Dipartimento di Scienze della Terra www.geo.unifi.it Tele-Rilevamento Europa TRE, a POLIMI spin-off company Land subsidence mapping and monitoring through PSInSAR: examples from the Arno river basin (Italy) P. Canuti1, N. Casagli1, P. Farina1, A. Ferretti2, F. Marks1, G. Menduni3 (1) Earth Sciences Department, University of Firenze, ITALY (2) TeleRilevamento Europa, T.R.E., ITALY (3) Autorità di Bacino del Fiume Arno, ITALY
Objectives to map land subsidence at a basin scale through spaceborne InSAR to analyze the causes of subsidence s spatial distribution, temporal variation and settlement rates for specific sensitive areas, integrating InSAR measurements with hydro-geological data to develop a conceptual framework for assessing land subsidence risk at a basin scale
Study area: the Arno river basin Spatial extension: 9,130 km 2 more than 3,500 km 2 of plain areas 2,580,000 residents
Permanent Scatterers (PS) technique Pixel-based analysis ESA - ERS Multi-image InSAR processing Developed and patented by POLIMI, it permits to assess on specific points (PS) the history of ground displacements with a millimetric accuracy. PS correspond to elements with high reflectivity with respect to microwaves (buildings, rock outcrops, towers, etc.). 35 days 100 Km SAR scenes dataset 100 Km time
Employed ERS1-ERS2 dataset Descending orbits: 3 frames 269 scenes Temporal coverage: (from 1992-2002) Ascending orbits: 3 frames 109 scenes Temporal coverage: (from 1992-2002)
Descending PS analysis: results Descending Permanent Scatterers (track 165)
Ascending PS analysis: results Ascending Permanent Scatterers (track 215)
PS analysis: results Descending Permanent Scatterers (track 122, 165, 394), 260.579 PS Ascending Permanent Scatterers (track 172, 215, 444), 178.347 PS
Land subsidence map Legend Displacement rate (mm/year) Combination of PS from ascending and descending orbits projected along the vertical direction and interpolated
The Firenze-Prato-Pistoia plain
The Lucca plain Lucca Arno river Arno river
Land subsidence during 1992-2002 Legend Displacement rate (mm/year) Lucca Porcari Arno river Bientina Dataset: 85 ERS1/ERS2 scenes PS analysis
Land subsidence during 2003-2005 Legend Displacement rate (mm/year) Lucca Porcari Dataset: 30 Radarsat scenes PS analysis Arno river Bientina
Geological setting W E Alluvial terrains: clays and silts (Holocene) Alluvial terrains: sands (Upper Pleistocene-Holocene) Gravels and sands (Med. Pleistocene) Red sands, conglomerates (Med. Pleistocene) m (a.s.l) Conglomerates and gravels (Villafranchian) Sandstones (Pliocene) Methamorphic bedrock (Trias) Faults Uncertain faults
Land subsidence effects Bridge over the Rio Ponticelli Power line pile
Comparison with topographic leveling Available topographic measurements during 1995-1996 (about 25 benchmarks) leveling
Comparison with topographic leveling Legend PS ( 95-96) vertical displacement (mm) Topographic lev. ( 95-96) vertical displacement (mm)
Comparison with topographic leveling 12 10,86; 10,66 Displacement Spostamento PS (mm) PS (mm) 10 8 6 4 R 2 = 0,96 5,60; 5,54 5,90; 5,82 3,50; 4,82 5,20; 4,78 3,80; 4,11 3,60; 3,73 7,80; 7,78 9,50; 10,02 8,00; 7,06 10,40; 9,64 Residuals Residui (mm) 3 2 1 0-1 -2-0,08-0,02-0,94-0,42 0,31-0,06-0,76-0,20 1,32 0,52 0,13-0,11 0,14 2 0 1,60; 1,49-3 0,40; 0,54 0 2 4 6 8 10 12 Displacement leveling (mm) Spostamento caposaldi (mm) Cross-correlation 0 2 4 6 8 10 12 14 Punti di misura Measurements Residuals
3D scheme of the Porcari area Subsidence map (1992-2002) (mm/year) boreholes Piezometric levels 10/1992 (m a.s.l.) Main contour lines (5 m) Contour lines (1 m) Piezometric levels 11/2001 (m ) Difference (2001-1992) (m ) Thickness of compressible terrains Contour lines (1 m)
