Application of levee breach safety Application of levee breach safety

evaluation for overtoppingevaluation for overtopping

Korea Institute of Construction Technology

Research fellow Yoon Kwang Seok

Researcher Chu Hyun Jae

May 6 2008

4th International Symposium on Flood Defence

1. Introduction

2. Previous Study Review

3. Application of Safety Evaluation

4. Concluding Remarks

CONTENTSCONTENTS

4th International Symposium on Flood Defence

1. Introduction1. Introduction

Motivations

• Increase of a levee breach by overflow

Objectives

• Safety evaluation of the levee when the overflow occurs

2. Previous study review2. 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

2. Previous study review2. Previous study review

Estimation of actual flow qa (Kortenhaus et al., 2002)

• Actual flow qa = A hE3/2

- 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

2. Previous study review2. Previous study review

Estimation of critical flow qcrit (Vrijling, 2000)

• Inner talus of a levee

• Critical flow qc (qcrit)

• Critical flow velocity vc

- vc : critical velocity (m/s)

- : inner talus (degree)

- k : roughness of the inner talus (m)

- fg : quality of the levee turf ( )

(0.7 for bad turf

1.4 for turf good quality)

- te : overflow duration (hour)

3. Application of safety evaluation3. 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

Outline of field survey

Basin River Management

Designfrequency Location No. of

BreachCause ofBreach Remarks

NamRiver

NamRiver

Nationalgovernment 100 years

Majinje 1

Overtopping

- Contraction of

section

- Bended channel

- Backwater effect

from the main

channel

Daegokje 3

Daegok stream

Localgovernment2nd Grade

50 years Deokgokje 5

YeongcheonRiver

Localgovernment2nd Grade

80 years

YeoncheonRiver 5

Munsanstream 1

 Total -  15 -   

3. Application of safety evaluation3. Application of safety evaluation

Inundation area

Breach : 68m

0

10

20

30

40

50

60

70

80

90

100

0. 0010. 010. 1110100

(mm)입경 (

%)통

과중

량백

분율

3. Application of safety evaluation3. Application of safety evaluation

Rainfall data collection

• The July 2006 flood in Jinju

Stations Period Office Note

Jinju8 July

~ 10 JulyKMA

Hourly

data

Jinyang, Chilgok,

Jungam

8 July

~ 10 JulyMOCT

Hourly

data

Sugok, Sinan8 July

~ 10 JulyKWRC

Hourly

data

Munsan, Gumgok,

Daegok, Jisu,…

8 July

~ 10 JulyJinju

Hourly

Data

Daega,

Yeonghyeon,

Yeongo,

Gaecheon

8 July

~ 10 JulyGosung

Hourly

data

3. Application of safety evaluation3. Application of safety evaluation

Flood discharge

• 5 sub-basins in the Nam River, 6 sub-basins in the Yeongcheo

n River

3. Application of safety evaluation3. Application of safety evaluation

Flood discharge

3. Application of safety evaluation3. Application of safety evaluation

Flood level

• Estimation of flood level from flood discharge (HEC-RAS)

3. Application of safety evaluation3. Application of safety evaluation

Flood level

• Calculated flood level in the breach points

Breachpoints

hE Cw CL CR Cm Cn A vc k α

A-1 0.27 0 1.000226 1.070 0.326 1.015 0.511 2.750 0.1 63.4

A-2 0.30 0 1.000229 1.100 0.326 1.080 0.560 2.565 0.1 24.1

A-3 0.27 0 1.000224 1.100 0.326 1.072 0.555 2.565 0.1 35.0

B-1 0.22 0 1.000268 1.100 0.326 1.063 0.551 2.565 0.1 21.4

B-2 0.51 0 1.000434 1.051 0.326 1.070 0.530 2.565 0.1 26.6

B-3 0.55 0 1.000443 1.088 0.326 1.058 0.542 2.565 0.1 32.0

B-4 0.42 0 1.000569 1.098 0.326 1.067 0.552 2.750 0.1 30.3

3. Application of safety evaluation3. 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

Breachpoints

qa qcrit qD Result

A-1 0.072 0.030 0.042 BreachA-2 0.092 0.082 0.009 BreachA-3 0.078 0.057 0.021 BreachB-1 0.057 0.091 -0.035 Safe(?)B-2 0.193 0.063 0.130 BreachB-3 0.221 0.063 0.158 BreachB-4 0.150 0.079 0.071 Breach

3. Application of safety evaluation3. 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”

4. Concluding remarks4. Concluding remarks

The evaluation method from previous studies was ap

plied to the levee breach points

Suggested method by Apel et al.(2006), Kortenhaus (20

02) et al. and Oumeraci(1999) is applicable for the safet

y evaluation of the levee

The turf-quality parameter fg would need to be studied

further

Thank you