Daene McKinney: Mitigation at Imja Lake 6(150ppi)

Mitigation Strategies for Risk Reduction at Imja lake, Nepal Daene C. McKinney University of Texas at Austin

Khumbu Region Nepal Himalaya

Nepal

Imja Glacier

1956

Imja Lake

2012 Photos Courtesy of Alton Byers

Sept 2011

Sept 2012

Imja Lake

Terminal Moraine

Lake

Glacier

Imja Glacier GPR Transect

Imja Glacier

South

North Imja Lake

Imja Glacier GPR Transect North

South

~220 m Ice

Bedrock

Bottom of Ice in Outlet Area

Interpreted from GPR results assuming velocity = 124x106 m/s

Background image Source: Google Earth 19 February 2010

Imja Lake Bathymetric Survey

Bathymetric Survey - Results Outlet

5

Iceberg Cover

10

5 20 10

60 40

Lake

80

110 100

Interpolated values

Bathymetric Survey - Results Area (km2)

Average Depth (m)

Maximum Depth (m)

Volume (106 m3)

Potential GLOF Water (106 m3)

1992

0.60

47.0

98.5

28.0

15

2002

0.86

41.6

90.5

35.8

21

2012

1.21

52.6

116

63.8

34

35

0

Potential GLOF Water

30

2002 Vo lum e (m illion m 3 )

1992 20

Depth (m)

40

60

2012 2002

2012

1992

80

25 20 15 10 5

100

Zone A

Zone B

120 500

1000

1500 2000 Distance from beginningof 2012 Survey (m)

2500

3000

0 4975

4980

4985

4990 4995 Elevation (m)

5000

5005

5010

Conceptual Model of Imja Lake 5100 5080

Glacier

5060 5040

Outlet

5020

Lake

5000

Potential GLOF Water

Rock/Ice?

4980 4960

Rock

4940

Ice

4920 4900

Rock

4880 4860

Zone B

Zone A

4840 4820

Rock

4800 -500

0

500

1000

1500

2000

2500

3000

3500

Imja Lake GLOF Modeling Terminal Moraine

HEC-RAS Unsteady Model Piping/Seepage trigger Peak outflow = 10,000 m3/s Impact at: Dingboche = 8.4 km Phakding = 33.6 km

Lake

Glacier

What Is Risk?

Risk:

Communities want to be safe, i.e., not flooded

Risk Reduction Alternatives: a. Lower lake (3 m, 10 m, 20 m, ‌)

b. Add downstream dam

Imja Lake

Dingboche

GLOF Stage and Discharge at Dingboche 4370

9000 8000 Stage

4365

7000

Flow

5000 4360 4000 3000 4355

2000 1000

4350

0 0.0

1.0

2.0 3.0 Time (hr)

4.0

Time breach peak and Dingboche peak = 20 minutes

5.0

Flow (m3/ sec)

15.2 m

Stage (m)

6000

Siphons to Drain Then Excavate 5100 5080 5060

Point 2 (top)

Siphon

Glacier

5040

Lake

5020 5000 4980

Point 1 (surface level)

4960

Rock Point 3 (outlet)

4940

Ice

4920 4900

Rock

4880 4860

Zone B

Zone A

4840 4820

Rock

4800 -500

0

500

1000

1500

2000

2500

3000

3500

Downstream Dam

Trail to Dingboch e

Possible Dam

60 m

Imja Khola

GLOF Risk Reduction Scenarios 100 90 80 Rela ve Flood Stage Reduc on (%)

Scenarios

60

70

m

Da

m

40

Feasible

60

Feasible

m

Feasible

m Da

am D m

20 20 m •Lake lowering: 0, 3, 10 and •Dams: 20, 40, or 60 m 50 40

No Dam-Dingboche

30

20 m Dam-Dingboche 20

Da o N

10

m

40 m Dam-Dingboche 60 m Dam-Dingboche

0 0

2

4

6

8 10 12 Lake Lowering(m)

14

16

18

20

Community Consultation at Imja

Thank You!