Maatregelen om regenwaterlenzen in zoute kwelgebieden robuuster te maken tegen klimaatverandering.

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1 PROJECTVOORSTEL AIO UNIVERSITEIT WAGENINGEN 1 LEERSTOELGROEP: Soil physics, ecohydrology and groundwater (SEG)management 1. PROJECTLEIDER/ PROMOTOR S.E.A.T.M. van der Zee 2. PROJECTTITEL Maatregelen om regenwaterlenzen in zoute kwelgebieden robuuster te maken tegen klimaatverandering. 3. ENGELSE TITEL Increasing the robustness and flexibility of freshwater lenses in saline seepage regions under climate stress. Het project wordt ondergebracht bij: 4 Naam Onderzoekschool: WIMEK/SENSE 5a. Het project wordt (deels) buiten Nederland uitgevoerd, nl. in: b. Is het project gericht op ontwikkelingssamenwerking? NEE 6a DIERPROEVEN: Worden in het onderzoek gewervelde dieren gebruikt? 6b ETHISCHE TOETSING: Is op dit onderzoek de besluitvorming omtrent ethische toetsing van biotechnologisch onderzoek van toepassing? NEE NEE 7. SAMENSTELLING PROJECTGROEP EN GEPLANDE TIJDSBESTEDING Naam + titel WP/OBP ten laste van/subsidiënt uren per week Pieter S. Pauw, MSc. AIO WUR 1 / Deltares 38 Prof. Dr. S.E.A.T.M. van der Zee Soil Physics/stochastic hydr. WUR 2 Dr. Ir. G.H.P. Oude Essink Geohydrology Deltares 4 Prof. Dr. Ir. Toon Leijnse Groundwater quality WUR p.m. Drs. P.G.B. De Louw Geohydrology Deltares p.m. 8. SAMENWERKING: met welke organisaties buiten de LU wordt in het kader van dit project samengewerkt? Nederland -- andere universiteiten: VU, TUD -- instituten, proefstations: Deltares, KWR Buitenlandse universiteiten en organisaties: Britih Geological Survey, USGS, NCGRT 1 Wageningen University and Research centre

2 9. SAMENVATTING van de PROBLEEM- en DOELSTELLING 2 A. History and backgrounds The diminishing availability of fresh groundwater reserves is a worldwide problem, mainly caused by anthropogenic activities that lead to overexploitation and contamination of aquifers. Sealevel rise, climate change, population growth and decreasing surface water quantity and quality will exacerbate this problem in the future. In coastal areas, these factors are most pronounced due to the risk of salt water intrusion into the fresh aquifers (Oude Essink et al. 2010). This research deals with freshwater availability in the coastal plain of western Netherlands, where large areas are at present situated several meters below mean sea level. Two ongoing processes of anthropogenic origin, taking place for nearly a millennium, have caused this situation. The first drainage of peaty and clayey soil by digging channels and building dikes is a slow and continuous process, leading to land subsidence by peat oxidation as well as compaction and shrinkage of clay. The largest land subsidence of this kind occurred in the western and northern parts of the Netherlands. The second process land reclamation resulted in a relatively abrupt change in the land surface level, creating the well-known Dutch polders. Drainage by tile drains and ditch networks make agricultural activities possible here. In general, the salinity of the water in the underlying aquifers is brackish to saline due to Holocene transgressions. The often higher hydraulic head than the controlled water level in the polder gives rise to saline seepage in polders. Despite this salinization process in polders, agricultural activities are being practiced rather intensively. Crops can take up low-salinity water from shallow freshwater reserves, formed by the precipitation excess. In a hypothetical steady state situation, precipitation excess, mixing processes at the fresh-saline interface due to saline seepage and discharge to the ditches form a dynamic equilibrium. Between two drainage components in vertical cross section (ditches or tile drains), the freshwater volume has the shape of a lens (Eeman et al. 2011). Although in reality the shape can be more complex (for instance in case of a heterogeneous subsurface, or when multiple drains are considered), shallow freshwater lenses in this document denote the shallow freshwater reserves in polder areas. Salinization processes can threaten agricultural activities. Due to seasonal changes in precipitation, evapotranspiration and ditch water level, the shallow freshwater lens has not a stable shape throughout the year. In winter, evapotranspiration is low and the freshwater lens expands. In summer, evapotranspiration is higher causing the freshwater lens to shrink. In areas where saline seepage is severe, the saline groundwater can enter the root zone in summer. This can lead to crop damage. A second, indirect problem arises due to surface water salinization. As a result, water in ditches is not suitable to serve as irrigation water in summer. During summer droughts, crops often need irrigation water to