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Oroville Dam, 2017 - Photo from Wikipedia
The flood spillways are key safety components in dams. They are designed to discharge flood flows in a controlled way.
The failure of Oroville Dam's spillway, which occurred in California in 2017, is an example of how spillways are fundamental structures for hydraulic risk management.
Two kinds of overflow spillways are inserted in an open channel flume to show how they work and help to dissipate the enormous flood discharge energy.
The two overflow spillway models: with ski jump and with a stilling basin.
Downstream view of the stilling basin.
Ski jump spillway
Ski jump spillway
At low discharge, flow forms a water cushion within the ski jump. When discharge increases the hydraulic jump initially confined inside the bottom part of the spillway is pushed away and the jet impinges far from the dam toe.
Ski jump in action! The higher the head the further the jet impact downstream the dam. The impinging jet must fall in solid bedrock.
Spillway with stilling basin
Spillway with stilling basin
Hydraulic jump in the stilling basin at different flood discharges. When flow rate is low the recirculating region is in the upstream part of the stilling basin, when the flood discharge is higher the air entrainment, as well as the hydraulic jump length increases.
Downstream view of the stilling basin and flow from the baffles.
Laboratory and numerical models
Laboratory and numerical models
Map of surface flow velocities from Badas et al (2020)
While the laboratory models here shown are planned to demonstrate physical phenomena and their scale is too small to perform quantitative analysis, spillways have to be modelled and tested in laboratory at an adequate reduction scale.
Numerical simulations can be used synergistically with laboratory experiments to design or modify existing spillways.
See for instance the 3D numerical modelling of Sa Stria Dam spillway (Sardinia, Italy) in Badas et al (2020).
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