Application of levee breach safety evaluation for overtopping

1. 4th International Symposium on Flood Defence Application of levee breach safety evaluation for overtopping May 6 2008 Korea Institute of Construction Technology Research fellow Yoon Kwang Seok Researcher Chu Hyun Jae

2. 4th International Symposium on Flood Defence CONTENTS 1. Introduction 2. Previous Study Review 3. Application of Safety Evaluation 4. Concluding Remarks

3. 1. Introduction • Motivations • Increase of a levee breach by overflow • Objectives • Safety evaluation of the levee when the overflow occurs

4. 2. Previous study review • Breach condition by overtopping (Apel et al., 2006) • Difference between a load factor and a resistance factor • Load factor: Critical flow qcrit • Resistance factor: Actual flow qa

5. 2. Previous study review • Estimation of actual flow qa (Kortenhaus et al., 2002) • Actual flow qa = AhE3/2 - hE: overflow depth (hu) + velocity head (v02/2g) - A: geometric parameter of levee (Oumeraci et al., 1999) hk = height of levee Bk = crest width Rk = radius of curvature Cw = contraction flow Cn = slope of outer talus Cm = slope of inner talus

6. 2. Previous study review • Estimation of critical flow qcrit (Vrijling, 2000) • Inner talus of a levee • Critical flow qc(qcrit) - vc: critical velocity (m/s) - : inner talus (degree) - k: roughness of the inner talus (m) • Critical flow velocity vc - fg: quality of the levee turf ( ) (0.7 for bad turf 1.4 for turf good quality) - te : overflow duration (hour)

7. 3. Application of safety evaluation • Levee breach cases by overtopping • The July 2006 flood in Jinju (July 8, 2006 ~ July 10, 2006) • Study reach : the Nam River Watershed : 711.9 km2 Length of river : 51.8 km Yeongcheon River basin

8. 3. Application of safety evaluation • Outline of field survey

9. 3. Application of safety evaluation • Rainfall data collection • The July 2006 flood in Jinju

10. 3. Application of safety evaluation • Flood discharge • 5 sub-basins in the Nam River, 6 sub-basins in the Yeongcheon River

11. 3. Application of safety evaluation • Flood discharge

12. 3. Application of safety evaluation • Flood level • Estimation of flood level from flood discharge (HEC-RAS)

13. 3. Application of safety evaluation • Flood level • Calculated flood level in the breach points

14. 3. Application of safety evaluation • Results of the safety evaluation • Using Apel et al.(2006) actual flow, critical flow • Parameters for the safety evaluation of the levee

15. 3. Application of safety evaluation • Results of the safety evaluation • Actual flow qa ( = A hE3/2 ) : field survey, hydraulic calculation • Critical flow qcrit ( = ) : fg =1.0 • Most breach points except the point B-1 were resulted as “Breach”

16. 4. Concluding remarks • The evaluation method from previous studies was applied to the levee breach points • Suggested method by Apel et al.(2006), Kortenhaus (2002) et al. and Oumeraci(1999) is applicable for the safety evaluation of the levee • The turf-quality parameterfg would need to be studied further

17. Thank you