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Erosion Reduction by Air Entrainment, Phase I

Principle Investigator: Brian Barkdoll, Civil & Env. Eng.
Sponsor: S. Florida Water Management District
Award Amount: $49,916
Project Duration: 3/1/2008 - 9/30/2008
MTU Reference Code: 080217

Project Summary

Excessive scour of sediment can be a problem at hydraulic structures if the scour depth is such that it undermines the structure’s foundation, which can lead to sliding, tilting, and potentially to the collapse of the structure. Scour is induced by flowing water in the various modes of sediment rolling, saltation, or entrainment into the flow as suspended load. Moreover, drought conditions followed by a large storm may result in excessive scour due to the low-flow depth protecting the sediment from scour downstream of hydraulic structures. Under such conditions the flow sediment carrying capacity can be exacerbated by the type and length of the hydraulic jump at the terminal structure, which will, in thurn, scour large holes in the channel bed downstream of the terminal structure. The SFWMD has numerous gated control structures in which there is not only flowing water but plunging water as well. Alteration of the gated structure is cost prohibitive. The implementation of structural changes for control of the hydraulic jump and installation of riprap can also be expensive. Use of an air-bubble curtain downstream of the terminal structure to be studied through Phase I of this project be an inexpensive method of scour reduction.

The primary objective of Phase I of this project is to demonstrate that the introduction of an air curtain downstream of the terminal structure of a gated spillway reduces the scour depth.