Flow in “boils” (pipe break-through
seepage) in Dutch polders and elsewhere
groundwater
MSc project:
Information:
Prof.dr.ir.T.N.Olsthoorn, t.n.olsthoorn@tudelft.nl, 06-20440256
Drs. Perry de Louw, perry.delouw@tno.nl, 030-256 4806
Global description/context/background/problem
The groundwater below the Holocene cover layer in the deep polders in the western
Netherlands is under permanent pressure. This not
only causes upwards seepage, it also causes local
break-throughs of the covering layer after which a
more or less permanent pipe flow of groundwater
develops, thus short-circuiting the ditches with the
underlying sandy aquifer. This phenomenon is quite
common in the deeper polders where the less pervious
cover layer is weak. Even though the existence of
boils has been known for many years, research has
recently taken off more intensively by Deltares.
Recent research showed that boil seepage is the
dominant mechanism of surface water salinisation in deep polders in the Netherlands and
contributes 60% of the total salt load of the polder; the concentrated large fluxes in boils
lead to strong upconing of deeper and therefore more saline groundwater in comparison
with diffuse seepage. Since surface-water salinisation has become an important issue for
water boards, especially with respect to future changes of climate, sea level and land
subsidence, more knowledge of the mechanism behind these boils is needed. Hence,
investigation is important for the long-term sustainability of these polders.
The current study will focus on the actual flow
inside a boil, i.e. a pipe-flow system, under
different (geohydrological) conditions. We
distinguish pin boils, which are small springs
or upwellings of water, and sand boils, which
are usually larger and discharge water
containing fluidized sediment. However, the
walls of the pipe are likely maintained
dynamically by the combination of upward
flow and the density of the fluidized sand in the pipe. The morphology of boils strongly
depends on the composition of the Holocene cover layer as it may have different conduits
or just one pipe through which water with or without sediment is discharged. Because it
is not known how the boil system exactly works, this MSc aims at modeling the pipe
flow under different geohydrological conditions, i.e. different type of boils, for which
different conceptual models may be investigated against an actual data set obtained by
Deltares over the last couple of years. Some simple field experiments will be carried out
to collect data about flow velocities, pipe-diameters, boil morphology and the relation
between head difference and flow velocities.
The Msc will be done in close cooperation with and partly at TNO/Deltares in Utrecht
under the supervision of Perry de Louw (Deltares, preparing his PhD on boils: in Dutch:
“wellen”) and Theo Olsthoorn (TU-Delft/Waternet)
(The pictures were borrowed from
http://www.rijnland.net/wat_doet_rijnland/onderzoek_aan_water/onderzoek_aan_water/p
ilot_weldichting. See this site for some background information.
Aim/objectives
 To analyze conceptually and from the literature the hydraulics of pipe flow of
break-though zones in deep polders.
 To implement one or more of the most likely conceptual models of this pipe flow
under different geohydrological conditions (different types of boils).
 To benchmark and possibly calibrate these models on actual site data..
Working methods
 Analysis and modeling with advanced software allowing implementation of
concepts at a high level (Matlab, Comsol, Maple).
Expected outcome
MSc report, and/or scientific paper
Drs Perry de Louw
DELTARES, Unit Bodem en Grondwater systemen
Postbus 85467, 3508 AL Utrecht
Princetonlaan 6, 3584 CB Utrecht
Tel: +31 030 256 4806
Olsthoorn, Prof. dr. ir. Theo N.
Professor Groundwater Hydrology / Sr. Hydrologist
TU Delft / Factulty of Civil Engineering and Geosciences (CITG)
Section Water Mgmt, Chair Hydrology
Stevinweg 1, room 4.96
2628 CN Delft, NL; T +31(0)15 27 87346; M +31(0)6 204 402 56