F.J.C. Smits, M.Sc.

The taming of brackish seepage

Besides his work for Waternet, Frank is doing a PhD about the reduction of brackish seepage.

The motto of the research is: 'Cum grano salis... '

In the area that is managed by the waterboard Amstel, Gooi and Vecht, some deep polders are located. Most of them attract large amounts of brackish seepage. This seepage not only contains salt, but also nutriënts. Without hydrological intervention, the waterquality in the area would suffer significantly from the brackish seepage. To prevent this, each year about 140 million cubic meter of water from the Markermeer, which equals a column of 20 cm, is let in at the river Vecht. This water is used to dilute the brackish water and flush it as soon as possible to the bigger parts of the watersystem like the Amsterdam-Rijncanal. However, this supply of a huge volume of water from the Markermeer is the reason that the water quality objectives, as set in the European Water Framework Directive, are not met in the area around the northern part of the river Vecht. Ecologically, this area needs local, fresh seepage from the hills of the Utrechtse Heuvelrug and not the foreign water from the Markermeer, which contains a lot of sulphate. Furthermore, the available amount of fresh water in the Markermeer is expected to become less due to the predicted climate change and the involved waterboards have agreed to reduce the intake from the Markermeer.

The PhD focusses on the following questions: Can the brackish groundwater be extracted by wells, to prevent the brackish seepage to reach the surface water system of the deep polder? Can this brackish groundwater be used as a new source for the drinking water supply for the city of Amsterdam? And if so, what should be done with the concentrate that is created with the purification of the brackish groundwater by the process of reverse osmosis? Can the concentrate be discharged via the sewer system? Can this concentrate be treated, diluted and discharged via a waste water treatment plant? What are the benefits, the costs and the risks of such a system?

For a comprehensive approach to the negative aspects of brackish seepage, also other ideas will be investigated. For example measures to lower the hydraulic conductivity of the toplayer of the deep polder areas. Or to limit the infiltration in the areas around the deep polders. Or to change the management of the surface water system, for example to push back the salt wedge at the northern part of the Amsterdam-Rhinecanal.

Because this research directly affects the interests of surface water, drinking water, groundwater, the sewer system and the purification of wastewater, it forms pre-eminently a water cycle project, which suits the strategy of Waternet.

The promotor of the PhD is prof.dr.ir. T.N. Olsthoorn. Other involved colleagues of Waternet are Lucas Smulders, Sanne Hillegers, Alice Fermont, René van der Aa, Maarten Ouboter, Jan Koedood, Joost Kappelhof, Kees van der Drift, Kees van der Lugt and Jan Peter van der Hoek. From the Technical University of Delft cooperation is found with Willem-Jan Zaadnoordijk, Mark Bakker, Bas Heijman, Luuk Rietveld and Amir Haidari. 


Frank holds a MSc in Hydrology at the Vrije Universiteit Amsterdam, which he has completed with one and a half year of courses at Wageningen University. In Amsterdam the focus was on groundwater, in Wageningen on surface water, and at both universities he studied water for quantity as well as quality. During this period, for an average of two months a year, fieldwork has been carried out in the Netherlands, Belgium, Luxembourg, Germany, France, Italy, Spain, Portugal and Israel.

In his master thesis Frank integrated gained knowledge and he coupled a computer program for surface water flow (Duflow) and for groundwater flow (MicroFEM). This thesis was nominated by the Vrije Universiteit for the ‘Escher prize’. This is an annual and national award for the best thesis in the discipline of Earth Science. His thesis was also nominated by the Technical University of Delft for the ‘Gijs Oskam prize’, awarded each two years to a young scientist in the field of drinking water technology.



Frank started his career with five years at Witteveen+Bos Consulting Engineers in Deventer, both in the surface water group and the groundwater group. He did many projects in the Netherlands, for example related to the widening of the river Maas near the city of Maastricht or the testing of a new dredging technique by Boskalis in the lake Ketelmeer. He worked also abroad, for example in Estonia and several countries in Central Europe, mostly in projects commissioned by the European Union.

Since 2007 Frank has worked as a researcher at Waternet. This is the merged oranisation of the waterboard Amstel, Gooi and Vecht, the Service for Surface Water and Sewerage Management of the city of Amsterdam, and the Amsterdam Water Supply. Waternet is the first and only governmental organisation in the Netherlands that manages the complete cycle of surface water, groundwater, drinking water, the sewerage system and wastewater. Waternet, started in 2006, is a relative young organisation, but its roots date back to 1307 when the oldest predecessor of the waterboard officially was founded, and to 1851 when the Amsterdam Water Supply started. Half of his time Frank spends as a resource hydrologist at the water supply part of Waternet, the other half is partioned between the rural and urban watermanagement.

Frank is also involved in several projects for World Waternet, for example in Surinam and Marocco, and for the Technical University of Delft in Romania.

Academic and others:

Each year Frank leads several excursions in the Amsterdam Water Supply Dunes for groups of students or interested colleagues from other drinking water companies.

Frank gave guestlectures at the Vrije Universiteit Amsterdam, the UNESCO-IHE Institute for water education in Delft, the Anton de Kom University of Surinam, Wageningen University, the University of Groningen, the University of Amsterdam and the Technical University of Civil Engineering in Bucharest.

Sometimes Frank acts as a member of the examination committee of the UNESCO-IHE Institute.

Together with C.J. Hemker, a short course about the use of PEST with MicroFEM was given at the Vrije Universiteit Amsterdam. Mary C. Hill was helped with three courses about model sensitivity analysis, data assessment, calibration and uncertainty evaluation. These courses were held in the cities of Utrecht in the Netherlands, Ostrava in the Czech Republic and Budapest in Hungary.

