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03-03-2020
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Consequence of Precipitation Patterns on
Rainfall Induced Landslides
Arindam Dey
Associate Professor
Department of Civil Engineering
IIT Guwahati
iGrip Conclave 2020
IIT Gandhinagar
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“Landslide is the movement of a mass of rock, debris or earthdown a slope“ - Cruden (1991)
Landslide
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http://pubs.usgs.gov/fs/2004/3072/images/Fig3grouping-2LG.jpg
Classification of Landslides
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Landslides: CAUSE and TRIGGER
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Causes of landslide
Factors that make the slope
vulnerable to failure
Factors that predisposes the
slope to become unstable
Landslide trigger
The single event that finally
initiates the landslide
Seismicity
Rainfall
Anthropogenic causes
Drainage blocks
Toe excavation
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Mostly rainfall triggered
Increasing trend over the years
Landslides in Guwahati, Assam
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Congregation of thematic maps to develop
Landslide Susceptibility map
Landslide Hazard Zonation mapo Semi – heuristic method
o Weight factors based on lithology• Soil and Rock given almost similar weights
o Hydrogeology – surface indications• Dry – Damp –Wet – Dripping – Flowing
Landslide Studies for Guwahati city
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Slope map Geology map
Distance to lineament map Distance to drainage map
Land use map
Landslide susceptibility map
of Guwahati city
What is missing? Landslide triggering mechanism
Influence of antecedent conditions
Temporal recurrence and likelihood
Study Area - Guwahati city
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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
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
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Characterization of Hillslope Soils
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Characterization of Hillslope Soils
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0
50
100
150
200
250
0 150 300 450 600
τ
σ'
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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 for infinite slope stability model 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
TRIGRS Model for Guwahati city (Regional scale)
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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)
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TRIGRS Model for Guwahati city (Regional scale)
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TRIGRS – SEEP/W calibration
TRIGRS Model for Guwahati city (Regional scale)
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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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TRIGRS Model for Guwahati city (Regional scale)
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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
Rainfall Triggered Landslides in Guwahati city
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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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Rainfall Triggered Landslides in Guwahati city
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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
Rainfall Triggered Landslides in Guwahati city
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TRIGRS simulation of 6-day triggering event
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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Rainfall Triggered Landslides in Guwahati city
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TRIGRS simulation of 6-day triggering event
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)
Antecedent Condition
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TRIGRS simulation of monthly antecedence
Rainfall events of
o June 2012 (01-6-2012 to 26-6-2012)
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Combination of Antecedent and Triggering Rainfall
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Comparison of rainfall events ofo June 2012 (01-6-2012 to 26-6-2012)
oMarch-April 2010 (No landslide reported)
Combination of Antecedent and Triggering Rainfall
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Comparison of rainfall events ofo June 2012 (01-6-2012 to 26-6-2012)
oMarch-April 2010
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Combination of Antecedent and Triggering Rainfall
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Comparison of rainfall events ofo June 2012 (01-6-2012 to 26-6-2012)
oMarch-April 2010 (No landslide reported)
Effect of Rainfall Pattern
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Cumulative rainfall ofo400 mm distributed over 5 days
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Effect of Rainfall Pattern
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Cumulative rainfall ofo400 mm distributed over 5 days
Effect of Rainfall Pattern
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Cumulative rainfall ofo400 mm distributed over 5 days
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Effect of Rainfall Pattern
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Cumulative rainfall ofo400 mm distributed over 5 days
Landslide Hazard
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Rainfall Intensity – Duration – Frequency
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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
Landslide Hazard Map
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FoS maps are combined
landslide hazard map
Location of probable landsliding
Within specified Return Period
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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 rainfall induced landslides Analysis of only triggering rainfall may be misleading Antecedent conditions play a substantial role Intricate combination of antecedent and triggering rainfall Influence of periodical rainfall pattern
Some Relevant Publications
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Sarma, C. P., Dey, A. and Murali Krishna, A. (2020) Investigation of rainfall induced landslides at the hillslopes of Guwahati region, Assam in Geotechnics for Natural Disaster Mitigation and Management, Ed. A. Murali Krishna and T. Katsumi, Springer, Singapore, pp. 75-87: ISBN No. 978-981-13-8827-9.
Sarma, C. P., Dey, A. and Murali Krishna, A. (2020) “Influence of digital elevation models on the simulation of rainfall-induced landslides in the hillslopes of Guwahati, India” Engineering Geology (Elsevier), Vol. 268, Article No. 105523.
Sarma, C. P., Murali Krishna, A. and Dey, A. (2015) “Landslide hazard assessment of Guwahati region using physically based models” 6th Annual Conference of the International Society for Integrated Disaster Risk Management (IDRIM-TIFAC 2015), New Delhi, India, pp. 1-13.
Sarma, C. P., Murali Krishna, A. and Dey, A. (2014) “Probabilistic slope stability analysis considering spatial variability of soil properties: Influence of correlation length” Proceedings of the 14th International Conference of the International Association for Computational Methods and Recent Advances in Geomechanics (IACMAG 2014) (Eds. F. Oka, A. Murakami, R. Uzuoka and S. Kimoto), Kyoto, Japan, pp. 1125-1130.
Sarma, C. P., Murali Krishna, A. and Dey, A. (2016) “Geotechnical characterization of hill slope soils of Guwahati region” Geotechnology Towards Global Standards, Indian Geotechnical Conference, IGC 2016 Department of Civil Engineering, IIT Madras, India, pp. 1-4.
https://www.iitg.ac.in/arindam.dey
https://www.researchgate.net/profile/Arindam_Dey11
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33 …….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
