Effect of Rainfall Patterns on Infiltration and its ... Presentations/2019/Dey, C2E2, 20… · Effect of Rainfall Patterns on Infiltration and its Consequence on Rainfall-induced

22-04-2019

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Effect of Rainfall Patterns on Infiltration

and its Consequence on Rainfall-induced

Landslide at Guwahati Region

Arindam Dey

Associate Professor

Department of Civil Engineering

IIT Guwahati

International Workshop

Climate Change and Extreme Events in the

Himalayan Region

C2E2, IIT Mandi, 2019

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“Landslide is the movement of a mass of rock, debris or earthdown a slope“ - Cruden (1991)

http://pubs.usgs.gov/fs/2004/3072/images/Fig3grouping-2LG.jpg

Introduction

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Mostly rainfall triggered

Increasing trend over the years

Landslides in Guwahati, Assam

Landslide studies for Guwahati city

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Landslide Studies concerning Guwahati city: o Landslide Hazard Evaluation Factor (LHEF)

o Semi – heuristic method

o Weight factors based on lithology

o Soil and Rock given almost similar weights

o Hydrogeology – surface indications• Dry – Damp – Wet – Dripping – Flowing

o Landslide triggering mechanism not included

o Landslide susceptibility map – (High – Moderate – Low)

o Spatial likelihood of landslide occurrences

o Temporal – Landslide recurrence – likelihood missing

Slope map Geology map

Distance to lineament map Distance to drainage map

Land use map

Landslide susceptibility map

of Guwahati city

Landslide Studies concerning Guwahati city: o Landslide Hazard Evaluation Factor (LHEF)

o Semi – heuristic method

o Weight factors based on lithology

o Soil and Rock given almost similar weights

o Hydrogeology – surface indications• Dry – Damp – Wet – Dripping – Flowing

o Landslide triggering mechanism not included

o Landslide susceptibility map – (High – Moderate – Low)

o Spatial likelihood of landslide occurrences

o Temporal – Landslide recurrence – likelihood missing

Influence of antecedent rainfall in triggering landslides

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The study area

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Study Area - Guwahati city Geomorphology

o Three prominent geomorphological feature

o Residual hills altitude ranging 100–300 meter above MSL

o Low-lying alluvial plains varying altitudes of 49–56 meter

o Marshy wetlands

Study Area - Guwahati cityo8 - hill series

8 major hill series:(1) Nabagraha and Sunsali hill series

(2) Japorigog hill

(3) Sonaighuli and Jutikuchi hill series

(4) Narakashur hill

(5) Nilachal hill

(6) Fatasil hill

(7) Jalukbari hill

(8) Khanapara hill

(9) Agyathuri hills

Characterization of Hillslope Soils

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Sample Collection


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Soil type and classification

Soil Characteristics

Das and

Saikia (2010;

2011) – SOIL

1

Das and

Saikia (2010;

2011) – SOIL

2

Chetia and

Sreedeep

(2013)

Experimental

Results – SOIL

1

Experimental

Results – SOIL

2

Referred as RSC PGSS RSC_CS RSC_EXP1 PGSS_EXP2

Specific Gravity 2.44 2.64 2.62 2.68 2.68

In-situ bulk density 1.65 1.79 -- 1.92 1.77

In-situ dry density 1.49 1.63 -- 1.50 1.57

Liquid Limit 49 39 46 47 35*

Plastic Limit 27 Non – Plastic 27 27 Non – Plastic

Fines Content 72.7 7.45 74 77.8 36.75

Natural Moisture

Content11.00 10.00 -- 27.72 12.69

In-situ Volumetric

Water Content16.60 16.52 -- 41.68 15.39

Void Ratio 0.78 0.62 -- 0.78 0.71

Porosity 0.44 0.38 -- 0.44 0.41

In-situ degree of

Saturation38 43 -- 95 47.79

Saturated Permeability

(m/s)1.86×10-7 1.2×10-6 -- 10-6 10-5

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In-situ Infiltration Characteristics

