Effect of driftwood on hydraulic head of Piano Key weirs

Pfister, Michael; Schleiss, Anton; Tullis, Blake P.

doi:10.1201/b15985-35

Cited by 13 publications

(5 citation statements)

References 14 publications

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“…The maximum absolute reservoir head increase never exceeded some 0.15 to 0.20 m (prototype scale) in reported tests with the reservoir type approach flow. This maximum was observed for unit discharges up to almost 13 m 2 =s and unit debris volumes up to 9 m 3 =m (Pfister et al 2013b). Furthermore, prototype observations at the EDF Malarce Dam (France) confirmed the above assumptions.…”

Section: Remarks On the Sensitivity Of Pkws Regarding Debrissupporting

confidence: 72%

Debris-Blocking Sensitivity of Piano Key Weirs under Reservoir-Type Approach Flow

et al. 2013

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The writers were pleased to read the overview of some work published so far on piano key weirs (PKWs) and labyrinth weirs as presented by the discusser. Besides the publications mentioned by the discusser, two recent workshop proceedings give a comprehensive summary on the current state of the art on PKWs and labyrinth weirs (Erpicum et al. , 2013.Regarding the discussed paper on the effect of driftwood on the discharge efficiency of PKWs (Pfister et al. 2013a), some additional insights can be added that have been gained in the meantime as a result of further model investigations and prototype observations, as well as discussions with dam operators using PKWs on their spillways. Remarks on the Sensitivity of PKWs Regarding DebrisPKWs are probably less sensitive to the effect of driftwood on the discharge capacity than classical weir types, as for instance ogees. However, there is presently a lack of explicit observations allowing for a direct comparison. Nevertheless, the following facts support this assumption:1. Considering a virtual approach flow channel upstream of built or planned PKWs owned by Électricité de France (EDF) ) with a width W and a height P þ H under their design discharge Q results in maximum channel approach flow Froude number F ¼ Q=½Wg 0.5 ðP þ HÞ 1.5 of 0.1 ≤ F ≤ 0.3. For reservoir conditions, these values tend to zero. The approach velocity of floating debris is thus rather small, supporting a plain and loose accumulation. Consequently, and contrary to classical weirs, no vertical stacking of debris was observed at PKWs; and 2. The plain blockage is often limited to the reach upstream of the PKW, ending close to the upstream crest of the outlet key. The PWK itself remains mostly clear, and the water can pass below the debris and enter the inlet key unhindered by the blockage. As indicated by numerical simulations (e.g., Ackers et al. 2013) and physical model tests (e.g., Machiels et al. 2011), a significant part of the spilled discharge travels into the inlet key from below, without reaching the free surface upstream of the PKW where the blockage occurs. The maximum absolute reservoir head increase never exceeded some 0.15 to 0.20 m (prototype scale) in reported tests with the reservoir type approach flow. This maximum was observed for unit discharges up to almost 13 m 2 =s and unit debris volumes up to 9 m 3 =m (Pfister et al. 2013b). Furthermore, prototype observations at the EDF Malarce Dam (France) confirmed the above assumptions. During a flood in November 2014 with a unit discharge of about 4 m 2 =s (near 30% of the design discharge) significant debris volumes arrived at the PKW. Most trunks passed the PKW, and few blocked at the upstream crest of the outlet key, mostly at the right part of the PKW (Fig. 1). Consequently, the PKW itself remained practically clear and unaffected, even at its right part where the debris blocked. The flow surfaces and depths in the inlet keys appeared to be similar between the right (blocked) and left (debris-free) sides of the PKW, because the inlet ke...

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Section: Remarks On the Sensitivity Of Pkws Regarding Debrissupporting

confidence: 72%

Debris-Blocking Sensitivity of Piano Key Weirs under Reservoir-Type Approach Flow

et al. 2013

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Section: Remarks On the Sensitivity Of Pkws Regarding Debrismentioning

confidence: 81%

Closure to “Debris-Blocking Sensitivity of Piano Key Weirs under Reservoir-Type Approach Flow” by Michael Pfister, Damiano Capobianco, Blake Tullis, and Anton J. Schleiss

2015

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“…As with labyrinth weirs, this technique might still be useful if space is limited. They have proven to be effective even in the presence of floating debris (Laugier, 2007;Pfister, 2013). Tests in Vietnam showed that conveyance was still good even if the spillway was submerged from downstream (Ho Ta Khanh et al, 2011;Dabling et al, 2012).…”

Section: The Plan Shape Of the Levee Spillwaymentioning

confidence: 99%

Spillways on River Levees

Degoutte¹,

Tourment²

2021

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Effect of driftwood on hydraulic head of Piano Key weirs

Cited by 13 publications

References 14 publications

Debris-Blocking Sensitivity of Piano Key Weirs under Reservoir-Type Approach Flow

Debris-Blocking Sensitivity of Piano Key Weirs under Reservoir-Type Approach Flow

Closure to “Debris-Blocking Sensitivity of Piano Key Weirs under Reservoir-Type Approach Flow” by Michael Pfister, Damiano Capobianco, Blake Tullis, and Anton J. Schleiss

Spillways on River Levees

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