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

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

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

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

Dobhal et al., 2013

The Event of June 2013: Glimpses

Landslides 1034

Building damages 717

River bank erosion 170

Alaknanda River: (i) Kedarnath (ii) Srinagar (iii) Deoprayag

Paleoflood records

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

Pollens and phytoliths from this debris flows indicate warm conditions

Occurrence of Rice is striking

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

Temple

Older event

Evidences of past cultures

Older Records

Older Records Srivastava et al (in progress)

~6 ka

~11 ka

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

• Indus river catchment, Ladakh Himalaya • ~100 mm/a rainfall • Cold desert conditions

Zanskar R

Paleoflood record: SSDs

Basal Flood sequence

Hearth (?) with charcoal Hiatus: Hill slope debris

Upper flood sequence

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

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

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

NE Himalaya: Records from Tsangpo-Siang-Brahmaputra River

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

3: Geku, ~98 m arl

6ka

235 m

333 m

2: Inkiyong, ~93 m arl

6 ka

235

286 m 379 m

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

-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)

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

Lamayuru Paleolake (Ladakh)

Thank you

Team Anil Kumar, WIHG YP sundriyal, HNBU Navin Juyal, PRL Jayant K Tripathi, JNU Rajesh Agnihotri, NPL

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