1.Synthetic rainfall events were generated corresponding to selected observed extreme

rainfall totals of given return period (RP), for a range of durations (1-day to 5-day)

• A Generalised Extreme Value distribution was fitted to observed annual maxima

data using L-moments. 207

207

196

147

109

218

210

204

159

233

237

231

224

208

167

237

237

225210

169

237237226214175

0

1

2

3

4

5

6

7

0 1 2 3 4 5 6

Caine 1980 - Worldwide

Innes 1983 - Worldwide

Crosta & Frattini 2001 - Worldwide

Crosta & Frattini 2001 - Southern Alps

Literature

values of

landslide

thresholds

Number of simulated landslides

Estimated curves for constant

number of simulated landslides

{

Results

Acknowledgements: This work forms part of the LESSLOSS FP6 project (www.lessloss.org) (GOCE-CT-2003-505448) and builds upon the DAMOCLES

FP5 project (EVG1-CT-1999-00007).

References: � Caine N. 1980, The rainfall intensity-duration control of shallow landslides and debris flows. Geografiska Annaler, 62 A, 1-2,23-27 � Crosta

G. B., Frattini P., 2001. Rainfall thresholds for triggering soil slips and debris flow. In Mugnai A., Guzzetti F., Roth G (eds) Mediterranean Storms, 2nd

Plinius Conference, pp 463-487 � Innes J. L., 1983. Debris Flows. Progress in Physical Geography, 7, 469-501

Focus Area & Input data

The Pioverna (Valsassina) catchment (160 km2) & Esino catchment (20 km2) are

located in the pre-Alps of the Lecco province in Northern Italy. The rivers discharge into

Lake Como (Lario). The area receives a mean annual rainfall of 1542 mm.

C. Isabella Bovolo and James C. Bathurst

School of Civil Engineering and Geosciences, University of Newcastle upon Tyne, UKIsabella.Bovolo@ncl.ac.uk, J.C.Bathurst@ncl.ac.uk

0

5

10

15

20

0 2 4 6 8 10

12

14

16

18

20

22

24

"Decreasing"

Rainfall

"Increasing"

Rainfall

0

10

20

30

402-year RP

5-year RP

10-year RP

25-year RP

50-year RP

"Peak" Rainfall

"Constant"

Rainfall

0

20000

40000

60000

80000

100000

120000

140000

0 20

40

60

80

100

120

140

160

Modelling the Timing and Location of Shallow Landslides and

Debris Flows using the SHETRAN Model

Introduction

Rainfall is an important factor for triggering landslides but its effect is poorly understood.

The aim of this work is to investigate the occurrence, and the associated sediment

release, of shallow landslides and debris flows at the river basin scale as a function of

rainfall return period. The timings and locations of landslides were simulated in

response to rainfall patterns of different combinations of intensity and duration. The

simulations were carried out using the SHETRAN landslide model.

Method

Soilcl20123No Data

Forests

Pastures and

meadows

Rocky outcrops

Conclusions

• The effects of different rainfall properties on simulated shallow landslide incidence and

sediment yield were explored.

• The relationship between the simulated number of landslides and rainfall event intensity

and duration was found to be similar to that in the literature. The upper bound

simulations were found to be too high but the lower bound simulations were found to be

consistent with Innes (1983) and Crosta & Frattini (2001).

• The timing and occurrence of landslides was shown to be influenced by rainfall

distribution pattern as well as magnitude. The effects of antecedent conditions should

now be explored.

• These results should help to develop forecasting, mitigation and hazard zonation

strategies.

Combined Sediment Yield for

Pioverna & Esino River outlets

Tota

l Sedim

ent Yie

ld (to

nnes)

Rainfall event intensity (mm/day)

Simulated number of landslides compared to published

zero-landslide thresholds for lower bound simulations

Avera

ge rain

fall

event in

tensity (m

m/h

r)

Rainfall duration (days)

Number of landslides associated with different return periods

for the upper bound simulations

Precipitation, river discharge and number of landslides

for a 1-day rainfall event with a 2 year return period

Num

ber of la

ndslid

es

Pre

cip

itation (m

m)

Hours

Location of landslides for

rainfall events of 1 day

duration & 2 year return

periodLandslide location (lower bound)

Landslide location (upper bound)

River

Evapotranspiration

Canopy interception

Root zone

Landslides,

erosion & sediment

transport

3D

Variably

saturated

subsurface

flow model

Snowmelt

Overland

& channel

flow

SHETRAN V4

The SHETRAN landslide model

• Landslide occurrence is determined as a function of the time- and space-varying soil

saturation conditions simulated by SHETRAN using infinite-slope, factor-of-safety

analysis.

• The SHETRAN landslide model is relevant to catchment scales of up to 500 km2.

• SHETRAN can predictively examine the impacts of possible future changes in climate

(including rainfall characteristics) and can therefore be used in hazard assessment and

as a tool for developing mitigation strategies.

The landslide component

uses the topographic index

to link the SHETRAN grid

resolution (typically 100m –

2km), at which the basin

hydrology and sediment

yield are modelled, to the

landslide component’s sub-

grid resolution (typically 10 –

20m), at which landslide

occurrence and erosion are

modelled.

• SHETRAN is a physically based, spatially distributed, integrated surface / subsurface

modelling system for water flow and sediment transport in river catchments.

• The landslide component models shallow landslide occurrence and the resulting

sediment yield at the catchment scale.

Elevation (m)

Esino river

Pioverna river

• 1- 5 day rainfall events, corresponding

to selected return periods, were

disaggregated to hourly resolution.

• Four rainfall disaggregation patterns

were evaluated with equal total

precipitation but variable hourly

intensity, called: Peak, Constant,

Increasing and Decreasing.

2.Uncertainty was allowed for by setting upper

and lower bounds on key model parameters.

3.The rainfall events were applied to the

SHETRAN model which simulated landslides

and the resulting sediment yield.

4.The results were analysed to investigate

relationships between rainfall properties and

the characteristics of the modelled landslides

and their sediment yield.

Rainfall disaggregation pattern.

1-day example shown below.

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

0 5 10 15 20 25 30 35 40 45 50

1 day events

2 day events

3 day events

4 day events

5 day events

Rainfall Return Period

Simulations without use of the landslide component

are the same as for the Lower Bound simulations

Upper Bound

Lower Bound

1 day events

2 day events

3 day events

4 day events

25 year RP

50 year RP

5 day events

2 year RP

5 year RP

10 year RP

Dis

charg

e (m

m/s

)

Num

ber of la

ndslid

es (/1

0)

Time (hours)

100 200150

SHETRAN grid resolution = 500 m.

Landslide grid resolution = 20 m.

Soil class and

sand content (%)

(32 – 44)

(48 – 54)

(60 – 74)

Stream – aquifer

interactions

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