Mini-disk Infiltrometer

Guelph Permeameter

Site name

Maximum

infiltration rate

×10-6(m/s)

Minimum

infiltration rate

×10-6(m/s)

Average

infiltration rate

×10-6(m/s)

Chunsali hill 8.68 4.42 6.55

Noonmati hill 1 3.51 0.051 2.01

Noonmati hill 2 3.06 1.4 2.23

Kailash nagar hill 1 3.14 0.21 1.67


Shree nagar Kailash nagar hill 2.93 0.911 1.92

Punnya nagar hill 6.33 0.98 4.84

Jyoti ban 8.4 1.12 2.53

Indupur kharghuli 12.9 1.9 7.82

Kamakhya hill 9.46 1.35 5.78

Shantipur hill 17.9 1.9 9.91

Site name

Maximum

infiltration rate

×10-6(m/s)

Minimum

infiltration rate

×10-6(m/s)

Average

infiltration rate

×10-6(m/s)Chunsali hill 0.955 0.867 0.911

Noonmati hill 1 1.75 0.160 0.955

Noonmati hill 2 7.36 6.70 4.02



Shree nagar Kailash nagar hill 0.566 0.462 0.514

Punnya nagar hill 4.59 4.48 4.53

Jyoti ban 17.5 11.1 1.43

Indupur kharghuli 113.0 9.00 10.1

Kamakhya hill 0.661 0.58 0.623

Shantipur hill 1.59 1.08 1.33


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Soil Water Characteristic Curve

Transient rainfall-seepage analysis (SEEP/W Geostudio) followed by slope stability analysis (Slope/W)

Van Genuchten SWCC parameters: a = 20.0 kPa; n = 1.7; m = 0.412;

θsat = 0.45; θres = 0.05;

1

s rw r m

n

a

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Shear – strength parameterso Triaxial Test

oDirect Shear Test

0

50

100

150

200

250

0 150 300 450 600

τ

σ'

0

50

100

150

200

250

0 150 300 450 600

τ

σ'

TRIGRS model for Guwahati city (Regional scale)

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Transient Rainfall Infiltration and Grid-Based Regional Slope-Stability Model (TRIGRS) - (Baum et al., 2002; Savage et al., 2004)

FORTRAN code Transient pore pressure response to rainfall infiltration Temporal and spatial distribution of shallow rainfall-induced

landslides Decrease in the factor of safety values Infiltration process is approximated as one-dimensional

vertical flow Each cell of the grid is considered as a vertical soil column Simple runoff routing process Drain excess surface water to adjacent downslope cells Implementation of complex storm events

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Input data (ALOS–3D DEM 1 Arc Sec) Thematic data

o Digital Elevation Model – Topography of study areao Slope mapo Aspect mapo Depth of Soil formation mapo Ground water level map

Rainfall – Applied surface infiltration Soil Parameters

o Cohesion (N/m2)o Angle of Internal Friction (φ⁰)o Saturated Permeability (ksat)o Soil Diffusivity (Do)o Saturated Volumetric Water Content, θs

o Residual Volumetric Water Content, θr

o α – parameter (Gardner, 1958)

0.07422.0z e Ground Water Table


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TRIGRS – SEEP/W calibration

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Calibrated Soil Parameters

c′ (kPa) φ′ (⁰) γs (kN/m3) ks (m/s) Do (m/s) θs θr α

10 27⁰ 18.5 2.5×10-6 2.5×10-5 0.45 0.05 0.8


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Output o Factor of Safety map of the study area

o Evaluation and Validation of the FoS map

Landslide Inventoryo “Rapid Visual Screening Potential Landslide Areas of

Guwahati”

o July, 2012 – Assam State Disaster Management Authority (ASDMA)

o Location of landslide occurrences in the month of June, 2012

o Landslide prone areas in the form of GPS Latitude-Longitude coordinates

o 347 locations – referred as RVS-points

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Rainfall event triggering landslide in Guwahati

