Landform Evolution Model Research Articles

Can modelling enable us to understand the rôle of humans in landscape evolution?

Landform-evolution models have typically failed to include human actions, or have done so only in a static, scenario-based way. This failure is despite the extensive empirical data that suggest rates of soil erosion are most sensitive to anthropic pressure. The C ybE rosion modelling framework overcomes this limitation by using an agent-based approach to simulating the dynamic interactions of people and their landscapes. The interactions simulated relate to basic processes of food acquisition (hunting, gathering and basic agriculture) in prehistoric communities. Simulations demonstrate the value of this approach in supporting the vulnerability of landform evolution to anthropic pressures, and demonstrate the limitations of existing models that ignore human and animal agency, which are likely to produce both quantitatively and qualitatively different results. The model is also a useful heuristic tool for understanding human–landscape interactions and for suggesting directions for future research. Despite the acknowledged limitations of agent-based approaches in simulating human populations, it is suggested that further research will be fruitful, especially if combined with a range of field evidence.

Laboratory simulation of the salt weathering of schist: II. Fragmentation of fine schist particles

AbstractRecent developments in long term landform evolution modelling have created a new demand for quantitative salt weathering data, and in particular data describing the size distribution of the weathered rock fragments. To enable future development of rock breakdown models for use in landscape evolution and soil production models, laboratory work was undertaken to extend existing schist/salt weathering fragmentation studies to include an examination of the breakdown of sub‐millimetre quartz chlorite schist particles in a seasonally wet tropical climate. Laser particle sizing was used to assess the impact of different experimental procedures on the resulting particle size distribution. The results reveal that salt weathering under a range of realistic simulated tropical wet season conditions produces a significant degree of schist particle breakdown. The fragmentation of the schist is characterized by splitting of the larger fragments into mid‐sized product with finer material produced, possibly from the breakdown of mid‐sized fragments when weathering is more advanced. Salinity, the salt addition method and temperature were all found to affect weathering rates. Subtle differences in mineralogy also produce variations in weathering patterns and rates. It is also shown that an increase in drying temperature leads to accelerated weathering rates, however, the geometry of the fracture process is not significantly affected. Copyright © 2006 John Wiley & Sons, Ltd.

Spatial organization of soil depths using a landform evolution model

The evolution of soil depths is investigated by modeling the interaction between soil production and surface erosion within a landform evolution model. An enhanced version of the landform evolution model SIBERIA that incorporates a soil evolution module is used to simulate evolving landforms and soils depths over geologic timescales. The spatial and temporal evolution of soil depths are examined at the hillslope scale. Though it is widely accepted among the geomorphology community that soil water enhances chemical, physical and biological weathering processes, its effect has not been explicitly included in published models of soil production. The main scientific questions that we address are (1) what are the implications of incorporating soil moisture dependency in the soil production function and (2) what type of soil production dynamics is needed to generate a bedrock topography that has a different spatial pattern from that of the ground surface. A range of physics for the soil production model is explored. The effect of soil moisture is included using the wetness index obtained from drainage analysis of either surface elevations or the bedrock topography. The results show that the various soil production functions that incorporate either a wetness index or subsurface flow depth based on the bedrock topography give rise to soils that self‐organize with well‐defined spatial patterns and bedrock elevations with spatial organization significantly different from that of the surface. The model that incorporates the influence of subsurface water on soil production is able to naturally generate a soil production rate with a maximum value for a nonzero soil depth and overcomes an inconsistency of previously published “humped” soil production models.

How does alluvial sedimentation at range fronts modify the erosional dynamics of mountain catchments?

