Laboratory Analysis of Debris Flow Characteristics and Berm Performance
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Abstract:
In this study, laboratory tests were used to determine the deposition characteristics (runout distance, lateral width, and deposition area) of debris flow and their relationships with the flow characteristics (flow velocity and flow depth) according to the presence of a berm. An experimental flume 1.3 to 1.9 m long, 0.15 m wide, and 0.3 m high was employed to investigate the effects of channel slope and volumetric concentration of sediment with and without the berm. The runout distance (0.201–1.423 m), lateral width (0.045–0.519 m), and deposition area (0.008–0.519 m2) increased as the channel slope increased and as the volumetric concentration of sediment decreased. These quantities also increased with the flow velocity and flow depth. In addition, the maximum reductions in the runout distance, lateral width, and deposition area were 69.1%, 65.9%, and 93%, respectively, upon berm installation. The results of this study illustrate general debris flow characteristics according to berm installation; the reported relationship magnitudes are specific to the experimental conditions described herein. However, the results of this study contribute to the design of site-specific berms in the future by providing data describing the utility and function of berms in mitigating debris flow.Keywords:
Berm
Flume
Debris flow
Deposition
Tailwater
The results from an experimental programme investigating the effect of tailwater depth and model scale on scour depths downstream of culverts are shown. Results are presented for cohesionless uniform sands and gravels. A model for predicting equilibrium scour depth and incorporating a correction function to take account of tailwater depth is shown to provide good agreement with previously published work. It is shown that the model scale does have an impact on the reliability with which scour hole data can be presented, in particular those experiments in which Reynolds number falls below 4 × 103.
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Culvert
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U-flumes are a subset of long-throated flumes suitable for use in wastewater metering. Although their mathematical characteristics are well defined so that they can be readily analyzed with existing design tools for long-throated flumes, specific tests of their performance are sparse in the literature. This study compares rating curves developed using a half-scale physical model, a computational fluid dynamics (CFD) model, and an analytical model (WinFlume). The physical model and CFD model were also used to determine the effects of increasing tailwater and to make comparisons to WinFlume's predictions of the limiting tailwater conditions for accurate flow measurement (modular limit). Based on the results obtained from the U-flume physical model, WinFlume estimated the rating curve for the study flume with an accuracy within 3%. The rating curve generated with the CFD model had a similar level of accuracy, corresponding to flow measurement errors of −1.2% to 3.8%. Both WinFlume and the CFD model gave reasonable estimates of the effect of high tailwater on the gauge level reading, but the limited CFD runs used in this study leave room for further work. The results of this portion of the study suggest that both WinFlume and CFD are useful tools for predicting the rating curves of long-throated flumes.
Flume
Tailwater
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The results from an experimental programme investigating the effect of tailwater depth and model scale on scour depths downstream of culverts are shown. Results are presented for cohesionless uniform sands and gravels. A model for predicting equilibrium scour depth and incorporating a correction function to take account of tailwater depth is shown to provide good agreement with previously published work. It is shown that the model scale does have an impact on the reliability with which scour hole data can be presented, in particular those experiments in which Reynolds number falls below 4 × 103.
Tailwater
Culvert
Scale model
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Finding the entrance into a fishway might be challenging for upstream migrating fish and especially so in large rivers. Auxiliary discharge, added into the downstream section of the fishway, will improve the attraction in the tailwater, but may impede passage in the fishway itself. In the present study we investigated a best practice design of an entrance channel with auxiliary water supply through a lateral screen in an experimental flume by means of hydraulic measurements and fish tests. Two screen sizes and angles and, relating thereto, two screen design velocities were compared and performed equally well. There was no difference in passage success for nase (Chondrostoma nasus), gudgeon (Gobio gobio), spirlin (Alburnoides bipunctatus), roach (Rutilus rutilus) and brown trout (Salmo trutta). The additional attempt to guide fish through the entrance channel by use of a slot which produced a more perceptible flow towards the upstream fishway section did not improve passage times of spirlin and brown trout. With a mean finisher rate of about 85%, which is a conservative assessment since it derives from an artificial, experimental situation, our flume layout turned out to be a good basis for a design recommendation. We suggest adding auxiliary discharge through a lateral screen with a design velocity of 0.4 ms−1 and we provide the necessary design specifications for geometry, hydraulics and screen arrangements in the entrance channel.
Flume
Tailwater
Rutilus
Section (typography)
Hydraulics
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