23 juni 2015

Land Subsidence

Simulation and Implications in Deltas.

Mahmoud Bakr

National Water Research Center

23 juni 2015

Contents

- Definition, causes, symptoms, and Data acquisition.

- Method of analysis and simulation

- Case study of Jakarta

- Land subsidence in the Nile Delta

23 juni 2015

Definition

Land subsidence is the lowering of the land

surface due to changes that take place

underground.

San Joaquin Valley subsidence

Mining ground water for agriculture has enabled the San

Joaquin Valley of California to become one of the world’s

most productive agricultural regions, while simultaneously

contributing to one of the single largest alterations of the

land surface attributed to humankind

9 m of land subsidence between 1925-1977 (52 years)

~ 17.3 cm/y

23 juni 2015

Land subsidence classification of Causes

23 juni 2015

Factors causing subsidence

Distribution of soft soil (e.g. clay) and organic soil (e.g. peat).

Excessive (unregulated, uncontrolled) groundwater abstraction for

domestic & industrial demand + reduced recharge (hard surface)

Drainage of soil oxidation of peat, soil compaction.

Erosion by rainwater runoff (sinkholes)

Construction of dams and changes of river channels reduced amount of

sediment supply no natural compensation of subsidence: fact of life in

city

23 juni 2015

Land subsidence effects on coastal areas

Pipeline Piles

Tall

buildings

Land

subsidence

High tide

Pipeline Piles

Tall

buildings

Land

subsidence

High tide

Aquifer salinization

High tide

Aquifer salinizationAquifer salinizationAquifer salinization

High tideHigh tide

Sinking velocity

> 5mm/year

Sinking velocity

> 5mm/year

Sinking velocity

> 5mm/year

Rising sea levels> 3mm/yearRising sea levels> 3mm/yearRising sea levels> 3mm/year

• Relative “sea level” higher due

to land subsidence

• Damage to flood protection

structures

• Different flood inundation maps

(land subsidence is a spatially

distributed phenomena).

• More significant sea water

intrusion.

23 juni 2015

Land subsidence effects on coastal areas; diagnosing

1. Predict change in topography in the future: impact on hydraulic

and hydrological models

2. Estimate effects of land subsidence of surface and deeper layers

on flood protection structures: impact on design of structures and

foundations

3. Possible damaging effects on sewerage/drainage systems and

other infrastructure.

23 juni 2015

Symptoms: Land subsidence observed at groundwater pumping wells

23 juni 2015

Data acquisition methods of land subsidence

1. Geometric leveling network (optical leveling ~0.3mm);

2. Global Positioning System Surveying;

3. Extensometers,

4. Remote sensing:

1. Interferometric Synthetic Aperture Radar (InSAR);

2. Differential InSAR (C-Band). It is capable of mapping centimeters to meters of contiguous deformation across large areas, with centimeter accuracy. DifSAR is capable of capturing wide are surface deformation, but unlikely to be able to resolve any highly localized surface deformation features; and

3. Permanent Scatterer (PS) InSAR measurements (L-Band). It is used to map order of millimeters subsidence trends in urban and semi-urban environments.

Geodetic station used by GPS; ~ 2-3 cmExtensometer; ~ 0.3cm

23 juni 2015

Contents

- Definition, causes, symptoms, and Data acquisition.

- Method of analysis and simulation

- Case study of Jakarta

- Land subsidence in the Nile Delta

23 juni 2015

Methodology: Integration of monitoring and modeling

Geological model

of the subsurface

Geomechanical

modelling

Forecasted

ground-motion

Ground-motion

monitoring data

Va

l ida

tion

&Im

pro

ve

me

nt

Comparison &

inverse modelling

Risk analysis &

Decision making

Specific requirements to satellite data

Geological model

of the subsurface

Geomechanical

modelling

Forecasted

ground-motion

Ground-motion

monitoring data

Va

l ida

tion

&Im

pro

ve

me

nt

Comparison &

inverse modelling

Risk analysis &

Decision making

Specific requirements to satellite data

STRATIGRAPHY HYDROGEOLOGY GEODESY GEOTECHNIQUESTRATIGRAPHY HYDROGEOLOGY GEODESY GEOTECHNIQUE

23 juni 2015

Methodology to predict subsidence

1. Modeling of causes

• Groundwater flow model

• Calibration of ground water flow model with head observations

• Prediction of drawdown development according to different groundwater management scenarios.

