Natural saltwater upconing caused by the preferential groundwater discharge of boils is a key pro... more Natural saltwater upconing caused by the preferential groundwater discharge of boils is a key process in the salinization of Dutch deep polders. The factors controlling upconing by boil discharge and boil water salinities are poorly constrained and have not been previously documented. We addressed this knowledge gap by investigating upconing mechanisms using field measurements and numerical simulation s of simplified situations. Boils occur as conduits in the upper aquitard connecting the underlying aquifer to the surface and allowing groundwater to discharge at rates up to 100 m 3 d À1 with Cl concentrations up to 5 g L À1 . Boils are found as isolated features or clustered in small areas of 20-100 m 2 . Field observ ations show that preferential flow through boils creates localized and narrow saltwater upconing spikes, causing the elevated boil water salinities. Model ing results indicate that boil water in Dutch polders comprises mixtures of groundwater from a wide range of depths and salinities with larger contributions from shallower and less saline groundwat er than from the deeper and more saline water. Similar to previous numerical studies of pumping-in duced upconing, the numer ical results show that the most impo rtant factors controll ing the boil salinity in Dutch polders are boil discharge, the horizontal hydraulic conductivity of the aquifer, the depth of the transition zone and the salinity (or density) contrast within the aquifer. When boils are clustered, natural saltwater upconing is a function of the total discharge of a boil cluster, whereas the boil-to-boil salinity variations within a cluster are determined by the discharge of individual boils and their position relative to neighboring boils. Regional lateral flow significantly modifies flow patterns by dividing the groundwater flow system into a local boil system overlying the regional flow system. Despite this, regional flow has only a minor effect on the relative contributions of saline and fresh groundwater to boil discharge and thus on boil salinity as well.
The dodo Raphus cucullatus Linnaeus, 1758, an extinct and flightless, giant pigeon endemic to Mau... more The dodo Raphus cucullatus Linnaeus, 1758, an extinct and flightless, giant pigeon endemic to Mauritius, has fascinated people since its discovery, yet has remained surprisingly poorly known. Until the mid-19th century, almost all that was known about the dodo was based on illustrations and written accounts by 17th century mariners, often of questionable accuracy. Furthermore, only a few fragmentary remains of dodos collected prior to the bird's extinction exist. Our understanding of the dodo's anatomy was substantially enhanced by the discovery in 1865 of subfossil bones in a marsh called the Mare aux Songes, situated in southeastern Mauritius. However, no contextual information was recorded during early excavation efforts, and the majority of excavated material comprised larger dodo bones, almost all of which were unassociated. Here we present a modern interdisciplinary analysis of the Mare aux Songes, a 4200-year-old multitaxic vertebrate concentration Lagerst€ atte. Our analysis of the deposits at this site provides the first detailed overview of the ecosystem inhabited by the dodo. The interplay of climatic and geological conditions led to the exceptional preservation of the animal and associated plant remains at the Mare aux Songes and provides a window into the past ecosystem of Mauritius. This interdisciplinary research approach provides an ecological framework for the dodo, complementing insights on its anatomy derived from the only associated dodo skeletons known, both of which were collected by Etienne Thirioux and are the primary subject of this memoir.
Data belonging to Kaandorp et al., Transient travel time distributions and age-ranked storage-dis... more Data belonging to Kaandorp et al., Transient travel time distributions and age-ranked storage-discharge relationships of three lowland catchments. Submitted to Water Resources Research, December 2017.
Dit artikel beschrijft de ontwikkeling van de zoetzoutverdeling in het Nederlandse grondwater. De... more Dit artikel beschrijft de ontwikkeling van de zoetzoutverdeling in het Nederlandse grondwater. Deze verdeling is sterk bepaald door de paleogeografische ontwikkeling gedurende het Holoceen en kent een groot langetermijngeheugen. Er worden twee typen grondwatersystemen beschreven: het West-Nederland systeem, waar autonome verzilting en wellen sleutelbegrippen zijn, en het Zeeuwse systeem, waar drie typen zoetwaterlenzen worden besproken. We laten aan de hand van de FRESHEM-Zeeland-resultaten zien dat airborne-elektromagnetische meettechnieken zeer geschikt zijn voor het in beeld brengen van de zoet-zoutverdeling. Vervolgens wordt ingegaan op het modelleren van de initiele zoet-zoutverdeling, waarbij de combinatie van paleomodellering en gebruik van metingen een geschikte methode lijkt. De initiele zoet-zoutverdeling is een belangrijke modelparameter bij het voorspellen van toekomstige veranderingen van zoete grondwatervoorraden als gevolg van ingrepen, klimaatverandering en zeespiege...
