Mitigation Strategies for Risk Reduction at Imja lake, Nepal

Daene C. McKinneyUniversity of Texas at Austin

Khumbu RegionNepal Himalaya

Nepal

1956

2012

Imja Lake

Imja Glacier

Photos Courtesy of Alton Byers

Sept2011

Sept2012

Imja LakeTerminal Moraine Lake Glacier

Imja Glacier GPR Transect

North

SouthImja Glacier

Imja Lake

Imja Glacier GPR Transect

Ice

Bedrock

SouthNorth

~220 m

Bottom of Ice in Outlet Area

Background image Source: Google Earth 19 February 2010Interpreted from GPR results assuming velocity = 124x106 m/s

Imja Lake Bathymetric Survey

Bathymetric Survey - Results

105

110100

80

60

40

20

10

5

Outlet

Lake

Interpolated values

IcebergCover

Bathymetric Survey - ResultsArea(km2)

Average Depth

(m)

Maximum Depth

(m)

Volume(106 m3)

Potential GLOF Water

(106 m3)

1992 0.60 47.0 98.5 28.0 152002 0.86 41.6 90.5 35.8 212012 1.21 52.6 116 63.8 34

19922002

2012

Potential GLOF Water

Ice

Glacier

LakeOutlet

Rock/Ice?

Rock

Rock

Rock

Zone A Zone B

Conceptual Model of Imja Lake

Potential GLOF Water

Imja Lake GLOF ModelingTerminal Moraine Lake Glacier

HEC-RAS Unsteady ModelPiping/Seepage triggerPeak outflow = 10,000 m3/sImpact at:Dingboche = 8.4 kmPhakding = 33.6 km

What Is Risk?

Dingboche

Imja Lake

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

b. Add downstream dam

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

GLOF Stage and Discharge at Dingboche

Time breach peak and Dingboche peak = 20 minutes

15.2 m

Ice

Glacier

Lake

Rock

Rock

Rock

Zone A Zone B

Siphons to Drain Then Excavate

Point 1 (surface level)

Point 2 (top)

Point 3 (outlet)

Siphon

Downstream Dam

60 m

Trail to Dingboche

Imja Khola

Possible Dam

Scenarios

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

60 m Dam

FeasibleFeasible

Feasible

40 m Dam

20 m Dam

No Dam

GLOF Risk Reduction Scenarios

Community Consultation at Imja

Thank You!