• Determine process contributing to compaction (i.e., primary, secondary)

• Oxidation potential of organic layers

• Estimation of location and thickness of unsaturated layers

2. Modeling of effects

• Either coupled or decoupled groundwater flow and geo-mechanics modeling

> Estimate compaction parameters

> Calibrate parameters with land subsidence observations

• Add oxidation (and erosion).

23 juni 2015

Terzaghi's Principle

Terzaghi's Principle states that when

a rock is subjected to a stress, it is

opposed by the fluid pressure of

pores in the rock.

σ = σ' + u

Also known as Terzaghi's theory of

one-dimensional consolidation; it

states that all quantifiable changes

in stress to a soil (compression,

deformation, shear resistance) are a

direct result of a change in effective

stress. The effective stress σ' is

related to total stress σ and the pore

pressure u by the relationship;

Consolidation of multiple layers

23 juni 2015

2

2

22 21

8 11 exp 2 1

42 1

v

i

c tU t i

di

Cv : consolidation coefficient [L2/T];

d : drainage length [L]; and

t : consolidation time [T].

1

1 ,

n

j nj i

jv v j

bb

c c

Calculating equivalent consolidation

coefficient

23 juni 2015

The NEN-Bjerrum method

• The NEN-Bjerrum model supports today’s international defacto standards for

settlement predictions, as contained for example in the Dutch standards.

• The model uses common linear strain soil parameters (Cc ,Cr, Ca).

• It assumes that the creep rate will reduce with increasing over-consolidation and

that over-consolidation can grow by unloading and by ageing.

• It decomposes total strain into two components; namely, a direct elastic contribution

(εd ) and a transient viscous contribution (εvp) where all inelastic compression is

assumed to result from visco- plastic creep.

• The Over-consolidation Ratio (OCR) is defined

as the ratio of pre-consolidation pressure and in-

situ.

23 juni 2015

Compressibility and specific storage; remarks

• Typically, skeletal compressibilities (and therefore storativities) of

interbeds and confining units are several orders of magnitude

larger than compressibilities of coarser-grained aquifers, which are

typically much larger than water compressibility, therefore, virtually

all of the water derived from interbed and confining-unit storage is

due to the compressibility of the granular skeleton.

• Skeletal specific storage is inversely related to effective stress.

• For deep sediments, σ will be large, and reductions in u resulting

from groundwater pumping are not likely to make large percentage

changes in σ. On the other hand, for shallow sediments where σ is

relatively small, changes in u could result in relatively large

percentage changes in σ

sk wS g n

23 juni 2015

Jakarta Case

23 juni 2015

Coastal flooding and land subsidence

Total2007-20251989-2007Pluit

8-12 cm4-6cm4-6 cmSea level rise

100-200 cm100-200 cmMinimum

Subsidence

200-400 cm

Total2007-20251989-2007Pluit

8-12 cm4-6cm4-6 cmSea level rise

100-200 cm100-200 cmMinimum

Subsidence

200-400 cm

Coastal Flooding!

Land subsidence and climate change…

23 juni 2015

Indications

Extensometer at old Geology Office Jalan Tongkol

41 cm

4,5 cm

3 cm

199

7

23 juni 2015

Data acquisition

• Leveling measurements in 1974, 1982, 1991, 1997

• GPS Surveys 1997, 1999, 2000, 2002, 2005, 2006, 2007, 2008,

2009, 2010

• Level on the tide gauge

• Extensometer, piezometric surface

• Remote sensing (InSAR, etc).

23 juni 2015

Data acquisition

Subsidence revealed from

Belakang Muka

Belakang Muka

Rambu-1

Rambu-2

Rambu-1

bb1

bm1

bb2bm2

TitikA

TitikB

HB – HA = (bb1 – bm1) + (bb2 – bm2)

Instrumensipat datar

Leveling survey

GPS survey

Extensometer

23 juni 2015

Measured land subsidence maps; 1974-1982

• Between 1974-1982, almost no land subsidence recorded around area of Jakarta. • This is could be because of less urban development at that time, and minimum usage of groundwater.

