Bedrock Rivers

2021 ◽  
Author(s):  
Kelin X. Whipple ◽  
Roman A. DiBiase ◽  
Benjamin Crosby ◽  
Joel P.L. Johnson
Keyword(s):  
Bedrock Rivers

scholarly journals FIELD EVIDENCE FOR THE INFLUENCE OF WEATHERING ON ROCK ERODIBILITY AND CHANNEL FORM IN BEDROCK RIVERS

2017 ◽  
Author(s):  
Gregory S. Hancock ◽  
◽  
Charles M. Shobe ◽  
M.C. Eppes ◽  
Eric E. Small
Keyword(s):  
Bedrock Rivers ◽  
Channel Form ◽  
Field Evidence

Multiscale structural and lithologic controls in the development of stream potholes on granite bedrock rivers

Geomorphology ◽  
2014 ◽  
Vol 204 ◽  
pp. 588-598 ◽  
Author(s):  
Jose A. Ortega ◽  
Miguel Gómez-Heras ◽  
Raúl Perez-López ◽  
Ellen Wohl
Keyword(s):  
Bedrock Rivers

scholarly journals Landslide Erosion Rate in the Eastern Cordillera of Northern Bolivia

2007 ◽  
Vol 11 (19) ◽  
pp. 1-30 ◽  
Author(s):  
Troy A. Blodgett ◽  
Bryan L. Isacks
Keyword(s):  
Erosion Rate ◽  
Aerial Photographs ◽  
Field Surveys ◽  
Bedrock Rivers ◽  
Eastern Cordillera ◽  
Erosion Rates ◽  
Landslide Volume ◽  
Tectonically Active ◽  
Dominant Process ◽  
Very High

Abstract The northeastern edge of the Bolivian Eastern Cordillera is an example of a tectonically active plateau margin where orographically enhanced precipitation facilitates very high rates of erosion. The topography of the steepest part of the margin exhibits the classic signature of high erosion rates consisting of high-relief V-shaped valleys where landsliding is the dominant process of hillslope erosion and bedrock rivers are incising into the landscape. The authors mapped landslide scars on multitemporal aerial photographs to estimate hillslope erosion rates. Field surveys of landslide scars are used to calibrate a landslide volume versus area relationship. The mapped area of landsliding, in combination with an estimate of the time for landslide scars to revegetate, leads to an erosion rate estimate. The estimated revegetation time, 10–35 yr, is based on analysis of multitemporal aerial photographs and tree rings. About 4%–6% of two watersheds in the region considered were affected by landslides over the last 10–35 yr. This result implies an erosion rate of 9 ± 5 mm yr−1 assuming that 90% of a single landslide reaches the river on average. Classified Landsat Thematic Mapper images show that landslides are occurring at approximately the same rate all across an approximately 40-km-wide swath within the high-relief zones of the cordillera.

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.

Compiling and Analysing Bedrock River Data Across the USA to Unpick Bedrock River Geomorphology

2021 ◽  
Author(s):  
James Buckley ◽  
Rebecca Hodge ◽  
Louise Slater
Keyword(s):  
Shear Stress ◽  
Landscape Evolution ◽  
Critical Shear Stress ◽  
Sediment Supply ◽  
Small Samples ◽  
Alluvial Rivers ◽  
Bedrock Rivers ◽  
Mountainous Regions ◽  
The Usa ◽  
Channel Properties

<p>Active incision of bedrock rivers exerts a vital control on landscape evolution in upland areas. Previous research found that bedrock rivers were typically steeper and sometimes narrower than alluvial rivers. However, most of the literature on partially-exposed bedrock rivers has employed small samples mostly from mountainous regions, so their geomorphological properties remain poorly understood. In contrast with the existing literature, a large-sample analysis of bedrock river channel properties would allow the controls on bedrock river width and slope to be unpicked and reveal whether or not the existing literature is biased towards pristine, mountainous bedrock rivers. Overall, such an analysis could improve the reliability of upland landscape evolution models.</p><p>Here we present an analysis of 1,924 river sites from the EPA National Rivers and Streams Assessment to assess the geomorphological differences between bedrock and alluvial rivers. The influences of lithology and uplift on bedrock channel properties are examined using external datasets. We find bedrock rivers to be significantly steeper and wider than alluvial rivers. Sedimentary bedrock rivers were seen to be significantly wider than igneous/ metamorphic bedrock rivers, consistent with findings from Ferguson et al. (2017). We estimated shear stress and critical shear stress for each river site and assessed correlation with bedrock exposure. We found that exposed bedrock could not always be explained by local sediment transport exceeding local sediment supply, indicating that bedrock exposure may be controlled by other factors in some bedrock rivers. Currently, uplift data are being compiled for further analysis.</p>

