Flash floods in the Himalayas andvulnerability analysis
Arun B. Shrestha
abshrestha@icimod.org
International Centre for International Centre forIntegrated Mountain Development(ICIMOD)

The East and South East Asia Regional Seminar on Flood
Hazard Mapping (FHM) 2007
Kuala Lumpur, 6-9 February 2007

Outline
1. About ICIMOD
2. Flash floods in the Hindu Kush-Himalayan (HKH) region
3. Glacial Lake Outburst Flood (GLOF)
4. GLOF vulnerability analysis• Case study
5. Conclusions

1. About ICIMOD► ICIMOD is an international independent mountain learning andknowledge centre► committed to improving the sustainable livelihoods of mountainpeoples in the extended Himalayan region.
► ICIMOD serves HKH area – Afghanistan, Bangladesh, Bhutan, China,India, Myanmar, Nepal, and Pakistan.
► Founded in 1983, ICIMOD is based in Kathmandu, Nepal,► Vision: Together with its partners and regional member countries,
ICIMOD is committed to a shared vision of prosperous and securemountain communities committed to peace, equity, andenvironmental sustainability.
► Mission: ICIMOD’s mission is to develop and provide integrated andinnovative solutions, in cooperation with national, regional, andinternational partners, which foster action and change for overcoming
mountain people’s economic, social, and physical vulnerability.

About ICIMODHKH Region

WATER TOWERS OF SOUTH ASIA!
Sustaining over 600 million people in the Region►River basins■ Indus■ Ganges■ Brahmaputra■ Irrawaddy■ Salween■ Mekong■ Yangtze■ YellowIntegrated Programs►IP1: Natural Resource Management (NRM)►IP2: Agricultural and Rural Income Diversification(ARID)►IP3: Water, Hazards, and Environmental
Management (WHEM)■ 1: Water and Floods■ 2: Climate Change and Responses■ 3: Environmental Services►IP4: Culture, Equity, Gender, and Governance (CEGG)►IP5: Policy and Partnership Development (PPD)►IP6: Information and Knowledge Management (IKM)■ Mountain Natural Resources Information System(MENRIS)Comparative Benefit of ICIMOD►Regional Organization►Non-political►Mountain related►Transboundary Issues

2. Flash Floods in HKH►Flash floods are■ sudden with little lead time
■ usually violent, present high risk to life andproperties■ small scale■ short in durationDifferent Types of Flash Floods►Intense Rainfall Flood (IRF)

Longitude30292827080501008115020082

25030035083

40045084

Latitude85868788

►Glacial Lake Outburst Flood (GLOF)

Landslide Dam Outburst Flood (LDOF)
Yigong landslide dam outburst flood,Tibet, China
Damming: 9 April 2000
Outburst: 10 June 2000

►Rapid Snow/Ice Melt Flood (RSMF)►Ice Dammed Lake Outburst Flood (IDLOF)

Kande in Shyok
sub-basin

Common in Hindu Kushand Karakorum

Flash Flood Events In HKHRegion

Characteristics of flashFloods► Rapid rise and fall in water level anddischarges (minutes)► Can occur any time in the year
► Occurs mainly in headwater areas► Highly unpredictable, difficult to forecast► Most effective measure is early warning,community preparedness and emergency
measures3. Glacial Lake Outburst Flood
Himalaya the Third PoleCHINANE
INDPA
L
BHUTANIABANGLADESH
Elevation
High : 8752

Low : 0± ±N► Water reservoir infrozen state► Deglaciation iswidespread► Retreating glaciers givebirth to glacial lakes► Glacial lakes mightburst out causing
GLOFs

Glacier and glacial lakes in theHKH region►There are 15,000 glaciers occupying 33,300 km2►There are 8863 glacial lakes occupying 796 km2►26 GLOF events have occurred in the past
►There are more than 50 potentially dangerous
lakes in the HKH region

Glacier and glacial lakes in Nepal► There are more than 2300
glacial lake in Nepal► There have been 25 GLOF
events in Nepal or affecting
Nepal (Shrestha and Shrestha,2005)► 20 glacial lakes have been
identified as potential
dangerous lakes (PDL;ICIMOD/UNEP, 2001)► A GLOF carries enormous
amount of water and debris
and can be devastating for thedownstream ripariancommunities