AbstractAt the geological time scale, the way in which the erosion of drainage catchments responds to tectonic uplift and climate changes depends on boundary conditions. In particular, sediment accumulation and erosion occurring at the edge of mountain ranges should influence the base level of mountain catchments, as well as sediment and water discharges. In this paper, we use a landform evolution model (LEM) to investigate how the presence of alluvial sedimentation at range fronts affects catchment responses to climatic or tectonic changes. This approach is applied to a 25 km × 50 km domain, in which the central part is uplifted progressively to simulate the growth of a small mountain range. The LEM includes different slope and river processes that can compete with each other. This competition leads to ‘transport‐limited’, ‘detachment‐limited’ or ‘mixed’ transport conditions in mountains at dynamic equilibrium. In addition, two end‐member algorithms (the channellized‐flow and the sheet‐flow regimes) have been included for the alluvial fan‐flow regime. The three transport conditions and the two flow algorithms represent six different models for which the responses to increase of rock uplift rate and/or cyclic variation of the precipitation rate are investigated.Our results indicate that addition of an alluvial apron increases the long‐term mountain denudation. In response to uplift, mountain rivers adapt their profile in two successive stages; first by propagation of an erosion wave and then by slowly increasing their channel gradients. During the second stage, the erosion rate is almost uniform across the catchment area at any one time, which suggests that dynamic equilibrium has been reached, although the balance between erosion and rock uplift rates has not yet been achieved. This second stage is initiated by the uplift of the mountain river outlets because of sedimentation aggradation at the mountain front. The response time depends on the type of water flow imposed on the alluvial fans domains (× by 1.5 for channelized flow regime and by 10 for the sheet flow one).Cyclic variations of precipitation rate generate cyclic incisions in the alluvial apron. These incision pulses create knick‐points in the river profile in the case of ‘detachment‐limited’ and ‘mixed’ river conditions, which could be mistaken for tectonically induced knick‐points. ‘Transport‐limited’ conditions do not create such knick‐points, but nevertheless trigger erosion in catchments. The feedbacks linked to sedimentation and erosion at range front can therefore control catchment incision or aggradation. In addition, random river captures in the range front trigger auto‐cyclic erosion pulses in the catchment, capable of generating incision–aggradation cycles.

Persistent drainage migration in a numerical landscape evolution model

Numerical landscape evolution models driven by uniform vertical uplift often develop a static drainage network and a precise balance between uplift and erosion. Small‐scale physical models of uplifting drainage basins, however, continually reorganize by ridge migration and do not reach an ideal steady state. Here I show that the presence or absence of persistent drainage migration in a bedrock numerical landform evolution model depends on the flow‐routing algorithm used to determine upstream contributing area. The model version that uses steepest‐descent routing achieves an ideal steady state, while the model version that uses bifurcation routing results in continually‐evolving drainage basins, even under conditions of uniform vertical uplift, bedrock erodibility, precipitation, and landsliding threshold. This result suggests that persistent drainage migration can occur by erosional processes alone. This result has important implications for numerical‐modeling methodology, our understanding of the natural variability of landform evolution, and the interpretation of thermochronological data.

Rugged Plateaus and Extensive Floodplains — Modelling Landform Evolution in a Northern Australian Catchment

AbstractMedium to large natural catchments are often more spatially heterogeneous than small catchments or single landforms. Attempting to model landform evolution of large areas is consequently more complex. This paper demonstrates that modelling landform evolution in medium to large catchments can be improved by calibrating the model to smaller, more geomorphologically homogenous sub‐catchments. The paper investigates landform evolution in the Ngarradj catchment in the Northern Territory of Australia (a medium scale catchment of approximately 67 km2). The catchment is complex and contains two distinct landform regions; an upland plateau region with highly dissected sandstone and shallow, sandy soils, and a lowlands region with gentle, wooded slopes and floodplains with deep, sandy soils. The SIBERIA landform evolution model is calibrated and applied to the Ngarradj catchment. The complexity of the Ngarradj catchment is incorporated into the modelling by dividing the catchment into three sub‐catchments (Swift Creek (SC), Upper Main (UM) and East Tributary (ET)) which are relatively homogeneous and for which hydrology and sediment transport data are available. A discharge‐area relationship and long‐term, sediment loss rates for the catchment are derived based on an annual series flood frequency analysis of a 20 year runoff record predicted in a previous study. Sediment transport modelling incorporates both suspended and bedload sediment loss. The denudation rates derived using these data are 37, 63 and 77 mm kyr−1 for the SC, UM and ET sub‐catchments, respectively. Model predictions indicate that the UM sub‐catchment will have the greatest mean erosion. This is balanced by the large amount of deposition that will occur in the upper Ngarradj valley of the UM sub‐catchment. Further deposition occurs on the floodplain of Ngarradj, with the area between the SC and ET/UM (up‐stream) sub‐catchments experiencing a small net accretion of sediment (15 mm kyr−1).

