scholarly journals The SPACE 1.0 model: A Landlab component for 2-D calculation of sediment transport, bedrock erosion, and landscape evolution

2017 ◽  
Author(s):  
Charles M. Shobe ◽  
Gregory E. Tucker ◽  
Katherine R. Barnhart
Keyword(s):  
Sediment Transport ◽  
Analytical Solutions ◽  
Landscape Evolution ◽  
Sediment Flux ◽  
Surface Processes ◽  
Stream Power ◽  
Space Model ◽  
Lithospheric Flexure ◽  
Hillslope Evolution ◽  
Bedrock Erosion

Abstract. Models of landscape evolution by river erosion are often either transport-limited (sediment is always available, but may or may not be transportable) or detachment-limited (sediment must be detached from the bed, but is then always transportable). While several models incorporate elements of, or transition between, transport-limited and detachment-limited behavior, most require that either sediment or bedrock, but not both, are eroded at any given time. We present SPACE (Stream Power with Alluvium Conservation and Entrainment) 1.0, a new model for simultaneous evolution of an alluvium layer and a bedrock bed based on conservation of sediment mass both on the bed and in the water column. The model treats sediment transport and bedrock erosion simultaneously, embracing the reality that many rivers (even those commonly defined as "bedrock" rivers) flow over a partially alluviated bed. The SPACE model is a component of the Landlab modeling toolkit, a Python-language library used to create models of earth surface processes. Landlab allows efficient coupling between the SPACE model and components simulating basin hydrology, hillslope evolution, weathering, lithospheric flexure, and other surface processes. Here, we first derive the governing equations of the SPACE model from existing sediment transport and bedrock erosion formulations and explore the behavior of local analytical solutions for sediment flux and alluvium thickness. We derive steady-state analytical solutions for channel slope, alluvium thickness, and sediment flux, and show that SPACE matches predicted behavior in detachment-limited, transport-limited, and mixed conditions. We provide an example of landscape evolution modeling in which SPACE is coupled with hillslope diffusion, and demonstrate that SPACE provides an effective framework for simultaneously modeling 2-D sediment transport and bedrock erosion.

scholarly journals The SPACE 1.0 model: a Landlab component for 2-D calculation of sediment transport, bedrock erosion, and landscape evolution

2017 ◽  
Vol 10 (12) ◽  
pp. 4577-4604 ◽  
Author(s):  
Charles M. Shobe ◽  
Gregory E. Tucker ◽  
Katherine R. Barnhart
Keyword(s):  
Sediment Transport ◽  
Analytical Solutions ◽  
Landscape Evolution ◽  
Sediment Flux ◽  
Process Models ◽  
Surface Processes ◽  
Flux Divergence ◽  
Space Model ◽  
Lithospheric Flexure ◽  
Bedrock Erosion

Abstract. Models of landscape evolution by river erosion are often either transport-limited (sediment is always available but may or may not be transportable) or detachment-limited (sediment must be detached from the bed but is then always transportable). While several models incorporate elements of, or transition between, transport-limited and detachment-limited behavior, most require that either sediment or bedrock, but not both, are eroded at any given time. Modeling landscape evolution over large spatial and temporal scales requires a model that can (1) transition freely between transport-limited and detachment-limited behavior, (2) simultaneously treat sediment transport and bedrock erosion, and (3) run in 2-D over large grids and be coupled with other surface process models. We present SPACE (stream power with alluvium conservation and entrainment) 1.0, a new model for simultaneous evolution of an alluvium layer and a bedrock bed based on conservation of sediment mass both on the bed and in the water column. The model treats sediment transport and bedrock erosion simultaneously, embracing the reality that many rivers (even those commonly defined as bedrock rivers) flow over a partially alluviated bed. SPACE improves on previous models of bedrock–alluvial rivers by explicitly calculating sediment erosion and deposition rather than relying on a flux-divergence (Exner) approach. The SPACE model is a component of the Landlab modeling toolkit, a Python-language library used to create models of Earth surface processes. Landlab allows efficient coupling between the SPACE model and components simulating basin hydrology, hillslope evolution, weathering, lithospheric flexure, and other surface processes. Here, we first derive the governing equations of the SPACE model from existing sediment transport and bedrock erosion formulations and explore the behavior of local analytical solutions for sediment flux and alluvium thickness. We derive steady-state analytical solutions for channel slope, alluvium thickness, and sediment flux, and show that SPACE matches predicted behavior in detachment-limited, transport-limited, and mixed conditions. We provide an example of landscape evolution modeling in which SPACE is coupled with hillslope diffusion, and demonstrate that SPACE provides an effective framework for simultaneously modeling 2-D sediment transport and bedrock erosion.