prevent yield loss. A conventional strategy in the Netherlands to reduce surface water salinity is to use large amounts of fresh surface water from the rivers Rhine and Meuse, in order to dilute the water in the ditches and make irrigation possible. This conventional strategy may not be robust as river discharges become more erratic, salt water wedge from the sea intrudes further upstream in rivers, water demand intensifies in drier growing seasons and saline groundwater seepage in polders increases. In some areas in the Western Netherlands phreatic groundwater can function as an additional source of irrigation water. Beneath the sandy, higher elevated areas in the Western Netherlands larger freshwater lenses have formed by the precipitation excess. In fossil sandy creeks in the province of Zeeland the vertical extent of this freshwater lens is 5 25 m. In the coastal dune area of the Western Netherlands over 100 m thick freshwater lenses can be encountered. Here, artificial infiltration takes place and large amounts of water are extracted for a wide range of anthropogenic purposes. In summer, when the water demand is high, water cannot be guaranteed because over-exploitation from these larger freshwater lenses may lead to salt water intrusion. Moreover, it is unclear whether or not they can cope with ongoing (sustainable) extraction rates under changing climate and socio-economical conditions. As freshwater demand is expected to increase in the future there is a growing need for measures that make the freshwater lenses more robust in order to minimize the reliance of external freshwater supply under saline and drought conditions. The general aim of this research is to extrapolate the current knowledge of salt water intrusion into shallow freshwater lenses from local to regional scale and to increase the freshwater availability from larger freshwater lenses. Although these aims are amplified on the situation in the Western Netherlands, the outcome of the research is believed to be of practical use in many other similar coastal areas in the world. Examples are the deltas of the Po (Italy), Mekong (Vietnam) and Nile (Egypt). The research is carried out within the Knowledge for Climate Program. It partially succeeds the Project Salinisation and freshening of phreatic groundwaters in the Province of Zeeland. Regarding the spatio-temporal characteristics of shallow freshwater lenses, this research and can be considered as an extension of two other PhD-studies (Eeman (WUR) and de Louw (Deltares/WUR/VU Amsterdam), where the presence and behavior of shallow fresh groundwater in areas with saline seepage under present conditions is being studied in detail. Regarding the shallow freshwater lens this research is more focused on adaptation strategies and upscaling local processes to a regional and national level. The research shows strong links with ongoing research on fresh-salt water relations within various projects and programs such as the Leven met Water BSIK programme Leven met Zout Water project; the project Salinisation and freshening of phreatic groundwater in the Province of Zeeland ; the Interreg projects Cliwat (on determining the effects of climate change on groundwater systems and through this on surface water and water supply, Climate Proof Areas and Scaldwin; the KfC project Demand and supply of fresh water in the South-western part of the Netherlands : an exploratory investigation (viz. Meta-studie Zuidwestelijke Delta) ; the Waterhouderij in the Province of Zeeland (WINN project); and the EU Water supply and sanitation Technology Platform Pilot Programme Mitigation of Water Stress in Coastal Zones. The research is subdivided according to the scale of the freshwater lenses (viz. shallow freshwater lenses, freshwater lenses within fossil sandy creeks and within the coastal dune area):

3 3 Shallow freshwater lens The ongoing research of Eeman and de Louw focuses on the spatiotemporal characteristics of shallow freshwater lenses. Numerical models involving density dependent groundwater flow and solute transport are used to simulate the processes on this scale (Eeman et al., 2011, De Louw in prep.). The modeling of such systems is however commonly restricted to individual agricultural parcels, or individual cross section. Larger and therefore coarser discretized models like the Netherlands Hydrological modeling Instrument (NHI) also exist, but attempt to simulate other processes. Although a model of this scale clearly cannot simulate the locale scale processes, it can model transient groundwater flow system processes on a larger (time)scale that influence the shallow freshwater lens, like saline seepage. Fine scale models attempting to model future saline intrusion into shallow freshwater lenses always need a boundary