Autogenic versus allogenic controls on the evolution of a coupled fluvial megafan–mountainous catchment system: numerical modelling and comparison with the Lannemezan megafan system (northern Pyrenees, France)

Mouchené, Margaux; Beek, Peter van der; Carretier, Sébastien; Mouthereau, Frédéric

doi:10.5194/esurf-5-125-2017

Cited by 23 publications

(11 citation statements)

References 75 publications

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“…Davy and Lague's () formulation has been used or adapted to obtain simple models (e.g., Carretier et al, ; Ganti et al, ; Langston & Tucker, ; Mouchené et al, ; Shobe et al, ), which assume that the net rate of topographic change is the sum of the erosion rate (controlled by the SPL model) and of the deposition rate, which is proportional to local suspended sediment flux and to a dimensionless deposition coefficient, and inversely proportional to drainage area, a proxy for water discharge. This parameterization is also receiving growing acceptance due to its ability to reproduce many depositional features of fluvial systems (Carretier et al, ; Mouchené et al, ; Shobe et al, ). However, because the local balance between erosion and deposition depends on sediment flux resulting from net upstream erosion, this parameterization is computationally demanding.…”

Section: Introductionmentioning

confidence: 99%

A New Efficient Method to Solve the Stream Power Law Model Taking Into Account Sediment Deposition

et al. 2019

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The stream power law model has been widely used to represent erosion by rivers but does not take into account the role played by sediment in modulating erosion and deposition rates. Davy and Lague (2009, https://doi.org/10.1029/2008JF001146) provide an approach to address this issue, but it is computationally demanding because the local balance between erosion and deposition depends on sediment flux resulting from net upstream erosion. Here, we propose an efficient (i.e., O(N) and implicit) method to solve their equation. This means that, unlike other methods used to study the complete dynamics of fluvial systems (e.g., including the transition from detachment‐limited to transport‐limited behavior), our method is unconditionally stable even when large time steps are used. We demonstrate its applicability by performing a range of simulations based on a simple setup composed of an uplifting region adjacent to a stable foreland basin. As uplift and erosion progress, the mean elevations of the uplifting relief and the foreland increase, together with the average slope in the foreland. Sediments aggrade in the foreland and prograde to reach the base level where sediments are allowed to leave the system. We show how the topography of the uplifting relief and the stratigraphy of the foreland basin are controlled by the efficiency of river erosion and the efficiency of sediment transport by rivers. We observe the formation of a steady‐state geometry in the uplifting region, and a dynamic steady state (i.e., autocyclic aggradation and incision) in the foreland, with aggradation and incision thicknesses up to tens of meters.

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Section: Introductionmentioning

confidence: 99%

A New Efficient Method to Solve the Stream Power Law Model Taking Into Account Sediment Deposition

et al. 2019

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“…10 4 years, is therefore difficult to model within a stream power (advective) end-member model for catchments of this scale (Table 2), although a version of such a model has been recently used to explore the controls on the evolution of later Miocene megafans in the northern Pyrenees (e.g. Mouchené et al, 2017). To use the stream power model would require a significant increase in the bedrock erodibility parameter, k, within the model (by greater than 1 order of magnitude), implying slopes and topography in the palaeo-Pyrenees that were highly subdued.…”

Section: Claret Conglomerate Spanish Pyreneesmentioning

confidence: 99%

Numerical modelling of landscape and sediment flux response to precipitation rate change