The history of the major rivers of southern Britain during the Tertiary

The evolution of the drainage system of lowland Britain is discussed on the basis of available geological evidence, including that from terrestrial sites and that which has more recently become available from offshore exploration of the North Sea, the English and Bristol Channels, and the Irish Sea. Tertiary stratigraphy throws considerable light on landform and river development. Paleocene destruction of a chalk cover, which seems to have been incomplete in western Britain, was accompanied by basin sedimentation under a tropical climate. The major elements, the Thames, Solent, Hampshire (?proto-Avon) river, Irish Sea river and possibly an early Trent river, existed almost throughout the Cenozoic. The influence of Atlantic rifting and thermal doming in NW Britain appears to have been stronger and more temporally focused than the persistent flexuring that determined and maintained Tertiary drainage lines in the SE. Here also the folded Mesozoic terrains on the surface contrast with the more dominant block-faulted relief of the Palaeozoic ‘oldlands’. The rivers of the SE can be shown to have extended or reduced their lengths in response to relative sea-level change and gentle warping. Drainage antecedence, the destruction of the Solent system and the breaching of the English Channel are also evident. By contrast, the major river systems of the west are now entirely submerged. Long-term stability of the drainage pattern reflects a persistent tectonic regime in the south, with a subdued low-relief landscape having a weathered regolith and dense vegetation cover. Meandering river channels and alluvial styles predominated, although channel forms varied according to sediment load, slope and discharge variability. Coarse gravel-dominated accumulations are rare and localized. Chemically stable lithologies dominate the clastic component throughout. It is apparent that the deeply incised river valleys seen today are related to high, predominantly coarse sediment yields, encouraged by substantial, rapid climate changes in the Pleistocene. This emphasizes the significance of mechanical compared with chemical weathering for the rate and nature of landscape dissection, and the modifications that have arisen as a result of glaciation, frost-climate weathering, rapidly changing climates and sea levels. The stratigraphical evidence here reviewed is at variance with older, largely geomorphologically based landform evolution models (‘denudational chronology’), but gives considerable support to the recent proposals emphasizing the significance of Paleocene erosion, and enduring low-relief landscapes and drainage systems evolving alongside fold development during the Paleogene. Given the depobasin evidence now available, postulated fluvially active episodes can, and must, be linked to contemporaneous deposition. Some at least of the many controversies involving the identity of erosion surfaces, the dating of them using only residual deposits and weathering mantles, and the selection of particular Tertiary episodes as ones of landscape development can now be resolved.

LANDSAP: a coupled surface and subsurface cellular automata model for landform simulation

Recent computer models of landform evolution have focused on surface processes of river networks and hillslopes (e.g., Ahnert, 1976; Kirkby, 1986; Willgoose et al., 1991a, b; Koltermann and Gorelick, 1992; Howard, 1994; Howard et al., 1994; Smith et al., 1997). Most of these models are based on complicated differential equations that are difficult to solve. Chase (1992) developed a cellular automata model (named Gilbert) that uses simple local rules of diffusion, erosion, and deposition to simulate the synoptic effects of fluvial processes. The Gilbert model applies simple rules iteratively to individual cells of a digital topographic grid after storm events (termed precipitons) randomly fall onto the grid. The rules are in a sense analogous to the natural processes. For example, precipitons move to lower elevations, simulating water running downhill; the amount of erosion is proportional to the local slope and to the erodibility of the rock, simulating speedier erosion of steeper slope and less erosion of hard rocks (Chase, 1992). The advantage of this approach is that it is simple and yet can still produce realistic first-order geomorphologic features and provide insights into landform evolution processes. The Gilbert model demonstrates that complex landscapes do not require complicated laws (Chase, 1992). Thus the cellular automata approach is ideal for simulating long-term landscape evolution that involves multiple interacting processes. This short note presents a model (LANDSAP) that extends the Gilbert model to combine both surface and subsurface processes. LANDSAP is designed to simulate the long-term landscape evolution from these processes and to test the effects of climatic changes. It is not designed to simulate every detail of the processes, but to help us understand the interactions among different processes and the overall effects of such interactions by comparing different simulation scenarios with field observations. A previous version of LANDSAP has been successfully used to model the groundwater sapping processes in Western Desert, Egypt and has provided insights into the paleoclimatic conditions of that area (Luo et al., 1997). The purposes of this Short Note are to describe the programming details in general terms and to make the updated program publicly available. LANDSAP could also be used as a teaching tool to demonstrate system interactions among surface, subsurface, and climatic processes.

