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!