Subsidence map of Jakarta 1974-1982:

23 juni 2015

Measured land subsidence maps; 1982-1991

• Between 1982-1991, subsidence begin to be recorded around Jakarta;• at the same time urban development has been growing up, where indeed much used of groundwater is observed.

Subsidence map of Jakarta 1982-1991:

Total subsidence -5 up to -90 cm ; rate -0.5 up to -9 cm/year

23 juni 2015

Measured land subsidence maps; 1991-2000

• Between 1991-2000, wider areas with land subsidence and larger land subsidence rates were observed. • During this time, acceleration of urban development, and the tremendous used of groundwater were observed.

Subsidence map of Jakarta 1991-2000:Total subsidence -10 up to -150 cm ; rate -1 up to -16 cm/year

23 juni 2015

Measured land subsidence maps; 2000 - 2010

Between 2000-2010, generally constant rate of subsidence is recorded as compared to the period 1991-2000.

Subsidence map of Jakarta 2000-2010:Total subsidence -10 up to -160 cm ; rate -1 up to -17 cm/year

23 juni 2015

Measured land subsidence maps; 1974 - 2010

Subsidence map of Jakarta 1974-2010:

1974-1982

1982-1991

1991-2000

2000-2010

Total subsidence -25 up to -400 cm ; rate -0.5 up to -17 cm/year -4,1 meter

-1,4 meter-2,1 meter

-0,7 meter

-0.25 meter

-4,1 meter

-2,1 meter-1,4 meter

-0,7 meter

-0.25 meter

23 juni 2015

Land subsidence simulation in Jakarta

23 juni 2015

Research Questions

What is the expected additional land subsidence in Northern Jakarta in case:

• The groundwater abstraction is continued as present and piezometric heads in the deeper aquifers will continue to lower in the coming 20 years.

• The groundwater abstraction is partially reduced and piezometric heads in the deeper aquifer will stabilize.

• The groundwater abstraction is reduced to 10% of present abstraction and piezometric heads will recover.

• The groundwater abstraction is reduced to 10% and clean water is infiltrated in the former pumping wells resulting in a rapid recovery of the piezometric heads.

What is the estimated influence of large complexes of high rise buildings in Northern Jakarta on land subsidence.

23 juni 2015

Study area, and land subsidence and piezometric head data

23 juni 2015

Conceptual lithological sequence of aquifer/aquitard

formations

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Annex

Input View

Layers

8. Aquifer 1

7. Aquitard 1

6. Aquifer 2

5. Aquitard 2

4. Aquifer 3

3. Aquitard 3

2. Aquifer 4

1. Aquitard 4

0.000 10.000

1

2

3

4

5

6

7

8

1 2

1

-4

-59

-69

-119

-129

-169

-179

-249

1

-4

-59

-69

-119

-129

-169

-179

-249

Level (m)

Piezometric heads of the considered scenarios.

23 juni 2015

1

1960 1970 1980 1990 2000 2010 2020 2030-50

-40

-30

-20

-10

0

Year

Pie

zom

etr

ic H

ead (

m)

"Aquifer 1"

"Aquifer 2"

"Aquifer 3"

"Aquifer 4"

1960 1970 1980 1990 2000 2010 2020 2030-80

-60

-40

-20

0

Year

Pie

zom

etr

ic H

ead (

m)

"Aquifer 1"

"Aquifer 2"

"Aquifer 3"

"Aquifer 4"

1960 1970 1980 1990 2000 2010 2020 2030-50

-40

-30

-20

-10

0

Year

Pie

zom

etr

ic H

ead (

m)

"Aquifer 1"

"Aquifer 2"

"Aquifer 3"

"Aquifer 4"

1960 1970 1980 1990 2000 2010 2020 2030-50

-40

-30

-20

-10

0

Year

Pie

zom

etr

ic H

ead (

m)

"Aquifer 1"

"Aquifer 2"

"Aquifer 3"

"Aquifer 4"

Case 1 Case 2

Case 3 Case 4

Average yearly drawdown in the area is about 1.2 m.