Assessing catchment-wide mining-related impacts on sediment movement in the Swift Creek catchment, Northern Territory, Australia, using GIS and landform-evolution modelling techniques

The Swift Creek catchment, the first catchment to be affected should any impact occur as a result of mining of the Jabiluka uranium ore deposit, is located partly within the World Heritage Kakadu National Park (KNP), and partly within the Jabiluka Mineral Lease (JML) that has been excised from KNP. Preliminary linking of a landform evolution model with a Geographic Information System (GIS) has been completed and tested on a catchment-wide basis for long-term total catchment management. This project represents the first attempt to apply the model on a catchment-wide basis in the region. Linking the model with a GIS enhances the modelling process, as the GIS assists in the derivation, storage, manipulation, processing and visualisation of geo-referenced data on a catchment-wide scale. This preliminary assessment of landform evolution in the Swift Creek catchment demonstrates the complex process associated with the parameterisation of the SIBERIA model, and illustrates the benefits of integrating GIS with landform evolution modelling techniques. Additional research is required to develop a more integrated GIS and landform evolution modelling approach to assessing the possible impacts of mining on catchment sedimentary and hydrological processes.

Sediment transport capacity relations for overland flow

Nearly all physically based models of soil erosion and landform evolution include an equation for the sediment transport capacity of flow, yet the choice of relation varies from one model to another. This raises the question of the empirical and theoretical support for particular choices. We review descriptions of the effect of discharge and slope on sediment transport capacity of overland flow. A limited range of relations is defined for which there is strong theoretical and empirical support. Nevertheless, suggestions are made for improved experimental designs that further evaluate theories of sediment transport capacity and reduce uncertainty in its application to catchment modelling of sediment transport.

Sediment transport capacity relations for overland flow

Nearly all physically based models of soil erosion and landform evolution include an equation for the sediment transport capacity of flow, yet the choice of relation varies from one model to another. This raises the question of the empirical and theoretical support for particular choices. We review descriptions of the effect of discharge and slope on sediment transport capacity of overland flow. A limited range of relations is defined for which there is strong theoretical and empirical support. Nevertheless, suggestions are made for improved experimental designs that further evaluate theories of sediment transport capacity and reduce uncertainty in its application to catchment modelling of sediment transport.

Sediment transport capacity relations for overland flow

Nearly all physically based models of soil erosion and landform evolution include an equation for the sediment transport capacity of flow, yet the choice of relation varies from one model to another. This raises the question of the empirical and theoretical support for particular choices. We review descriptions of the effect of discharge and slope on sediment transport capacity of overland flow. A limited range of relations is defined for which there is strong theoretical and empirical support. Nevertheless, suggestions are made for improved experimental designs that further evaluate theories of sediment transport capacity and reduce uncertainty in its application to catchment modelling of sediment transport.

Post-mining landform evolution modelling: 2. Effects of vegetation and surface ripping

Computer simulations of the topographic evolution of the proposed post-mining rehabilitated landform for the ERA Ranger Mine, showed that for the unvegetated and unripped case, the landform at 1000 years would be dissected by localized erosion valleys (maximum depth = 7·6 m) with fans (maximum depth = 14·8 m) at the outlet of the valleys. Valley form simulated by SIBERIA has been recognized in nature. This indicates that SIBERIA models natural processes efficiently. For the vegetated and ripped case, reduced valley development (maximum 1000 year depth = 2·4m) and deposition (maximum 1000 year depth = 4·8m) occurred in similar locations as for the unvegetated and unripped case (i.e. on steep batter slopes and in the central depression areas of the landform). For the vegetated and ripped condition, simulated maximum valley depth in the capping over the tailings containment structure was c. 2·2 m. By modelling valley incision, decisions can be made on the depth of tailings cover required to prevent tailings from being exposed to the environment within a certain time frame. A reduction in thickness of 1 m of capping material over tailings equates to c. 1 000 000 Mm3 over a 1 km2 tailings dam area. This represents a saving of c. $1 500 000 in earthworks alone. Incorporation of SIBERIA simulations in the design process may result in cost reduction while improving confidence in environmental protection mechanisms. Copyright 2000 © Environmental Research Institute of the Supervising Scientist, Commonwealth of Australia.

