scholarly journals Interpreting the Manning Roughness Coefficient in Overland Flow Simulations with Coupled Hydrological-Hydraulic Distributed Models

Water ◽  
2021 ◽  
Vol 13 (23) ◽  
pp. 3433
Author(s):  
Marcos Sanz-Ramos ◽  
Ernest Bladé ◽  
Fabián González-Escalona ◽  
Gonzalo Olivares ◽  
José Luis Aragón-Hernández
Keyword(s):  
Channel Flow ◽  
Overland Flow ◽  
Roughness Coefficient ◽  
Runoff Water ◽  
Distributed Models ◽  
Water Volumes ◽  
Manning Roughness ◽  
Runoff Hydrographs ◽  
Manning Roughness Coefficient

There is still little experience on the effect of the Manning roughness coefficient in coupled hydrological-hydraulic distributed models based on the solution of the Shallow Water Equations (SWE), where the Manning coefficient affects not only channel flow on the basin hydrographic network but also rainfall-runoff processes on the hillslopes. In this kind of model, roughness takes the role of the concentration time in classic conceptual or aggregated modelling methods, as is the case of the unit hydrograph method. Three different approaches were used to adjust the Manning roughness coefficient in order to fit the results with other methodologies or field observations—by comparing the resulting time of concentration with classic formulas, by comparing the runoff hydrographs obtained with aggregated models, and by comparing the runoff water volumes with observations. A wide dispersion of the roughness coefficients was observed to be generally much higher than the common values used in open channel flow hydraulics.

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 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.

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 a local balance 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.

Correction coefficients for uniform channel flow

1991 ◽  
Vol 18 (1) ◽  
pp. 156-158 ◽  
Author(s):  
Damei Li ◽  
Willi H. Hager
Keyword(s):  
Kinetic Energy ◽  
Channel Flow ◽  
Dynamic Pressure ◽  
Local Variation ◽  
Roughness Coefficient ◽  
Correction Coefficient ◽  
Uniform Channel ◽  
Energy And Momentum ◽  
Manning Roughness ◽  
Manning Roughness Coefficient

The kinetic energy and momentum correction coefficients are considered. After a review of pertinent literature, the discussion is restricted to uniform open channel flow. It is found both theoretically and experimentally that the coefficients depend significantly on the Manning roughness coefficient, and that the kinetic energy correction coefficient may directly be related to the momentum correction coefficient. Further, the effect of local variation of correction coefficients is much smaller than the variation of dynamic pressure times the correction coefficient. Therefore, the concept of constant coefficient as proposed earlier is justified. Key words: backwater curve, channel, distribution, flow, river.

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.  

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