Glacier: AX010

4. GLOF vulnerability analysis
Flood risk

Modified fromGoulby and Samuals(2005)

Framework for GLOF VulnerabilityAnalysis

Colombo et al. (2002)

Area characterization►Selection of area under question►Inventory of glaciers and glacial lakes►Lake development trend►Lake volume►Surrounding environment

Hazard Identification►Collecting information about the physical process■ Hydrology■ Ice calving■ Buried ice in the moraine dam►Dam properties■ Stability■ Karst areas■ piping►Triggering mechanism■ Ice avalanche■ landslideHazard Assessment►Dam breach scenarios■ Dam break modeling►Downstream Impact■ Flood routing►Flood map for different breach scenarios

Vulnerability Analysis► Susceptibility and exposure► Physical vulnerability■ Lithology■ Channel slope■ River meandering■ Land use► Social Vulnerability■ Accessibility■ Health■ Communication■ Emergency response system■ Economic diversity■ Awareness, attitude …
► Total Vulnerability

Case Study
Imja GLOF

Study Area
Sagarmatha National park (SNP) and its Buffer Zone

The Imja Glacial Lake5050 m a.s.l.

Imja Lake Development

15 December 1962 (Corona image)
Area – 27,916 sqm.

15 October 1975 (Landsat MSS)
Area – 309,573 sqm.

22 September 1992 (Landsat5 TM)
Area – 635,945 sqm.

02 December 1983 (Space Shuttle)
Area – 568,824 sqm.

11 December 1989 (Landsat5 TM)
Area – 633,214 sqm

30 October 2000 (Landsat7 ETM+)
Area – 775,065 sqm.

m90

According to GEN/DHM
ground survey of 2001
the surface area is 0.86
sq km

70

5030

1000200

400600800 Km

Dig Tsho Lake Development
15 December 1962 (Corona image)
Area – 201,172 sqm.

15 October 1975 (Landsat MSS)
Area – 334,861 sqm.

11 December 1989 (Landsat5 TM)
Area – 315,865 sqm

02 December 1983 (Space Shuttle)
Area – 597,923 sqm.

22 September 1992 (Landsat5 TM)
Area – 376,575 sqm.

30 October 2000 (Landsat7 ETM+)
Area – 361,867 sqm.

Deglaciation in SNP

1976: 612.94 km2
1992: 606.69 km2
2000: 583.29 km2

31.50369 km

Methodology►Geometric and topographic information■ Topographic info from DEM (Dept. of Survey)■ Geometric info extracted using HEC GeoRAS■ Stream centreline and banks digitized using
IKONUS images►Lake information■ Bathymetric survey of 2001
■ Moraine topography: survey of 1994 and 2001
■ Dig Tsho- data from literature (area and max depth)

Methodology (contd.)
Parameters/Input Data

Values for GLOF
Simulation
Dig Tsho► Breach Simulation

UnitImja

Lake surface area

0.4

0.86

km2

Lake maximum depth

42.9

90m

4395

5030

m a.s.l.

4360

4960

m a.s.l.

1:0.47

1:8

1:1.7

1:6

210

600

m

600

650m

11mm

d90300

300

mm

d30

0.10.1mmd90/303000

3000

Unit Weight20002000

Porosity

0.4

0.4

Manning's n of outer core of thedam

0.15

0.15

Internal Friction Angle (ø)

3434

Cohesiveness00■ NWS BREACH
Dam top elevation■ Geometric data from 1994 & Dam bottom elevation
2001 survey (Imja) and DEM Dam inside slope(Dig Tsho)
Dam outside slope
Dam width■ Geotechnical info fromliterature (mainly Tsho Rolpa Dam lengthd50case study)

kg m-2

Methodology (contd.)► Flood Routing■ NWS FLOODWAVE■ NWS BREACH output hydrograph - upper boundary condition■ Routing up to SNP buffer zone border (Dig Tsho ~35 km; Imja~45 km)► Flood Map■ NWS FLOODWAVE result → HEC GeoRAS■ Inundation area and depth of inundation► GLOF Vulnerability Assessment■ Method of RGSL (2003)■ Input: topography (slope), geology and geomorphology(compactness), hydrology (river meandering) and land use