Medium-term erosion simulation of an abandoned mine site using the SIBERIA landscape evolution model

This study forms part of a collaborative project designed to validate the long-term erosion predictions of the SIBERIA landform evolution model on rehabilitated mine sites. The SIBERIA catchment evolution model can simulate the evolution of landforms resulting from runoff and erosion over many years. SIBERIA needs to be calibrated before evaluating whether it correctly models the observed evolution of rehabilitated mine landforms. A field study to collect data to calibrate SIBERIA was conducted at the abandoned Scinto 6 uranium mine located in the Kakadu Region, Northern Territory, Australia. The data were used to fit parameter values to a sediment loss model and a rainfall–runoff model. The derived runoff and erosion model parameter values were used in SIBERIA to simulate 50 years of erosion by concentrated flow on the batters of the abandoned site. The SIBERIA runs correctly simulated the geomorphic development of the gullies on the man-made batters of the waste rock dump. The observed gully position, depth, volume, and morphology on the waste rock dump were quantitatively compared with the SIBERIA simulations. The close similarities between the observed and simulated gully features indicate that SIBERIA can accurately predict the rate of gully development on a man-made post-mining landscape over periods of up to 50 years. SIBERIA is an appropriate model for assessment of erosional stability of rehabilitated mine sites over time spans of around 50 years.

Post-mining landform evolution modelling: 1. Derivation of sediment transport model and rainfall-runoff model parameters

Data were collected from three sites on the waste rock dump at ERA Ranger Mine: (1) the cap site which was unvegetated and unripped with a surface slope of 2·8 per cent; (2) the batter site, surface slope 20·7 per cent, also unvegetated and unripped but with a covering of coarse rock material; and (3) the soil site, surface slope 1·2 per cent, which had c. 90 per cent vegetation cover of low shrubs and grasses and had been topsoiled and surface ripped. Natural rainfall events were monitored on the sites to collect rainfall, runoff and soil loss data to parameterize a sediment transport model of the form T = β S ∫ Q dt, and the DISTFW rainfall–runoff model. Low frequency, high intensity events resulted in the greatest soil loss. To accurately predict sediment loss during high intensity events, storms with a range of intensities were selected to derive the sediment transport model. DISTFW hydrology model parameters were derived by fitting four monitored events simultaneously. The selected parameters for the vegetated and ripped case may overpredict discharge for some rainfall events resulting in conservative design of erosion control features on rehabilitated landforms. Copyright 2000 © Environmental Research Institute of the Supervising Scientist, Commonwealth of Australia.

Geomorphic Systems of North America

In the first chapter of this book, editor William L. Graf states that the volume's most important purpose is to provide the scientific community with a review of selected research problems from each of the major geomorphic provinces of North America and to delineate recent efforts to solve them. What makes this book exciting and different is its emphasis on geomorphic process and analysis of landforms.After an introductory chapter, the book appropriately begins with a chapter concerning the Appalachian Mountains and plateaus where many basic ideas concerning North American geomorphology were developed. Of particular importance here are models of landform evolution, quantitative relations between landforms, rock type, and structure, and consideration of fluvial systems.

Landscape Sensitivity and Change

The general concepts generated by modern studies of geomorphological processes are examined in terms of their utility for models of long-term landform evolution. The work is summarized by four fundamental propositions of landform genesis. These include the idea that each set of environments is represented by constant processes and characteristic landforms which tend to persist over time. 'Geomorphological' time is divided into the time taken to attain this characteristic state and the time over which it persists. The systems and forms are subject, over Io2-Io5 years, to perturbations caused by high magnitude-low frequency events, environmental change and internal structural instabilities which initiate change. The responses to these impulses are complex and include damped, sustained and reinforcing changes taking place by ubiquitous, linear or diffusive propagation which reflect the sensitivity of the landscape to change. This sensitivity is dependent on the path density of the process and the strength of the coupling between the system components and has two end members, mobile-sensitive systems and slowly responding-insensitive areas. Some of the results include the concepts of (i) relief and pattern persistence; (2) stagnancy of development and the hypothesis of unequal activity; (3) convergence of form; (4) the concept of transient forms; (5) stability-instability phases and episodic landscape evolution, which together form a coherent framework for long-term landform evolution. Davis's great mistake was the assumption that we know the processes involved in the development of land forms. We don't; and until we do we shall be ignorant of the general course of their development. LEIGHLY, 1940