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Detailed Rainfall record

TRMM Daily (24–hour) rainfall data

o1998 – 2015, July

o The yearly reports of landslide occurrence

oRelation of rainfall events and landslide


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Detailed Rainfall record

TRMM Daily (24–hour) rainfall data

o1998 – 2015, July

o The yearly reports of landslide occurrence

oRelation of rainfall events and landslide

Year

No

of

day

s w

ith

Rai

nfa

ll

Cu

mu

lati

ve R

ain

fall

(mm

)

No

of

day

s fo

r D

aily

R

ain

fall

(10m

m -

25 m

m)

No

of

day

s fo

r D

aily

R

ain

fall

(25m

m-5

0mm

)

No

of

day

s fo

r D

aily

R

ain

fall

(50m

m -

80m

m)

No

of

day

s fo

r D

aily

R

ain

fall

(80m

m -

100m

m)

No

of

day

s fo

r D

aily

R

ain

fall

> 10

0mm

Max

Dai

ly R

ain

fall

(mm

)

Max

Cu

mu

lati

ve R

ain

fall

wit

hin

48

ho

urs

(m

m)

Max

Cu

mu

lati

ve R

ain

fall

wit

hin

72

ho

urs

(m

m)

Lan

dsl

ides

Rep

ort

ed

1998 170 3185 39 20 6 8 4 148 238 263 y

1999 179 2978 47 32 11 0 1 106 144 190

2000 171 3058 26 26 9 2 5 144 157 169

2001 178 2404 43 25 8 0 0 70 101 138

2002 178 2878 44 26 7 2 2 104 158 180

2003 179 2881 51 15 7 3 4 147 237 313 y

2004 167 3647 38 27 9 7 4 223 316 363 y

2005 180 2977 42 22 15 2 1 106 153 186

2006 159 1973 41 16 6 0 1 108 109 124

2007 169 3466 38 24 8 4 6 185 202 254 y

2008 182 2731 47 34 6 1 0 91 122 152

2009 148 2265 29 14 10 2 2 119 136 141

2010 171 3356 46 29 11 5 1 105 181 226

2011 156 2229 51 19 6 1 1 101 185 202

2012 152 2877 34 28 10 1 2 131 209 212 y

2013 151 2457 38 25 9 0 1 104 150 185

2014 146 2513 33 29 3 3 2 190 347 362 y

2015 143 2547 37 22 8 1 3 111 173 234

Maximum 182 3647 51 34 15 8 6 223 347 363

Average 166 2801 40 24 8 2 2 127 184 216

Minimum 143 1973 26 14 3 0 0 70 101 124

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TRIGRS simulation

Rainfall events of

oOctober, 2004 (3-10-2004 to 8-10-2004)

o June, 2012 (20-6-2012 to 26-6-2012)

o September, 2014 (20-9-2014 to 25-9-2014)


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TRIGRS simulation

Rainfall events of

oOctober, 2004 (3-10-2004 to 8-10-2004)

o June, 2012 (20-6-2012 to 26-6-2012)

o September, 2014 (20-9-2014 to 25-9-2014)

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Effect of Antecedent Condition

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TRIGRS simulation

Rainfall events of

o June, 2012 (01-6-2012 to 26-6-2012)

Intricate combination of the Antecedent and Triggering Rainfall

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Rainfall events ofo June, 2012 (01-6-2012 to 26-6-2012)

oMarch-April 2010

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oMarch-April 2010


24


oMarch-April 2010

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Effect of Rainfall Pattern

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Cumulative rainfall ofo400 mm distributed over 5 days


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Landslide Hazard

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Rainfall Intensity – Duration – Frequency

Landslide Hazard

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Combining the FoS maps for generating the landslide recurrence map:

