Event Title

New Restoration Tools: Turbulence and Sediment Transport through Vegetation and Complex Topography

Presenter Information

Mark Schmeecle

Location

ECC 303/305

Event Website

http://water.usu.edu/

Start Date

4-6-2007 1:30 PM

End Date

4-6-2007 2:10 PM

Description

Numerical models of flow, sediment transport, and channel morphodynamics can be very useful tools in the design and prediction of river restoration efforts. However, these models often work poorly in rivers with vegetation and complex topography. Flow models often fail because they are based on temporally- and vertically-integrated equations of motion. Flow separation occurs in river channels with abrupt changes in geometry, such as flow expansion zones in the Colorado River. Secondary flows in and downstream of separation zones are dramatic and have low frequency time variations that must be taken into account. We have developed a three-dimensional large eddy simulation (LES) model of turbulence that is coupled to a particle-based model of suspended sediment transport in rivers. The LES technique directly integrates the equations of motion at scales larger than the grid spacing, and the particle-based suspended sediment model does not rely on an equilibrium Rouse-type profile. Current models of sediment transport through vegetation account for the fact that vegetation can increase the flow roughness and reduce the bed shear stress and sediment transport rates, but they do not account for the dramatic increase in turbulent kinetic energy relative to the mean downstream velocity, and the flow acceleration around individual vegetation elements that can increase the sediment transport rate. We measured the turbulence and sediment transport fields through vegetation patches of varying density in a laboratory flume using a high-speed video camera and particle imgaging velocimetry (PIV) techniques. These experiments suggest that sediment transport through vegetation placed along a river bank or in a floodplain can be effectively modeled with current sediment transport relations and a reduced shear stress. However, vegetation placed at the head of a bar where there is significant flow acceleration may actually increase the sediment transport rate relative to an unvegetated bar.

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Apr 6th, 1:30 PM Apr 6th, 2:10 PM

New Restoration Tools: Turbulence and Sediment Transport through Vegetation and Complex Topography

ECC 303/305

Numerical models of flow, sediment transport, and channel morphodynamics can be very useful tools in the design and prediction of river restoration efforts. However, these models often work poorly in rivers with vegetation and complex topography. Flow models often fail because they are based on temporally- and vertically-integrated equations of motion. Flow separation occurs in river channels with abrupt changes in geometry, such as flow expansion zones in the Colorado River. Secondary flows in and downstream of separation zones are dramatic and have low frequency time variations that must be taken into account. We have developed a three-dimensional large eddy simulation (LES) model of turbulence that is coupled to a particle-based model of suspended sediment transport in rivers. The LES technique directly integrates the equations of motion at scales larger than the grid spacing, and the particle-based suspended sediment model does not rely on an equilibrium Rouse-type profile. Current models of sediment transport through vegetation account for the fact that vegetation can increase the flow roughness and reduce the bed shear stress and sediment transport rates, but they do not account for the dramatic increase in turbulent kinetic energy relative to the mean downstream velocity, and the flow acceleration around individual vegetation elements that can increase the sediment transport rate. We measured the turbulence and sediment transport fields through vegetation patches of varying density in a laboratory flume using a high-speed video camera and particle imgaging velocimetry (PIV) techniques. These experiments suggest that sediment transport through vegetation placed along a river bank or in a floodplain can be effectively modeled with current sediment transport relations and a reduced shear stress. However, vegetation placed at the head of a bar where there is significant flow acceleration may actually increase the sediment transport rate relative to an unvegetated bar.

https://digitalcommons.usu.edu/runoff/2007/AllAbstracts/45