condition, which accounts for a change in saline seepage in the future. This research will provide insight into the various levels of accuracy at various degrees of spatial discretization (cell size) of simulating freshwater lenses. Fossil sandy creeks International research on abstraction strategies and aquifer storage and recovery (ASR) techniques in freshwater lenses on the scale of fossil sandy creeks is surprisingly scarce. Considerable research in the Netherlands has however been conducted in the province of Zeeland. In the period , the Commission on Water control and desalinization (Ontzilting, in Dutch) (CWO) coordinated research on the localization, artificial storage and extraction possibilities of freshwater stored within sandy creeks using computer models, analytical solutions and field investigations ((van Meerten 1986), (Werkgroep Kwelschermstudie 1988), Vermaas 1988)). The field investigations showed that artificial infiltration by vertical wells has a low efficiency. This was due to high maintenance costs due to chemical clogging and the risk of upconing of salt groundwater. Numerical models and analytical solutions showed that a considerable higher efficiency is obtained when the filter length and the distance between the wells decrease. Therefore, horizontal wells are used nowadays to extract water from fossil sandy creeks. Users (farmers) are allowed to abstract 3000 m 3 groundwater per month and in total 8000 m 3 per year, provided that the interface is lower than 15 m from the surface. Many small fossil sandy creeks are however found in the province of Zeeland and have interfaces less than 15 m depth. In order to increase the freshwater supply from fossil sandy creeks, optimal abstraction strategies are needed for the whole range of fossil sandy creek dimensions. Coastal dune area In order to combat flood risk due to sealevel rise, the Sustainable Coastal Development Committee (Deltacommissie) advised the Dutch government in 2008 to increase the sediment nourishments beyond the necessary demand for shoreline preservation. With this additional amount, about 40 million m 3 sediment per year, a shoreline progradation of about 1 km in 100 years could be realized (Deltacommissie, 2008). This will increase the freshwater lens of the coastal dune area, because the natural recharge area extends seaward. The hydrological impacts of such a shoreline progradation will be investigated, with the emphasis on the formation time of a seaward extended freshwater lens. B. Objectives The specific objectives of this research are: I: Shallow freshwater lens - To investigate how the grid cell size influences the accuracy of (finite difference) numerical models that simulate salt water intrusion into shallow freshwater lenses. - To quantify this salt water intrusion into shallow freshwater lenses in the future, on a regional/national scale, including effects of possible countermeasures to increasing their robustness. II: Freshwater stored in fossil sandy creeks - To quantify an optimal safe yield from fossil sandy creeks of various dimensions, on a regional scale (Zeeland), now and in the future. - To investigate whether an optimal freshwater supply from fossil sandy creeks is sufficient for the irrigation demand of agriculture in a region. - To investigate whether artificial infiltration in fossil sandy creeks by means of horizontal wells can be feasible. III: Coastal dune area - To investigate the influence of land reclamation on the (seaward) extension of freshwater lenses in the coastal dune area of the Western Netherlands. C. Methodology Each subject has it s own specific historical research. Some relevant and read references have been added at the end of each subject. In general: description of the use of a numerical model A numerical model simulating the future development of salt water intrusion into freshwater lenses has to be able to compute coupled density dependent groundwater flow and advective and dispersive transport of solute. Several model codes are available such as SEAWAT, MOCDENS3D, SUTRA and FEFLOW. The latter two are finite element codes, and have the advantage of a flexible and distorted grid. A general disadvantage of the codes is that severe numerical problems (such as numerical dispersion and over- and