Land subsidence data at DNMG location.

23 juni 2015

Year Time step Subsidene

(m)

1974 3285 0.28

1991 9490 0.48

1992.4 10000 0.55

1995 10950 0.68

2000 12775 0.83

2005 14600 1.24

2010 16425 1.64

23 juni 2015

Geo-mechanical parameters for the Bejrrum method

Values in yellow cells are adopted as initial values

Soil Unit Weight Condolidation Coeff. Overconsolidation Reloading/Swelling Compression index Sec. compression

kN/m3

(Cv) m2/s ratio OCR (-) ratio RR (-) CR (-) coeff. Ca (-)

Aquifer 1 26 N/A 1.1 0.02 0.02 0.002

Aquifer 2 26 N/A 1.1 0.02 0.02 0.002

Aquifer 3 26 N/A 1.1 0.02 0.02 0.002

Aquifer 4 26 N/A 1.1 0.02 0.02 0.002

Aquitard 1 27 3.80E-07 1.3 0.02 0.16 0.002

Aquitard 2 27 3.80E-07 1.3 0.02 0.16 0.002

Aquitard 3 27 3.80E-07 1.3 0.02 0.16 0.002

Aquitard 4 27 3.80E-07 1.3 0.02 0.16 0.002

Layer RR CR C a OCR C v

[-] [-] [-] [-] m 2 /s

Aquitard 1 0.001 0.600 0.013 1.52 9.38E-07

Aquitard 2 0.002 0.044 0.030 1.27 4.31E-09

Aquitard 3 0.004 0.285 0.009 5.05 1.39E-08

Aquitard 3 0.048 0.225 0.005 4.06 2.52E-09

Calibrated parameter values

Calculated versus measured subsidence and

forecasted subsidence

23 juni 2015

1

1960 1980 2000 2020 2040 2060 2080 2100

0

1

2

3

4

Year

Subsid

ence (

m)

Simulated

Measured

1960 1980 2000 2020 2040 2060 2080 2100

0

1

2

3

4

Year

Subsid

ence (

m)

Simulated

Measured

1960 1980 2000 2020 2040 2060 2080 2100

0

0.5

1

1.5

2

2.5

Year

Subsid

ence (

m)

Simulated

Measured

1960 1980 2000 2020 2040 2060 2080 2100

0

0.5

1

1.5

2

2.5

Year

Subsid

ence (

m)

Simulated

Measured

Case 2 Case 1

Case 3 Case 4

ID Case Description

Case 1: Drawdown zero after 2010

Case 2: Drawdown increases 5m every 5 years from 2010 till 2030

Case 3: Piezometric heads are recovered to the values of 1995 by 2015

Case 4: Piezometric heads recovered to the maximum of all aquifers in

1995 by 2015

Year Case 1 Case 2 Case 3 Case 4

2020 1.97 2.48 1.74 1.73

2025 2.08 2.75 1.80 1.77

2030 2.18 2.92 1.85 1.81

2100 3.01 3.91 2.43 2.30

MS

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1

An

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x

Input View

Layers

8. Aquifer 1

7. Aquitard 1

6. Aquifer 2

5. Aquitard 2

4. Aquifer 3

3. Aquitard 3

2. Aquifer 4

1. Aquitard 4

0.000 10.000

1

2

3

4

5

6

7

8

1 2

1

-4

-59

-69

-119

-129

-169

-179

-249

1

-4

-59

-69

-119

-129

-169

-179

-249

Level (m)

Compaction of aquitard layers (Case 1)

23 juni 2015

1960 1980 2000 2020 2040 2060 2080 2100

0

0.5

1

1.5

2

Year

Com

paction (

m)

"Aquitard 1"

"Aquitard 2"

"Aquitard 3"

"Aquitard 4"

23 juni 2015

Degree of Consolidation

• Delay effect due to slow dissipation in the most bottom aquitard could be significant.

• This is due the assumption that the lower boundary is undrained. The undrained lower

boundary can be simply because the layer is overlaid on basement rock.

• Note that most aquitards have not reached full dissipation at end of simulation (2100).

This means a continuous subsidence till the layers reach hydrostatic condition.

