scholarly journals River sinuosity describes a continuum between randomness and ordered growth

Geology ◽  
2021 ◽  
Author(s):  
Ajay B. Limaye ◽  
Eli D. Lazarus ◽  
Yuan Li ◽  
Jon Schwenk
Keyword(s):  
Line Length ◽  
Coupled Analysis ◽  
River Channels ◽  
Channel Migration ◽  
Geologic Structure ◽  
Quantitative Criterion ◽  
Stream Length ◽  
Essential Characteristic ◽  
Straight Line ◽  
Meander Bends

River channels are among the most common landscape features on Earth. An essential characteristic of channels is sinuosity: their tendency to take a circuitous path, which is quantified as along-stream length divided by straight-line length. River sinuosity is interpreted as a characteristic that either forms randomly at channel inception or develops over time as meander bends migrate. Studies tend to assume the latter and thus have used river sinuosity as a proxy for both modern and ancient environmental factors including climate, tectonics, vegetation, and geologic structure. But no quantitative criterion for planform expression has distinguished between random, initial sinuosity and that developed by ordered growth through channel migration. This ambiguity calls into question the utility of river sinuosity for understanding Earth’s history. We propose a quantitative framework to reconcile these competing explanations for river sinuosity. Using a coupled analysis of modeled and natural channels, we show that while a majority of observed sinuosity is consistent with randomness and limited channel migration, rivers with sinuosity ≥1.5 likely formed their geometry through sustained, ordered growth due to channel migration. This criterion frames a null hypothesis for river sinuosity that can be applied to evaluate the significance of environmental interpretations in landscapes shaped by rivers. The quantitative link between sinuosity and channel migration further informs strategies for preservation and restoration of riparian habitat and guides predictions of fluvial deposits in the rock record and in remotely sensed environments from the seafloor to planetary surfaces.

scholarly journals The effect of ignition protocol on grassfire development

2020 ◽  
Vol 29 (1) ◽  
pp. 70
Author(s):  
Duncan Sutherland ◽  
Jason J. Sharples ◽  
Khalid A. M. Moinuddin
Keyword(s):  
Wind Speed ◽  
Temporal Resolution ◽  
Line Length ◽  
Forward Rate ◽  
High Temporal Resolution ◽  
Quasi Equilibrium ◽  
Rate Of Spread ◽  
Straight Line ◽  
Shortest Distance ◽  
Physics Based Simulation

The effect of ignition protocol on the development of grassfires is investigated using physics-based simulation. Simulation allows measurement of the forward rate of spread of a fire as a function of time at high temporal resolution. Two ignition protocols are considered: the inward ignition protocol, where the ignition proceeds in a straight line from the edges of the burnable fire plot to the centre of the plot; and the outwards ignition protocol, where the ignition proceeds from the centre of the burnable fire plot to the edges of the plot. In addition to the two ignition protocols, the wind speed, time taken for the ignition to be completed and ignition line length are varied. The rate of spread (R) of the resultant fires is analysed. The outwards ignition protocol leads to an (approximately) monotonic increase in R, whereas the inward ignition protocol can lead to a peak in R before decreasing to the quasi-equilibrium R. The fires simulated here typically take 50m from the ignition line to develop a quasi-equilibrium R. The results suggest that a faster ignition is preferable to achieve a quasi-equilibrium R in the shortest distance from the ignition line.

Large Deformation Analysis and Experiments With Double Parallelogram Compliant Mechanisms

2018 ◽  
Author(s):  
Abhijit A. Tanksale ◽  
Prasanna S. Gandhi
Keyword(s):  
Large Deformation ◽  
High Precision ◽  
Large Deformations ◽  
Compliant Mechanisms ◽  
Compliant Mechanism ◽  
Vertical Plane ◽  
Coupled Analysis ◽  
Deformation Analysis ◽  
Flexible Beams ◽  
Straight Line

