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Paleoflood records in Himalaya
Pradeep Srivastava Wadia Institute of Himalayan Geology
Dehradun, INDIA
Future Floods: an exploration of a cross disciplinary approach to flood risk forecasting
NUS, Singapore
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I
Peter J. Webster,
and Jun Jian Phil.
Trans. R. Soc. A
2011;369:4768-
4797
Himalaya-Tibetan Plateau is source of Indus, Ganga, Brahmaputra and Yangtse
Supports >15% of worlds population Monsoon trajectory interacts with Mountainous relief Fragile rocks Glaciated & snow covered zones
Floods are dominated by Extreme rainfall Glacial lake outburst Landslide dammed lake outburst
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PT-2
PT-1
PT-2
Extreme rainfall events
I
G
B
Bookhagen et al., 2005
General rainfall profile of Himalaya
• Extreme rainfall events • GLOF • Landslides
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Rambara, Garhwal Himalaya Gohna Tal, Garhwal Himalaya
• Significant agents of physical change on the Earth's surface • Leave diagnostic imprints in the geologic record
Examples
Pre-Event
Post-Event
29 m of riverbed
aggradation at Sitapur
Sundriyal et al., under
review
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Dobhal et al., 2013
The Event of June 2013: Glimpses
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Landslides 1034
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Building damages 717
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River bank erosion 170
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Alaknanda River: (i) Kedarnath (ii) Srinagar (iii) Deoprayag
Paleoflood records
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5 AMS 14-C ages centred at 850±50 AD
9th century event, occurred during warmer climate & destroyed a culture 2013
Ancient event
Kedarnath Headwaters of Ganga R. system
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Pollens and phytoliths from this debris flows indicate warm conditions
Occurrence of Rice is striking
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Trees Herbs Fern
Asteraceae Sunflower family
Caryophyllaceae
Samples (Po3 and P6) characterized by the alpine steppe which includes mainly grasses, sedges, Apiaceae, Artemisia, Asteraceae and caryophyllaceae flourish in the warm and moist conditions
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Temple
Older event
Evidences of past cultures
Older Records
Older Records Srivastava et al (in progress)
~6 ka
~11 ka
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Alaknanda River
1000 yr record of
extreme floods from
Alaknanda R. 40 events
are records
June 2013 flood was
largest in the last
millennium
Wasson et al., 2013
Srivastava et al., 2008
• Increased flood frequency
during Medieval anomaly
• LIA experienced lesser
number floods
Paleoflood records
SWDs Alaknanda R. @Srinagar and Devprayag, Raiwala
LIA Medieval Warm
yrs
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• Indus river catchment, Ladakh Himalaya • ~100 mm/a rainfall • Cold desert conditions
Zanskar R
Paleoflood record: SSDs
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Basal Flood sequence
Hearth (?) with charcoal Hiatus: Hill slope debris
Upper flood sequence
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10±1 ka; LD-1651
11±1 ka; LD-1652
10±1 ka; LD-1653
9±1 ka; LD-1654
9±1 ka; LD-1656
9±1 ka; LD-1655
22 flood couplets
15 flood couplets
7 floods
15 floods
Slack Water Deposits
Average summer discharge of Indus River: 9000 𝑚3/sec 6 times higher discharge
as recorded in SWDs
1. William (1978) Q = 4 𝐴1.21 𝑆0.28 Q = 52452 𝑚3/sec
2. Bjerklie et al., 2005
Q = 7.14 𝐴 𝑅0.67 𝑆0.33 Q = 59856 𝑚3/sec
where A = River’s cross-sectional area = 𝑤 × 𝑑 = 599 m × 11 m = 6589 m R = hydraulic radii ≈ depth of the river = 11m S = slope of the river = 0.016
10±1 ka; LD-1716
9±1 ka; LD-1715
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22 floods in Indus River
SW Monsoon Intensity controls floods in Ladakh Himalaya
Paleoclimate record: Wünnemann et al., 2010
11 10 90
10
20
Yrs BP
No o
f F
loo
ds
Flo
od r
ecu
rre
nce (
yrs
)
66
142
7
15
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Historical records of Glacial Lake outburst floods in upper Indus Basin
Higher frequency of GlOF in Ladakh occurs during Above normal spring rainfall Suggestive of stronger SW Monsoon
16
4
7
3
69 events since 1826 AD
Source: GLOF inventory: Hewitt and Liu, 2009 Climate data: tree ring record, Singh et al, 2006
Frequency distribution of GLOF events
Re-building of Ladakh Invasion of Ladakh Influx of tourists, Geologists started
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NE Himalaya: Records from Tsangpo-Siang-Brahmaputra River
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0
1
2
3
600 400 200 0
Ele
vation
(km
am
sl)
Distance from the mountain front (km)
Imponded lakes
Tuting
InkiyongGeku
Pasighat
9-8 ka BP
1-2 ka BP
Peak discharge 5 × 106 m3/s :
Montgomery et al., 2004
1 2
3 4
Flood Deposits AD 2000
volumes estimated to be
as much as ~800 km3
Glacial impounded lakes in SE Tibet
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3: Geku, ~98 m arl
6ka
235 m
333 m
2: Inkiyong, ~93 m arl
6 ka
235
286 m 379 m
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1: Tuting ~40 m arl
Fine sediments sitting much above the river level all along the Brahmaputra valley
Holocene Mega flood (?) Dated to 7-8 ka
≈8 ka
Srivastava et al., 2009
4: Pasighat
~7 ka
U-Pb provenance data to demonstrate that
these high-magnitude events originated in
Tibet Lang et al., 2013
~7 ka
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-3.0 -2.5 -2.0 -1.5
0
2000
4000
6000
8000
10000
Cale
nd
er
ag
e (
years
B.P
.)
18OPDB (%o) G. sacculifer
600 -2002001000
P-E (mm)
0 5 10 15 20 25 30
G.bulloides (%)
Floods in Indus (Drier Himalaya)
Megafloods in NE Himalaya
Increased flooding during Medieval warming
With increasing trends in SW Monsoon Frequency of extreme floods increase
In Drier Himalaya (Ladakh) such conditions may lead to the conditions conducive for settlements
In wetter Himalaya where although floods help in building a new landscape but the ignorance of natural processes increase the vulnerability in the society
Left Panel: Sarkar et al (2000) SEAS Right panel: Gupta et al(2003)NWAS
Pangong-Tso spilled into Tangtse river (Dortch et 2011)
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Pre-Monsoon
Monsoon
Prepare accordingly
Agnihotri et al (in prep)
Modern conditions
Floods in major Indian Rivers and rainfall
All India Rainfall Anomaly
Kale, 2011
Sontakke et al. (2008)
B. N. Goswami et al. Science
2006;314:1442-1445
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Lamayuru Paleolake (Ladakh)
Thank you
Team Anil Kumar, WIHG YP sundriyal, HNBU Navin Juyal, PRL Jayant K Tripathi, JNU Rajesh Agnihotri, NPL
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Himalaya and its foreland is drained by some of the most flood-prone rivers in the world. In 2014, due to flood, Kashmir alone suffered a loss of over 16 billion US dollars. In Himalaya, during the last two centuries several massive floods have occurred Answer to the question whether flooding in Himalaya is getting worse and more frequent requires longer records