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Vito Ferro - One of the best experts on this subject based on the ideXlab platform.
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assessing Flow Resistance in gravel bed channels by dimensional analysis and self similarity
Catena, 2018Co-Authors: Vito FerroAbstract:Abstract In this paper a new Flow Resistance equation for open channel Flow, based on the integration of a power velocity profile, was tested for gravel bed channels. First this Flow Resistance equation, theoretically deduced by dimensional analysis and incomplete self-similarity condition, was reported. Then a relationship between the Γ function of the velocity profile, the channel slope and the Froude number was calibrated by the available laboratory measurements of Flow velocity, water depth and bed slope carried out in 416 flume experimental runs with a gravel bed. Then the relationship for estimating Γ function and the theoretical Resistance equation was tested by 83 independent flume measurements. The analysis also showed that the proposed Flow Resistance equation allows an estimate of the Darcy-Weisbach friction factor which is more reliable and accurate than that obtained by a semi-logarithmic Flow Resistance law or a variable-power Resistance equation, calibrated with the same gravel bed measurements. For testing the applicability of the proposed Γ function (Eq. (17)), whose coefficients were estimated by flume measurements, available fields measurements were used. The analysis demonstrated that a scale factor (equal to 0.7611) is necessary to convert Γ values obtained by flume measurements into those corresponding to gravel bed rivers. The similitude between Flow Resistance in a gravel bed flume and in a gravel bed river is governed by the Γ function and a scale factor, equal to 1.6, is required to upscale the Darcy-Weisbach friction factor values obtained by flume measurements to the river case. In conclusion, the analysis showed that the Darcy-Weisbach friction factor for gravel bed channels can be accurately estimated by the proposed theoretical approach based on a power-velocity profile.
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the influence of roughness geometry and shields parameter on Flow Resistance in gravel bed channels
Earth Surface Processes and Landforms, 1997Co-Authors: Giorgio Baiamonte, Vito FerroAbstract:The spatial variability of bed particles of a gravel-bed channel is analysed and treated experimentally in order to simulate the effects of the arrangement of coarse bed elements on the Flow Resistance law. For the studied bed patterns, characterized by the concentration Γ of coarser elements arranged on the bed layer, a particle arrangement parameter α is proposed. The α parameter is useful for estimating the intercept b0 of the semi-logarithmic Flow Resistance law deduced by flume measurements carried out for the hydraulic condition of large-scale and transition roughness. The differences between the experimental friction factor parameter values and the ones calculated by the proposed semi-logarithmic relationship are explained by the ratio between the Shields parameter and its critical value. The analysis shows that estimates of the friction factor parameter are not improved by introducing the Froude number into the Flow Resistance law. © 1997 by John Wiley & Sons, Ltd.
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applying hypothesis of self similarity for Flow Resistance law of small diameter plastic pipes
Journal of Irrigation and Drainage Engineering-asce, 1997Co-Authors: Vito FerroAbstract:In this paper the writer reports the results of an investigation carried out to test the applicability of the self-similarity hypothesis for determining the Flow-Resistance law in small-diameter plastic pipes. The incomplete self-similarity (ISS) hypothesis is applied for establishing both the Flow-Resistance law and the velocity distribution. The analysis shows that the head loss per unit length can be accurately estimated using a theoretical approach based on the ISS hypothesis for the velocity profile in a circular smooth pipe. A new relationship between the Γ coefficient of the power-velocity profile and the Flow Reynolds number, based on previous measurements carried out in plastic polyethylene (PE) pipes with nominal diameter equal to 16, 20, and 25 mm and for Flow Reynolds numbers ranging from 3,037 to 36,112, is also established.
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experimental study on Flow Resistance law for small diameter plastic pipes
Journal of Irrigation and Drainage Engineering-asce, 1995Co-Authors: Vincenzo Bagarello, Giuseppe Provenzano, Vito Ferro, Domenico PumoAbstract:In this paper the writers report the results of an experimental investigation on Flow-Resistance law in small-diameter plastic pipes. The experiments were carried out for a wide range of Reynolds number values obtained by varying the discharge and the water temperature. The experimental results are analyzed by both a purely empirical and a semitheoretical approach based on the hypothesis that the velocity distribution has a power-law form. The analysis shows that both the empirical and the semitheoretical approach allow accurate head loss per unit length estimate. In most cases (96–97% of runs) the estimate errors are less than 5%.