Methodology (contd.)► Flood Routing■ NWS FLOODWAVE■ NWS BREACH output hydrograph - upper boundary condition■ Routing up to SNP buffer zone border (Dig Tsho ~35 km; Imja~45 km)► Flood Map■ NWS FLOODWAVE result → HEC GeoRAS■ Inundation area and depth of inundation► GLOF Vulnerability Assessment■ Method of RGSL (2003)■ Input: topography (slope), geology and geomorphology(compactness), hydrology (river meandering) and land use

Results
Main output of NWS BREACH
Breach Output

UnitDig
Tsho

Imja

6000
Dig Tsho5000

Duration of theOutflow (Tout)

hr5613

Imja

5463
3 -1

m3s-1

Discharge (m s )Maximum Outflow(Qmax)

2.0

3.2

Initial Water Levelm a.s.l.

4395.05030.6

Final Water Levelm a.s.l.

4373.64982.3

4000
3000
2000
1000
00.00.5

1.0

1.52.02.53.0

3.5Time (hr)Final Depth of theBreachm35.065.2

Final Width of theTop of the Breachm231.0300.5

Shrestha et al., 2006

Results (contd.)
6000

3 -1

Discharge (m s )Dig Tsho
5000

Qmax

Imja

4000
3000
2000
1000
9Flood Depth(m)Hmax

Dig Tsho
Imja Lake

876543504030

20100

Distance from the outlet (km)Shrestha et al., 2006

Results (contd.)
Comparison with measured flood
depth
Simulation

Peak Flood Depth (m)1412Simulation withincreased roughness
Observed

1086420051015

2025303540

Distance (km)Shrestha et al., 2006

Legend
Inundation Depth, m
ValueHigh : 58

Low : 0"snp_villages
snp_bld
main_trail

Results (contd.)
Imja lakePlace

Time (min)Elevation (ma.s.l.)Maximum Flood Depth(m)Imja lake outlet

0.0

5458

Dhumsum

6.0

5419

3.92

Syalja goth

7.2

5409

5.06

Dinboche

8.4

5401

5.81

Chure

10.8

5387

8.12

Orse

12.0

5382

5.77

Panboche

14.4

5374

6.76

Litho goth

18.0

5356

7.79

Confluence

22.85329

8.68

Bengkar25.25316

9.29

Gumela

26.4

5315

8.47

Thulo Gumela

27.6

5310

7.76

Sano Gumela

28.8

5304

8.01

Ghat

30.0

5297

8.13

Nakchung

33.6

5275

5.71

Dambreak flood scenarios

Methodology (contd.)
GLOF vulnerability rating scheme
Vulnerability
Rating Maps
Map 1:
Compactness
Map 2:
Slope map

Map 3: River
Meandering

Map 4:
Land Use

Vulnerability
WeightingIndex Score
Glacial Deposit
1
2
Cohesive Sediment
2
Loose Sediment
30-2°
112-11°
2>11°
3
Inside bend of ameander
11Straight
2
Outside bend of ameander
3
Scrub/forest, nohuman activities
0Pasture1Agriculture,3commercial
forestry
2
Infrastructure
2.5
RGSL (2003)
Settlement
3
Scoring Criteria

Vulnerability Analysis

Total vulnerability
Social Vulnerability

Physical Vulnerability

Total Vulnerability+Conclusion► HKH region is highly prone to flash floods► Capacity to manage the risk of flash flood is low► ICIMOD is supporting capacity building► FHM is important as a DS tool
► Attempt to use GIS and hydrodynamic modeling to simulate GLOF
impact in Himalayan catchment► GLOF vulnerability analysis■ Physical + Social vulnerability■ Community involvement► Results- input for early warning system (EWS)► Several limitation: data, appropriate tool, ownership, etc► But most important thing is how the information is transferred to thecommunities

Thank you