Critical Zone Hydrology Group

Saline seepage

Supervisors and collaborators:

• P.J. Stuyfzand - VU University
• S. van der Zee - Wageningen University
• G. Oude Essink - Deltares

Duration: 5 years
Funding: Deltares Research Program

Research questions

In many deltaic areas, the groundwater is saline because of seawater intrusion and marine transgressions. In areas that lie below mean sea level saline groundwater may reach the surface by upward groundwater flow, which we define here as seepage. This leads to salinization of surface waters and shallow fresh groundwater bodies and makes the water unfit for irrigation, drinking water supply or industrial purposes. A future rise in sea level and climate change is expected to increase the seepage and salt loads to surface waters and reduce the availability of both fresh surface water and groundwater. Study area is the Netherlands. The objective of my PhD is to describe and quantify the main and most important processes / mechanisms of saline seepage in time and space. Looking at the fresh water availability of the Dutch delta, two important saline seepage related phenomena are observed and subject of research:

• Preferential saline seepage via boils in deep polders as main salinization mechanism;
• Floating thin rainwater lenses on top of seeping saline groundwater.

These two phenomena act in different regions which different characteristics (geohydrology, salinity, etc.). Preferential saline seepage occurs mainly in the deep polders with large hydraulic gradients, which are characterized by a moderate deep fresh-brackish interface (20 to 50 m). The objective is to describe and quantify the salinization processes by preferential seepage via boils. Rainwater lenses are important in areas with saline groundwater at shallow depth like the southwestern Dutch delta, i.e. 50 to 100% seawater is found at 1 to 5 meter depths. The objective is to characterize and quantify the mixing and dynamic behavior of these small lenses on top of saline seeping groundwater.

Publications

• Eeman, S., S. E. A. T. M. van der Zee, A. Leijnse, P. G. B. de Louw, and C. Maas (2012). Response to recharge variation of thin rainwater lenses and their mixing zone with underlying saline groundwater. Hydrology and Earth System Sciences , 16, pp. 3535-3549.
• Faneca Sànchez, M., Gunnink, J. L., van Baaren, E.S., Oude Essink, G. H. P., Siemon, B., Auken, E., Elderhorst, W. and P.G.B. de Louw (2012). Modelling climate change effects on a Dutch coastal groundwater system using airborne Electro Magnetic measurements. Hydrology and Earth System Sciences Discuss. , 9, 6135-6184.
• Pauw, P.S., Louw, P.G.B., de, Oude Essink, G.H.P. (2012). Groundwater salinization in the Wadden Sea area of the Netherlands; quantifying the effects of climate change, sea level rise and anthropogenic interferences, Netherlands Journal of Geosciences (in press).
• De Louw, P.G.B., Van Der Velde, Y., T. M. Van Der Zee, S.E.A. (2011). Quantifying water and salt fluxes in a lowland polder catchment dominated by boil seepage: A probabilistic end-member mixing approach. Hydrology and Earth System Sciences, 15 (7), pp. 2101-2117.
• De Louw, P.G.B., S. Eeman, B. Siemon, B. R. Voortman, J. Gunnink, E. S. van Baaren, and G. H. P. Oude Essink. (2011). Shallow rainwater lenses in deltaic areas with saline seepage. Hydrology and Earth System Sciences, 15, pp. 3659-3678.
• Van der Velde, Y., Rozemeijer, J.C., De Rooij, G.H., Van Geer, F.C., Torfs, P.J.J.F., De Louw, P.G.B. (2011). Improving catchment discharge predictions by inferring flow route contributions from a nested-scale monitoring and model setup. Hydrology and Earth System Sciences, 15 (3), pp. 913-930.
• De Louw, P.G.B., Oude Essink, G.H.P., Stuyfzand, P.J., van der Zee, S.E.A.T.M. (2010). Upward groundwater flow in boils as the dominant mechanism of salinization in deep polders, The Netherlands. Journal of Hydrology, 394 (3-4), pp. 494-506.
• Oude Essink, G.H.P., Van Baaren, E.S., De Louw, P.G.B. (2010). Effects of climate change on coastal groundwater systems: A modeling study in the Netherlands. Water Resources Research, 46 (10), art. no. W00F04, doi:10.1029/2009WR008719.