4 undershooting) are introduced when the element size becomes larger than a few times of the longitudinal dispersivity. This criterion is known as the grid Peclet number. This criterion makes modeling of large 3d domains difficult with these types of codes. SEAWAT and MOCDENS3D are finite difference codes, both based on the groundwater flow code MODFLOW. In concept, SEAWAT is similar to MOCDENS3D when advection is solved using the Method of Characteristics. The dispersion term is solved by a finite difference scheme. The advantage of this so called mixed Eulerian Lagrangian approach in finite difference codes, is that large grid cells can be used in combination with small dispersion lengths. Large 3d domains can therefore be modeled more efficient, which is the prime reason to use either of these two codes as large areas need to be captured. Moreover, the researcher and his daily supervisor have experience with these codes. I: Shallow freshwater lens The spatial and temporal factors that determine the dimensions of a shallow freshwater lens in saline seepage areas follow from the research by Eeman and de Louw. Using this knowledge, a highly discretized model of an agricultural plot will first be constructed. The researcher may choose for the monitored plot of Eeman and de Louw, and verify model outcomes. From this, the discretization is coarsened and the model performance is evaluated simultaneously. Attention is also paid to the ability of the model to simulate measures to increase the robustness of the shallow freshwater lens with respect to salt water intrusion. In the end, the largest allowable cell size is chosen. This cell size is then used to model other areas in the low-lying part of at least the Province of Zeeland, and if applicable, also other parts in The Netherlands, ultimately leading to a regional quantification of freshwater lenses including future scenarios. Effictive field verification measurements are also considered. Hydrogeological data (including concentration data to deduce the groundwater density distribution) will be used from the REGIS II and GEOTOP databases of TNO. Future scenarios for groundwater recharge will be deduced from meteorological data of the KNMI. Datasets from Alterra are used for ditch geometries and drain information.(voortman 2010) (Vos et al. 2002) (Viezzoli et al. 2010) (Corwin & Lesch 2005) (Cirkel et al. 2010) II: Freshwater stored in fossil sandy creeks A regional (Province of Zeeland) or subregional (one of the islands) assessment of the current freshwater reserves stored within fossil sandy creeks and the current abstractions (including its regimes) will first be made. Numerical models are then used to construct optimal, save yield abstraction strategies for fossil sandy creeks of different geometries. This will also be done for future scenarios. Special attention will be given to abstractions by horizontal drains, as this has not yet been assessed previously. Some attention will also be paid at chemical clogging during abstraction and artificial infiltration. (van Meerten 1986) (Werkgroep Kwelschermstudie 1988) (Vermaas 1988) (Ward et al. 2007) (Ward et al. 2008) III: Influence of land reclamation on large freshwater lenses There is very little information about the offshore groundwater salinity. However, it has been recognized that active meteoric coastal groundwater systems can continue offshore when (semi-) confining layers are present. As the subsurface of the dune area of the Western Netherlands is heterogeneous, fresh offshore groundwater is likely to be present. SEAWAT will be used to model offshore fresh groundwater flow and to predict the groundwater salinity distribution offshore. The offshore subsurface will be deduced from seismic data and interpolation with onshore (hydro)geological information. Subsequently, the influence of land reclamation is investigated by means of numerical models. (Beets 1992) (Kooi & Groen 2001) (Mulligan et al. 2011) (Li & Chen 1991) 11. HAALBAARHEID a. Op welke wijze is een goede begeleiding verzekerd? De aio werkt met zijn dagelijkse begeleider in Utrecht bij Deltares, waar voldoende expertise is op het gebied van ondiepe geohydrogeologie en waar andere AIO-ers werken aan soortgelijke thema s. Er zal 2-wekelijks worden overlegd met de promotor. Het projectteam dekt alle terreinen van dit voorstel inhoudelijk af, met langjarige expertise. b. Op welke wijze is de uitvoerbaarheid verzekerd? Benodigd materiaal allemaal reeds aanwezig. Gestelde doelen worden door begeleiders zeer haalbaar geacht op grond van eerder verschenen artikelen en ervaringen met vergelijkbare onderwerpen. Op elk deelterrein is een deskundige in de onderzoeksgroep aanwezig, die het gedeelte op zijn terrein heeft beoordeeld. c. Welke afspraken zijn er t.a.v. de samenwerking met derden gemaakt? Buiten het projectteam: (nog niet, wellicht Koen Zuurbier; KWR/VU) 4