Analysis of geometric relationships of bedrock and alluvial channels: a comparison between rivers from the Scottish Highlands and San Gabriel Mountains (USA)

2021 ◽  
Author(s):  
Mel O. Guirro ◽  
Rebecca A. Hodge ◽  
Fiona Clubb ◽  
Laura Turnbull
Keyword(s):  
Sediment Transport ◽  
Transport Processes ◽  
Sediment Supply ◽  
Spatial Distributions ◽  
Alluvial Channels ◽  
Transport Capacity ◽  
Alluvial Rivers ◽  
Bedrock Rivers ◽  
San Gabriel Mountains ◽  
Scottish Highlands

<p>Sediment transport in rivers depends on interactions between sediment supply, topography, and flow characteristics. Erosion in bedrock rivers controls topography and is paramount in landscape evolution models. The riverbed cover indicates sediment transport processes: alluvial cover indicates low transport capacity or high sediment supply, and bedrock cover demonstrates high transport capacity or low sediment supply. This study aims to evaluate controls on the spatial distributions of bedrock and alluvial covers, by analysing scaling geometric relations between bedrock and alluvial channels. A Principal Component Analysis (PCA) was conducted to evaluate correlations between river slope, depth, width, and sediment size. The two principal components were used to implement a clustering analysis in order to identify differences in alluvial and bedrock sections. Spatial distributions of mixed bedrock-alluvial sections were investigated from two datasets - Scottish Highlands (Whitbread 2015) and the San Gabriel Mountains in the USA (Dibiase 2011)-, representing different environmental conditions, such as erosion rates, lithology, tectonics, and climate. The rock strength of both areas is high, and therefore it is excluded as a factor that explains the difference between the areas. The results of the cluster analysis were different in each environment. The main sources of variation among river sections identified by PCA were slope and width for the San Gabriel Mountains, and drainage area and depth for the Scottish Highlands. The rivers in the Scottish Highlands formed clusters that differentiate bedrock and alluvial patches, showing a clear geometric distinction between channels. However, the river analysis from the San Gabriel Mountains showed no clusters. Bedrock rivers are typically described as narrower and steeper than alluvial rivers, as demonstrated by rivers in the Scottish Highlands (e.g. slope was around 0.1 m/m for bedrock sections and 0.01 m/m for alluvial sections). However, this may not be always the case: both bedrock and alluvial sections in San Gabriel Mountains presented similar slope around 0.1 m/m. The inability to demonstrate significant geometry differences in bedrock and alluvial sections in the San Gabriel Mountains may be due to the frequency and magnitude of sediment supply of that region, which are influenced by tectonics and climate. A major difference in the supply of sediment in rivers of the San Gabriel Mountains is the frequent occurrence of debris flow. Non-linear interactions between hydraulic and sediment processes may constantly modify the geometry of bedrock-alluvial channels, increasing the complexity of analysis at larger temporal and spatial scales. This study is part of the i-CONN project, which links connectivity in different scientific disciplines. A sediment connectivity assessment in different environments and scales may be useful to evaluate the controls on the spatial distribution of bedrock and alluvial rivers.</p><p> </p><p>Dibiase, R.A. 2011. Tectonic Geomorphology of the San Gabriel Mountains, CA. PhD Thesis. Arizona State University, Phoenix, 247pp.</p><p>Whitbread, K. 2015. Channel geometry data set for the northwest Scottish Highlands. British Geological Survey Open Report, OR/15/040. 12pp.</p>

