Velocity of Debris Flow Determined by Grain Composition
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Abstract:
Velocity is one of the most important parameters of debris flows, and it is usually calculated using Manning formula in hydraulics, mostly ignoring the granular effects due to flow materials. This study proposes a method in term of grain composition of debris flow, incorporating the physical effects of grain on roughness. It is found that the Manning resistance coefficient can be well related to the grain size distribution (GSD) and thus the method is expected to have a wide application. A new formula incorporating the influence of granular effects is built based on observation data of debris flows in Jiangjia Gully (JJG), China, and then it is tested by data from debris flows in other regions.Keywords:
Debris flow
Hydraulic roughness
Hydraulics
The properties of buoyant and dense discharges in a horizontal mixing channel are evaluated analytically and experimentally. The mixing channel is shallow, of specified length and roughness, and connected to a reservoir or stream. The flow in the channel consists of a mixing zone and a gradually varied counterflow. Mixing modes associated with four possible interactions are described. A hydraulic theory is formulated and used to develop synthesized dilution curves. Experiments conducted in a laboratory flume confirmed the existence of four mixing modes, and dilution measurements are consistent with predicted trends. In practice, the theory would be useful in the design and operation of such a facility.
Hydraulics
Flume
Hydraulic roughness
Micromixing
Dilution
Complete mixing
Mixing patterns
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In environmental flood management, an essential task is to improve channel conveyance using environmentally preferable methods, which aim to preserve natural morphological and hydraulic characteristics of a river. This requires a reliable channel design method that accounts for complex hydraulics, i.e. two-stage channel or considerable bank vegetation. Hydraulic field measurements were carried out in two rivers to find out how different factors affected flow resistance. In one of the study reaches, the effects of bioengineering on channel hydraulics were investigated under boreal climatic conditions. The Darcy-Weisbach friction factor, the Manning coefficient and the roughness height were related to the characteristics of channel geometry and flow. Comparison between the field data and the investigated channel design methods gave accurate results only in reaches having simple hydraulic properties. In reaches with complex hydraulics the results were poor.
Hydraulics
Hydraulic resistance
Hydraulic roughness
Hydraulic Engineering
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Flume
Hydraulic roughness
Flow conditions
Hydraulics
Hydraulic jump
Flow resistance
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This report describes the hydraulic effects of dikes on water surface elevation (WSE) and velocities in the Mississippi River near Vicksburg, MS, from Interstate 20 to Highway 80 using a previously calibrated 2D Adaptive Hydraulics numerical model. Dike heights and their associated hydraulic roughness values were varied to quantify the overall effects of adjustments to dike fields. Steady flows characterized as low, medium, and high conditions were simulated. The WSE and velocity difference plots were generated to illustrate the hydraulic effects on the river under all scenarios discussed above. Overall, the dike adjustments had negligible impacts on WSEs and showed minimal effects on velocities on a system-wide scale.
Dike
Hydraulics
Hydraulic roughness
Hydraulic Engineering
Elevation (ballistics)
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The characteristics of 82 flow velocity profiles were analyzed from nine different gravel bed stream reaches. A statistical test of the linearity of flow velocity profiles indicates that contrary to what is frequently assumed, velocity profiles are often not semilogarithmic but segmented - that is, they can be divided in two (or more) semilog-linear segments. The results show that segmented velocity profiles are not confined to streams with very coarse bed material, but that they also occur in streams with relatively small bed particles. Segmented velocity profiles were modeled using a technique called spline modeling. This technique allowed the objective identification of semilog-linear velocity profile segments and of the corresponding knots where they join. An analysis of the pattern of flow over natural bed obstacles revealed that velocity profile segments correspond to distinct layers of the flow adjusted to different scales of roughness: a grain roughness scale controlling the shape of near-bottom velocity segment and a bedform roughness scale controlling the shape of the segment located immediately above.
Hydraulic roughness
Bedform
Flow conditions
Length scale
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The purpose of this study is to investigate the roughness characteristics and the velocity profile in vegetated and non-veg-elated channels through hydraulic model experiments, and to find a relationship between the velocity profile and the roughness height. The velocity is logarithmically distributed from the channel bottom to 0.8 of flow depth(h) in the non-vegetated channel and from the upper part of vegetation to 0.8 of flow depth() over the vegetation deflected by the flow in vegetated channel. The elevation() corresponding to zero velocity is calculated by using measured velocity profiles. In a non-vegetated channel, is 0.18 of mean diameter(d) of crushed rock over the channel bottom and in a vegetated channel, is 0.40 of mean height() of deflected vegetation. The roughness height is calculated by using velocity profiles in a vegetated channel and it is shown that the flow resistance tends to increase with the density of vegetation. The velocity profiles measured in a vegetated channel is a relatively good agreement with those predicted from formulae proposed by Kouwen et al.(1969), Haber(1982) and El-Hakim et al.(1992).
