Debris-flow monitoring in the Catalan Pyrenees. Lessons learnt ...

De ebris-flow 

monito oring in the Pyren nees 

Debris-flow monitoring in the Pyrenees 

Lessons learnt applying wired and wireless 

sensor networks 

Marcel ace Hürlimann, ,Càuda Clàudia Abancó, Jose Moya 

Dep. Geotechnical Engineering and Geosciences 

Technical University of Catalonia (UPC). Barcelona 

BOZEN

BOZEN De ebris-flow 


Index 

• Introduction 

ti 

• Monitoring 

• Overview of monitoring sites in Pyrenees 

• Detailed description of monitoring set-up in Senet 

• Some results from Senet 

• Lessons learnt 

• Experiences and problems 

• Wired vs. wireless 

• Ground vibration measurements for alarm issues 

• Final remarks 

Focus on monitoring topics, not on process ! 

(only few graphs of results)



Introduction 

• Problems - challenges: 

• In the Pyrenees, debris flows are not as frequent as in other 

mountain ranges 

• Debris flows are not considered as “real” hazard 

• Volume classes: 

• small: 10000 m 3 

Riu Runer (2008) 

National Park 

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Hürlimann et al. (2012) - ISL



Introduction 

• Objectives of debris-flow monitoring in the Pyrenees 

• Set-up of a monitoring system with limited budget 

• Improve knowledge on initiation and dynamic behaviour 

• First estimate on rainfall threshold for debris-flow triggering 

• Design of a simple and reliable alarm system 

• Funding: 

• National projects on debris-flow hazards 

(monitoring is only one task!) 

• Consortium (main partners) 

• Geobrugg Ibérica SA 

• Worldsensing SA 

• Geological Institute of Catalonia (IGC)



Chronology of set-up: 

• 2005: Erill. Axial Pyrenees (Geobrugg Ibérica SA) 

• 2009: Ensija. Pre-Pyrenees 

• 2009: Senet. Axial Pyrenees master site 

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Erill (Geobrugg Ibérica SA) 

Characteristics: 

• Axial Pyrenees 

• Bedrock: slates 

• Glacial till 

• Elevation: 1310 – 2100 m asl 

• Catchment area: 0.4 km 2 

Events monitored: 

2010: debris flow (1300 m 3 ) 

2007-2011: several debris floods (




Sensors installed: 

• 4 Geophones 

• 1 video camera 

• raingauge & temperature sensor 

• flexible ring net 

• 5 load-cells (wireless, since 2010) 

• 5 piezometers (since 2011) 

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Raïmat et al. (2011) - DFHM




• Bore hole with 5 piezometers 

prof. (m) tipo terreno 

K (m/s) POS.PIEZOPIEZO 

1 

suelos arcillosos 

3,88 · 10 (-5) PIEZO 5 

5 

arcillas arenosas 6,05 · 10 (-6) 

gravas gruesas 3,04 ·10 (-5) 

PIEZO 4 

10 

15 


20 

PIEZO 3 

gravas gruesas 9,05 · 10 (-5) 

25 

30 

arcillas arenosas 582 5,82 · 10(6) 

(-6) 

35 PIEZO 2 


40 



45 PIEZO 1 

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50 

55 

cuarcitas y mármoles 

(Devónico)



Ensija 


• Pre-Pyrenees 

• Bedrock: marls, conglomerates, 

limestones 

• Periglacial colluvium 



Monitoring: 

• Flow station (4 geophones & US) 

• Meteorological station 

Events monitored: 

• 2009 debris flood 

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Senet: El Rebaixader test site 


• Axial Pyrenees 

• Bedrock: slates 

• Glacial till 



Events monitored (2009-2012): 2012): 

• 6 debris flows 

• 23 debris floods 

initiation 

channel 

fan 

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Advantage: 

- rather high frequency 

- initiation, transit and accumulation zone within ~1 km 

- no torrent control measures




• Difficult access to initiation area (slopes >35º) 

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• Rather steep transit zone, ~21º 

(location of flow stations) 

• Accumulation zone (fan), ~10º 

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Upstream (2011)



Monitoring: Senet 

Three major parts regarding the different debris-flow processes 

• Initiation 

• 2 meteorological stations 

• 2 infiltration stations 

• Weather radar 

• TLS 

• Flow dynamics 

• 2 flow stations 

• TLS 

• Accumulation and max runout 

• TLS 

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TLS started in spring 2012. 

Thus, no results herein.