Cross section of the Porcari area Height (m a.s.l.) Velocity (mm/year) Distance (km) Clay and silt Sand and gravel
Geotechnical analysis sforzi efficaci (kn/m 2 ) Profondità (m p.c.) 0 50 100 150 200 250 300 0 1 2 3 4 5 6 7 8 log σ σ in σ fi Above groundwater level σ p e σ in = log σ σ fi n σ p Camp. C3 Compressibility behavoir of the terrain from oedometric tests Assessment of the terrain preconsolidation pressure and the tensional history 9 e n Camp. C4 10 pressione di preconsolidazione sforzi eff. iniziali sforzi eff. finali Borehole S5 plastic conditions elastic conditions Borehole S3 Profondità (m p.c.) 0 50 100 150 200 250 300 350 0 above log σ 1 groundwater σ p 2 level σ Camp. C1 in σ fi = 3 n e 4 Camp. C2 5 log σ 6 σ p 7 8 9 sforzi efficaci (kn/m 2 ) sforzi eff. iniziali pressione di preconsolidazione sforzi eff. finali e σ inσ fi n Camp. C4
3D scheme of the Bientina area Subsidence map (1992-2002) (mm/year) boreholes (m a.s.l.) Piezometric levels 10/1992 Piezometric levels 11/2002 Contour lines (1 m) (m ) Difference (2002-1971)
3D scheme of the Bientina area 135/S3 BS3 (2.1 km) S5 (4.1 km) S4 (7.2 km) MVP (9.4 km) S01 COOP (12.5 km) (11.1 km) S1 (11.4 km) 20 20 15 15 Quota Height (m s.l.m.) (m a.s.l.) 10 5 0-5 -10-15 -20?? 10 5 0-5 -10 Velocità Velocity (mm/year) (mm/anno) -25-15 -30 0 1 2 3 4 5 6 7 8 9 10 11 12 13 Distance Distanza (km)? -20 TOPOGRAFIA Topgraphy PIEZO 09/1971 PIEZO 10/2002 DIFF 2002-1971 PS Argille Clay and e limi silt Sabbie Sand and gravel
Temporal series: displ. vs groundwater Displacement (mm) Water level (m g.l.)
Temporal series: displ. vs groundwater Displacement (mm) Water level (m g.l.)
Land subsidence risk assessment Conceptual framework: R = H E V Hazard (H) represents the probability that a certain phenomenon of a given intensity* will occur in a certain area within a given time span Exposure (E) is defined as the values of properties exposed at risk Vulnerability (V) is the expected degree of loss for an element at risk as a consequence of a certain event (expressed in percentage) *Intensity represents the severity of the phenomenon, in terms of potential destructive power
Land subsidence risk assessment Proposed methodology: Reconnaissance and mapping of elements at risk through digital cartography and land use maps Classification of elements at risk based on their typology and utilization to create exposure classes Definition of the vulnerability for each exposure class as a function of the different intensity of the phenomenon, based on historical records and land user experience Definition of intensity based on the classification of settlement rates obtained from the interpolated PS measurements D = V(I) E, potential worth of losses
Land subsidence risk assessment Code Description Exposure Class Vulnerability (% loss) V(I=I0) V(I=I1) V(I=I2) V(I=I3) 201 PUBLIC/SOCIAL/ADMINISTRATIVE BUILDING E4 10 30 60 100 202 INDUSTRIAL/COMMERCIAL BUILDING - FACTORY E4 10 30 50 90 203 RELIGIOUS BUILDING/BELLTOWER/TABERNACLE E4 10 40 60 100 204 BUILDING UNDER CONSTRUCTION E2 10 40 60 80 205 ABANDONED/RUINED BUILDING E2 10 60 80 100 212 POWER STATION/POWER SUBSTATION/POWER SHED E3 10 30 50 90 213 MONUMENT E3-E4 10 40 70 100 223 HOSPITAL COMPLEX E4 10 40 70 100 224 SCHOOL COMPLEX E4 10 40 70 100 225 SPORT FACILITIES E3 10 20 50 80 227 CIVIL COMPLEX E4 10 30 60 100 301 TOLLROAD/HIGHWAY E3 10 30 50 80 302 STATE HIGHWAY/ PROVINCIAL HIGHWAY E2 10 40 60 100 303 PROVINCIAL ROAD E1 10 50 80 100 304 LOCAL ROAD E1 10 60 80 100 Hazard (H), evaluated from past records of ground settlement, is 1 (certain event) where today we measured movement, by assuming stationary conditions (of the subsidence causes) for the future
Land subsidence risk assessment Subsidence Intensity Hazard Element at risk Vulnerability Exposure