A typology of sculpted forms in open bedrock channels

2005 ◽  
Author(s):  
Keith Richardson ◽  
Paul Anthony Carling
Keyword(s):  
Bedrock Channels

scholarly journals A probabilistic framework for the cover effect in bedrock erosion

2016 ◽  
Author(s):  
Jens M. Turowski ◽  
Rebecca Hodge
Keyword(s):  
Time Scales ◽  
Channel Morphology ◽  
Scale Model ◽  
Probabilistic Framework ◽  
Channel Dynamics ◽  
Base Level ◽  
Bedrock Channel ◽  
Bedrock Erosion ◽  
Long Time ◽  
Bedrock Channels

Abstract. The cover effect in fluvial bedrock erosion is a major control on bedrock channel morphology and long-term channel dynamics. Here, we suggest a probabilistic framework for the description of the cover effect that can be applied to field, laboratory and modelling data and thus allows the comparison of results from different sources. The framework describes the formation of sediment cover as a function of the probability of sediment being deposited on already alleviated areas of the bed. We define benchmark cases and suggest physical interpretations of deviations from these benchmarks. Furthermore, we develop a reach-scale model for sediment transfer in a bedrock channel and use it to clarify the relations between the sediment mass residing on the bed, the exposed bedrock fraction and the transport stage. We derive system time scales and investigate cover response to cyclic perturbations. The model predicts that bedrock channels achieve grade in steady state by adjusting bed cover. Thus, bedrock channels have at least two characteristic time scales of response. Over short time scales, the degree of bed cover is adjusted such that they can just transport the supplied sediment load, while over long time scales, channel morphology evolves such that the bedrock incision rate matches the tectonic uplift or base level lowering rate.

Bedrock channels

Geomorphology ◽  
2010 ◽  
pp. 422-451
Author(s):  
Robert S. Anderson ◽  
Suzanne P. Anderson
Keyword(s):  
Bedrock Channels

scholarly journals Simulations of Lateral Erosion in Bedrock Channels

2016 ◽  
Vol 72 (2) ◽  
pp. I_527-I_536
Author(s):  
Jagriti Mishra ◽  
Takuya Inoue ◽  
Yasuyuki Shimizu
Keyword(s):  
Lateral Erosion ◽  
Bedrock Channels

scholarly journals Mass balance, grade, and adjustment timescales in bedrock channels

2020 ◽  
Vol 8 (1) ◽  
pp. 103-122 ◽  
Author(s):  
Jens Martin Turowski
Keyword(s):  
Steady State ◽  
Mass Balance ◽  
Mechanistic Model ◽  
Channel Width ◽  
Bedrock Rivers ◽  
Channel Incision ◽  
Bedrock Channel ◽  
Lateral Incision ◽  
Lateral Erosion ◽  
Bedrock Channels

Abstract. Rivers are dynamical systems that are thought to evolve towards a steady-state configuration. Then, geomorphic parameters, such as channel width and slope, are constant over time. In the mathematical description of the system, the steady state corresponds to a fixed point in the dynamic equations in which all time derivatives are equal to zero. In alluvial rivers, steady state is characterized by grade. This can be expressed as a so-called order principle: an alluvial river evolves to achieve a state in which sediment transport is constant along the river channel and is equal to transport capacity everywhere. In bedrock rivers, steady state is thought to be achieved with a balance between channel incision and uplift. The corresponding order principle is the following: a bedrock river evolves to achieve a vertical bedrock incision rate that is equal to the uplift rate or base-level lowering rate. In the present work, considerations of process physics and of the mass balance of a bedrock channel are used to argue that bedrock rivers evolve to achieve both grade and a balance between channel incision and uplift. As such, bedrock channels are governed by two order principles. As a consequence, the recognition of a steady state with respect to one of them does not necessarily imply an overall steady state. For further discussion of the bedrock channel evolution towards a steady state, expressions for adjustment timescales are sought. For this, a mechanistic model for lateral erosion of bedrock channels is developed, which allows one to obtain analytical solutions for the adjustment timescales for the morphological variables of channel width, channel bed slope, and alluvial bed cover. The adjustment timescale to achieve steady cover is of the order of minutes to days, while the adjustment timescales for width and slope are of the order of thousands of years. Thus, cover is adjusted quickly in response to a change in boundary conditions to achieve a graded state. The resulting change in vertical and lateral incision rates triggers a slow adjustment of width and slope, which in turn affects bed cover. As a result of these feedbacks, it can be expected that a bedrock channel is close to a graded state most of the time, even when it is transiently adjusting its bedrock channel morphology.

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