1960 1980 2000 2020 2040 2060 2080 21000

0.2

0.4

0.6

0.8

1

Year

U (

%)

"Aquitard 1"

"Aquitard 2"

"Aquitard 3"

"Aquitard 4"

Subsidence for several drainage and creep

conditions of "Case 1"

23 juni 2015

1960 1980 2000 2020 2040 2060 2080 2100

10-4

10-3

10-2

10-1

100

101

0.0067

3.0129

1.3748

8.7908

0.0002

0.0240

0.0055

0.1733

Year

Subsid

ence (

m)

CrNoDr (Case 1)

CrDr

NoCrNoDr

NoCrDr

General conclusions (Jakarta Case)

23 juni 2015

• The NEN-Bjerrum method has been used to evaluate land subsidence in

deltaic environment due to change in pore water pressures as a result of

applying different groundwater management schemes.

• The method is combined with the Terzaghi’s consolidation theory to

account for consolidation of multiple homogeneous layers of soil between

drained layers

• The method decomposes total strain into a direct elastic contribution (d)

and a transient visco-plastic contribution (vp).

• The results showed significance of creep compaction on calculated land

subsidence where for the case studied here with the calibrated

parameters set, creep presented about 99% of total land subsidence for

the year 2100.

• The results also showed that coupled processes of consolidation and

creep produced a favorable situation where consolidation reduced total

land subsidence by 66% as compared to the case of drained layers (and

consequently 100% consolidation).

23 juni 2015

Land subsidence in the Nile Delta

(proposal stage)

Research Objectives

1. Establishing a national monitoring network to provide continuous

measurements of land subsidence in the Nile Delta

2. Identifying risk areas prone to land subsidence by:

1. Mapping the thickness of soft soils within the Nile Delta to help in

identification of areas with high risks to land subsidence,

2. To characterize clay-cap in the Nile Delta in terms of geo-mechanical

parameters,

3. Developing a preliminary coupled groundwater flow model and land

subsidence of the Nile Delta; this will be used to investigate the relationship

between groundwater abstraction and land subsidence.

4. Investigation processes (e.g. primary or secondary compaction) controlling

potential risk area of land subsidence,

5. Initial evaluation of consequences of land subsidence on flood mapping in

the coastal area of the Nile Delta; this includes how climate change and

groundwater management could affect flooding risks of the delta.

6. Evaluating the change in freshwater-seawater interface due to land

subsidence.

23 juni 2015

Research Approach and Methodology

23 juni 2015

1. Data inventory

2. Monitoring of land subsidence

1. Geodetic techniques

2. Remote sensing (Radar Interferometry Technique)

3. Tide gauges

3. Characterization of geo-mechanical properties of the clay layer,

4. Mapping risk areas of land subsidence.

5. Modeling land subsidence and consequences to flood inundation.

1. Theoretical development of a method to handle creep in clay

2. Hydrogeological conditions of the Nile Delta

3. Consequences of land subsidence and sea level rise on flood

inundation in the Nile Delta

GPS stations by National Institute of Astronomy

and Geophysics (NIAG)

23 juni 2015

Groundwater aquifers in the Nile Delta

23 juni 2015

23 juni 2015

Land Subsidence in the Nile Delta

Land Subsidence in the Nile Delta: Inferences from Radar Interferometry, The Holocene v.

19(6), doi:10.1177/0959683609336558

• Average elevation of

approximately 1 m above

sea level within 30 km of

the coast and

• A predicted rise in sea

level of 1.8—5.9 mm/yr

• Evaluate rates of

subsidence of sections of

the northeastern Nile

Delta (a total length of 110

km, up to 50 km from the

coastline) using Ps-InSAR

techniques applied to 14

ERS-1 and ERS-2 scenes.

B The highest subsidence rates (~8 mm/yr; twice average Holocene rates) do not

correlate with the distribution of the thickest Holocene sediments, but rather with the

distribution of the youngest depositional centers (major deposition occurred between

~3500 yr BP and present) at the terminus of the Damietta branch.

