Effect of an abrupt slope change on air entrainment and flow depths at stepped spillways

Mirza, Mohammad J. Ostad (Laboratory of Hydraulic Constructions (LCH), Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland ; Instituto Superior Técnico (IST), Universidade de Lisboa, Lisbon, Portugal) ; Matos, Jorge (Department of Civil Engineering, Architecture and Georesources, Instituto Superior Técnico (IST), Universidade de Lisboa, Lisbon, Portugal) ; Pfister, Michael (Laboratory of Hydraulic Constructions (LCH), Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland ; School of Engineering and Architecture (HEIA-FR), HES-SO // University of Applied Sciences Western Switzerland) ; Schleiss, Anton J. (Laboratory of Hydraulic Constructions (LCH), Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland)

Several stepped spillways have been built in recent decades, mostly integrated in the downstream faces of roller compacted concrete dams. Among them, only a few have changing bottom slopes. Comprehensive information on the effect of a slope change on the flow features is lacking. This paper reports a systematic study of air entrainment and flow bulking in skimming flow along stepped spillways in the vicinity of abrupt slope changes. Physical modelling was conducted using a large facility with abrupt pseudo-bottom slope changes from 50° to 30° and from 50° to 18.6°. Air–water flow measurements were conducted at several flow cross-sections upstream and downstream of the slope change. The results indicate a significant influence of the slope change on the air pattern and flow bulking. Four main flow sub-regions were identified to describe the typical air–water flow patterns. The normalized length of the influence reach induced by the slope change was found to depend mainly on the critical flow depth, regardless of the slope change and step height.


Keywords:
Article Type:
scientifique
Faculty:
Ingénierie et Architecture
School:
HEIA-FR
Institute:
iTEC - Institut des technologies de l'environnement construit
Date:
2016-12
Pagination:
14 p.
Published in:
Journal of Hydraulic Research
Numeration (vol. no.):
2017, vol. 55, no. 3, pp. 362-375
DOI:
ISSN:
0022-1686
Appears in Collection:

Note: The status of this file is: restricted


 Record created 2020-11-03, last modified 2020-11-10

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