Instrumentation: Senet 

• Initiation process 

• 2 meteo stations 

• 2 infiltration stations 

• TLS 

• Flow dynamics 

• 2 flow stations 

• TLS 

• Accumulation 

• TLS 

TLS 

METEO-CHA 

FLOW-WR 

FLOW-SPI 

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METEO-TOP 

INF-TOP 

INF-SCARP



Instrumentation: Senet 

Chronology of sensor installation: 

Abbreviation 

of station 

wired 

wireless 

Sensors 2009 2010 2011 2012 

Rain gauge 

METEO-CHA 

wr Air temperature sensor 

Relative air humidity 

Rain gauge 

Initiation METEO-TOP wl Air temperature sensor 

Snow height 

Soil moisture 

INF-TOP & 

wl Water potential 

INF-SCARP 

Soil temperature 

Geophones 

Flow dynamics 

FLOW-WR 

wr Ultrasonic device 

Video camera 

FLOW-SPI wr Geophones



Monitoring flow dynamics 

• Focus on ground vibration produced by passing debris flow 

• geophones are triggering device of monitoring system 

• key-issue for alarm systems 

• Different approaches to record ground vibration: 

• the ground velocity signal (GVS) is recorded by raw data 

• “WSL approach”: GVS is transformed into impulse-per-second (IS) time 

series by defining a ground velocity threshold in the signal conditioner 

• “French approach”: GVS transformation ti (integrating) 

ti BOZEN 

Abancó et al. (2012) - Sensors



Flow station “FLOW-WR” 

• Sensor/devices 

• 5 geophones (trigger devices, Geospace), 

• 1 ultrasonic device (Pepperl+Fuchs), 

• 1 video camera (Mobotix) + infrared spot lights 

• GPS receiver (for time synchronization, Garmin) 

• Datalogger (CR1000 Campbell Sci.) 

• Modem GSM (Wavecom) 

• Power supply: 

• Solar panels: 30 W (DL), 50W (VC), 10W (IR) 

• Batteries: 12V 24Ah (DL), 35Ah (VC), 17Ah (IR), 

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Flow station “FLOW-WR”: datalogger programming 

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Debris-flow 

monitoring in the Pyrenees



Flow station “FLOW-SPI” (2012) 


• 3 geophones (Geospace) 

• GPS receiver (for time synchronization) 

• Seismic recording device (Nanospider, Worldsensing) 

• Sampling rate of 250 Hz recording raw data 

• Gateway of wireless network (Worldsensing) 

• Power supply: 

• Solar panels: 50 W (Spider), 60W (gateway) 

• Batteries: 12V 22Ah (Spider), 120Ah (gateway) 

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Flow station “FLOW-SPI” 

• Real-time visualization by internet tool 

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Initiation: meteo station “METEO-CHA” (2009) 


• Rain gauge (YOUNG) 

• not heated 

• standard tipping bucket (resolution:0.1mm) 

• Temperature and relative humidity 

sensor (Campbell Sci.) 

• Datalogger (CR200 Campbell Sci.) 

• Log rate: 5 min (constant) 

• Modem GSM (Wavecom) 

• Power supply 

• Solar panel 10 W, Battery 12V 7Ah 

METEO-CHA 

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Initiation: Meteo station “METEO-TOP” (2012) 


• Rain gauge (Decagon) 

• not heated 

• standard tipping bucket (resolution:0.2mm) 

• Temperature sensor (Decagon) 

• Ultrasonic device measuring snow height 

(Campbell Scientific) 

• Wireless nodes (Worldsensing) 

powered by two 3.6V batteries 

• Wireless connection to gateway 

• Log rate: 5 min (constant). 

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METEO-TOP



Initiation: weather radar 


• Three Doppler C-band radar from 

Meteorological Service of Catalonia 

• Some preliminary results: 

• Compare radar with monitoring data 

• Type of triggering storm 

(shape by autocorrelation function) 

• Test of warning system 

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Abancó et al. (2012) - EGU



Infiltration station “INF-TOP” and “INF-SCARP” (2012) 


• 3 water content sensors (DECAGON) 

• 2 water potential/soil temperature sensors 

(DECAGON) 

• Wireless nodes (Worldsensing) 

powered by two 3.6V batteries 

• Wireless connection 

to gateway 

• Log rate: 5 min 

(constant) 

INF-TOP 

INF-SCARP 

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Infiltration station “INF-TOP” and “INF-SCARP” 

INF-SCARP 

INF-TOP 

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Some results (Senet) 

Events observed (August 2009 – Sept 2012): 

• 6 debris flows (2100 – 11000 m 3 ) 

• 23 debris floods (hundreds of m 3 ) 

• 3 rock falls (15 – 55 m 3 ) 

Effect of snowmelt 

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Initiation: 

• Rainfall characteristics 

Two different thresholds (spring and summer) 

Effect of snowmelt 

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Initiation: 

• effect of snowmelt and freezing-thawing 

Debris flow: March 25, 2010 

25/03/2010 

SENET 

BOÍ 

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Hürlimann et al. (2010)




Flow dynamics: Debris flow July 4, 2012 

• Ground vibration (Geo) 

• Flow depth (US) 

• Flow velocity (US+Geo, VC) 

Volume estimate: ~11000 m 3 

uncertainty: 

- flow velocity 

- event duration 

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Lessons learnt: general problems 

Senet: 

• Rockfalls 

• 2010, 2011 and 2012 (during snowmelt) 

Don’t forget other torrential processes! 

