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

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

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 q crit Resistance factor: Actual flow q a

5. 2. Previous study review  Estimation of actual flow q a (Kortenhaus et al., 2002) Actual flow q a = A h E 3/2 - h E : overflow depth (h u ) + velocity head (v 0 2 /2g) - A: geometric parameter of levee (Oumeraci et al., 1999) h k = height of levee B k = crest width R k = radius of curvature C w = contraction flow C n = slope of outer talus C m = slope of inner talus

6. 2. Previous study review  Estimation of critical flow q crit (Vrijling, 2000) Inner talus of a levee Critical flow q c (q crit ) Critical flow velocity v c - v c : critical velocity (m/s) - : inner talus (degree) - k : roughness of the inner talus (m) - f g : quality of the levee turf ( ) (0.7 for bad turf 1.4 for turf good quality) - t e : 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 km 2 Length of river : 51.8 km Yeongcheon River basin

8.  Outline of field survey BasinRiver Managem ent Design frequency Location No. of Breach Cause of Breach Remarks Nam River Nam River National government 100 years Majinje1 Overtopping - Contraction of section - Bended channel - Backwater effect from the main channel Daegokje3 Daegok stream Local government 2 nd Grade 50 yearsDeokgokje5 Yeong cheon River Local government 2 nd Grade 80 years Yeoncheon River 5 Munsan stream 1 Total- 15- 3. Application of safety evaluation

9.  Rainfall data collection The July 2006 flood in Jinju StationsPeriodOfficeNote Jinju 8 July ~ 10 July KMA Hourly data Jinyang, Chilgok, Jungam 8 July ~ 10 July MOCT Hourly data Sugok, Sinan 8 July ~ 10 July KWRC Hourly data Munsan, Gumgok, Daegok, Jisu,… 8 July ~ 10 July Jinju Hourly Data Daega, Yeonghyeon, Yeongo, Gaecheon 8 July ~ 10 July Gosung Hourly data

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. Breach points hEhE CwCw CLCL CRCR CmCm CnCn Avcvc kα A-10.2701.0002261.0700.3261.0150.5112.7500.163.4 A-20.3001.0002291.1000.3261.0800.5602.5650.124.1 A-30.2701.0002241.1000.3261.0720.5552.5650.135.0 B-10.2201.0002681.1000.3261.0630.5512.5650.121.4 B-20.5101.0004341.0510.3261.0700.5302.5650.126.6 B-30.5501.0004431.0880.3261.0580.5422.5650.132.0 B-40.4201.0005691.0980.3261.0670.5522.7500.130.3 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. Breach points qaqa q crit qDqD Result A-10.0720.0300.042Breach A-20.0920.0820.009Breach A-30.0780.0570.021Breach B-10.0570.091-0.035Safe(?) B-20.1930.0630.130Breach B-30.2210.0630.158Breach B-40.1500.0790.071Breach 3. Application of safety evaluation  Results of the safety evaluation Actual flow q a ( = A h E 3/2 ) : field survey, hydraulic calculation Critical flow q crit ( = ) : f g =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 parameter f g would need to be studied further

17. Thank you