Water and Hazards

Rajiv Sinha

Department of Earth Sciences

IIT Kanpur

Future Ganga: Science needs for water securityIndia-UK workshop, 2-4 December, 2015, Delhi

River Hazards in the Ganga basin

Sediment

dynamics

River

Dynamics

Extensive

flooding

Bank instability

Channel readjustments

Stream power

Sediment supply

Precipitation

Runoff

• What do we know about the process and impacts?

• What has been done for their mitigation?

• What needs to be done for mitigation and prevention?

The Ganga Basin: Modern climatic factors

Consequences:• Complex spatial response of rivers• Stream power variable water & sediment discharge, slope• Changes river’s equilibrium profile Incision / Aggradation• Geomorphic diversity across the plains

• Monsoonal climate –

2000 mm in 3 mths

• Precipitation 2x

W to E in Plains

• Slopes variable

600 mm 1200 mm

1400 mm

(Sinha et al., 2005, Himalayan Geology)

(Courtesy: J. Lave)

Spatial Variability in River Energy

Tectonics and Climate in the Ganga dispersal systems

Consequences:

• Complex spatial response of rivers

• Changes river’s equilibrium profile

Incision / Aggradation

• Differential sensitivity to external forcings

such as climate change

WGP EGP

= .Q.S/w

(Sinha et al., 2005, Geomorphology)

Tectonic +Climate Stream power

Sediment Output Variability

0 200 400 600

Drainage basin area (sq km)

0.0

2.0

4.0

6.0

Se

dim

en

t Y

ield

(x

10

00

t/sq

km

/yr)

West Ganga plains

Rapti-Ghaghra system

East Ganga plains

Precipitation increases

WGP

EGP

Legend

River Style No.I

II

III

IV

IX

V

VI

VII

VIII

X

Tributary

Reach

Intervention

Canal

III

III

IV

VI

VIII

IXVII

VIIV

V

X

VIII

IV

River Styles of the Ganga River

(Sinha et al., Submitted, Geomorphology)

3 | P a g e

a

b

c

Figure 6 a, b, c: River Style 3entire view with the actual field photographs

225

230

235

0 500 1000

2 | P a g e

a

b

Figure 5 a, b: River Style 2 entire view and actual photograph showing the channel belt

River Style II

River Style III

960

965

970

975

0 50 100 150

343

348

353

358

363

0 50 100 150 200 250

1 | P a g e

Appendix I- Geomorphic maps of the different River Styles of the Ganga River and field characteristics

a

b

c

d

e

Figure 4 a, b c, d, e: River Style 1 entire view; Zoomed view of River style 1 near Uttarkashi; Zoomed view of River style 1 near Sunagarh; actual field photographs showing bed material and the river valley along with the channel belt

River Style I

Himalayan, Partly Confined Floodplain and Channel, Braided

Himalayan, steep valley

Steep, confined valley

Floodplain pocket

No floodplain

River Style IV

River Style V

5 | P a g e

c

d

e

f

g

Figure 7 c, d, e, f, g: River Style 4 from Fatehgarh to Bilhaur, River Style 4 from Bilhaur to Fatehpur, actual field photograph showing the river bank, cultivated mid channel bars and the high cliffs near Jajmau

Cliff line

Floodplain

6 | P a g e

a

b

c

d

e

Figure 8 a, b, c, d, e: River Style 5(Narora to Qadirganj); River Style 5(Qadirganj to Fatehgarh); River Style 5(Sirathu to Allahabad); actual field photograph showing the cultivated side bar and the extensional view of the river

Unconfined floodplain and channel

191

196

201

0 500 1000

128

133

138

0 500 1000 1500 2000 2500

Valley-Interfluve, Partly Confined Floodplain and

Channel, Braided

Valley-Interfluve, Unconfined Floodplain and Channel, Braided

Piedmont, Partly Confined Floodplain and Channel, Braided

Flood Plain Features

Flood channel

Marshy/Wetland

Bar accretionary surface

Sand patches

Meander Scrolls

Abandoned meander belt

Abandoned point bar

Ox bow lake

Abandoned/dry channel

Abandoned meander loop

Meander cutoff

Channel Belt Features

Point bar

Alluvial island

Side bar

Secondary channel

Chute channel

Confluence bar

Mid channel bar

Abandoned braid bar

Transverse bar

Legend

Tributary

Main channel

Valley Margin

Inactive floodplain

Active floodplain

w/d ratio : 40.8

w/d ratio : 60

w/d ratio : 193.4

w/d ratio : 87.2

w/d ratio : 138

X-axis-Distance from left bank in meter.Y-axis-Elevation from MSL in meter.