Hydraulic roughness
Elevation (ballistics)
Roughness length
Shear velocity
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Onsite surveys and 75 measurements of discharge were made on 21 high‐gradient streams (slopes greater than 0.002) for the purpose of computing the Manning roughness coefficient, n, and to provide data on the hydraulics of these streams. These data show that: (1) n varies inversely with depth; (2) n varies directly with slope; and (3) streams thought to be in the supercritical flow range were actually in the subcritical range. A simple and objective method was employed to develop an equation for predicting the n of high‐gradient streams by using multiple‐regression techniques and measurements of the slope and hydraulic radius. The average standard error of estimate of this prediction equation was 28% when tested with Colorado data. The equation was verified using other data available for high‐gradient streams. Regimeflow equations for velocity and discharge also were developed.
Hydraulics
Supercritical flow
Hydraulic roughness
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Citations (470)
Bedload roughness is the roughness produced by sediment transported near the bed. While it is well established that the magnitude of this roughness is proportional to the thickness of the moving sediment layer, the effect of sediment concentration remains largely unknown. This paper presents the results of a flume experiment that was designed to investigate the effect of sediment concentration on bedload roughness. The experiment consisted of creating flow conditions where bedload transport is supply-limited and injecting gravel size particles (D50=7·4 mm) at the upstream end of the flume in order to produce bedload transport. While keeping flow conditions constant, sediment concentration was varied by successively increasing the injection rate of gravel in the flow. For each injection rate, flow velocity profiles were measured in order to evaluate changes of mean flow velocity U, shear velocity u*, roughness length zo and resistance to flow f. The results indicate that low sediment concentration affects mainly the near bed portion of the flow where it causes a reduction of mean flow velocity and an increase of shear velocity and roughness length. For larger sediment concentration, the whole flow velocity profile becomes affected by bedload roughness but the importance of this effect always remain larger near the bed. As sediment concentration is augmented, mean flow velocity is consistently reduced but shear velocity and roughness length increase until a plateau is reached where these two variables become constant. Copyright © 1999 John Wiley & Sons, Ltd.
Flume
Hyperconcentrated flow
Hydraulic roughness
Bedform
Shear velocity
Flow conditions
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Citations (31)
Bedload roughness is the roughness produced by sediment transported near the bed. While it is well established that the magnitude of this roughness is proportional to the thickness of the moving sediment layer, the effect of sediment concentration remains largely unknown. This paper presents the results of a flume experiment that was designed to investigate the effect of sediment concentration on bedload roughness. The experiment consisted of creating flow conditions where bedload transport is supply-limited and injecting gravel size particles (D50=7·4 mm) at the upstream end of the flume in order to produce bedload transport. While keeping flow conditions constant, sediment concentration was varied by successively increasing the injection rate of gravel in the flow. For each injection rate, flow velocity profiles were measured in order to evaluate changes of mean flow velocity U, shear velocity u*, roughness length zo and resistance to flow f. The results indicate that low sediment concentration affects mainly the near bed portion of the flow where it causes a reduction of mean flow velocity and an increase of shear velocity and roughness length. For larger sediment concentration, the whole flow velocity profile becomes affected by bedload roughness but the importance of this effect always remain larger near the bed. As sediment concentration is augmented, mean flow velocity is consistently reduced but shear velocity and roughness length increase until a plateau is reached where these two variables become constant. Copyright © 1999 John Wiley & Sons, Ltd.
Hyperconcentrated flow
Hydraulic roughness
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Citations (2)
This paper is a discussion of an ASCE paper which presented the effect of longitudinal and transverse spacing of roughness on the flow in rigid open channels. The authors continue the discussion by reporting the results obtained by applying the analysis to a different type of roughness element consisting of round bars, and to consider a possible extension to field conditions. The study of the roughness effect was made in connection with the model testing of arch bridges.
Hydraulics
Hydraulic roughness
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