Visit Report (Derek Clarke)
SPAIN : UPC Technical University of Barcelona September 19-21, 2007
Visitors : Derek Clarke (Southampton), Tom Dijsktra (Loughborough), Stephanie Glendinning (Newcastle), David Hughes (QuB), Paul Hughes (Newcastle).
Purpose : To network with a team already actively working on long term monitoring of slopes in a Mediterranean climatic environment.
Summary of presentations & Meetings 20/9/2007. DC.
Prof Jordi Corominas.
Jordi leads a team of scientists working of slope stability and movement in eastern Spain. The work is driven by problems of extreme rainfall events triggering landslides. Severe events in 1982, especially in and around Andorra, resulted in the commencement of work on slope hazard mapping (1989-1991). Intensive settlement development in areas prone to landslides and movements triggered by rain events has increased exposure to risk. The work made a statistical correlation of contributory factors related to over 200 observed slope failures and landslides. These factors (slope, triggering rainfall amount and intensity, movement type) were mapped using a GIS approach. However the results derived are empirical. A frequency analysis of events demonstrated that there were certain critical rainfall thresholds, typically 190mm in 24-36hours would produce slope failures with a recurrence interval of 1 in 40 to 1 in 70 years. This was based on a series of field approaches including dendro-chronology, tree ring deformations and C14 dating. The Department also is monitoring existing large scale active slopes by monitoring climate, pre water pressures, water table levels and slope displacements. (See notes on field trip 21/09/07). (Notes : a) GIS approach may be useful. B) Extreme rain events seem to be the key, c) This work is mainly focussed on natural slopes in a semi mountainous region, d) Annual rainfall in Barcelona is similar to that of London (650mm/y) and UKCIP 2080’s suggests that S England may get as hot as this region of Spain.)
Christina described the GIS mapping of landslide susceptibility. There are about 200+ problem slopes and landslides in the area north of Barcelona, mainly “small”. The work mapped these slides using a Digital Elevation Model with a 15x15m grid, storing data such as slope angle, area drained, vegetation, soil type. These were processed with SPSS to calculate susceptibility to failure. The work found that a Geomorphological, rather than an Engineering approach worked better, partly because the data availability was simpler using non engineering descriptors. (Notes : see published paper. May be useful for UK work in upscaling local field sites into linear spatially distributed regions of slopes)
Work on debris flows and extreme landslides. Mainly caused by 180-200mm of rain in 24-48hours ( labelled as “moderate intensity (!!)), which are usually caused by summer thunderstorms. Antecedent conditions are not relevant in this process. Main problems are permeable materials overlying bedrock. Publications available at www.etcg.epc.es/usr/hurlman.
Working on the monitoring of a large slow moving landslide 1200m x 600m at Valcembre about 140km north of Barcelona. System includes climate observations and a network of piezometers and displacement sensors. Site visit 21/9/07 to see the slope and network of instruments. Used wire displacement sensors in PVC tubes, piezometers, DGPS and satellite location equipment. Movement is typically 5-10mm/year downslope but is episodic. Discussion with Jordi shows that they have some unexplained data problems. DC suggested correcting the data set by subtracting air pressure changes to de-trend peziometric records as we have done at Newbury.
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