Maaiveldafvoer is in Nederland slecht bekend. Om meer grip op dit verschijnsel te krijgen is in 2... more Maaiveldafvoer is in Nederland slecht bekend. Om meer grip op dit verschijnsel te krijgen is in 2014 en 2015 op een aantal percelen nabij Ootmarsum een eerste meetonderzoek uitgevoerd. De uitkomsten zijn meegenomen in een theoretische vervolgstudie omtrent maatgevende afvoeren in het werkgebied van Waterschap Vechtstromen. Dat heeft geresulteerd in een set kaarten die de (theoretische) maaiveldafvoer gebiedsdekkend duiden. Het is de bedoeling om de waarde van deze kaarten (en de gehanteerde methode) te toetsen met aanvullende veldproeven.
For the Province of Zeeland in the Netherlands, a 3D‐model for density‐dependent groundwater flow... more For the Province of Zeeland in the Netherlands, a 3D‐model for density‐dependent groundwater flow and coupled solute transport is developed to assess the impact of sea level rise and changing precipitation and evapotranspiration patterns on the freshening and salinisation processes of shallow groundwater systems. The model is used to determine feasible and robust adaptation or mitigation measures in the water system to secure the vulnerable fresh water resources in this low‐lying coastal zone. We will present the building of the complex 3D numerical model (15 million model cells), and with the focus on the determination of the initial chloride distribution. For this different types of (geophysical) techniques are combined with groundwater sampling data.
In zoute kwelgebieden zijn dunne regenwaterlenzen van groot belang voor de landbouw omdat ze vaak... more In zoute kwelgebieden zijn dunne regenwaterlenzen van groot belang voor de landbouw omdat ze vaak de enige zoetwaterbron zijn en voorkomen dat (te) zout kwelwater de wortelzone bereikt. Veldonderzoek in Zeeland heeft voor het eerst in beeld gebracht hoe deze lenzen er precies uitzien, hoe ze veranderen in de tijd en welke processen daarbij een rol spelen. De lenzen blijken erg kwetsbaar voor klimaatverandering. De opgedane systeemkennis maakt het mogelijk hiervoor mitigerende maatregelen te formuleren.
Weber, T., McPhee, M.J. and Anderssen, R.S. (eds) MODSIM2015, 21st International Congress on Modelling and Simulation, Nov 29, 2015
Local water storages can contribute significantly to meet regional demands for water and offer go... more Local water storages can contribute significantly to meet regional demands for water and offer governments a strategy for reducing or delaying investment in large-centralised water infrastructure. Local water storages include ponds, canals, drainage systems and subsurface aquifers. Augmentation of local water storages and determination of their regional feasibility is not fully understood. Cost-effectiveness, physical characteristics, interactions between measures and interactions with the national water system are of crucial importance here. Dutch national and regional water managers currently negotiate about water distribution and regional self-reliance. However, in the Dutch negotiation, the potential of local groundwater storage, as a way to overcome periods of drought, is generally underestimated. In this study, we assessed the potential of local groundwater storage measures, regarding technical storage capacity (in cubic meters (m 3)) and costs (euro/ha/year and euro/m 3), in a case study area in the Netherlands (Wieringen+Wieringermeerpolder) by means of a novel dynamic modelling method, called the Fresh Water Options Optimizer (FWOO). The first results of the FWOO method show that Wieringen+Wieringermeerpolder is able to store between 35 million cubic meters (Mm 3) and 80 Mm 3 with the seven local groundwater storage measures that are taken into account. This is 80% to 180% of the summer demand, based on a water demand of 200 mm during the growing season. The costs for the combination of measures in Wieringen+Wieringermeerpolder are between 0.10 euro/m 3 and 0.13 euro/m 3. The FWOO is not ready yet. Not all dynamics of augmenting local waters storage measures are (modelling wise) properly addressed. For example, temporal aspects of water supply and demand are not yet taken into account. Besides, preferences and needs of other water users (nature, industry, and urban areas) might lead to undiscovered options to store and reuse water. To inform regional water managers, efforts to compare the costs of local measures with centralized water storage and provision strategies are needed. Although the model is still under improvement, these first results open new perspectives on the potential of regional self-reliance and should be taken into account during negotiations around water distribution between national and regional water managers.
