Brackish groundwater as a new
resource for drinking water ?
Consequences of density flow.
Benefits for the environment ?
Theo Olsthoorn
Waternet (Amsterdam Water Supply) / TU-Delft
home.planet.nl/~hans.farjon/nederland.htm
peat
Amsterdam
Amsterdam
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Schematic cross section
6m
fresh
fresh
Brackish upflow
Water management of the Polder
Groot Mijdrecht North
Brackish-brown
water with nutrients
Algae blooms,
Salinity fluctuations
Aquatic ecosystem
is frustrated in
summer
Lake ecosystem
is also frustrated
in summer
Ground level 1960
Ground level 2004
Ground surface elevations in cm above current surface water level
Average settling + shrinkage + oxidation = 30 cm in 40 yrs
Water management of the Polder
Groot Mijdrecht North
Brackish-brown
water with nutrients
Settling, shrinkage
and oxidation of
peat 7 mm/yr
Too wet and saline for
agriculture over time
Algae,
ecosystem
frustrated in
summer
Lake ecosystem
frustrated in
summer
Spontaneous
break-through of
covering peat layer
What about the future of this polder ?
Prime
Minister
crown prince
and water
manager of the
Netherlands
Investigation
Committee
Report
handover
infiltration
Polder with low surface water level
infiltration
infiltration
Polder with low surface water level
Qbrackish=3.95m2/d
infiltration
Polder  lake  stagnant salt bulge
infiltration
Polder with low head and
extraction of brackish water
infiltration
fresh
fresh
Brackish
Brackish / saline
Jan van Dam
SWIMMER
from 19682004
Conclusions
• Sustainability of deep polders with a peat soil and brackish seepage
are officially questioned, they may be turned into lakes again.
• The flow analysis for like brackish systems can no longer be done
without variable density modeling (enquiry committee report).
• Brackish water may be a good source for drinking water and its
extraction may solve brackish seepage, but it cannot solve
subsidence and peat oxidation.
• Brackish water extraction increases fresh equilibrium seepage to the
polder, which is a density effect.
• However, increasing seepage is nowadays politically unacceptable.