Mass balance controls on sediment scour and bedrock erosion in waterfall plunge pools

Geology ◽  
2021 ◽  
Author(s):  
Joel S. Scheingross ◽  
Michael P. Lamb
Keyword(s):  
Sediment Transport ◽  
Mass Balance ◽  
River Discharge ◽  
Sediment Load ◽  
Sediment Flux ◽  
Habitat Availability ◽  
Flux Divergence ◽  
Plunge Pool ◽  
Bedrock Erosion ◽  
Recurrence Intervals

Waterfall plunge pools experience cycles of sediment aggradation and scour that modulate bedrock erosion, habitat availability, and hazard potential. We calculate sediment flux divergence to evaluate the conditions under which pools deposit and scour sediment by comparing the sediment transport capacities of waterfall plunge pools (Qsc_pool) and their adjacent river reaches (Qsc_river). Results show that pools fill with sediment at low river discharge because the waterfall jet is not strong enough to transport the supplied sediment load out of the pool. As discharge increases, the waterfall jet strengthens, allowing pools to transport sediment at greater rates than in adjacent river reaches. This causes sediment scour from pools and bar building at the downstream pool boundary. While pools may be partially emptied of sediment at modest discharge, floods with recurrence intervals >10 yr are typically required for pools to scour to bedrock. These results allow new constraints on paleodischarge estimates made from sediment deposited in plunge pool bars and suggest that bedrock erosion at waterfalls with plunge pools occurs during larger floods than in river reaches lacking waterfalls.

scholarly journals Bedload transport controls bedrock erosion under sediment-starved conditions

2015 ◽  
Vol 3 (3) ◽  
pp. 291-309 ◽  
Author(s):  
A. R. Beer ◽  
J. M. Turowski
Keyword(s):  
Erosion Rate ◽  
Landscape Evolution ◽  
Bedload Transport ◽  
Minor Importance ◽  
Stream Power ◽  
Catchment Scale ◽  
Data Set ◽  
Erosion Processes ◽  
Bedrock Erosion ◽  
Mountainous Landscape

Abstract. Fluvial bedrock incision constrains the pace of mountainous landscape evolution. Bedrock erosion processes have been described with incision models that are widely applied in river-reach and catchment-scale studies. However, so far no linked field data set at the process scale had been published that permits the assessment of model plausibility and accuracy. Here, we evaluate the predictive power of various incision models using independent data on hydraulics, bedload transport and erosion recorded on an artificial bedrock slab installed in a steep bedrock stream section for a single bedload transport event. The influence of transported bedload on the erosion rate (the "tools effect") is shown to be dominant, while other sediment effects are of minor importance. Hence, a simple temporally distributed incision model, in which erosion rate is proportional to bedload transport rate, is proposed for transient local studies under detachment-limited conditions. This model can be site-calibrated with temporally lumped bedload and erosion data and its applicability can be assessed by visual inspection of the study site. For the event at hand, basic discharge-based models, such as derivatives of the stream power model family, are adequate to reproduce the overall trend of the observed erosion rate. This may be relevant for long-term studies of landscape evolution without specific interest in transient local behavior. However, it remains to be seen whether the same model calibration can reliably predict erosion in future events.

Influence of oscillating vegetation cover, precipitation, and sediment transport on topography: Insights from a landscape evolution model

2020 ◽  
Author(s):  
Hemanti Sharma ◽  
Todd A. Ehlers ◽  
Manuel Schmid
Keyword(s):  
Sediment Transport ◽  
Vegetation Cover ◽  
Landscape Evolution ◽  
Sediment Flux ◽  
Temperate Climate ◽  
Vegetation Density ◽  
Coupled Oscillations ◽  
Erosion Rates ◽  
Uplift Rates ◽  
Surface Vegetation

<p>Erosion and sediment transport in river catchments depend significantly on tectonics, climate and associated vegetation-cover. In this study, we used a numerical modelling approach to quantify the effects of temporal variations in precipitation rates and vegetation-cover over different uplift rates (0.05 mm a<sup>-1</sup>, 0.1 mm a<sup>-1</sup>, 0.2 mm a<sup>-1</sup>) and periodicities (23 kyr, 41 kyr and 100 kyr) of climate and associated vegetation-cover oscillations on erosion, sediment transport and deposition at catchment scale. Landlab, a landscape evolution modelling toolkit was modified to incorporate surface vegetation-cover dependent hillslope and coupled detachment-transport limited fluvial processes, weathering and soil production. The model was applied to (two) sites in the Coastal Chilean Cordillera namely Pan de Acuzar (~26), and La Campana (~33). These sites show a steep gradient in climate and vegetation density from arid climate and sparse vegetation density in northern latitudes to wetter temperate climate and abundant vegetation in the south, with granitic bedrock. The model simulations were run for 15 Myr to create steady-state topographies for both model domains. The sensitivity of these landscapes to changing climate and surface vegetation-cover was analyzed for 3 Myr for five transient model scenarios: (1) oscillating precipitation and constant vegetation cover, (2) constant precipitation and oscillating vegetation cover, (3) coupled oscillations in precipitation and vegetation cover, (4) coupled oscillations in precipitation and vegetation cover with variable periodicities, (5) coupled oscillations in precipitation and vegetation cover with variable rock uplift rates. The results suggest that erosion and sediment transport in densely vegetated landscapes are dominated by changes in precipitation, rather than vegetation-cover change in the southern study area (La Campana), as a result of higher amplitude of precipitation change i.e., 460 mm. Arid (northern) and sparsely vegetated landscapes are dominated by changes in vegetation density rather than precipitation, explained by higher erosion rates in periods with no surface vegetation-cover. Coupled oscillations in climate and vegetation cover suggested dampened influence of transient forcing on climate or vegetation-cover. The influence of periodicity of climate oscillations is significantly pronounced for shorter period (23 kyr oscillations) in terms of erosion rates. Results from different uplift rates suggested a positive linear relationship of topographic elevation and slope, erosion and sediment transport. However, sediment thickness decreases with increasing uplift rates, attributed to higher sediment flux on hillslopes due to linear dependence of slope on rock uplift rates.  These results broadly demonstrate the implications of long term climate change with associated vegetation density on geomorphic processes shaping the topography.</p>