Compliant mechanisms are highly preferred in applications demanding motion with high precision. These mechanisms provide friction-less, backlash-free precise motion obtained through deformation of flexible members. The double parallelogram compliant mechanism (DPCM) is one the most important compliant mechanisms to obtain highly precise straight-line motion. DPCM when operated in horizontal plane yield high precision straight-line motion (even with large deformations) useful in several engineering applications. However, constraints such as space, dead loads, etc. may demand DPCMs to be used in the vertical plane. For DPCMs operating in a vertical plane, the axial load due to gravity causes tension and compression in flexible beams which get coupled to bending under large deformations. This ultimately affects the parasitic error of straight-line motion. This paper presents a coupled analysis, along with experimental validation, of DPCM operating in vertical plane considering gravity effects with large deformation.

scholarly journals The Response of Stream Competence to Topographic and Seasonal Variations in The Bamenda-Menchum Drainage Basin, North West Region, Cameroon

2019 ◽  
Vol 11 (2) ◽  
pp. 21 ◽  
Author(s):  
Kang Edwin Mua ◽  
Kometa Sunday Shende
Keyword(s):  
Drainage Basin ◽  
Flow Direction ◽  
Control Policy ◽  
Slope Instability ◽  
River Channels ◽  
Stream Network ◽  
Stream Length ◽  
Alluvial Deposits ◽  
North West ◽  
Development Prospects

The flow direction of streams remains an establishing mechanism in understanding drainage basin function and stream competence. The ability of streams to erode, transport and deposit loads in fluvial geomorphology exert a benchmark precursor for slope dynamics given the differential geological outcrop of the Bamenda-Menchum basin. Such competence in stream network generates slope instability as materials continuously move down slope from the volcanic escarpment face of Bamenda highlands to the sedimentary lowland area of Lower Bafut-Menchum basin. This paper investigate the influence of stream flow direction and stream competence on slope dynamics and how such dynamism affects the development prospects of the drainage basin. Slope range was obtained from AVL/EBI.JHO measurement. Stream length, density and flow direction were gotten from GIS Arc 21. Stream depth, channel width, flow rate and sedimentation levels were measured. Gully depth on slopes and landslide angles were measured using 30m tape and a graduated pole. Questionnaires were used to collect information on the vulnerability of households to slope dynamics orchestrated by stream competence. Findings revealed that stream competence varies from the two geological basements and that the escarpment face respond to high flow gravity and hydraulic action contributing to rapid erosion and transportation of loads. The results equally showed that the Bamenda escarpment face that is linked to the crystalline rocks produce differential erosion and landslide. 76.7% of slope instability is explained by geological structure and seasonality effect in the basin while 23.3% of slope dynamics is explained by other variables not specified in the study. The lower basin remains liable to deposition of materials on river channels and flood plain. The accumulation of sand, stones and alluvial deposits are extracted and exploited for the development prospects of the basin. The study recommends channel and slope management by integrating slope development control policy in drainage basin management and development.

scholarly journals Channel Migration of the Meandering River Fan: A Case Study of the Okavango Delta

Water ◽  
2021 ◽  
Vol 13 (23) ◽  
pp. 3319
Author(s):  
Xue Yan ◽  
Jinliang Zhang ◽  
Yang Li ◽  
Long Sun
Keyword(s):  
Sedimentary Facies ◽  
Google Earth ◽  
Okavango Delta ◽  
River Channels ◽  
Fluvial System ◽  
Channel Migration ◽  
Sinuosity Index ◽  
Meandering River ◽  
The Difference ◽  
River Migration

Okavango delta is a typical distributive fluvial system, which is composed of a series of sand island-river-swamp networks. River migration in the Okavango delta is analyzed by using satellite images from Google Earth and Alaska Satellite Facility (ASF). Four configuration characterization parameters are selected to depict and measure the meandering river. These four parameters are sinuosity index (S), curvature (C), the difference of along-current deflection angle (Δθ) and expansion coefficient (Km). In the fan, the channel migration is mainly asymmetric. According to geomorphic elements and associated features, Okavango Delta can be subdivided into three zones: axial zone, median zone and distal zone. Under the influence of slope, climate and vegetation, different migration modes are developed in different zones. As the river moves downstream, the sinuosity index of the river on the Okavango Delta decreases downstream. Based on the characteristics of different zones, the sedimentary facies model of a single source distributive fluvial system of a meandering river is proposed. The models of channel migration and sedimentary facies have wide application. This research will not only provide a basis for the prediction of future river channels but will also provide important theoretical guidance for the study of the sedimentary morphology of underground reservoirs.

