1. Mechanics and modeling of flow, sediment transport, and morphologic change in riverine lateral separation zones Brandy Logan, Jonathan Nelson, Rich McDonald, and Scott Wright USGS Golden, CO USGS Sacramento CA Courtesy of Scott Wright

2. A well calibrated flow model does not necessarily accurately predict morphologic change

3. Outline Project background Flow model calibration Morphodynamic modeling Process not accounted for in the model Courtesy of Scott Wright

4. Background: 2008 High Flow Experiment

5. Background: Study area Flow direction rapid eddy Eminence Break bar DATA COLLECTED: Detailed bathymetry ADCP velocity profiles Water-surface elevations Sediment concentration by size class D50 of the bed surface pool

6. Flow calibration: Delft3D Model 2D and 3D Steady and unsteady flow Several turbulence models Various sediment transport relationships

7. Flow calibration: water surface Difference between measured and modeled ws (m) ks=0.03 and 1.5 ~zo=0.001 and 0.05 2D3D zo=0.001 and 0.05 RMS=0.028 m for 3D and 0.043 for 2D

8. Flow calibration: velocity Modeled eddy-eye is shifted upstream Black = Measured Blue = 3D Red = 2D RMS error is 0.34 for 3D and 0.36 m/s for 2D x x x

9. Flow calibration: velocity MeasuredModeled

10. Flow calibration: Summary 2D and 3D models are well calibrated based on water surface elevations and velocity 3D flow model is marginally better than 2D

11. Morphodynamic modeling Input –HFE Hydrograph –Suspended sediment concentration –Sediment thickness on the bed –Initial bed grain size distribution Output –Evolution of bed through time –Suspended sediment concentration –Composition of bed

12. Morphodynamic modeling: Measured data Elevation (m) March 2 17:00March 5 12:00March 5 17:00March 6 10:00March 6 15:00March 8 09:00March 10 16:00

13. Morphodynamic modeling: 3D results Topography at end of flood event 3D ModelMeasured

14. Morphodynamic modeling: 2D results Topography at end of flood event 2D ModelMeasured

15. Process not in model: measured data Courtesy of Scott Wright and Matt Kaplinski Erosion No change Deposition Difference between surveys on the rising limb of the flood

16. March 2 17:00 Process not in model: measured data March 5 12:00March 5 17:00 Elevation (m)Slope (degree)

17. Process not in model: modeled data Elevation (m)Slope (degree) March 10 02:00

18. Conclusions: 2D and 3D models produce well calibrated flow solutions 2D and 3D morphodynamic predictions are different Both over predict deposition in the eddy Erosional processes such as slumping are not accounted for by the models

19. Questions?