Velocity Field Measurements at an Overfall

Robinson, K. M.; Cook, K. R.; Hanson, G. J.

doi:10.13031/2013.2748

Cited by 22 publications

(21 citation statements)

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“…Recent developments in acoustic Doppler velocimeter (ADV) techniques make it possible to obtain detailed velocity measurements not only in relatively large channels (e.g. Robinson et al, 2000) but also in much narrower streams such as a rill. By using a miniaturized acoustic Doppler velocimeter (mADV) detailed velocity measurements are now possible in flows with a width of only 75 mm and a depth of only 20 mm.…”

Section: Introductionmentioning

confidence: 99%

Longitudinal velocity patterns and bed morphology interaction in a rill

Giménez

Planchon

Silvera

et al. 2004

Earth Surf Processes Landf

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Present-day understanding of rill dynamics is hampered by a lack of detailed data on velocity distributions in rills. The latter are difficult to collect with traditional techniques due to the very low water depths and the relatively high flow velocities in rills. The objectives of this paper were to investigate the feasibility of miniaturized acoustic Doppler velocimeter (mADV) measurements in rill flow and to explore longitudinal variations in flow velocities and their relationship with rill bed morphology. Detailed data on longitudinal flow velocity were required to achieve these objectives.A 1·8 m long rill was formed freely in a flume at 5° slope and 0·001 m 3 s −1 discharge. Rill topography was characterized by an alternation of steps and pools. The flume surface was then fixed to preserve rill roughness. A topographical scanning of the entire flume surface was made. Velocity was measured with a mADV along the rill, and at different depths. Flow depth in a longitudinal direction was also measured using an elevation gauge.A strong relationship exists between rill topography and flow hydraulics. Over steps, flow was unidirectional and rapidly accelerating until a threshold Froude number (Fn) value between 1·3 and 1·7 was reached and a hydraulic jump occurred leading to the formation of a pool. In the pool, the flow pattern was multidirectional and complex. The flow was subcritical when leaving the pool and accelerated over the next step until the threshold Froude number value was again reached. Energy loss in the rill was concentrated in the pools, mainly due to the action of a hydraulic jump. This mechanism of energy dissipation appeared to be an essential factor in rill formation and bedform evolution.

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Section: Introductionmentioning

confidence: 99%

Longitudinal velocity patterns and bed morphology interaction in a rill

Giménez

Planchon

Silvera

et al. 2004

Earth Surf Processes Landf

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“…While flume-based investigations of engineered jumps may span values of 4 ≤ F 1 ≤ 14 (Vischer and Hager, 1998), previous field investigations have not reported natural Froude numbers larger than 2 (Kieffer, 1990;Grant, 1997;Tinkler, 1997b,c;Tinkler and Wohl, 1998b). In part, this discrepancy arises from an ability to induce high F 1 values with a flume sluice gate and an inability to measure field-based values of F 1 in high-velocity and highly aerated flows (Abt et al, 1989;Robinson, 1989;Robinson et al, 2000;Vallé and Pasternack, 2002a). Because F 1 values of 2-4 have been hypothesized to be common in mountain systems (Tinkler and Wohl, 1998b), large natural knickpoints (Tinkler and Wohl, 1998a;Wohl, 2000) are likely to have flow conditions similar to the range of conditions discussed in Peterka (1983).…”

Section: Supercritical Flow Values In Natural Channelsmentioning

confidence: 99%

Submerged and unsubmerged natural hydraulic jumps in a bedrock step-pool mountain channel

Vallé

Pasternack

2006

Geomorphology

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“…This technique is called the end-depth method [4]- [18]. Gill [19], Robinson [20] [21], Wu and Rajaratnam [23], Davis et al [11], Robinson et al [24] and Lin et al [25] measured the water stage at the downstream end of the drop, including the nappe or tail water depth. They focused on the steady water surface and measured its profile using single-point instruments such as a point gauge, pressure transmitter, and wave gauge.…”

Section: Introductionmentioning

confidence: 99%

Oscillating Water Surface Measurement of Free Overfall with a Plunge Pool

Tsung¹,

Lai²,

Wang³

2015

JFCMV

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This study presents a laser-sheet imaging technique to measure the water surface of free overfalls with plunge pool. Varying the plunge pool length of a constant approach discharge created skimming, periodic oscillatory, and nappe flows. This study analyzes the resulting oscillating water surfaces and temporal variations of water stages at particular positions in the periodic oscillatory flow condition. The oscillation period and amplitude of temporal water stage variation were determined by directly measuring the time interval and water stage differences in water stage variations, respectively. The plunge pool length and air pocket characteristics seriously affected the periodic oscillatory flow. The oscillation period increased as the plunge pool length increased. On the other hand, the water stage amplitude decreased sharply when the plunge pool exceeded a specific length. The absence of an air pocket beneath the falling nappe significantly increased the oscillation period and decreased the water stage amplitude. This study investigates water surface oscillation in the plunge pool and the upstream side of the drop. However, the mean end depth of a periodic oscillatory flow with an air pocket is also applicable to discharge estimation using the end depth method.

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Velocity Field Measurements at an Overfall

Cited by 22 publications

References 0 publications

Longitudinal velocity patterns and bed morphology interaction in a rill

Longitudinal velocity patterns and bed morphology interaction in a rill

Submerged and unsubmerged natural hydraulic jumps in a bedrock step-pool mountain channel

Oscillating Water Surface Measurement of Free Overfall with a Plunge Pool

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