Ellen Wohl - One of the best experts on this subject based on the ideXlab platform.
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Flow Resistance dynamics in step pool stream channels 1 large woody debris and controls on total Resistance
Water Resources Research, 2006Co-Authors: Andrew C Wilcox, Ellen WohlAbstract:[1] Flow Resistance dynamics in step-pool channels were investigated through physical modeling using a laboratory flume. Variables contributing to Flow Resistance in step-pool channels were manipulated in order to measure the effects of various large woody debris (LWD) configurations, steps, grains, discharge, and slope on total Flow Resistance. This entailed nearly 400 flume runs, organized into a series of factorial experiments. Factorial analyses of variance indicated significant two-way and three-way interaction effects between steps, grains, and LWD, illustrating the complexity of Flow Resistance in these channels. Interactions between steps and LWD resulted in substantially greater Flow Resistance for steps with LWD than for steps lacking LWD. LWD position contributed to these interactions, whereby LWD pieces located near the lip of steps, analogous to step-forming debris in natural channels, increased the effective height of steps and created substantially higher Flow Resistance than pieces located farther upstream on step treads. Step geometry and LWD density and orientation also had highly significant effects on Flow Resistance. Flow Resistance dynamics and the Resistance effect of bed roughness configurations were strongly discharge-dependent; discharge had both highly significant main effects on Resistance and highly significant interactions with all other variables.
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large woody debris and Flow Resistance in step pool channels cascade range washington
Geomorphology, 2003Co-Authors: Janet H Curran, Ellen WohlAbstract:Abstract Total Flow Resistance, measured as Darcy–Weisbach f, in 20 step-pool channels with large woody debris (LWD) in Washington, ranged from 5 to 380 during summer low Flows. Step risers in the study streams consist of either (1) large and relatively immobile woody debris, bedrock, or roots that form fixed, or “forced,” steps, or (2) smaller and relatively mobile wood or clasts, or a mixture of both, arranged across the channel by the stream. Flow Resistance in step-pool channels may be partitioned into grain, form, and spill Resistance. Grain Resistance is calculated as a function of particle size, and form Resistance is calculated as large woody debris drag. Combined, grain and form Resistance account for less than 10% of the total Flow Resistance. We initially assumed that the substantial remaining portion is spill Resistance attributable to steps. However, measured step characteristics could not explain between-reach variations in Flow Resistance. This suggests that other factors may be significant; the coefficient of variation of the hydraulic radius explained 43% of the variation in friction factors between streams, for example. Large woody debris generates form Resistance on step treads and spill Resistance at step risers. Because the form Resistance of step-pool channels is relatively minor compared to spill Resistance and because wood in steps accentuates spill Resistance by increasing step height, we suggest that wood in step risers influences channel hydraulics more than wood elsewhere in the channel. Hence, the distribution and function, not just abundance, of large woody debris is critical in steep, step-pool channels.
Juha Jarvela - One of the best experts on this subject based on the ideXlab platform.
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modeling the Flow Resistance of woody vegetation using physically based properties of the foliage and stem
Water Resources Research, 2014Co-Authors: Kaisa Vastila, Juha JarvelaAbstract:[1] Both the foliage and stem essentially influence the Flow Resistance of woody plants, but their different biomechanical properties complicate the parameterization of foliated vegetation for modeling. This paper investigates whether modeling of Flow Resistance caused by natural woody vegetation can be improved using explicit description of both the foliage and stem. For this purpose, we directly measured the drag forces of Alnus glutinosa, Betula pendula, Salix viminalis, and Salix x rubens twigs in a laboratory flume at four foliation levels, parameterized with the leaf-area-to-stem-area ratio AL/AS. The species differed in the foliage drag but had approximately equal stem drag. For the foliated twigs, increasing AL/AS was found to increase the reconfiguration and the share of the foliage drag to the total drag. The experiments provided new insight into the factors governing the Flow Resistance of natural woody vegetation and allowed us to develop a model for estimating the vegetative friction factor using the linear superposition of the foliage and stem drag. The model is novel in that the foliage and stem are separately described with physically based parameters: drag coefficients, reconfiguration parameters, and leaf area and frontal-projected stem area per ground area. The model could satisfactorily predict the Flow Resistance of twig to sapling-sized specimens of the investigated species at velocities of 0.05–1 m/s. As a further benefit, the model allows exploring the variability in drag and reconfiguration associated with differing abundance of the foliage in relation to the stem.
