Objectives. to map land subsidence at a basin scale through spaceborne

Transcription

1 Dipartimento di Scienze della Terra 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

2 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

3 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

4 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

5 Employed ERS1-ERS2 dataset Descending orbits: 3 frames 269 scenes Temporal coverage: (from ) Ascending orbits: 3 frames 109 scenes Temporal coverage: (from )

6 Descending PS analysis: results Descending Permanent Scatterers (track 165)

7 Ascending PS analysis: results Ascending Permanent Scatterers (track 215)

8 PS analysis: results Descending Permanent Scatterers (track 122, 165, 394), PS Ascending Permanent Scatterers (track 172, 215, 444), PS

9 Land subsidence map Legend Displacement rate (mm/year) Combination of PS from ascending and descending orbits projected along the vertical direction and interpolated

10 The Firenze-Prato-Pistoia plain

11 The Lucca plain Lucca Arno river Arno river

12 Land subsidence during Legend Displacement rate (mm/year) Lucca Porcari Arno river Bientina Dataset: 85 ERS1/ERS2 scenes PS analysis

13 Land subsidence during Legend Displacement rate (mm/year) Lucca Porcari Dataset: 30 Radarsat scenes PS analysis Arno river Bientina

14 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

15 Land subsidence effects Bridge over the Rio Ponticelli Power line pile

16 Comparison with topographic leveling Available topographic measurements during (about 25 benchmarks) leveling

17 Comparison with topographic leveling Legend PS ( 95-96) vertical displacement (mm) Topographic lev. ( 95-96) vertical displacement (mm)

18 Comparison with topographic leveling 12 10,86; 10,66 Displacement Spostamento PS (mm) PS (mm) 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) ,08-0,02-0,94-0,42 0,31-0,06-0,76-0,20 1,32 0,52 0,13-0,11 0, ,60; 1,49-3 0,40; 0, Displacement leveling (mm) Spostamento caposaldi (mm) Cross-correlation Punti di misura Measurements Residuals

19 3D scheme of the Porcari area Subsidence map ( ) (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 ( ) (m ) Thickness of compressible terrains Contour lines (1 m)

20 Cross section of the Porcari area Height (m a.s.l.) Velocity (mm/year) Distance (km) Clay and silt Sand and gravel

21 Geotechnical analysis sforzi efficaci (kn/m 2 ) Profondità (m p.c.) 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.) 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 sforzi efficaci (kn/m 2 ) sforzi eff. iniziali pressione di preconsolidazione sforzi eff. finali e σ inσ fi n Camp. C4

22 3D scheme of the Bientina area Subsidence map ( ) (mm/year) boreholes (m a.s.l.) Piezometric levels 10/1992 Piezometric levels 11/2002 Contour lines (1 m) (m ) Difference ( )

23 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) Quota Height (m s.l.m.) (m a.s.l.) ?? Velocità Velocity (mm/year) (mm/anno) Distance Distanza (km)? -20 TOPOGRAFIA Topgraphy PIEZO 09/1971 PIEZO 10/2002 DIFF PS Argille Clay and e limi silt Sabbie Sand and gravel

24 Temporal series: displ. vs groundwater Displacement (mm) Water level (m g.l.)

25 Temporal series: displ. vs groundwater Displacement (mm) Water level (m g.l.)

26 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

27 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

28 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 E INDUSTRIAL/COMMERCIAL BUILDING - FACTORY E RELIGIOUS BUILDING/BELLTOWER/TABERNACLE E BUILDING UNDER CONSTRUCTION E ABANDONED/RUINED BUILDING E POWER STATION/POWER SUBSTATION/POWER SHED E MONUMENT E3-E HOSPITAL COMPLEX E SCHOOL COMPLEX E SPORT FACILITIES E CIVIL COMPLEX E TOLLROAD/HIGHWAY E STATE HIGHWAY/ PROVINCIAL HIGHWAY E PROVINCIAL ROAD E LOCAL ROAD E 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

29 Land subsidence risk assessment Subsidence Intensity Hazard Element at risk Vulnerability Exposure