<p&amp... more <p>Surface runoff is widely recognized as playing an important and unique role in contaminant<br>transport from agricultural fields to the river system. Its quantification however is still<br>underdeveloped, especially in flat areas. Because micro-topography (< 10 cm) likely is an<br>important controlling factor in such landscapes, accurate predictions of the occurrence and<br>quantity of surface runoff are limited by a lack of high-quality data and/or computational power.<br>This project will explore the applicability of both conceptual (fill-and-spill) and state-of-the-art<br>physically based models to estimate surface runoff at the field scale. Laser technology will provide<br>high resolution surface topography data and direct measurements of surface runoff will aid in<br>validating the hydrologic models. The goal of this research is to use the results of the field study to<br>develop an efficient and accurate upscaling scheme, centred around a generic parameterization of<br>micro-topographic variability. This could support decision and policy making and contribute to<br>increasing the water quality of river systems.</p>
<p&amp... more <p>In large parts of Europe, the year 2018 is known as an extremely dry year. In the Netherlands this 2018 drought caused over 1 billion euros of economic damage to different sectors like agriculture, nature, industry, shipping, infrastructure and buildings. A large part of economic damage was due to extreme low groundwater levels and large soil moisture deficits. Many streams stopped flowing since groundwater levels were too low to feed the streams. The extreme low rainfall amount, in combination with above average high potential evaporation rates, caused a precipitation deficit of 300 mm in the growing season, which is normally less than 100 mm. In 2019, the year after, the spatial variability of precipitation in the Netherlands was high with only a precipitation deficit in the growing season of a few tens of millimeters in the low-lying western part of the Netherlands. However, in the higher sandy areas in the south and east part of the Netherlands, the precipitation deficit was again extreme and more than 240 mm. For the higher sandy areas this was the second dry year in a row and the question arose what the effect of two consecutive dry years on the water system was and how fast it may recover.</p><p>This question has been analyzed by applying an integrated nationwide groundwater and surface water model (De Lange et al., 2014). The model results showed that for the higher sandy areas, groundwater levels and stream discharges were even lower in the second than in the first dry year. In addition, the recovery period of the groundwater system after two extremely dry years was examined by simulating ten "normal" years with average precipitation and evaporation patterns following the two extremely dry years. The model results showed a large spatial variation in groundwater level recovery.  In the first recovery year groundwater levels increased for most of the area, except for the higher-lying sandy areas lacking any surface waters (ditches and streams), like the largest Dutch forest area, the Veluwe. In these slow-responding regional recharge areas, groundwater levels are still dropping. For the central part of the Veluwe, this dropping continues until the seventh recovery year.  The model results showed that two consecutive dry years have a large impact on the water system, and that full recovery of groundwater levels and stream discharges may take 2 to 4 years in most of the sandy areas, yet the recovery of the highest parts may take up to 7 to 8 years.</p><p> </p><p>De Lange, W.J., Prinsen, G.F., Hoogewoud, J.C., Veldhuizen, A.A., Verkaik, J., Oude Essink, G.H.P., Van Walsum, P.E.V., Delsman, J.R., Hunink, J.C., Massop, H.Th.L., Kroon T. (2014). An operational, multi-scale, multi-model system for consensus-based, integrated water management and policy analysis: The Netherlands Hydrological Instrument. Accepted for publication in Environmental Modelling & Software</p>
Peat oxidation in deep Dutch polders leads – in addition to subsidence - to the development of ne... more Peat oxidation in deep Dutch polders leads – in addition to subsidence - to the development of new saline boils, enhancing the salinization of these polders. This on-going process is studied in detail in the Middelburg-Tempelpolder. The objective of the study was to get more in-depth knowledge about this process and to assess it for the present situation and for future landscapes (after 10, 50, 100 and 500 years).
Nature area Rammegors, which has recently been transformed from a fresh inner-dyke nature area to... more Nature area Rammegors, which has recently been transformed from a fresh inner-dyke nature area to a salt tidal area. Due to this transformation, salt water is infiltrating in a fresh waterlens. This salinisation process is investigated in more detail by two- and three dimensional models together with mearsurements in the area. Zeeland project FRESHEM has provided detailed isohaline maps of the area and Deltares is making transient isohaline maps based on measurements made by an ERT-cable which is situated in Rammegors. These data has been and will be used to investigate which factors; bathymetry, lithology, tides or regional groundwater flow, will have the largest impact on the salinization process in Rammegors. This investigation shows that discretization size has an influence on the speed and spatial distribution of salt plumes. Lithology has the largest influence on the salinization process, followed by bathymetry. Spring and neap tides do differ from the normal tides situation o...