scholarly journals Numerical modelling landscape and sediment flux response to precipitation rate change

2017 ◽  
Author(s):  
John J. Armitage ◽  
Alexander C. Whittaker ◽  
Mustapha Zakari ◽  
Benjamin Campforts
Keyword(s):  
Sediment Transport ◽  
Response Time ◽  
Transport Model ◽  
Numerical Models ◽  
Water Flux ◽  
Sediment Flux ◽  
Precipitation Rate ◽  
Stream Power ◽  
Sediment Transport Model ◽  
End Member Model

Abstract. Laboratory-scale experiments of erosion have demonstrated that landscapes have a natural (or intrinsic) response time to a change in precipitation rate. In the last few decades there has been a growth in the development of numerical models that attempt to capture landscape evolution over long time-scales. Recently, a sub-set of these numerical models have been used to invert river profiles for past tectonic conditions even during variable climatic conditions. However, there is still an uncertainty over validity of the basic assumption of mass transport that are made in deriving these models. In this contribution we therefore return to a principle assumption of sediment transport within the mass balance for surface processes, and explore the sensitivity of the classic end-member landscape evolution models to change in precipitation rates. One end-member model takes the mathematical form of a kinetic wave equation and is known as the stream power model, where sediment is assumed to be transported immediately out of the model domain. The second end-member model takes the form of a diffusion equation, and assumes that the sediment flux is a function of the water flux and slope. We find that both of these end-member models have a response time that has a proportionality to the precipitation rate that follows a negative power law. For the stream power model the exponent on the water flux term must be less than one, and for the sediment transport model the exponent must be greater than one in order to match the observed concavity of natural systems. This difference in exponent means that sediment transport model responds more rapidly to an increase in precipitation rates, on the order of 105 years for a landscape with a scale of 105 m. In nature, landscape response times to a rapid environmental change have been estimated for events such as the Paleocene-Eocene thermal maximum (PETM). In the Spanish Pyrenees, a relatively rapid, 20 to 100 kyr, duration of deposition of gravel during the PETM is observed for a climatic shift that is thought to be towards increased precipitation rates. We suggest the rapid response observed is more easily explained through a diffusive sediment transport model, as (1) this model has a faster response time, consistent with the documented stratigraphic data, and (2) the assumption of instantaneous transport is difficult to justify for the transport of large grain sizes as an alluvial bed-load.

scholarly journals Constraining plateau uplift in southern Africa by combining thermochronology, sediment flux, topography, and landscape evolution modeling

2020 ◽  
Author(s):  
Jessica R. Stanley ◽  
Jean Braun ◽  
Guillaume Baby ◽  
François Guillocheau ◽  
Cecile Robin ◽  
...  
Keyword(s):  
Southern Africa ◽  
Landscape Evolution ◽  
Sediment Flux ◽  
Plateau Uplift ◽  
Evolution Modeling

scholarly journals Landscape evolution models using the stream power incision model show unrealistic behavior when <i>m</i> ∕ <i>n</i> equals 0.5

2017 ◽  
Vol 5 (4) ◽  
pp. 807-820 ◽  
Author(s):  
Jeffrey S. Kwang ◽  
Gary Parker
Keyword(s):  
Steady State ◽  
Landscape Evolution ◽  
Drainage Area ◽  
Uplift Rate ◽  
Stream Power ◽  
River Incision ◽  
Vertical Incision ◽  
Small Scales ◽  
Insight Into

Abstract. Landscape evolution models often utilize the stream power incision model to simulate river incision: E = KAmSn, where E is the vertical incision rate, K is the erodibility constant, A is the upstream drainage area, S is the channel gradient, and m and n are exponents. This simple but useful law has been employed with an imposed rock uplift rate to gain insight into steady-state landscapes. The most common choice of exponents satisfies m ∕ n = 0.5. Yet all models have limitations. Here, we show that when hillslope diffusion (which operates only on small scales) is neglected, the choice m ∕ n = 0.5 yields a curiously unrealistic result: the predicted landscape is invariant to horizontal stretching. That is, the steady-state landscape for a 10 km2 horizontal domain can be stretched so that it is identical to the corresponding landscape for a 1000 km2 domain.

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