1 Department of Physical Geography, Utrecht University, The Netherlands
2 Department of Subsurface and Groundwater Systems, Deltares Research Institute, Utrecht, The Netherlands
3 Division of Water Resources Planning and Investigation for the South of Vietnam (DWRPIS), Ho Chi Minh city, Vietnam
Interbed
Subsidence Confined aquifer
Unconfined aquifer
water table
Creep
Ripening Oxidation
Consolidation
Creep
Isostasy Consolidation
Creep
Consolidation
T otal
Subsidence
S hallow
D eep
DRIVERS OF SUBSIDENCE
Colourcode:
Loading Artificial lowering
of groundwater table
Fluid extraction Tectonics &
Isostasy
Process Natural driver Antropogenic driver
Natural loading Infrastruc tur e Buildings Lar ge construc tions Drainage of sur fac e wat er Gr oundwat er Ear th crust dynamics
H ydr ocarbons
Aquitard
Aquitard
Bedrock Consolidation
Seismicity Autocompaction
Boundary shallow/deep
w w w
waaaatttteeerrrr tttttaaaabbbblllleeee
C C C Cr r r r re e e ee e e e e
R R R R
Ri i i ip p p pe e e e en n n ni i i i in n n ng g g g g O
O O O
Ox x x x xi i i id d d d da a a at t t t ti i io o o on n n n
C C C C
Co o o o on n n n ns s s so o o o ol l l l li i i id d d d da a a at t t t ti i i io o o o on n n n C
C C C
Cr r r re e e e ee e e e ep p p p C
C C
Co o o on n n ns s s so o o ol l l li id d d da a a at t ti i i io o o o on n n n A
A A A
Au u u u ut t t t to o o oc c c co o o o om m m m mp p p p pa a a ac c c c ct t t ti i i io o o on n n n n
U U U U
Un n n n nc c c co o o o on n n nfi fi fi fi fin n n ne e e ed d d d d C
C C C
Cr r r r re e e e ee e e ep p p p
A A A A A A A A A A
Aq q q q q q q q q qu u u u u u u u u u u u ui i i i i i i i i it t t t t t t t t ta a a a a a a a a ar r r r r r r r r rd d d d d d d d d d
B B B B B B B B B
Booooooooooooouuuuuuuuunnnnnnnnnndddddddddddaaaaaaaaaarrrrrrrrryyyyyyyyyy yyy
A A A A A A
Aq q q q q q qu u u u u u u ui i i i i i i i it t t t t ta a a a a ar r r r rd d d d d d d C
C C Cr r r re e e ee e e e d
d d
d a a a aq q q q qu u u u ui i i if f f f fe e e e e
Subsidence Colourcode: Process Natural driver Antropogenic driver
y y y y C
C C C
Co o o o on n n n nfi fi fi fi fin n n n ne e e e ed d d d d a a a a aq q q q qu u u u ui i i i if f f f fe e e e er r r r C C C Cr r r r re e e e ee e e e ep p p p
s s s
shhhhhaaaallllllllloooowwww/////dddddeeeeeeeepppp
C C C C
Co o o o on n n ns s s so o o ol l l li i i id d d da a a a at t t ti i i i i
A A A A A A A
Aq q q q q q q q q q qu u u u u u u u ui i i i i i i i i it t t t t t t t t ta a a a a a a a a ar r r r r r r rd d d d d d d d d p
p p p p p p p e e e er r r r C
C C C
Co o o o on n n n ns s s s so o o ol l l li i i id d d d da a a a at t t ti i i io o o o on n n n n
I I I I I I I I I
Innnnnnnnntttttttttteeeeeeeerrrrrrrrbbbbbbbbbbeeeeeeeeedddddddddd
i i io o o o on n n n n
Interbed
Subsidence Confined aquifer
Unconfined aquifer
water table
S S
Se e e e eis s s sm m m m mi i i ic c c ci it t t t ty y y y C
C C C
Co o o o on n n ns s s s so o o o oli i i id d d d da a a at t t ti i i io o o o on n n n n S
S S S
Se e e e ei i i is s s s sm m m m mi i i i ic c c ci i it t t t ty y y y y Creep
Ripening Oxidation
I I
Is s s so o o os s s s st t t ta a a a as s s sy y y y Consolidation
Creep
Isostasy Consolidation
Creep
Consolidation
T otal
Subsidence
S hallow
D eep
PROCESSES OF SUBSIDENCE
Colourcode:
Loading Artificial lowering
of groundwater table
Fluid extraction Tectonics &
Isostasy
Process Natural driver Antropogenic driver
Natural loading Infrastruc tur e Buildings Lar ge construc tions Drainage of sur fac e wat er Gr oundwat er Ear th crust dynamics
H ydr ocarbons
Aquitard
Aquitard
Consolidation Seismicity Autocompaction
Boundary shallow/deep
Bedrock
a
0% 20% 40% 60% 80% 100%Mud
Muddy clay Clay
Silty clay Clayey silt Silt
Sandy silt Silty sand Sand Sand and gravel 0
-100
-200
-300
-400
1: Standard penetration test 2: Logging while drilling 3: Vertical electronical sounding
c c
Channel deposits (sand)
Natural levee deposits (fine sand, sandy-sily clay)
Crevasse deposits (fine sand, sandy-silty clay)