<p>Innovative, sustainable and cost-effective coastal protection solutions are requ... more <p>Innovative, sustainable and cost-effective coastal protection solutions are required to adapt to environmental change and enhance ecosystem functioning. Managed realignment is an example of an ecosystem engineering coastal management approach motivated by concerns about biological conservation and sea-level rise. It involves relocating the line of defense landward, thereby mimicking what would normally happen with marine environments during a period of sea-level rise. The retreat allows new salt marshes to develop offering a range of ecosystem services. Despite the ongoing execution of managed realignment projects in, amongst others, the UK, Germany, the Netherlands, Belgium and Spain, it remains unclear whether management realignment is able to deliver on the expected socio-economic and environmental benefits.</p> <p>Here we report on the short-term (0-4 years) development of physical and ecological processes of the Perkpolder managed realignment area in the Scheldt estuary, the Netherlands, following tidal restoration in 2015. The overarching goal of the Perkpolder project was to realize 75 hectares of low-dynamic tidal nature contributing to Natura2000 conservation goals for the Western Scheldt estuary as well as serving as a compensation measure for the extension of the navigation channel for the Antwerp harbor.</p> <p>The Perkpolder managed realignment is considered a unique opportunity to monitor and study the biotic and abiotic changes in an area transforming from a freshwater agricultural area to a tidal saline natural area. An interdisciplinary monitoring framework was set up to record the abiotic and biotic developments of the Perkpolder realignment area, particularly focusing on morphological changes, colonization of the new tidal area by benthic macrofauna and vegetation, and its function as foraging area for water birds. Also the groundwater system is studied and its effect on the surrounding agricultural land.</p> <p>A mitigation measure, called ‘SeepCat’, was installed on the border of the new tidal area and the agricultural land to protect the freshwater lens used by farmers for irrigation. The lens was expected to shrink by this local sea level rise. From the groundwater measurements, it was concluded that the SeepCat system was functioning well enough to compensate for the effects of the new tidal area.</p> <p>Using a Delft3D numerical model simulation, it was shown that the design of the morphological template has a large impact on the rates of morphological change. Additionally, the sediment import, estimated from SPM concentration and discharge measurements, varied strongly in time, and sediment was also being exported for a number of tides. Controlled laboratory experiments show that seedlings of pioneer marsh plant species survive best in a well-drained soil without sediment dynamics. Yet, seedlings can tolerate some moderate sediment dynamics. From a benthic community perspective, the development of the managed realignment Perkpolder is encouraging. A biologically active intertidal area has formed within a short time frame. Within 3 years, the benthic macroinfaunal community shows a development towards a community found on natural tidal mudflats and is expected to reach a stable community in years rather than decades. The area is also frequently visited by birds, which forage during low tide and rest on the surrounding dikes during high tide.</p>
Surface waters are under pressure of diffuse pollution from agricultural activities and groundwat... more Surface waters are under pressure of diffuse pollution from agricultural activities and groundwater is known to be a connection between the agricultural fields and streams. We calculated in-stream concentrations by coupling input curves for tritium, chloride and nitrate with dynamic groundwater travel time distributions (TTDs) derived from a distributed, transient 3D groundwater flow model using forward particle tracking. We tested our approach in a lowland stream and found that the variable contribution of different groundwater flow paths to stream water quality reasonably explained the majority of longterm and seasonal variation in the measured stream nitrate concentrations. A sensitivity analysis was done to study the breakthrough of agricultural nitrate and it was found that an unsaturated zone, increased mean travel time and a longer distance between agricultural fields and stream cause a lag in the breakthrough of agricultural solutes. Similarly, the recovery of concentrations after measures that aim to reduce the solute inputs is determined by these parameters, with combinations of slow reduction rates and long MTT tending to result in considerable lag times after start of the reductions. We labelled the part of the catchment area where the seepage water infiltrated that contributes to stream discharge at a certain moment in time the 'groundwater contributing area'. This groundwater contributing area was shown to increase and shrink based on wetness conditions within the catchment. Especially the location of agricultural fields in the groundwater contributing area in relation to the catchments' drainage network was found to be an important factor that largely governs the travel times of the agricultural pollutants. We conclude that groundwater functions as a buffer on the effect of agricultural pollution, by distributing water in time and space and making it possible for different waters to mix.
Groundwater seepage influences the temperature of streams and rivers by providing a relatively co... more Groundwater seepage influences the temperature of streams and rivers by providing a relatively cool input in summer and warm input in winter. Because of this, groundwater seepage can be a determining factor in the provision of suitable water temperatures for aquatic biota. Climate warming affects stream and groundwater temperatures, and changes the thermal characteristics of streams leading to the potential disappearance of habitats. In this study the importance of groundwater for the temperature of two Dutch lowland streams and its possible role in mitigating the effects of climate change was determined by combining field measurements and a modelling experiment. Stream temperature measurements using fibre optic cables (FO-DTS) and sampling of 222 Rn were done to map localized groundwater inflow. Several springs and seepage 'hot-spots' were located which buffered the water temperature in summer and winter. A stream temperature model was constructed and calibrated using the FO-DTSmeasurements to quantify the energy fluxes acting on stream water. This way, the contribution to the stream thermal budget of direct solar radiation, air temperature and seepage were separated. The model was then used to simulate the effects of changes in shading, groundwater seepage and climate. Shading was shown to be an important control on summer temperature maxima. Groundwater seepage seemed to buffer the effect of climate warming, potentially making groundwater dominated streams more climate robust. Protecting groundwater resources in a changing climate is important for the survival of aquatic species in groundwater-fed systems, as groundwater seepage both sustains flow and buffers temperature extremes.
