Tom J. Coulthard, Mark G. Macklin, John Lewin
    Abstract:

    van de Wiel, M. J., Coulthard, T. J., Macklin, M. G., Lewis, J. (2007). Embedding reach-scale fluvial dynamics within the CAESAR cellular automaton Landscape Evolution model. Geomorphology, 90(3-4), 283-301. Sponsorship: NERCWe introduce a new computational model designed to simulate and investigate reach-scale alluvial dynamics within a Landscape Evolution model. The model is based on the cellular automaton concept, whereby the continued iteration of a series of local process ?rules? governs the behaviour of the entire system. The model is a modified version of the CAESAR Landscape Evolution model, which applies a suite of physically based rules to simulate the entrainment, transport and deposition of sediments. The CAESAR model has been altered to improve the representation of hydraulic and geomorphic processes in an alluvial environment. In-channel and overbank flow, sediment entrainment and deposition, suspended load and bed load transport, lateral erosion and bank failure have all been represented as local cellular automaton rules. Although these rules are relatively simple and straightforward, their combined and repeatedly iterated effect is such that complex, non-linear geomorphological response can be simulated within the model. Examples of such larger-scale, emergent responses include channel incision and aggradation, terrace formation, channel migration and river meandering, formation of meander cutoffs, and transitions between braided and single-thread channel patterns. In the current study, the model is illustrated on a reach of the River Teifi, near Lampeter, Wales, UK.Peer reviewe

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