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22-04-2019
1
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
2
“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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3
Mostly rainfall triggered
Increasing trend over the years
Landslides in Guwahati, Assam
Landslide studies for Guwahati city
4
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
5
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
6
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Characterization of Hillslope Soils
7
Sample Collection
Characterization of Hillslope Soils
8
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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Characterization of Hillslope Soils
9
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
Kailash nagar hill 2 0.81 0.614 0.444
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
Kailash nagar hill 1 2.12 1.83 1.97
Kailash nagar hill 2 0.828 0.614 0.721
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
Characterization of Hillslope Soils
10
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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Characterization of Hillslope Soils
11
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)
12
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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TRIGRS model for Guwahati city (Regional scale)
13
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
TRIGRS model for Guwahati city (Regional scale)
14
TRIGRS – SEEP/W calibration
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TRIGRS model for Guwahati city (Regional scale)
15
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
TRIGRS model for Guwahati city (Regional scale)
16
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
17
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
Rainfall event triggering landslide in Guwahati
18
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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Rainfall event triggering landslide in Guwahati
19
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)
Rainfall event triggering landslide in Guwahati
20
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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11
Effect of Antecedent Condition
21
TRIGRS simulation
Rainfall events of
o June, 2012 (01-6-2012 to 26-6-2012)
Intricate combination of the Antecedent and Triggering Rainfall
22
Rainfall events ofo June, 2012 (01-6-2012 to 26-6-2012)
oMarch-April 2010
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12
Intricate combination of the Antecedent and Triggering Rainfall
23
Rainfall events ofo June, 2012 (01-6-2012 to 26-6-2012)
oMarch-April 2010
Intricate combination of the Antecedent and Triggering Rainfall
24
Rainfall events ofo June, 2012 (01-6-2012 to 26-6-2012)
oMarch-April 2010
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Effect of Rainfall Pattern
25
Cumulative rainfall ofo400 mm distributed over 5 days
Effect of Rainfall Pattern
26
Cumulative rainfall ofo400 mm distributed over 5 days
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Effect of Rainfall Pattern
27
Cumulative rainfall ofo400 mm distributed over 5 days
Effect of Rainfall Pattern
28
Cumulative rainfall ofo400 mm distributed over 5 days
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Landslide Hazard
29
Rainfall Intensity – Duration – Frequency
Landslide Hazard
30
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
31
FoS maps are combined
landslide hazard map
Location of probable landsliding
Within specified Return Period
Summary and Final Remarks
32
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
33
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
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