Rainfall Intensity in

mm/day

Rainfall Return Period

2 year 5 year 10 year 20 year 50 year

Rai

nfa

ll D

ura

tio

n

24 hour 142 186 215 243 278

36 hour 107 140 163 184 211

48 hour 87 115 133 151 174

60 hour 74 98 114 129 149

72 hour 65 87 101 114 132

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Landslide Hazard Map

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FoS maps are combined

landslide hazard map

Location of probable landsliding

Within specified Return Period

Summary and Final Remarks

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Study of the rainfall induced landslides in the hills of Guwahati city Field and laboratory investigations for hillslope material

characterizationo Strength and hydrogeological parameters (stratification,

permeability, infiltration, GWT and depth of basal rock)

Calibration of TRIGRS model for Guwahati city ALOS-3D DEM 1 arc-second

Analysis of rain-fall induced landslides Analysis of only triggering rainfall may be misleading Antecedent conditions play a substantial role

o Intricate combination of antecedent and triggering rainfall

Influence of periodical rainfall pattern

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Some Relevant References

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Baum, R.L., Godt, J.W. and Savage, W.Z., (2010), “Estimating the timing and location of shallow rainfall‐induced landslides using a model for transient, unsaturated infiltration”, Journal of Geophysical Research, 115: F03013

Baum, R. L., Savage, W. Z., and Godt, J. W, (2008), “TRIGRS – A FORTRAN program for transient rainfall infiltration and grid-based regional slope stability analysis, version 2.0”, U.S. Geological Survey Open-File Report 2008-1159.

Bhusan, K., Kundu, S.S., Goswami, K., and Sudhakar, S., (2014), "Susceptibility mapping and estimation of rainfall threshold using space based input for assessment of landslide hazard in Guwahati city in North East India", The International Archives of the Photogrammetry

Gasmo, J.M., Rahardjo, H. and Leong, E.C., (2000), “Infiltration effects on stability of a residual soil slope”, Computers and Geotechnics, 26 (2000) 145-165.

GeoSlope (2007), Manuals of Geostudio 2007 software suite, GEO-SLOPE International Ltd.

Godt, J. W., Baum, R. B., Savage, W. Z., Salciarini, D., Schulz, W. H. and Harp, E. L. (2008) “Transient deterministic shallow landslide modeling: Requirements for susceptibility and hazard assessments in a GIS framework”, Engineering Geology, vol. 102, pp. 214–226

Goswami, D., (2013), "Rapid Visual Screening for Potential Landslide Areas of Guwahati", Assam State Disaster Management Authority

Kalita, U. C. (2001), “A study of landslide hazards in North Eastern India.” Proceedings of the Fifteenth International Conference on Soil Mechanics and Geotechnical Engineering, Istanbul, Turkey, 27-31 August 2001. Volumes 1-3 2001, 1167-1170.

Kim, J., Jeong, S., Park, S. and Sharma, J., (2004), “Influence of rainfall-induced wetting on the stability of slopes in weathered soils”, Engineering Geology, 75 (2004) 251–262

Montrasio, L., Valentino, R., and Losi, G. L. (2012) “Shallow landslides triggered by rainfalls: modeling of some case histories in the Reggiano Apennine (Emilia Romagna Region, Northern Italy)”, Natural Hazards, vol. 60, pp. 1231–1254.

34 …….Thank You

Acknowledgments

DST-NRDMS Project

Comprehensive rainfall induced landslide hazard analysis of ‘Sunsali’ and ‘Noonmati’ hills in Guwahati region (2018-2021)

Chiranjib Prasad Sarma

Bedanta Kalita

Mrinmoy Sarma

A Murali Krishna

Documents

Effect of Rainfall Patterns on Infiltration and its ... Presentations/2019/Dey, C2E2, 20… · Effect of Rainfall Patterns on Infiltration and its Consequence on Rainfall-induced