Remove installation during winter? 

Wireless network? 

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Hürlimann et al. (2012) - Landslides



Lessons learnt: general problems 

Senet: 

• Rockfalls (during snowmelt) 

• 2010: US and rain gauge g damaged → installed downstream 

• 2011: cable cut 

• 2012: rain gauge destroyed → installed downstream 

• Slow data transmission (Edge connection)→change change to 3G network 

• Large distance from Barcelona (4h) for in-situ check after small 

events (debris floods) 

→ daily picture (video camera) 

Ensija: 

• Closer to Barcelona, but (too?) low frequency of events 

Erill: 

• limited time-support by private company 

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Lessons learnt: instrumentation problems 

Senet: 

• Geophones 

• See later 

• Ultrasonic device 

• Irregular target average measurement (underestimation) 

better accuracy by radar or laser device? 

• Video camera 

• Download data in-situ change to 3G connection (more power) 

• Rain gauge 

• Sealed cover by net 

• Unheated heated device (additional power) 


• Crucial in remote areas 

• Problematic when continuous increase of devices 

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Lessons learnt: wired vs wireless 

General characteristics: 

• Wired networks: 

• Sensors 

• Recording device 

• Data transmission device 


• Wireless networks 

• Sensors 

Power supply 

(solar panel + 

12V battery) 

• Wireless nodes (temporary recording device) 

• Gateway (temporary recording device) 


Wireless node 

(3.6V battery) 

Recording device 

Data transmission device 

Wireless node 

(3.6V battery) 

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Power supply 

(solar panel + 

12V battery)



Lessons learnt: wired vs wireless 

• Advantages of wired networks: 

• Long time of experience 

• Robust and reliable 

• Advantages of wireless networks 

• Easier/free selection of sensor location 

(not conditioned to wires; e.g. crossing 

torrent etc.) 

• Easy installation 

• Ultralow power consumption 

(3-5 years battery life) 

• Licence free (ISM bands): 868MHz for 

long range 

• Permanent remote readings/control 

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Wi-Fi 

3G

Lessons learnt: wireless remote reading/control 

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Lessons learnt: 

Ground vibration measurements for alarm issues 

• Characteristics of ground vibration (here IS data): 

• 

Important for process distinction 

Debris flow 

Debris flood 

Rockfall 

False alarm 

good understanding of ground vibration 

data is compulsory for alarm system 

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Abancó et al. (2012) - Sensors




Definition threshold is crucial! 

• In the case of our IS-approach: 

• 1 st threshold for signal transformation (velocity threshold) 

• e.g. 0.17 mm/sec 

• 2 nd threshold for alarm trigger (impulse threshold) 

• e.g. 20 Imp/ sec during 3 sec 

• Aspects to be considered defining the thresholds: 

• 

Damping of vibration (effect of different geological g materials) 

• 

Changing distances between geophone and active channel 

• 

Too small signal ( amplification of signal is needed) 

• 

Mounting 

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• Design of wireless alarm system 

• General set-up 

• 2 – 3 geophones installed close to the torrent 

• 1 gateway activating SMS, optical and acoustic alarm devices 

• Specifications 

• Each geophone connected via the signal conditioner 

to Vibrating Wire (VW) wireless node 

• If alarm threshold is exceeded at VW node, 

node sends alarm signal to gateway 

• gateway concentrates signals from different nodes and 

activates main alarm 

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Wi-Fi 

3G 

SMS 

alarm 

devices



Final remarks: general aspects 

• Monitoring is time-consuming 

• Time effort of set-up & maintenance equal/larger than of data 

analysis 

• Periodic field reconnaissance is fundamental to understand data 

recorded 

• Support of electronic expert is necessary 

• Best-case = multidisciplinary team 

• Expert on debris flow 

• Expert on monitoring 

• Expert on geophysics (GV-data) 

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Final remarks: scientific aspects 

• Switch between no-event and event mode is crucial. 

• Best solution? Threshold related to ground vibration, rainfall… 

• Early warning and alarm system 

• Early warning by rainfall 

• Alarm by ground vibration (and/or flow depth; infrasound…) 

• Senet experience: 

Initiation: 

• Not only convective (summer) storms, but also 

combination of (spring) rainfalls with snowmelt can trigger events 

• Summer: P crit 15 mm/h 

• Spring: P crit < ~10 mm/h 

• Fast increase of soil moisture during rainfall 

Flow behaviour: 

• Mean front velocity: 5 – 9m/s

Muchas gracias 

BOZEN

Debris-flow monitoring in the Catalan Pyrenees. Lessons learnt ...

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