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Flow Resistance of emergent rigid and flexible floodplain vegetation
Journal of Hydraulic Research, 2013Co-Authors: Jochen Aberle, Juha JarvelaAbstract:This paper summarizes current practices for the estimation of Flow Resistance caused by floodplain vegetation in emergent Flow conditions. The current state-of-the-art for the parameterization of vegetative form drag and associated Flow Resistance was explored with a view on practical applicability. Specifically, the dissimilar Resistance behaviour of simply shaped rigid elements and foliated natural vegetation was emphasized by compiling and reanalysing data published by the authors’ research teams as well as others. It was shown that describing the key hydraulic properties of plants, geometry, and flexibility, with species-specific parameters is superior to the rigid cylinder analogy commonly used in hydraulic engineering practice. The discussion on the limitations of many existing approaches for the determination of vegetative Flow Resistance is intended to advance the use of modern practices such as the parameterization of vegetation density with the leaf area index, a parameter that can be derived us...
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determination of Flow Resistance caused by non submerged woody vegetation
International Journal of River Basin Management, 2004Co-Authors: Juha JarvelaAbstract:Abstract This paper investigates the determination of Flow Resistance caused by stiff and flexible woody vegetation. A new procedure has been developed which allows the determination of friction factor f or Manning's n using measurable characteristics of vegetation and Flow. The procedure is capable of predicting Flow Resistance due to: (1) leafless bushes or trees and (2) leafy bushes or trees. The application of the procedure is limited to non‐submerged Flow (h ≤ H) and relatively low velocity (U < 1 m/s), which are typical conditions in low‐gradient stream valleys, floodplains and wetlands. The procedure is novel in that it uses sound hydraulic principles and methods that are available but incorporates some adjustments based on the knowledge on mechanical design of trees and deformation of foliage in a Flow. The procedure is able to account for the natural branched structure in determining area or volume of a woody plant. This makes the prediction of Resistance caused by plants more accurate than if th...
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Flow Resistance of flexible and stiff vegetation a flume study with natural plants
Journal of Hydrology, 2002Co-Authors: Juha JarvelaAbstract:Flow Resistance of natural grasses, sedges and willows was studied in a laboratory flume. The objective was to investigate, how type, density and placement of vegetation, Flow depth and velocity influence friction losses. The plants were studied in various combinations under nonsubmerged and submerged conditions in a total of 350 test runs. The results show large variations in the friction factor, f, with depth of Flow, velocity, Reynolds number, and vegetative density. The friction factor was dependent mostly on (1) the relative roughness in the case of grasses; (2) the Flow velocity in the case of willows and sedges/grasses combined; and (3) the Flow depth in the case of leafless willows on bare bottom soil. Leaves on willows seemed to double or even triple the friction factor compared to the leafless case despite the fact that the bottom was growing sedges in both cases. For the leafless willows, f appeared to increase with depth almost linearly and independently of velocity. Unexpectedly, different spacing of the same number of leafless willows with grasses did not have any significant effect on f. Based on the experimental work, a better understanding of Flow Resistance due to different combinations of natural stiff and flexible vegetation under nonsubmerged and submerged conditions was gained. q 2002 Elsevier Science B.V. All rights reserved.
Athol D Abrahams - One of the best experts on this subject based on the ideXlab platform.
