Laboratory Experiments on Three-Dimensional Seepage Erosion Undercutting of Vegetated Banks

1. Laboratory Experiments on Three-Dimensional Seepage Erosion Undercutting of Vegetated Banks R. Cancienne, M. Chu-Agor, and G. A. Fox

2. Riparian Vegetation OKLAHOMA STATE UNIVERSITY Biosystems & Agricultural Engineering Department • Stabilizing Effects • Increased soil cohesion from roots • Precipitation interception via canopy • Destabilizing Effects • Increased infiltration due to macropore formation along roots • Greater surcharge from plant mass Riparian vegetation on Rio Nigua, Puerto Rico; www.pr.nrcs.usda.gov

3. Objective OKLAHOMA STATE UNIVERSITY Biosystems & Agricultural Engineering Department Analyze the effects of vegetation and root reinforcement on seepage erosion and undercutting.

4. OKLAHOMA STATE UNIVERSITY Biosystems & Agricultural Engineering Department Vegetated Soil Block Experiments • Simulation Constraints • Loamy sand • α= 90o • ρb = 1.6 g cm-3 • H = 25 cm • Experiments: 3 vegetated and 1 unvegetated soil block • Used 3D scanner to collect seepage images

5. Vegetated Soil Block Experiments OKLAHOMA STATE UNIVERSITY Biosystems & Agricultural Engineering Department Growing period: (November to January) Vegetation 1 Vegetation 2 Vegetation 3 Control

6. Vegetated Soil Block Experiments OKLAHOMA STATE UNIVERSITY Biosystems & Agricultural Engineering Department • Loamy sand • α= 90o • ρb = 1.6 g cm-3 • H = 25 cm • Switchgrass: 2 months old

7. Vegetated Soil Block Experiments Root Cohesion: Wu et al. (1979): OKLAHOMA STATE UNIVERSITY Biosystems & Agricultural Engineering Department • Root Area Ratio, Ar/A • Ar=root area; A=Area of failure plane (b) Root tensile strength. Tr Measuring length and diameter of roots on the failure plane Universal Testing Machine

8. OKLAHOMA STATE UNIVERSITY Biosystems & Agricultural Engineering Department Results

9. Vegetated Soil Block Experiments Root tensile strength OKLAHOMA STATE UNIVERSITY Biosystems & Agricultural Engineering Department

10. Vegetated Soil Block Experiments Wu et al. (CGJ, 1979): Field cr values for switchgrass = 18 kPa (Simon and Collison, ESPL 2002) OKLAHOMA STATE UNIVERSITY Biosystems & Agricultural Engineering Department

11. Vegetated Soil Block Experiments Effects of root reinforcement on time to failure OKLAHOMA STATE UNIVERSITY Biosystems & Agricultural Engineering Department

12. OKLAHOMA STATE UNIVERSITY Biosystems & Agricultural Engineering Department Vegetated Soil Block Experiments • Shape different from unvegetated, unweathered soil block. Unvegetated bank (Chu-Agor et al, 2008) Vegetated bank

13. Vegetated Soil Block Experiments Shape of undercut dependent on root presence OKLAHOMA STATE UNIVERSITY Biosystems & Agricultural Engineering Department (a) (b)

14. Conclusions Laboratory cr values less than field values Seepage erosion patterns differed with unvegetated soil block experiments Additional experiment during active growing stage of switchgrass OKLAHOMA STATE UNIVERSITY Biosystems & Agricultural Engineering Department

15. OKLAHOMA STATE UNIVERSITY Biosystems & Agricultural Engineering Department Vegetated Soil Block Experiments Previously ….. This time… 20 clusters, March to May 10 clusters, November to January

16. OKLAHOMA STATE UNIVERSITY Biosystems & Agricultural Engineering Department Vegetated Soil Block Experiments Root puller

17. Thank you! Questions?