Natural hazards, road construction, increased vulnerability in the Nepal Himalayas: what future for a developing country? Presented by Monique Fort at the "Perth II: Global Change and the World's Mountains" conference in Perth, Scotland in September 2010.

1. NATURAL HAZARDS, ROAD CONSTRUCTION, INCREASED
VULNERABILITY IN THE NEPAL HIMALAYAS: WHAT FUTURE
FOR A DEVELOPING COUNTRY?
M. FORT, E. COSSART
UMR 8586 PRODIG
Global Change and the World’s Mountains
Perth, Scotland, September 26-30 2010

2. NATURAL HAZARDS, ROAD CONSTRUCTION, INCREASED
VULNERABILITY IN THE NEPAL HIMALAYAS: WHAT FUTURE
FOR A DEVELOPING COUNTRY?
M. FORT, E. COSSART
UMR 8586 PRODIG
OUTLINE
-Environmental, geographic context
-Methods and functioning of the system
-Study cases along the new Kali Gandaki road
-Concluding remarks
Global Change and the World’s Mountains
Perth, Scotland, September 26-30 2010

3. Tibet-China
India
Jomosom (2700m)
Dhaulagiri
8172 m
Annapurna
8091 m
Benighat (800m)

4. Tibet-China
India
Jomosom (2700m)
Dhaulagiri
8172 m
Annapurna
8091 m
Monsoon Pre-
Monsoon
storms
Benighat (800m)

5. Landslides of varying size, all rainfall triggered

6. 5 cm a-1
The Himalayas:
•A collisional range
•Average uplift rate: 6-8 mm a-1
•River incision keeping pace with
uplift
Consequences:
•High relief, steep mountainslopes
•Strong dynamic hillslope-river coupling
=> Slope instabilities, the nature of
which varying with type of substrate
(bedrock vs colluvium), topography, etc.

7. Road construction: a long,
difficult and dangerous process
5 cm a-1
The Himalayas: a collisional range
Consequences:
•Average uplift rate: 6-8 mm a-1
•High relief, stepp slopes
•River incision keeping pace with uplift
•Slope instabilities

8. Landslides distribution in Nepal (1968-2002)
Active landslides, mostly in:
Active landslides, mostly in: -
Middle Hills (Lesser Himalaya),
Middle Hills (Lesser Himalaya), -
south of the Greater Himalaya,
south of the Greater Himalaya, -
and along the roads
and along the roads
(ICIMOD)
(ICIMOD)

9. Methods to assess
threats to the road
Bedrock nature •Extensive fieldwork
and structure •Repeated surveys
•Interactions hillslopes-road-
river, sediments budgets
•Cascading & process-
Old landslide response system approach
material
Active landslides
and debris flows
Threat to the
new road
River incision
Old fluvial
material

10. Middle Kali Gandaki

12. 1977 2000
2008
New road and bridges  induced development of Beni Ghat
Bazaar  more assets  increased vulnerability

13. 1998 Landslide
(upstream view)

14. +500m Quartzite and chloritoschists of
the upper Lesser Himalaya
dip
1998
Wedge failure (north
dip + vertical joints)
30m
Emplacemento
f the lake  1.1 M m3
 A landslide-dammed
lake started to build up
rapidly
 relative height of
+23m reached in 7
2007 hours

15. Tatopani Village: lower
part under water
Landslide
(downstream view)

16. Sept. 28 1998, 8 a.m. 9 a.m. 3 p.m., 23 m above the river
First lake
15 m drop
Residual lake depth : 3-to-5 m
Definitive drainage, at the onset
of the next monsoon (June 1999)
Sept. 29 1998, 10 a.m.

17. Inflow (Q)
estimated to
be 54 m3/s 
 According to local reports, the lake developed in 7-8 hours

18. Downstream of Tatopani landslide
Bank erosion following the
landslide dam (1998):
landslide breach (1998) 1,1 x 106m3
 coarse boulder lag in Upstream landslide
the KG channel dam lake:
1,5 x 106m3
Sedimentary archives
reflecting older events
landslide
of similar nature

19. 1978 2000
Changes during the last 3 decades
2007
Original landscape: set of 3 terraces
Channel widening and change in
channel course
 Bank undercutting and cleaning off
of former alluvial terraces  loss of
cultivated lands and village sites
 Threat to the new road

23. Debris flow dam 6 p.m.
Dana village
Distally confined debris fan
At the confluence with Kali Gandaki 6.15 p.m. Next morning
7 p.m. 6.25 p.m.

24. 2000 Cause of Dana debris-
flow ?
• Persistent planar landslide
Bank erosion  occasional damming of
the Ghatte khola (during a
few hours or days)
• When the dam fails:
sudden outburst flood 
debris flow  widening of
river bed  potential losses
(crops and cattle)
• Occurrence: once or twice
a year, when very intense
(storm) rainfall.

25. 2000 Very dynamic change of
river bed with time:
 Channel widening:
Bank erosion 15 m wide in 1974
35 m wide in 2009
 Bed surface morphology:
aggradation/incision stages
(short term) in a general
trend of river incision
2007 (note gabions) 2009

26. April 2009 The Ghatte khola typifies a
« landslide watershed », with
unsteady landforms and strong
debris inputs to the trunk river
New road open to traffic in Spring
2008, across the Ghatte khola
: undersized bridge
=> management problems and
increased vulnerability for
travellers
Dec. 2007
360 m2
42 m2

27. April 2009 The Ghatte khola typifies a
« landslide watershed », with
unsteady landforms and strong
debris inputs to the trunk river
New road open to traffic in Spring
2008, across the Ghatte khola
: undersized bridge
=> management problems and
increased vulnerability for
travellers
: management problems and
increased vulnerability for Dec. 2007
travellers
360 m2
42 m2

28. TALBAGAR DEBRIS AVALANCHE CONE

29. 23
18

30. Upstream of debris 2000
avalanche cone 2007
2000 2007

31. Comments and implications
Himalayas: large potential for landslide and debris flow
events, with possible temporary dams, outburst floods
and related damages
These short term events: most common mode of erosion
and sediment transfer that control sediment fluxes
outward this mountain: « minor » events at the Himalayan
and geological scale history, yet « huge » events for human
beings
Other potential, similar hazards may impact settlements and
infrastructures; they represent a major threat to villages and road along
the full length of the river system
In the future, indirect threats might arise from:
• poor maintenance of the road, hence more
geomorphic hazards => more physical, functional
and economic vulnerabilities to come
• collapse of the tourism economy?
Uncertainties:
• aggravation of natural hazards due to
climate change (monsoon strengthening)?

32. Thank you for your attention Nilgiri South Peak, 6971 m
Co-author Etienne COSSART For further details, see FORT & al., Geomorphology, in press