Expected Major Outputs

23 juni 2015

1. A national spatial geo-database system of land subsidence

measurements and parameters (NGDLS)

2. Several risk maps of land subsidence as inferred from different data

3. A complete geo-mechanical characterization of the clay-cap in the

delta (results are to be integrated into NGDLS),

4. Time series of land subsidence at different locations a long the

coastline of the Nile Delta (results are to be integrated into NGDLS),

5. Several modeling/data integrated tools to forecast spatial variability of

land subsidence in the Nile Delta, to forecast flood inundation due to

sea level rise and land subsidence, and to forecast impacts of

groundwater management on land subsidence and seawater

intrusion.

Thank you for your attention

23 juni 2015

well scheme in homogeneous aquifer and pore pressure

variation

23 juni 2015

Artesian well in confined aquifer and pore pressure

variation

23 juni 2015

Consolidation ratio as function of depth and time factor

uniform initial excess pore pressure

23 juni 2015

The Bjerrum method; explained

Idealized primary and secondary settlement during time (drained

conditions)

Idealized primary settlement during loading

(drained conditions)

23 juni 2015

Common parameter values (The Netherlands)

RR CR e0 Cr Cc sigma Ske Skv Percentage

Clay (Holocene) 0.08 0.24 0.1 0.0992 0.264 20 0.00196 0.00521 0.37576

Peat (Holocene) 0.6 1.81 0.3 1.686 2.353 20 0.02814 0.03928 0.71653

Clay (Pleistocene) 0.06 0.17 0.08 0.0702 0.1836 20 0.00141 0.00369 0.38235

Peat (Pleistocene) 0.3 0.9 0.25 0.57 1.125 20 0.00990 0.01953 0.50667

sk wS g n

23 juni 2015

Data requirements; The NEN-Bjerrum method

• Three dimensional model of the subsurface (lithology),

• Groundwater flow and related variability of water table and piezometric heads,

• Soil properties:

• The well-established constitutive models are based on common soil parameters for virgin compression, unloading/reloading and secondary creep. For example, for the NEN-Bjerrum method: the following parameters are required:

> RR: Reloading/swelling ratio

> CR: Compression ration

> Ca: Coefficient of secondary compression

> POP: Pre-overburden pressure (defines the over-consolidation by the difference between the initial vertical pre-compression stress and the initial field stress)

• Consolidation is either modeled by means of a consolidation coefficient or by means of permeability per layer.

• Total stresses is calculated using soil unit weights.

• Water unit weight to calculate effective stresses.

• Land subsidence data to calibrate/ validate relevant model parameters.

23 juni 2015

The Jakarta Case; Conclusions

• Groundwater abstraction is the main reason for land subsidence in Jakarta.

• Groundwater flow and land subsidence are coupled phenomena since dynamics of groundwater flow systems lead to a time-variant geo-mechanical system where change in effective stresses in time, and consequently evolution of land subsidence in time, follows the change in water levels/piezometric heads in porous media.

• In deltaic environment with extensive appearance of soft soils, secondary (creep) and delayed primary settlement play significant roles in the estimation of land subsidence and relation to different groundwater management schemes.

• The forward geo-mechanical model using the Bjerrum method is developed based on conceptual information about the subsurface as well as piezometric head data at the “DNMG” area located north-west of Jakarta.

• A time series of land subsidence at the studied location is used to condition the parameters of the forward model.

23 juni 2015

The Jakarta Case; Conclusions (cont.)

• The calibrated model estimates the compression ratio as 0.33, the re-compression ratio as 0.008, and the secondary compression ratio (creep) as 0.012.

• The developed model simulates the behavior of the measured land subsidence time series accurately with simulated subsidence value of 1.6m at 2010 (corresponds to 1.64m measured value).

• The model estimates 2.6m and 3.88m of land subsidence at 2030 and 2100, respectively, considering no further groundwater drawdown after 2010. This reflects the delay effect due to slow dissipation in aquitard systems.

• A moderate drawdown of 1m/y every 5 years till 2030 would cause land subsidence of 3.25m and 5.7m at 2030 and 2100, respectively.

• Several groundwater scenarios of stopping abstraction and artificial recharge of aquifers are examined. For example, recovering piezometric heads to measured values in 1995 (this corresponds to 15 m recovery), will result land subsidence (still) of 2.4m and 3.1m at 2030 and 2100, respectively.