The geologic support to subsidence analysis in Emilia

The geologic support to subsidence
analysis in Emilia-Romagna alluvial plain
Ubaldo Cibin & Paolo Severi
Servizio Geologico, Sismico e dei Suoli, Regione Emilia-Romagna, Italy
PO PLAIN
EMILIA-ROMAGNA
SUBSIDENCE IN EMILIA-ROMAGNA ALLUVIAL PLAIN:
The land-subsidence velocity map (ARPA-ER monitoring network)
E-R Geological Survey were involved to study two critical areas:
Bologna alluvial plain and Ravenna coast
LAND
SUBSIDENCE
VELOCITY
Data source:
ARPA-ER geodetic levelling of 1999 compared
with previous local non homogeneous data
THE PROJECTS
Study of the Reno River alluvial fan to realize a
hydrologic and subsidence model for water resource
management
Regione Emilia-Romagna, Provincia di Bologna, Comune di Bologna,
Autorità di Bacino del Fiume Reno, ARPA-ER, Hera Spa.
Anthropogenic Land Subsidence due to groundwater
withdrawal in the Emilia-Romagna coastland
ENI-AGIP, Comune di Ravenna, ARPA-ER, Servizio Geologico, Sismico e
dei Suoli RER, MED Ingegneria Srl
Angela Angelina Project for aquifer pressure
maintenance (Ravenna)
ENI-AGIP, Regione Emilia-Romagna, Provincia di Ravenna, Comune di
Ravenna
SUBSIDENCE IN BOLOGNA AREA:
Groundwater pumping from the Reno River alluvial fan and plain
Detail of land-subsidence velocity map near Bologna
(subsurface alluvial fan of Reno River at the valley mouth)
Piezometry drop at the drinking water
wells of Bologna city
10.9
PANARO
RENO
13.0
2.5
-0.5
4.2
3.4
5
5.4
18.9
8.2
-4.2
8.1
-2.7
4.3
20.8
12.8
0.1
9.7
1.9
-0.8
1.5
31.8
-4.2
18.7
-2.9
3.8
25.0
-2.9
38.2
11.5
33.1
40.7
52.045.3
75.1
47.3
63.0
63.2
12.5
5.3
39.2
-8.3
-12.7
-15.3
-12.3 -12.0 20.9
-12.4
-15.8
-13.5
58.3 53.2
BOLOGNA
65.6
Piezometry contour
Water-well for public utility
subsidence distribution - piezometry depression:
relationships between groundwater pumping and land lowering
11.5
11.9
9.6
14.3 18.9
29.8
20.4
25.1
14.2
38.9
69.8
31.9 19.3
22.8
SUBSIDENCE IN THE COASTAL AREA: the knowledge (data ARPA-ER)
Land-subsidence velocity map based on
Interferometry - SAR data (1992-2000)
VOLANO
10mm/y
Contour of
lowering velocity mm/y
ARPA-ER monitoring
network 1999
16mm/y
IAT
ADR
-0.05
1984-1987
-0.10
-0.15
-0.20
-0.20
-0.25
-0.30
CESENATICO
-0.35
-0.35
1984-1999
1984 - 1987
1984 - 1999
CATTOLICA
RICCIONE
MAREBELLO
RIMINI
RIMINI
VISERBA
TORRE PEDRERA
IGEA MARINA
VILLAMARINA
CESENATICO
CESENATICO
CERVIA
MILANO MARITTIMA
LIDO DI DANTE
RAVENNA
LIDO ADRIANO
PUNTA MARINA
MARINA DI RAVENNA
DOSSO DEGLI ANGELI
LIDO DI SPINA
LIDO DELLE NAZIONI
VOLANO
0.00
0m
VOLANO
LIDO DI VOLANO
12mm/y
ABBASSAMENTI LUNGO IL LITORALE EMILIANO-ROMAGNOLO
NEI PERIODI 1984-1987 e 1984-1999
EA
IC S
RAVENNA
Land-lowering diagram from
the coast levelling line
SUBSIDENCE IN THE COASTAL AREA: the risks
The 40 % of the coast line is affected by sea erosion
A great part of the coastal plain is below sea level
and exposed to flooding and sea inundation
Surface elevation
THE APPROACH TO SUBSIDENCE PROBLEM IN
EMILIA-ROMAGNA
• Previous subsidence studies indicate that groundwater
withdrawal comes up as one of major responsible for
subsidence in the E-R alluvial plain
• By now a) the mathematical modelling and b) subsurface
monitoring by settlement gages are considered the
successful instruments for subsidence understanding
• The definition of a subsurface geologic architecture
(bodies geometry, lithology, geotechnical proprieties, etc.)