Natural saltwater upconing caused by the preferential groundwater discharge of boils is a key pro... more Natural saltwater upconing caused by the preferential groundwater discharge of boils is a key process in the salinization of Dutch deep polders. The factors controlling upconing by boil discharge and boil water salinities are poorly constrained and have not been previously documented. We addressed this knowledge gap by investigating upconing mechanisms using field measurements and numerical simulation s of simplified situations. Boils occur as conduits in the upper aquitard connecting the underlying aquifer to the surface and allowing groundwater to discharge at rates up to 100 m 3 d À1 with Cl concentrations up to 5 g L À1 . Boils are found as isolated features or clustered in small areas of 20-100 m 2 . Field observ ations show that preferential flow through boils creates localized and narrow saltwater upconing spikes, causing the elevated boil water salinities. Model ing results indicate that boil water in Dutch polders comprises mixtures of groundwater from a wide range of depths and salinities with larger contributions from shallower and less saline groundwat er than from the deeper and more saline water. Similar to previous numerical studies of pumping-in duced upconing, the numer ical results show that the most impo rtant factors controll ing the boil salinity in Dutch polders are boil discharge, the horizontal hydraulic conductivity of the aquifer, the depth of the transition zone and the salinity (or density) contrast within the aquifer. When boils are clustered, natural saltwater upconing is a function of the total discharge of a boil cluster, whereas the boil-to-boil salinity variations within a cluster are determined by the discharge of individual boils and their position relative to neighboring boils. Regional lateral flow significantly modifies flow patterns by dividing the groundwater flow system into a local boil system overlying the regional flow system. Despite this, regional flow has only a minor effect on the relative contributions of saline and fresh groundwater to boil discharge and thus on boil salinity as well.
The dodo Raphus cucullatus Linnaeus, 1758, an extinct and flightless, giant pigeon endemic to Mau... more The dodo Raphus cucullatus Linnaeus, 1758, an extinct and flightless, giant pigeon endemic to Mauritius, has fascinated people since its discovery, yet has remained surprisingly poorly known. Until the mid-19th century, almost all that was known about the dodo was based on illustrations and written accounts by 17th century mariners, often of questionable accuracy. Furthermore, only a few fragmentary remains of dodos collected prior to the bird's extinction exist. Our understanding of the dodo's anatomy was substantially enhanced by the discovery in 1865 of subfossil bones in a marsh called the Mare aux Songes, situated in southeastern Mauritius. However, no contextual information was recorded during early excavation efforts, and the majority of excavated material comprised larger dodo bones, almost all of which were unassociated. Here we present a modern interdisciplinary analysis of the Mare aux Songes, a 4200-year-old multitaxic vertebrate concentration Lagerst€ atte. Our analysis of the deposits at this site provides the first detailed overview of the ecosystem inhabited by the dodo. The interplay of climatic and geological conditions led to the exceptional preservation of the animal and associated plant remains at the Mare aux Songes and provides a window into the past ecosystem of Mauritius. This interdisciplinary research approach provides an ecological framework for the dodo, complementing insights on its anatomy derived from the only associated dodo skeletons known, both of which were collected by Etienne Thirioux and are the primary subject of this memoir.
Data belonging to Kaandorp et al., Transient travel time distributions and age-ranked storage-dis... more Data belonging to Kaandorp et al., Transient travel time distributions and age-ranked storage-discharge relationships of three lowland catchments. Submitted to Water Resources Research, December 2017.
Dit artikel beschrijft de ontwikkeling van de zoetzoutverdeling in het Nederlandse grondwater. De... more Dit artikel beschrijft de ontwikkeling van de zoetzoutverdeling in het Nederlandse grondwater. Deze verdeling is sterk bepaald door de paleogeografische ontwikkeling gedurende het Holoceen en kent een groot langetermijngeheugen. Er worden twee typen grondwatersystemen beschreven: het West-Nederland systeem, waar autonome verzilting en wellen sleutelbegrippen zijn, en het Zeeuwse systeem, waar drie typen zoetwaterlenzen worden besproken. We laten aan de hand van de FRESHEM-Zeeland-resultaten zien dat airborne-elektromagnetische meettechnieken zeer geschikt zijn voor het in beeld brengen van de zoet-zoutverdeling. Vervolgens wordt ingegaan op het modelleren van de initiele zoet-zoutverdeling, waarbij de combinatie van paleomodellering en gebruik van metingen een geschikte methode lijkt. De initiele zoet-zoutverdeling is een belangrijke modelparameter bij het voorspellen van toekomstige veranderingen van zoete grondwatervoorraden als gevolg van ingrepen, klimaatverandering en zeespiege...