et al. 2018

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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 growth in the development of numerical models that attempt to capture landscape evolution over long timescales. However, there is still an uncertainty regarding the validity of the basic assumptions of mass transport that are made in deriving these models. In this contribution we therefore return to a principal assumption of sediment transport within the mass balance for surface processes; we explore the sensitivity of the classic end-member landscape evolution models and the sediment fluxes they produce to a 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, in which sediment is assumed to be transported immediately out of the model domain. The second end-member model is the transport model and it takes the form of a diffusion equation, assuming 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. However, for the stream power model the exponent on the water flux term must be less than one, and for the 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 the transport model generally responds more rapidly to an increase in precipitation rates, on the order of 10 5 years for post-perturbation sediment fluxes to return to within 50 % of their initial values, for theoretical landscapes with a scale of 100 × 100 km. Additionally from the same starting conditions, the amplitude of the sediment flux perturbation in the transport model is greater, with much larger sensitivity to catchment size. An important finding is that both models respond more quickly to a wetting event than a drying event, and we argue that this asymmetry in response time has significant implications for depositional stratigraphies. Finally, we evaluate the extent to which these constraints on response times and sediment fluxes from simple models help us understand the geological record of landscape response to rapid environmental changes in the past, such as the Paleocene-Eocene thermal maximum (PETM). In the Spanish Pyrenees, for instance, a relatively rapid (10 to 50 kyr) duration of the deposition of gravel is observed for a climatic shift that is thought to be towards increased precipitation rates. We suggest that the rapid response observed is more easily explained through a diffusive transport model because (1) the model has a faster response time, which is consistent with the documented stratigraphic data, (2) there is a high-amplitude spike in sediment flux, and (3) the assumption of instantaneous transport is difficult to justify for the transport of large grain sizes as an alluvi...

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“…When aggradation occurs at the tributary junction, one may expect to temporarily see an evolution similar to that proposed in the "aggrading alluvial fan" scenario, with the development on an alluvial fan that may alter the sediment dynamics of the main channel, modulating the sediment mobilized in the upper and lower sections of the river and delaying main-channel adjustments. In our experiment, instead, a prolonged erosional regime within the main channel may have led to fan entrenchment and fansurface abandonment (Clarke et al, 2008;Nicholas and Quine, 2007;Pepin et al, 2010;Van Dijk et al, 2012). Despite the lack of fan progradation, an increase in bank contribution following incision of the main channel did occur (Fig.…”

Section: Incising Main Channel: Geometric Adjustments and Tributary-mmentioning

confidence: 60%

Interactions between channels and tributary alluvial fans: channel adjustments and sediment-signal propagation

Savi¹,

Tofelde²,

Wickert³

et al. 2019

Preprint

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Abstract. Climate and tectonics impact water and sediment fluxes to fluvial systems. These boundary conditions set river form and can be recorded by fluvial deposits. Reconstructions of boundary conditions from these deposits, however, is complicated by complex channel-network interactions and associated sediment storage and release through the fluvial system. To address this challenge, we used a physical experiment to study the interplay between a main channel and a tributary under different forcing conditions. In particular, we investigated the impact of a single tributary junction, where sediment supply from the tributary can produce an alluvial fan, on channel geometries and associated sediment-transfer dynamics. We found that the presence of an alluvial fan may promote or prevent sediment to be moved within the fluvial system, creating different coupling conditions. A prograding alluvial fan, for example, has the potential to disrupt the sedimentary signal propagating downstream through the confluence zone. By analyzing different environmental scenarios, our results indicate the contribution of the two sub-systems to fluvial deposits, both upstream and downstream of the tributary junction, which may be diagnostic of a perturbation affecting the tributary or the main channel only. We summarize all findings in a new conceptual framework that illustrates the possible interactions between tributary alluvial fans and a main channel under different environmental conditions. This framework provides a better understanding of the composition and architecture of fluvial sedimentary deposits found at confluence zones, which is essential for a correct reconstruction of the climatic or tectonic history of a basin.

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Autogenic versus allogenic controls on the evolution of a coupled fluvial megafan–mountainous catchment system: numerical modelling and comparison with the Lannemezan megafan system (northern Pyrenees, France)

Cited by 23 publications

References 75 publications

A New Efficient Method to Solve the Stream Power Law Model Taking Into Account Sediment Deposition

A New Efficient Method to Solve the Stream Power Law Model Taking Into Account Sediment Deposition

Numerical modelling of landscape and sediment flux response to precipitation rate change

Interactions between channels and tributary alluvial fans: channel adjustments and sediment-signal propagation

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