scholarly journals New Method for Estimating Roughness Coefficient for Debris Flows

Water ◽  
2020 ◽  
Vol 12 (9) ◽  
pp. 2341
Author(s):  
Xinghua Zhu ◽  
Bangxiao Liu ◽  
Yue Liu
Keyword(s):  
Debris Flow ◽  
Cross Sections ◽  
Resistance Coefficient ◽  
Roughness Coefficient ◽  
Observation Data ◽  
Research Papers ◽  
Factors Affecting ◽  
Manning Roughness ◽  
Published Research ◽  
Manning Roughness Coefficient

Flow resistance is a fundamental control of flow hydraulics in streams and rivers. In this paper, five dimensionless factors affecting the Manning roughness coefficient n and attributed to the external roughness coefficient n1 and the internal roughness coefficient n2 were analyzed comprehensively. And then, dimensionless factors affecting n1 and n2 with precise physical meanings were proposed. With a calculation method for roughness coefficient fitted and analyzed based on observation data from published research papers, the analysis results showed that the external resistance coefficient is closely related to the dimensionless factor D84/R. The correlation between the dimensionless factor (D16/D50) and the internal roughness coefficient n2 was not significant. While the factors H/D50, J, and Sv showed significant correlation. In addition, the expression of external roughness n1 is calibrated based on the observation data of 102 cross-sections listed in previous works, while the internal roughness n2 is calibrated by 20 experimental model tests. Finally, an equation describing the Manning’s roughness coefficient is presented and verified based on 24 groups of observation data from Dongchuan Debris Flow Observation Station (DDFORS) in China. This study is contributing toward a comprehensive model for the Manning coefficient, which provide a scientific reference for the research on disaster prevention and mitigation of debris flow.

scholarly journals Overland Flow Resistance Law under Sparse Stem Vegetation Coverage

Water ◽  
2021 ◽  
Vol 13 (12) ◽  
pp. 1657
Author(s):  
Jingzhou Zhang ◽  
Shengtang Zhang ◽  
Si Chen ◽  
Ming Liu ◽  
Xuefeng Xu ◽  
...  
Keyword(s):  
Flow Resistance ◽  
Overland Flow ◽  
Vegetation Coverage ◽  
Dominant Factor ◽  
Roughness Coefficient ◽  
Hydraulic Parameters ◽  
Slope Condition ◽  
Manning Roughness ◽  
The Relationship ◽  
Manning Roughness Coefficient

To explore the characteristics of overland flow resistance under the condition of sparse vegetative stem coverage and improve the basic theoretical research of overland flow, the resistance characteristics of overland flow were systematically investigated under four slope gradients (S), seven flow discharges (Q), and six degrees of vegetation coverage (Cr). The results show that the Manning roughness coefficient (n) changes with the ratio of water depth to vegetation height (h/hv) while the Reynolds number (Re), Froude number (Fr), and slope (S) are closely related to vegetation coverage. Meanwhile, h/hv, Re, and Cr have strong positive correlations with n, while Fr and S have strong negative correlations with n. Through data regression analysis, a power function relationship between n and hydraulic parameters was observed and sensitivity analysis was performed. It was concluded that the relationship between n and h/hv, Re, Cr, Q, and S shows the same law; in particular, for sparse stem vegetation coverage, Cr is the dominant factor affecting overland flow resistance under zero slope condition, while Cr is no longer the first dominant factor affecting overland flow resistance under non-zero slope condition. In the relationship between n and Fr, Cr has the least effect on overland flow resistance. This indicates that when Manning roughness coefficient is correlated with different hydraulic parameters, the same vegetation coverage has different effects on overland flow resistance. Therefore, it is necessary to study overland flow resistance under the condition of sparse stalk vegetation coverage.

scholarly journals Experimental study on determining Manning roughness coefficient during slope runoff process

2020 ◽  
Vol 39 (4) ◽  
pp. 651-659
Author(s):  
Yashan CHENG ◽  
Zhonggen WANG ◽  
Jun LI ◽  
Zhen HUANG ◽  
Xiangyu YE ◽  
...  
Keyword(s):  
Experimental Study ◽  
Roughness Coefficient ◽  
Manning Roughness ◽  
Slope Runoff ◽  
Manning Roughness Coefficient

scholarly journals Landslides triggered by the 2015 Gorkha Earthquake and analysis of their long-lasting impact

2018 ◽  
Vol 55 (1) ◽  
pp. 77-84
Author(s):  
Hikaru Tomita ◽  
Alessandra Mayumi Nakata ◽  
Kazuo Konagai ◽  
Takashi Matsushima ◽  
Masataka Shiga ◽  
...  
Keyword(s):  
Prediction Error ◽  
Critical Angle ◽  
Numerical Approach ◽  
Angle Of Repose ◽  
Roughness Coefficient ◽  
Mass Movements ◽  
Gorkha Earthquake ◽  
2015 Gorkha Earthquake ◽  
Manning Roughness ◽  
Manning Roughness Coefficient

The Gorkha earthquake of April 25, 2015 has caused many landslides along the Trishuli River in the Rasuwa District. A numerical approach has been taken to assess the remaining risk of landslides. The debris mass movements are described in simulations with only three parameters, namely, the critical angle if, Gauckler–Manning roughness coefficient n, and angle of repose id. The optimum set of these three parameters, obtained through a batch of numerical simulations to minimize the prediction error, was then used to identify locations of unstable colluvium deposits remaining along gullies on steep valley walls of the Trishuli River.  

scholarly journals The role of sediment transport in the mechanics of jökulhlaups

1996 ◽  
Vol 22 ◽  
pp. 255-259 ◽  
Author(s):  
A. C. Fowler ◽  
F. S. L. Ng
Keyword(s):  
Water Pressure ◽  
Channel Morphology ◽  
Roughness Coefficient ◽  
Detailed Model ◽  
Channel Opening ◽  
Theoretical Predictions ◽  
Ice Pressure ◽  
Manning Roughness ◽  
Manning Roughness Coefficient

The classical theory of jökulhlaups used Röthlisberger’s earlier theory of ice-channel drainage to describe the development of the flood hydrograph. This theory has some drawbacks: the mechanism of initiation (breaking the seal) is opaque, the Manning roughness coefficient is too large and the hydrographs can reveal a sudden switching from channel opening to channel closure which is not simulated by the model. In this paper, we examine these features by exploring a more detailed model, which takes into account the physics of sediment erosion and its effect on channel morphology. We propose a theory in which channels need not be semicircular, but have shapes determined by alocalbalance between closure and melting, and in which erosion of the tunnel margins is taken into account; in particular, we derive theoretical predictions for sediment discharge, and we also propose a mechanism whereby the pressure seal over the caldera rim at Grímsvötn in Vatnajökull, Iceland, can be broken when the lake-level water pressure is still some 6 bar below the maximum overburden ice pressure.

Determination of the Manning roughness coefficient influenced by vegetation in the river Aa and Biebrza river

2009 ◽  
Vol 9 (5) ◽  
pp. 549-567 ◽  
Author(s):  
L. De Doncker ◽  
P. Troch ◽  
R. Verhoeven ◽  
K. Bal ◽  
P. Meire ◽  
...  
Keyword(s):  
Roughness Coefficient ◽  
Manning Roughness ◽  
Manning Roughness Coefficient
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