Maaiveldafvoer is in Nederland slecht bekend. Om meer grip op dit verschijnsel te krijgen is in 2... more Maaiveldafvoer is in Nederland slecht bekend. Om meer grip op dit verschijnsel te krijgen is in 2014 en 2015 op een aantal percelen nabij Ootmarsum een eerste meetonderzoek uitgevoerd. De uitkomsten zijn meegenomen in een theoretische vervolgstudie omtrent maatgevende afvoeren in het werkgebied van Waterschap Vechtstromen. Dat heeft geresulteerd in een set kaarten die de (theoretische) maaiveldafvoer gebiedsdekkend duiden. Het is de bedoeling om de waarde van deze kaarten (en de gehanteerde methode) te toetsen met aanvullende veldproeven.
For the Province of Zeeland in the Netherlands, a 3D‐model for density‐dependent groundwater flow... more For the Province of Zeeland in the Netherlands, a 3D‐model for density‐dependent groundwater flow and coupled solute transport is developed to assess the impact of sea level rise and changing precipitation and evapotranspiration patterns on the freshening and salinisation processes of shallow groundwater systems. The model is used to determine feasible and robust adaptation or mitigation measures in the water system to secure the vulnerable fresh water resources in this low‐lying coastal zone. We will present the building of the complex 3D numerical model (15 million model cells), and with the focus on the determination of the initial chloride distribution. For this different types of (geophysical) techniques are combined with groundwater sampling data.
In zoute kwelgebieden zijn dunne regenwaterlenzen van groot belang voor de landbouw omdat ze vaak... more In zoute kwelgebieden zijn dunne regenwaterlenzen van groot belang voor de landbouw omdat ze vaak de enige zoetwaterbron zijn en voorkomen dat (te) zout kwelwater de wortelzone bereikt. Veldonderzoek in Zeeland heeft voor het eerst in beeld gebracht hoe deze lenzen er precies uitzien, hoe ze veranderen in de tijd en welke processen daarbij een rol spelen. De lenzen blijken erg kwetsbaar voor klimaatverandering. De opgedane systeemkennis maakt het mogelijk hiervoor mitigerende maatregelen te formuleren.
Weber, T., McPhee, M.J. and Anderssen, R.S. (eds) MODSIM2015, 21st International Congress on Modelling and Simulation, Nov 29, 2015
Local water storages can contribute significantly to meet regional demands for water and offer go... more Local water storages can contribute significantly to meet regional demands for water and offer governments a strategy for reducing or delaying investment in large-centralised water infrastructure. Local water storages include ponds, canals, drainage systems and subsurface aquifers. Augmentation of local water storages and determination of their regional feasibility is not fully understood. Cost-effectiveness, physical characteristics, interactions between measures and interactions with the national water system are of crucial importance here. Dutch national and regional water managers currently negotiate about water distribution and regional self-reliance. However, in the Dutch negotiation, the potential of local groundwater storage, as a way to overcome periods of drought, is generally underestimated. In this study, we assessed the potential of local groundwater storage measures, regarding technical storage capacity (in cubic meters (m 3)) and costs (euro/ha/year and euro/m 3), in a case study area in the Netherlands (Wieringen+Wieringermeerpolder) by means of a novel dynamic modelling method, called the Fresh Water Options Optimizer (FWOO). The first results of the FWOO method show that Wieringen+Wieringermeerpolder is able to store between 35 million cubic meters (Mm 3) and 80 Mm 3 with the seven local groundwater storage measures that are taken into account. This is 80% to 180% of the summer demand, based on a water demand of 200 mm during the growing season. The costs for the combination of measures in Wieringen+Wieringermeerpolder are between 0.10 euro/m 3 and 0.13 euro/m 3. The FWOO is not ready yet. Not all dynamics of augmenting local waters storage measures are (modelling wise) properly addressed. For example, temporal aspects of water supply and demand are not yet taken into account. Besides, preferences and needs of other water users (nature, industry, and urban areas) might lead to undiscovered options to store and reuse water. To inform regional water managers, efforts to compare the costs of local measures with centralized water storage and provision strategies are needed. Although the model is still under improvement, these first results open new perspectives on the potential of regional self-reliance and should be taken into account during negotiations around water distribution between national and regional water managers.