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Effect of saltating sediment on Flow Resistance and bed roughness in overland Flow
Earth Surface Processes and Landforms, 1998Co-Authors: Athol D Abrahams, Gary LiAbstract:The acceleration of saltating grains by overland Flow causes momentum to be transferred from the Flow to the grains, thereby increasing Flow Resistance and bed roughness. To assess the impact of saltating sediment on overland Flow hydraulics, velocity profiles in transitional and turbulent Flows on a fixed sand-covered bed were measured using hot-film anemometry. Five discharges were studied. At each discharge, three Flows were measured: one free of sediment, one with a relatively low sediment load, and one with a relatively high sediment load. In these Flows from 83 to 90 per cent of the sediment was travelling by saltation. As a result, in the sediment-laden Flows the near-bed velocities were smaller and the velocity profiles steeper than those in the equivalent sediment-free Flows. Sediment loads ranged up to 87·0 per cent of transport capacity and accounted for as much as 20·8 per cent of Flow Resistance (measured by the friction factor) and 89·7 per cent of bed roughness (measured by the ratio of the roughness length to median grain diameter). It is concluded that saltating sediment has a considerable impact on overland Flow hydraulics, at least on fixed granular beds. Saltation is likely to have a relatively smaller effect on overland Flow on natural hillslopes and agricultural fields where form and wave Resistance dominate. Still, saltation is generally of greater significance in overland Flow than in river Flow, and for this reason its effect on overland Flow hydraulics is deserving of further study. © 1998 John Wiley & Sons, Ltd.
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step pool streams adjustment to maximum Flow Resistance
Water Resources Research, 1995Co-Authors: Athol D Abrahams, Joseph F AtkinsonAbstract:Steep headwater streams are often characterized by alternating steps and pools, which may be described by mean step height and mean step length . A conceptual model is developed based on the notion that the largest floods are just capable of moving the largest debris in the channel. The model suggests that step pools evolve toward a condition of maximum Flow Resistance because maximum Resistance implies maximum stability and that this condition is achieved when steps are regularly spaced and the mean step steepness is slightly greater than the channel slope S. To test this conceptual model, four series of flume experiments were performed. These experiments show that the relation between Resistance to Flow and is convex upward with maximum Flow Resistance occurring when steps are regularly spaced and have values between 1 and 2. Field measurements reveal that 18 natural step-pool streams also satisfy the inequality , strongly suggesting that the form of such streams is adjusted to maximize Resistance to Flow. The results of the flume experiments are inconsistent with the proposition that step pools form as antidunes, as Froude numbers for the flume step pools at which Flow Resistance was maximized fall well below those values usually associated with these bed forms.
Janet H Curran - One of the best experts on this subject based on the ideXlab platform.
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large woody debris and Flow Resistance in step pool channels cascade range washington
Geomorphology, 2003Co-Authors: Janet H Curran, Ellen WohlAbstract:Abstract Total Flow Resistance, measured as Darcy–Weisbach f, in 20 step-pool channels with large woody debris (LWD) in Washington, ranged from 5 to 380 during summer low Flows. Step risers in the study streams consist of either (1) large and relatively immobile woody debris, bedrock, or roots that form fixed, or “forced,” steps, or (2) smaller and relatively mobile wood or clasts, or a mixture of both, arranged across the channel by the stream. Flow Resistance in step-pool channels may be partitioned into grain, form, and spill Resistance. Grain Resistance is calculated as a function of particle size, and form Resistance is calculated as large woody debris drag. Combined, grain and form Resistance account for less than 10% of the total Flow Resistance. We initially assumed that the substantial remaining portion is spill Resistance attributable to steps. However, measured step characteristics could not explain between-reach variations in Flow Resistance. This suggests that other factors may be significant; the coefficient of variation of the hydraulic radius explained 43% of the variation in friction factors between streams, for example. Large woody debris generates form Resistance on step treads and spill Resistance at step risers. Because the form Resistance of step-pool channels is relatively minor compared to spill Resistance and because wood in steps accentuates spill Resistance by increasing step height, we suggest that wood in step risers influences channel hydraulics more than wood elsewhere in the channel. Hence, the distribution and function, not just abundance, of large woody debris is critical in steep, step-pool channels.