Water level

Bankfull level

(a)

(b)

(c)

(d)

(e)

21

26

31

36

0 1000 2000 3000 4000

87

92

97

102

107

0 500 1000 1500 2000 2500

River Style VII

Flood Plain Features

Flood channel

Marshy/Wetland

Bar accretionary surface

Sand patches

Meander Scrolls

Abandoned meander belt

Abandoned point bar

Ox bow lake

Abandoned/dry channel

Abandoned meander loop

Meander cutoff

Channel Belt Features

Point bar

Alluvial island

Side bar

Secondary channel

Chute channel

Confluence bar

Mid channel bar

Abandoned braid bar

Transverse bar

Legend

Tributary

Main channel

Valley Margin

Inactive floodplain

Active floodplain

River Style VIII

River Style VI

Floodplain pocket

River Style IX

River Style X

7 | P a g e

a

b c

Figure 9 a, b, c: River Style 6(Fatehpur to Sirathu) and actual field photographs showing the cultivated mid channel bars and an extensional view of the river

Unconfined floodplain

10 | P a g e

a

b

c d

Figure 12 a, b, c, d: River Style 9(Chapra to Barh), River Style 9(Barh to Pansalla); actual field photographs showing loose unconsolidated material in the river bank and the extensional view of the river

9 | P a g e

a

b

c

d

Figure 11 a, b, c, d: River Style 8(Gopiganj to Chunar), River Style 8(Pansalla to Kursela), Actual field photograph showing the active floodplain coinciding with the valley margin defined by the craton boundary and muddy river bank

8 | P a g e

a

b

c

d

e

f

g

Figure 10 a, b, c, d, e, f, g: River Style 7(Allahabad to Gopiganj), River Style7(Chunar to Gahmar), River Style 7(Gahmar to Chapra); actual field photographs showing unconfined nature of channel, cultivated active floodplain, unused active floodplain covered with vegetation and calcrete cliffs near Rudauli(~ 15 Km upstream of Varanasi)

Bedrock

Unconfined floodplain

57

67

77

87

0 500 1000

35

40

45

50

55

0 1000 2000 3000 4000 5000 6000

Alluvial, Unconfined Floodplain and Channel,

Sinuous

Valley-Interfluve, Unconfined Floodplain, Partly Confined Braided

Craton Margin, Partly Confined Floodplain and

Channel

15

20

25

30

35

0 1000 2000 3000

Craton margin, Confined Floodplain,

Partly Confined, Braided

Valley-Interfluve, Partly Confined Floodplain and Channel, Anabranching

BedrockPhoto not available

w/d ratio : 100.0

w/d ratio : 40.8

w/d ratio : 88.3

w/d ratio : 100.7

w/d ratio : 152.6

X-axis-Distance from left bank in meter.Y-axis-Elevation from MSL in meter.

Water level

Bankfull level

11 | P a g e

a

b c

Figure 13a, b, c: River Style 10(Kursela to Farakka); actual field photographs showing extensively cultivated floodplain and vegetated alluvial islands with settlements and the extensional view of

the river

Alluvial Island

Alluvial Island

(f)

(g)

(h)

(i)

(j)

Buxar

Geomorphic

Diversity

Ganga River

Incised valleys

Wide floodplain on

one side

Geomorphic

map

Western

Ganga plains

11 | P a g e

a

b c

Figure 13a, b, c: River Style 10(Kursela to Farakka); actual field photographs showing extensively cultivated floodplain and vegetated alluvial islands with settlements and the extensional view of

the river

Ganga River

Geomorphic

map

Eastern

Ganga plains

Aggradational valleys

Migratory rivers

River disasters:

Natural or human-

induced?

Uttrakhand, 2013The furious Kosi: August 2008

Kosi

Megafan

Until 18 August, 2008

120 km

18 August, 2008

~22km widechannel

Emban

kmen

t

Seep

age C

hannel

Kosi River

Super-elevated River

Excessive sediment

flux and

embankments have

caused excessive

aggradation of river

bed and frequent

breaching and

extensive flooding

Unplanned

management and

encroachment of

river space,

construction of

river projects and

dumping of

sediments

(Dis) connectivity over the Kosi Megafan

1955 1983 2010

(Kumar et al., 2014, Geomorphology)

Waterlogged area is positively correlated to the density of intersection point – results in major drainage congestion and longer periods of inundation (Kumar et al., 2014, Geomorphology)

Sediment Management: a central problem!

Hinterland characteristics

River dynamics

Aggradation/

degradation

Flooding

Tectonics

Precipitation

Runoff

Deforestation

Bank instability

and Erosion +

+

++

Sediment

Flux

Drainage congestion

and Waterlogging

Human

Interventions

Major Research Questions• How to define the resilience and threshold of geomorphic

system to floods and its relationship to other river processes such as river dynamics and bank erosion?

• How do we develop the best engineering practices for flood management in sediment-charged Himalayan rivers?

• How to quantify sediment dynamics in high and middle mountains and its linkage with basin properties? Impact on infrastructures?

• How to assess the impact of floods on ecological services?• How do we develop effective floodplain zoning and policy

options for the Ganga basin taking into account biophysical as well as socio-economic factors?

• How can we develop an efficient flood warning system and building codes against flood resistant buildings?

• How can we map vulnerability and resilience to flooding and standardize the methodology to help the policy managers?