<p&amp... more <p>Surface runoff is widely recognized as playing an important and unique role in contaminant<br>transport from agricultural fields to the river system. Its quantification however is still<br>underdeveloped, especially in flat areas. Because micro-topography (< 10 cm) likely is an<br>important controlling factor in such landscapes, accurate predictions of the occurrence and<br>quantity of surface runoff are limited by a lack of high-quality data and/or computational power.<br>This project will explore the applicability of both conceptual (fill-and-spill) and state-of-the-art<br>physically based models to estimate surface runoff at the field scale. Laser technology will provide<br>high resolution surface topography data and direct measurements of surface runoff will aid in<br>validating the hydrologic models. The goal of this research is to use the results of the field study to<br>develop an efficient and accurate upscaling scheme, centred around a generic parameterization of<br>micro-topographic variability. This could support decision and policy making and contribute to<br>increasing the water quality of river systems.</p>
<p&amp... more <p>In large parts of Europe, the year 2018 is known as an extremely dry year. In the Netherlands this 2018 drought caused over 1 billion euros of economic damage to different sectors like agriculture, nature, industry, shipping, infrastructure and buildings. A large part of economic damage was due to extreme low groundwater levels and large soil moisture deficits. Many streams stopped flowing since groundwater levels were too low to feed the streams. The extreme low rainfall amount, in combination with above average high potential evaporation rates, caused a precipitation deficit of 300 mm in the growing season, which is normally less than 100 mm. In 2019, the year after, the spatial variability of precipitation in the Netherlands was high with only a precipitation deficit in the growing season of a few tens of millimeters in the low-lying western part of the Netherlands. However, in the higher sandy areas in the south and east part of the Netherlands, the precipitation deficit was again extreme and more than 240 mm. For the higher sandy areas this was the second dry year in a row and the question arose what the effect of two consecutive dry years on the water system was and how fast it may recover.</p><p>This question has been analyzed by applying an integrated nationwide groundwater and surface water model (De Lange et al., 2014). The model results showed that for the higher sandy areas, groundwater levels and stream discharges were even lower in the second than in the first dry year. In addition, the recovery period of the groundwater system after two extremely dry years was examined by simulating ten "normal" years with average precipitation and evaporation patterns following the two extremely dry years. The model results showed a large spatial variation in groundwater level recovery.  In the first recovery year groundwater levels increased for most of the area, except for the higher-lying sandy areas lacking any surface waters (ditches and streams), like the largest Dutch forest area, the Veluwe. In these slow-responding regional recharge areas, groundwater levels are still dropping. For the central part of the Veluwe, this dropping continues until the seventh recovery year.  The model results showed that two consecutive dry years have a large impact on the water system, and that full recovery of groundwater levels and stream discharges may take 2 to 4 years in most of the sandy areas, yet the recovery of the highest parts may take up to 7 to 8 years.</p><p> </p><p>De Lange, W.J., Prinsen, G.F., Hoogewoud, J.C., Veldhuizen, A.A., Verkaik, J., Oude Essink, G.H.P., Van Walsum, P.E.V., Delsman, J.R., Hunink, J.C., Massop, H.Th.L., Kroon T. (2014). An operational, multi-scale, multi-model system for consensus-based, integrated water management and policy analysis: The Netherlands Hydrological Instrument. Accepted for publication in Environmental Modelling & Software</p>
Peat oxidation in deep Dutch polders leads – in addition to subsidence - to the development of ne... more Peat oxidation in deep Dutch polders leads – in addition to subsidence - to the development of new saline boils, enhancing the salinization of these polders. This on-going process is studied in detail in the Middelburg-Tempelpolder. The objective of the study was to get more in-depth knowledge about this process and to assess it for the present situation and for future landscapes (after 10, 50, 100 and 500 years).
Nature area Rammegors, which has recently been transformed from a fresh inner-dyke nature area to... more Nature area Rammegors, which has recently been transformed from a fresh inner-dyke nature area to a salt tidal area. Due to this transformation, salt water is infiltrating in a fresh waterlens. This salinisation process is investigated in more detail by two- and three dimensional models together with mearsurements in the area. Zeeland project FRESHEM has provided detailed isohaline maps of the area and Deltares is making transient isohaline maps based on measurements made by an ERT-cable which is situated in Rammegors. These data has been and will be used to investigate which factors; bathymetry, lithology, tides or regional groundwater flow, will have the largest impact on the salinization process in Rammegors. This investigation shows that discretization size has an influence on the speed and spatial distribution of salt plumes. Lithology has the largest influence on the salinization process, followed by bathymetry. Spring and neap tides do differ from the normal tides situation o...