scholarly journals Planform river channel perturbations resulting from active landsliding in the High Himalaya of Bhutan

2020 ◽  
Author(s):  
Larissa de Palézieux ◽  
Kerry Leith ◽  
Simon Loew
Keyword(s):  
Early Period ◽  
Pink Noise ◽  
River Channels ◽  
Channel Migration ◽  
Stream Power ◽  
Study Region ◽  
Term Evolution ◽  
Lateral Channel ◽  
Mountainous Landscapes

Abstract. Large creeping landslides are persistent features in mountainous landscapes. Evaluating the long-term evolution of these features and associated present-day hazards is however difficult. We use a Fourier transform to characterize planform channel sinuosity and find that the amplitude at given wavelengths follows the power law of pink noise (1 / fnoiseα) with an exponent of α = 1.1, which is consistent with a fractal distribution. This allows us to distinguish local landslide perturbations from the background sinuosity of the unperturbed channels. In order to quantify the interaction of landslides with river channels, we use a new metric for landslide-induced channel offset, which allows us to identify exceptional amplitudes associated with landslide activity. We find that 83 % of the 226 mapped large creeping landslides in the High Himalaya of Bhutan have generated lateral channel migration in the direction of the landslide displacement. Assuming landslide initiation is associated with knickpoint propagation, our derived stream power normalized rates of landslide-induced channel offset range from 2 · 10−1 to 2 · 10−2 m−0.9. These rates are consistent with an early period of relatively rapid landslide displacement followed by a long period of stabilization, and finally, a gradual acceleration of more mature landslides. Assuming constant bedrock erodibility, displacement rates derived from the landslides in our study region may provide inside into the evolution of large creeping landslides over a period of 1 Myr.

scholarly journals River bank erosion opposite to transverse groynes

2018 ◽  
Vol 40 ◽  
pp. 03013 ◽  
Author(s):  
Alessandra Crosato ◽  
José Bonilla-Porras ◽  
Arthur Pinkse ◽  
Tsegaye Yirga Tiga
Keyword(s):  
Numerical Models ◽  
Bank Erosion ◽  
River Channels ◽  
Channel Migration ◽  
River Bank ◽  
Inland Navigation ◽  
Short Series ◽  
Bed Erosion ◽  
River Bed ◽  
Lateral Channel

Long series of groynes are built from both river sides to narrow river channels and prevent bank erosion with the aim to improve the conditions for inland navigation and prevent lateral channel migration. Single groynes or short series of groynes are built to impede local bank erosion, deviate the water flow, free an intake or fix the position of migrating bars at certain locations. These structures divert the flow towards the opposite river side where channel bed erosion increases the risk of bank failure. Flow and river bed adaptation have been extensively studied, especially for long series of groynes. Instead, studies dealing with opposite bank erosion caused by single or short series of groynes are still lacking. We investigated this phenomenon in the laboratory and using 2D numerical models with LES. This paper shows some preliminary results.

A Synthesis and Optimal Method for Straight Line Mechanism with Burmester Points

2011 ◽  
Vol 199-200 ◽  
pp. 1240-1243 ◽  
Author(s):  
Lai Rong Yin ◽  
Jian You Han ◽  
Tong Yang
Keyword(s):  
Infinite Number ◽  
Line Length ◽  
Point Contacts ◽  
Optimal Method ◽  
Region Method ◽  
Straight Line ◽  
Solution Region ◽  
Straight Line Mechanism ◽  
Ball Point

When a Burmester point coincides with the Ball point at the inflection circle pole, given a fixed joint and the point, which is on the expecting straight-line and direction can synthesize an infinite number of mechanisms with coupler curve having a five-point contacts with its tangent, namely, Burmester point. Any displacement is corresponding to three four-bar straight-line linkages with the synthesis formulations given. The property charts, which include the bar ratio, the sum of bars, the relative straight-line length, mechanism types, and so on, are drawn by developing a mechanism software based on vc++6.0 with the solution region method. So the users can find out the involved linkages information intuitively, and also the aimlessness in choosing optimal mechanisms is avoided effectively.

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