SUB-CR: an improved subsidence package,

Vietnam-example

Gilles Erkens & Henk Kooi

in cooperation with

Philip Minderhoud

iMOD International User Day 1 November 2016

1 november 2016

Land subsidence = land level lowering

Land subsidence is the lowering of the land surface

- due to changes that take place underground and

- relatively to a certain level (sea level)

9 m of land subsidence

between 1925-1977 (52 years)

~ 17.3 cm/y

Mekong Delta Yellow River Delta

Nile Delta

Ganghes Delta Mekong Delta

Sources: USGS; Syvitski et al., 2009

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Land subsidence vs absolute sea-level rise

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Source: Erkens et al., 2016

Consequences

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What can we do? The circular approach

Erkens et al 2015

Measuring

Understanding

Mechanisms

Modelling

Cost-Benefit

Analyses

Measures

Monitoring

iMOD SUB-CR

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Causes and modelling options

Natural subsidence

• Tectonics, isostacy, autocompaction

Human-induced subsidence:

Oil/gas extraction

Groundwater extraction

Drainage

Loading

D-Settlement

iMOD SUB-CR

Coupled grondwater flow and compression

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groundwater model hydraulic head (x,y,z,t) Effective stress changes (x,y,z,t)

compression; strain (x,y,z,t)

Subsidence (x,y,t)

‘interbed fraction’:

are the compressible

sediments

Standing on the shoulders of Giants

2016/2017: Deltares iMOD SUB-CR:

Bjerrum (NEN)

RR recompression/swelling ratio

CR compression ratio

Ca secular compression ratio (creep)

Isotache (abc model)

a recompression/swelling constant

b compression constant

c secular compression constant (creep)

Bjerrum

The addition of creep is the most important innovation

compared to existing MODFLOW subsidence modules)

2000: USGS MODFLOW SUB package

2005: USGS MODFLOW SUB-WT

Kooi et al., in prep

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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

Sources: IT Bandung, Deltares

Modelling subsiding Jakarta

Subsidence history (m)

creep

no creep

‘oberserved’ subsidence

Predicted Subsidence (m), with constant hydraulic heads

~ 70 cm

(2010-2100)

Figures from Deltares, 2015

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Integration extensive data sets: Mekong Delta

Meteo data (monthly) > 500.000 extraction wells and history

Geological boreholes and cross-sections 3D hydrogeological subsurface model

• Period: 1991-2015 • Monthly increments

• Parameterization and

calibration: based on data from Vietnamese partners

• Deltares open-source software suites: iMOD shell for MODFLOW

SUB-CR subsidence mod.

Data is provided by the Division of Water Resources Planning and Investigation for the South of Vietnam (DWRPIS)

Minderhoud et al., 2015

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iMOD-SUB-CR

is a module for modelling groundwater extraction driven subsidence

can be used at local, regional and continental scale

is equipped with two types of creep calculation methods, building on

the existing MODFLOW subsidence packages

has been rigorously tested, using existing well known geotechnical

packages as benchmark

has most benefits when used in clay-rich complex aquifer systems

(current deltas for instance)

is introduced in a paper, which will be submitted soon

will hopefully be simultaneously released as a MODFLOW (USGS)

and iMOD (Deltares) package by the end of 2017

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