is believed essential to approach to subsidence modelling
and for a correct planning of the groundwater
management
THE METHOD
COLLECTION OF SUBSURFACE GEOLOGICAL DATA:
The geognostic data-base of Geological Survey in GIS environment
The data base include:
50.000 subsurface stratigraphy from several archives
200 continuous cores and 2000 cone penetration tests CPTU curried out by RER
circa
50.000stratigraphy
stratigrafiecollected
di sottosuolo
(puntiand
blu)
subsurface
from public
private archives
continuous
cores and
cone prove
penetration
tests of new execution
circa
200 sondaggi
e 2000
penetrometriche
realizzati ex-novo (punti rossi)
STRUCTURAL – STRATIGRAPHIC FRAMEWORK AT BASIN SCALE:
the seismic analysis (ENI-AGIP data set)
The deep Po plain structures affect strata geometry
up to the first 100s m of continental sediments
Base of AES sinthem (continental unconf. Pleistocene)
Base of AEI sinthem (continental unconf. Pleistocene)
Early Pliocene marine unconformity
Thrusts and faults
GEOLOGICAL MODEL AT A BASIN SCALE AND DATA REPORTING:
Reconstruction of geologic cross-sections and strata geometry
Thickness of permeable deposits in the subsurface
(“A” aquifer group in RIS project 1998)
Geologic cross-section
(permeable sediments in colour, RIS project 1998)
FROM BASIN TO LOCAL SCALE:
Grids of detailed geologic cross-sections 100s m to few km spaced
Ravenna coastal plain
Cross-section
Water well
AGIP exploration well
RER continuous
borehole
Bologna alluvial plain
20 km
10 km
RAVENNA
DRILLING CONTINUOUS BOREHOLES (50-200m depth):
Core stratigraphy, in situ and laboratory analyses
Detailed core
STRATIGRAFIA
DIstratigraphy
SONDAGGIO
In situ sampling and
Biostratigraphy
(microfossils, pollen, …)
investigation
SAND AND
GRAVEL
(AQUIFER)
FINES
(AQUITARD)
TEST AND SAMPLE
MEASURED PARAMETER
Lefranc test
hydraulic conductivity
water sample
Ph, electric conductivity,
geochemistry, isotopes
Pocket Penetrometer
and Tor Vane
Cohesion
Shear resistance
geo-technique sample
grain-size,
hydraulic conductivity,
compressibility coefficient
organic matter sample
In situ
facies analysis
Grain-size
Mineralogy and petrography
Lm
Curve cumulative 204 S16
100
frequenza %
80
60
32,7
50,8
40
83,8
114,9
20
142,8
181,4
0
>1 mm
1/2-1 mm
1/4-1/2
mm
1/8-1/4
mm
1/16-1/8 <1/16 mm
mm
intervallo vaglio (mm)
Lv
Ls+c
Sand sample
analysis
14C
radiocarbon age
DATA INTEGRATION AT SEVERAL SCALE:
The geologic and stratigraphic model of the investigated area
Detailed cross-section from the Apenninic margin to the Adriatic coast
nin
en
Ap
e
FORLI’
Subsurface data-base stratigraphy:
water well, continuous cores, oil-exploration well
RUSSI
Unconformity surfaces in
dashed lines
300 m
coast
Correlation geometries based
on seismic interpretation
(+ outcrop survey at basin margin)
5 km
Sand and gravel bodies
in coloured dots
DATA SELECTION FOR SUBSIDENCE MODELLING AND
CONVERSION IN MATHEMATICAL FORMAT
Mathematic elaboration
by Med Ingegneria Srl
simplified cross-section
3D aquifers geometry
Elevation (m)
Aquitard
Aquifer (Po river source)
Aquifer (Apenninic rivers
source)
The stratigraphic data are
now available for the
mathematic model together
with water extractions,
mechanical parameters,
water flux estimations, …..
Depth (m)
THE EXAMPLES OF
METHOD APPLICATION
BOLOGNA ALLUVIAL PLAIN: reconstruction of the hydrostratigraphic
framework and location of settlement gages for subsidence monitoring
Bologna urban area
2 settlement gages at
100 and 200m depth
Piezometry level
surface
Lowering velocity at
Since spring 2005:
Continuous monitoring of
land lowering
20
200m
100m
mm 0
Piezometric drop due to
groundwater pumping in
Bologna city
57 million m3 of water
withdrawal in the Reno
alluvial fan (43 for drinking
water)
sand
gravel
piezometric level
A1
hydrostratigraphic unit
100 m
AQUIFERS
2 KM
Thickest aquitards
in the maximum
subsidence area
RAVENNA COAST (data from final report ENI AGIP–ARPA ER):
Mathematical simulations for historical reconstructions and future scenarios
Subsidence simulation for
1946-2001
Coherence between model and
observation: subsidence is
explained by groundwater
pumping
subsidence
m
Subsidence prevision for
2001-2016
A prevision of decrease in
water pumping will imply a
return to low subsidence
values
Discrepancy between model
and observations
Model result doesn’t fit
completely with observation:
along the coast-line
subsidence requires other
causes then groundwater
pumping
model
simulation
measures
Subsidence m
Measured subsid. (ARPA)
Model results
Measured subsid. (Ra)
Model uncertainty
CONCLUSIONS
•
In these first experiences of the last few years E-R Geological
Survey developed a methodology to define geologic
architecture of the subsurface to support analysis of Po Plain
subsidence
•
Such a geological framework can be successfully integrated
and used in mathematical modelling
•
It is a valid support to design the 3D monitoring system by
surface measurements and subsurface settlement gages
•
In the very next future geologic & mathematic modelling will be
the needful support for the sustainable management of
groundwater resource