Event Title

Fine-Sediment Entrainment in Coarse-Bedded Rivers

Location

Eccles Conference Center

Event Website

http://water.usu.edu/

Start Date

3-27-2006 10:20 AM

End Date

3-27-2006 10:25 AM

Description

Explicit coupling between channel morphology and sediment transport requires a modeling approach in which the transport field is sensitive to changes in the bed boundary condition. In coarse-bedded fluvial systems, an important bed variation is the amount of sand cover as patches, longitudinal stripes, or interstitial storage. Most methods used to estimate suspended sediment concentrations are developed for fully sand-covered beds and do not address sand entrainment from gravel or cobble beds.

We conducted a series of laboratory flume experiments designed to test a proposed formulation for sand entrainment from a partially covered coarse bed. To simulate field conditions, we imposed a non-uniform transport field that resulted in longitudinally and temporally variable concentration profiles and sand-bed elevations. The experiments were scaled such that immobile bed particles were much larger than the sediment in transport and less than 10% of flow depth, the transported sediment was in the same size-range as occurs in field settings, and the bed shear stress scaled by the grain size of the transported sediment was also similar to those that occur in natural rivers. The experiments included five different combinations of flow rate, sediment feed rate, and bed-material grain size.

Testing of the entrainment formulation required a morphodynamic model of the nonuniform transport field. Sand entrainment is predicted as a function of the velocity field, bed shear, grain size and the ratio of the average sand bed elevation to the bed roughness size. Predicted concentration profiles and sand deposition agree favorably with observed results.

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Mar 27th, 10:20 AM Mar 27th, 10:25 AM

Fine-Sediment Entrainment in Coarse-Bedded Rivers

Eccles Conference Center

Explicit coupling between channel morphology and sediment transport requires a modeling approach in which the transport field is sensitive to changes in the bed boundary condition. In coarse-bedded fluvial systems, an important bed variation is the amount of sand cover as patches, longitudinal stripes, or interstitial storage. Most methods used to estimate suspended sediment concentrations are developed for fully sand-covered beds and do not address sand entrainment from gravel or cobble beds.

We conducted a series of laboratory flume experiments designed to test a proposed formulation for sand entrainment from a partially covered coarse bed. To simulate field conditions, we imposed a non-uniform transport field that resulted in longitudinally and temporally variable concentration profiles and sand-bed elevations. The experiments were scaled such that immobile bed particles were much larger than the sediment in transport and less than 10% of flow depth, the transported sediment was in the same size-range as occurs in field settings, and the bed shear stress scaled by the grain size of the transported sediment was also similar to those that occur in natural rivers. The experiments included five different combinations of flow rate, sediment feed rate, and bed-material grain size.

Testing of the entrainment formulation required a morphodynamic model of the nonuniform transport field. Sand entrainment is predicted as a function of the velocity field, bed shear, grain size and the ratio of the average sand bed elevation to the bed roughness size. Predicted concentration profiles and sand deposition agree favorably with observed results.

https://digitalcommons.usu.edu/runoff/2006/AllPosters/9