Floodbasin deposits (clay, humic clay) Organic deposits (peaty clay, peat)
Available data Additions to existing models Outcomes
Geo-hydrological cross-sections Lithological borehole
descriptions
Geological cross-sections SPT
1, LWD
2and VES
3measurements
Physical and chemical sediment properties
Lithostratigraphical analysis Conceptual models of delta
evolution
Palaeogeographical analysis (Depositional environments
& sediment preservation)
3D lithological subsurface model
3D lithological interpolation
Better understanding aquifer - aquitard architecture / properties
Improved distribution of sediment properties
Improved geo-hydrological model
Gain
2. Evaluate future groundwater management scenario’s
Identify subsidence drivers and develop mitigation strategies
Supporting decision-making towards sustainable groundwater management
1. Unravel the subsidence balance Hydrological model with
subsidence module:
d
Subsidence in the Mekong Delta, Vietnam:
Impact of groundwater extraction
Introduction
Land subsidence rates of ~1-4 cm yr
-1are measured in the low-lying Vietnamese Mekong Delta (Fig. 1).
These relatively high subsidence rates are attributed to groundwater extraction. On daily basis over two million m
3of groundwater is extracted from the upper 500 m of the multi-aquifer subsurface. As a result, hydraulic heads in aquifers are dropping, on average 0.3-0.7 m yr
-1.
P.S.J. Minderhoud 1,2 , G. Erkens 2,1 , V.H. Pham 1,2,3 , B.T. Vuong 3 , E. Stouthamer 1
Land subsidence increases flood risk, and, on the longer term, threatens the delta with drowning.
To evaluate the impact of future land subsidence, we need to go from measurements to predictions.
Here we present our approach to assess the subsidence potential of the multi-aquifer subsurface of the Mekong delta due to groundwater extraction under different groundwater management scenarios.
Figure 1. Satellite based (InSAR) subsidence rates between 2006-2010 for the Mekong Delta. Data © JAXA, METI 2011 (Erban et al., 2014).
Figure 2. Schematization of the main subsidence drivers and processes within the upper (phreatic) aquifer and deeper (confined) aquifer(s). Both natural and anthropogenic drivers are distinguished. The subsidence balance equation is given on the left side, being the total sum of all shallow and deep subsidence rates.
Figure 3. Workflow of the approach to develop the 3D lithological subsurface model a) Cross-section of current geo-hydrological model. b) Example of a cross-section including geomorphological elements (Bierkens & Weerts, 1994). c) 3D view of the available lithological borehole data. d) Depth distribution of lithological classes for the Mekong delta.
From monitoring to predicting
Total measured subsidence at the earth surface is the sum of subsidence resulting from all natural and human-induced drivers, the subsidence balance (Fig. 2). We distinguish between shallow and deep drivers and processes of subsidence.
To determine the contribution of groundwater extraction, and to go from measuring to predicting subsidence, the cumulative signal needs to be unraveled. We develop a 3D geohydrogical model hydrology and calculate subsidence to evaluate the impact of groundwater extraction
References
Bierkens, M. F. P., & Weerts, H. J. T. (1994). Application of indicator simulation to modelling the lithological properties of a complex confining layer. Geoderma, 62(1-3), 265–284.
Erban, L. E., Gorelick, S. M., & Zebker, H. A. (2014). Groundwater extraction, land subsidence, and sea-level rise in the Mekong Delta, Vietnam. Environmental Research Letters, 9(8), 1–6.
Acknowledgements
This poster is part of a PhD research carried out by P.S.J. Minderhoud at the Dept. of Physical Geography, Utrecht University, The Netherlands. The PhD project is funded by NWO-WOTRO (W 07.69.105), Deltares and TNO-Geological Survey of the Netherlands.
The Division of Water Resources Planning and Investigation for the South of Vietnam (DWRPIS), Ho Chi Minh city, Vietnam is thanked for providing subsurface and hydrological data for this research.
Faculty of Geosciences Dep. Physical Geography
rlands.