From 2007 to 2010 Frank was a member of the editoral staff of 'Stromingen', the scientific journal of the Dutch Hydrological Association.


Frank likes cooperating with ambitious, hard-working students, and he was involved in the supervision of the following master theses:

Fitsum Woldemeskel, A water balance in parts of the storage canals in the Amsterdam Water Supply Dunes, July 2009, Technical University of Delft

Heleen Kiela, Pumping test near the village of the Zilk, August 2009, University of Utrecht

David Haro Monteagudo, Swinging with SWI, a guide to implement the Modflow 2000 Sea Water intrusion package into the Dutch National Hydrological Instrument (NHI) with Matlab, August 2009, Technical University of Delft

Ruben Johannes Caljé, Future use of Aquifer Thermal Energy Storage below the historic centre of Amsterdam, January 2010, Technical University of Delft

Muriël M. Houdé, Cleaning a fifty year old drain in the Amsterdam Water Supply Dunes, February 2010, Technical University of Delft

Reinert Huseby Karlsen, Postaudit and automatic parameter estimation of a 1D reactive transport model of artificial recharge in the Amsterdam Water Supply Dunes, August 2010, Vrije Universiteit Amsterdam

Willem-Bart Bartels, Investigation of a possible leakage in the WRK-I-transport main, in a dyke made of peat near the village of Vinkeveen, August 2010, University of Utrecht

Beatriz de la Loma González, Evolution of the chemical compositon of injected Rhine water in the Amsterdam Water Supply Dunes by 3D reactive transport modelling, November 2010, Vrije Universiteit Amsterdam

Harmen W. van den Berg, The influence of ponds above the drains, on the proces of artificial recharge in the Amsterdam Water Supply Dunes, December 2010, Vrije Universiteit Amsterdam

Trude Rutgrink, Evaluation of the redesign of the Gagelpolder; vegetation, waterquality and - quantity in the nature reserve, January 2011, Vrije Universiteit Amsterdam

Robbert Martens, Subsurface extraction in the Amsterdam Water Supply Dunes; the hydrological part, May 2011, Technical University of Delft

Marcus J.H. van der Valk, A fresh-keeper for Noard Burgum, the future for a salinated well field?, June 2011, Technical University of Delft

Amir Haidari, Condition of drain 16; salt dilution test and measuring of the flow in different segments, December 2011, Technical University of Delft

Gemma Serra Prat, The effect of sub-oxic conditions on the removal of viruses with the use of sodium chloride and bacteriophages tracers in groundwater field experiments at the Amsterdam Water Supply Dunes, January 2012, Technical University of Catalonia

Ine Beyen, Comparison of the infiltration rate below reed and through the sludge layer in recharge ponds in the Amsterdam Water Supply Dunes, February 2012, Vrije Universiteit Amsterdam

Rob Tijsen, Intrusion of salt water in the Cottica river; a risk analysis for the future watersupply of the municipality of Moengo, Surinam, August 2012, Vrije Universiteit Amsterdam

Marieke de Goede, Subsurface extraction in the Amsterdam Water Supply Dunes; the design of a drinking water production proces that is adjusted to a subsurface extraction, December 2012, Technical University of Delft

Gert Mulder, Modelling the temperature gradient in the WRK-transport main resulting from a discharge of heat near Schiphol Airport, December 2012, Technical University of Delft

Kyra Hu-A-ng, Phosphoros removal Botshol, investigation to a possible groundwater flux through a peat layer, July 2013, University of Utrecht

Ermias Tseggai Berhe, Spatial analysis for energy from water in transport mains in the city of Amsterdam, calculations of the surface water system in the polder de Horstermeer and several other projects, October 2013, internship to gain Dutch working experience

Inez Caris, The influence of brackish groundwater seepage on the surface water quality in the Bovenste Blik, Naardermeer, January 2014, University of Amsterdam

Vince Kaandorp, Assessing the feasibility of deep well injection of brackish groundwater reverse osmosis concentrate with reactive transport modelling at the Zevenberg production plant of Brabant Water, May 2014, Vrije Universiteit Amsterdam

Coert Strikker, Groundwater modelling of the khettara area of Fezna-Jorf-Hannabou, Morocco, August 2014, Technical University of Delft


Frank Smits & Kick Hemker  (2004) Coupling Duflow-MicroFEM. Stromingen, volume 10/2, 2004; in Dutch.

F.J.C. Smits & C.J. Hemker  (2004) Modelling the interaction of surface water and groundwater flow by linking Duflow to MicroFEM. Abstract as a contribution to the FEM_MODFLOW conference in Karlovy Vary, Czech Republic.

Frank Smits & Arie Biesheuvel  (2005) A simple way of calibrating numerical groundwater models with PEST; the routine ‘multiply’. Stromingen, volume 11/3, 2005; in Dutch.

F.J.C. Smits, T.N. Olsthoorn & R.J. Caljé  (2012) Calibration of a density dependent model of a system for aquifer thermal energy storage, based on the measured data of a heat injection system. Abstract as a contribution to the 22nd Salt Water Intrusion meeting in Armação dos Búzios, Brazil.

R.H. Karlsen, F.J.C. Smits, P.J. Stuyfzand, T.N. Olsthoorn & B.M. van Breukelen  (2012) A post audit and inverse modeling in reactive transport: 50 years of artificial recharge in the Amsterdam Water Supply Dunes. Journal of Hydrology, 454–455 (2012) 7–25.

Frank Smits

PhD Researcher