<p>Innovative, sustainable and cost-effective coastal protection solutions are requ... more <p>Innovative, sustainable and cost-effective coastal protection solutions are required to adapt to environmental change and enhance ecosystem functioning. Managed realignment is an example of an ecosystem engineering coastal management approach motivated by concerns about biological conservation and sea-level rise. It involves relocating the line of defense landward, thereby mimicking what would normally happen with marine environments during a period of sea-level rise. The retreat allows new salt marshes to develop offering a range of ecosystem services. Despite the ongoing execution of managed realignment projects in, amongst others, the UK, Germany, the Netherlands, Belgium and Spain, it remains unclear whether management realignment is able to deliver on the expected socio-economic and environmental benefits.</p> <p>Here we report on the short-term (0-4 years) development of physical and ecological processes of the Perkpolder managed realignment area in the Scheldt estuary, the Netherlands, following tidal restoration in 2015. The overarching goal of the Perkpolder project was to realize 75 hectares of low-dynamic tidal nature contributing to Natura2000 conservation goals for the Western Scheldt estuary as well as serving as a compensation measure for the extension of the navigation channel for the Antwerp harbor.</p> <p>The Perkpolder managed realignment is considered a unique opportunity to monitor and study the biotic and abiotic changes in an area transforming from a freshwater agricultural area to a tidal saline natural area. An interdisciplinary monitoring framework was set up to record the abiotic and biotic developments of the Perkpolder realignment area, particularly focusing on morphological changes, colonization of the new tidal area by benthic macrofauna and vegetation, and its function as foraging area for water birds. Also the groundwater system is studied and its effect on the surrounding agricultural land.</p> <p>A mitigation measure, called ‘SeepCat’, was installed on the border of the new tidal area and the agricultural land to protect the freshwater lens used by farmers for irrigation. The lens was expected to shrink by this local sea level rise. From the groundwater measurements, it was concluded that the SeepCat system was functioning well enough to compensate for the effects of the new tidal area.</p> <p>Using a Delft3D numerical model simulation, it was shown that the design of the morphological template has a large impact on the rates of morphological change. Additionally, the sediment import, estimated from SPM concentration and discharge measurements, varied strongly in time, and sediment was also being exported for a number of tides. Controlled laboratory experiments show that seedlings of pioneer marsh plant species survive best in a well-drained soil without sediment dynamics. Yet, seedlings can tolerate some moderate sediment dynamics. From a benthic community perspective, the development of the managed realignment Perkpolder is encouraging. A biologically active intertidal area has formed within a short time frame. Within 3 years, the benthic macroinfaunal community shows a development towards a community found on natural tidal mudflats and is expected to reach a stable community in years rather than decades. The area is also frequently visited by birds, which forage during low tide and rest on the surrounding dikes during high tide.</p>
Surface waters are under pressure of diffuse pollution from agricultural activities and groundwat... more Surface waters are under pressure of diffuse pollution from agricultural activities and groundwater is known to be a connection between the agricultural fields and streams. We calculated in-stream concentrations by coupling input curves for tritium, chloride and nitrate with dynamic groundwater travel time distributions (TTDs) derived from a distributed, transient 3D groundwater flow model using forward particle tracking. We tested our approach in a lowland stream and found that the variable contribution of different groundwater flow paths to stream water quality reasonably explained the majority of longterm and seasonal variation in the measured stream nitrate concentrations. A sensitivity analysis was done to study the breakthrough of agricultural nitrate and it was found that an unsaturated zone, increased mean travel time and a longer distance between agricultural fields and stream cause a lag in the breakthrough of agricultural solutes. Similarly, the recovery of concentrations after measures that aim to reduce the solute inputs is determined by these parameters, with combinations of slow reduction rates and long MTT tending to result in considerable lag times after start of the reductions. We labelled the part of the catchment area where the seepage water infiltrated that contributes to stream discharge at a certain moment in time the 'groundwater contributing area'. This groundwater contributing area was shown to increase and shrink based on wetness conditions within the catchment. Especially the location of agricultural fields in the groundwater contributing area in relation to the catchments' drainage network was found to be an important factor that largely governs the travel times of the agricultural pollutants. We conclude that groundwater functions as a buffer on the effect of agricultural pollution, by distributing water in time and space and making it possible for different waters to mix.
Groundwater seepage influences the temperature of streams and rivers by providing a relatively co... more Groundwater seepage influences the temperature of streams and rivers by providing a relatively cool input in summer and warm input in winter. Because of this, groundwater seepage can be a determining factor in the provision of suitable water temperatures for aquatic biota. Climate warming affects stream and groundwater temperatures, and changes the thermal characteristics of streams leading to the potential disappearance of habitats. In this study the importance of groundwater for the temperature of two Dutch lowland streams and its possible role in mitigating the effects of climate change was determined by combining field measurements and a modelling experiment. Stream temperature measurements using fibre optic cables (FO-DTS) and sampling of 222 Rn were done to map localized groundwater inflow. Several springs and seepage 'hot-spots' were located which buffered the water temperature in summer and winter. A stream temperature model was constructed and calibrated using the FO-DTSmeasurements to quantify the energy fluxes acting on stream water. This way, the contribution to the stream thermal budget of direct solar radiation, air temperature and seepage were separated. The model was then used to simulate the effects of changes in shading, groundwater seepage and climate. Shading was shown to be an important control on summer temperature maxima. Groundwater seepage seemed to buffer the effect of climate warming, potentially making groundwater dominated streams more climate robust. Protecting groundwater resources in a changing climate is important for the survival of aquatic species in groundwater-fed systems, as groundwater seepage both sustains flow and buffers temperature extremes.
Uploads
Papers by Perry Louw