Transient signs in bedrock rivers of the southernmost Brazilian and Uruguayan shields

2020 ◽  
Author(s):  
Marcio Cardoso Junior ◽  
Ariane Santos da Silveira ◽  
Mateus Rodrigues de Vargas ◽  
José Manuel Marques Teixeira de Oliveira ◽  
Vinicius Lôndero ◽  
...  
Keyword(s):  
Evolutionary Model ◽  
Drainage Basins ◽  
Bedrock Rivers ◽  
Geomorphic Indices ◽  
Base Level ◽  
The North ◽  
Digital Elevation ◽  
Dom Feliciano Belt ◽  
Brasiliano Orogeny ◽  
Integrate Study

<p>The Earth’s surface is a result of tectonic and erosional processes shaping landscapes and preserving transient signs of different evolutionary stages. These transient signs are produced by a gradual adjustment of rivers to an equilibrium stage through channel incision and uplift. The processes effects have different magnitudes according to lithologic contrasts and base level changes that combined influence in disequilibrium phases of bedrock rivers. A integrate study of geomorphic indices in bedrock rivers of the southernmost Brazilian and Uruguayan Shields is developed to identify key signs of transience associated to those surface process and compared between the contrasting drainage basins results. These indices are combined to published thermochronology ages to build a landscape evolution model of these shields. The study area is essentially composed by igneous-metamorphic rocks of Precambrian ages of the Dom Feliciano Belt amalgamated during the Proterozoic-Phanerozoic boundary in the Brasiliano Orogeny. Digital elevation models are used to extract geomorphic indices through interactive MATLAB tools and compared the erosional stages and uplifted regions. This study reveals lineament structures signatures aligned with knickpoints as indicator of the suture zones of distinct terranes in the area. These terranes also feature different erosional stages according to hypsometric results. Thermochronological data support the tectonic framework of three uplift phases starting by the exhumation of western terranes during Devonian ages. A second stage is connected to an uplift preceding the Pangea breakup with the reactivation of Brasiliano Orogeny lineaments. And, the third phase is associated with plate flexural responses of the adjacent oceanic crust during the Cenozoic Era. Finally, the evolutionary model shows strong transient signs in the north region of the studied area indicating a locus of a possible stronger uplift process. In this part of the Dom Feliciano Belt all exhumation phase are evidenced by transient signs of disequilibrium. Differently, the southern region in the Uruguayan Shield shows a more denudated landscape with more mature stages of erosional process.</p>

scholarly journals Multiple knickpoints in an alluvial river generated by a single instantaneous drop in base level: experimental investigation

2014 ◽  
Vol 2 (1) ◽  
pp. 271-278 ◽  
Author(s):  
A. Cantelli ◽  
T. Muto
Keyword(s):  
Experimental Investigation ◽  
Equilibrium State ◽  
Hydraulic Jump ◽  
Dam Removal ◽  
Supercritical Flow ◽  
Alluvial Rivers ◽  
Bedrock Rivers ◽  
Alluvial River ◽  
Base Level ◽  
Level Lowering

Abstract. Knickpoints often form in bedrock rivers in response to base-level lowering. These knickpoints can migrate upstream without dissipating. In the case of alluvial rivers, an impulsive lowering of base level due to, for example, a fault associated with an earthquake or dam removal commonly produces smooth, upstream-progressing degradation; the knickpoint associated with suddenly lowered base level quickly dissipates. Here, however, we use experiments to demonstrate that under conditions of Froude-supercritical flow over an alluvial bed, an instantaneous drop in base level can lead to the formation of upstream-migrating knickpoints that do not dissipate. The base-level fall can generate a single knickpoint, or multiple knickpoints. Multiple knickpoints take the form of cyclic steps, that is, trains of upstream-migrating bedforms, each bounded by a hydraulic jump upstream and downstream. In our experiments, trains of knickpoints were transient, eventually migrating out of the alluvial reach as the bed evolved to a new equilibrium state regulated with lowered base level. Thus the allogenic perturbation of base-level fall can trigger the autogenic generation of multiple knickpoints which are sustained until the alluvial reach recovers a graded state.

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