5 5 12. WERKPLAN a. Gedetailleerd werkplan eerste helft onderzoekproject Month 1-24: Step 1 Literature review, preliminary modeling schematizations. Oct 10 : Start literature review, learn modeling techniques, produce deliverables for stakeholders KfC. Mar 11 : Model runs and literature review, submission of research proposal Apr - Oct 11: Model runs on fossil sandy creeks and coastal dunes. Define and start necessary field measurements Nov 11 Apr 12: Continue field measurements and modeling, also on upscaling. May 12 - Jul 12: Continue modeling, field measurements and start writing articles. Jul 11 Sep 12:Comparison analytical and numerical model, verification of analytical model b. Globaal werkplan tweede helft onderzoekproject Month 25-30: Upon PhD completion of Eeman and de Louw, start upscaling shallow freshwater lens. Finalize field measurements. Month 31-39: Upscaling, finishing articles of fossil sandy creek and coastal dune area. Month 40-42: Write article on upscaling Month 43-48: Writing of the thesis 13. Alle benodigde voorzieningen (personeel én materieel) zijn aanwezig, dan wel geregeld JA 14. ONDERTEKENING Voorzitter vakgroep NAAM: S.E.A.T.M. van der Zee Projectleider NAAM: G.H.P. Oude Essink HANDTEKENING: HANDTEKENING: Wetenschappelijk Directeur Onderzoekschool NAAM: R. Leemans HANDTEKENING:

6 TOELICHTING OP DE AFZONDERLIJKE VRAGEN VAN HET FORMULIER 'PROJECTVOORSTEL AIO' 6 Algemeen: Vraag 1: Vraag 2: Vraag 3: Vraag 4: Vraag 5: Vraag 6a: Vraag 6b: Vraag 7: Vraag 8: Vraag 9: Vraag 10: Vraag 11: Vraag 12: Vraag 13: Vraag 14: De voor de antwoorden op de gestelde vragen beschikbare ruimte is beperkt. U wordt met klem verzocht bij de formulering van de antwoorden hiermee rekening te houden. Mocht u echter van mening zijn dat u voor een antwoord meer ruimte nodig heeft dan het formulier biedt, dan dient u het antwoord te vervolgen op een blanco A4-vel en dit vervolgens in te voegen in het formulier. Naam van de projectleider (eindverantwoordelijke) en van de hoogleraar die als promotor van de AIO zal optreden. Gaarne een zo kort mogelijke en toch specifieke titel van het onderzoek. Engelse vertaling van de titel. Indien het project ingebed wordt in een onderzoekschool, dan hier de naam van de onderzoekschool en het betreffende (sub)thema vermelden. Voor de goede orde wordt nog eens onderstreept dat het project slechts tot één programma kan behoren. Indien (een deel van) het project buiten Nederland wordt uitgevoerd, dan desbetreffende land(en) vermelden. Bij een groot aantal projecten wordt gebruik gemaakt van proefdieren. Het proefdiergebruik wordt gereglementeerd door de Wet op de Dier proeven. De Dier- Experimenten Commissie (DEC) is belast met het toezicht op de naleving van deze wet bij het universitaire onderzoek. Indien in een nieuw aangemeld project gewervelde proefdieren worden gebruikt, zal de DEC u een apart vragenformulier sturen. Het College van Bestuur heeft in januari 1992 besloten voor biotechnologisch onderzoek bij gewervelde dieren een ethische toetsing verplicht te stellen. Het betreft hierbij dan met name transgenese (inclusief het houden van transgene dieren), chimaere-vorming en clonering. De ethische toetsing zal worden uitgevoerd door de DEC. Indien u de vraag bevestigend beantwoordt zal de DEC met u contact opnemen. U wordt verzocht bij deze vraag de personen te vermelden, wp + obp, die direct zijn of worden betrokken bij de uitvoering van dit onderzoek. Vermeld tevens ten laste van welke vakgroep, instituut of andere instelling betrokkenen zijn aangesteld en maak een schatting van het aantal uren dat een ieder per week aan het onderzoek besteedt. U gelieve hier de organisaties te vermelden waarmee in het kader van het project wordt samengewerkt. Bedoeld is daadwerkelijke samenwerking die tot uiting komt in gezamenlijke activiteiten zoals gemeenschappelijke publikaties. De namen van subsidiënten (in geval van tweede of derde geldstroom) hoeft u hier niet te vermelden. De korte samenvatting dient als toelichting op de titel van het onderzoek. Deze vraag valt in drie onderdelen uiteen: Onder a. wordt u verzocht de voorgeschiedenis te beschrijven die tot het project heeft geleid. U gelieve hier de plaats te beschrijven van het onderzoek in de ontwikkeling van het betreffende vakgebied alsmede de plaats van het onderzoek binnen bepaalde maatschappelijke ontwikkelingen. Literatuurverwijzingen in een bijlage vermelden. Onder b. dient u het op te lossen probleem te formuleren door aan te geven wat u met het project wilt bereiken. Onder c. geeft u aan welke werkwijze u zult volgen (methoden en technieken). U wordt verzocht op drie aspecten van de haalbaarheid van het projectvoorstel nader in te gaan: a. Op welke wijze is een goede begeleiding verzekerd? - welke leden van de vakgroep(en) of instituut zullen de AIO begeleiden? - wat is hun taak in de begeleiding? - indien te voorzien is dat tijdens de loopduur van het project veranderingen optreden in het team van begeleiders, hoe wordt de begeleiding dan verder geregeld? b. Op welke wijze is de uitvoerbaarheid geregeld? Hierbij dient u in te gaan op - de binnen de projectgroep aanwezige kennis en know how - de beschikbaarheid en bereikbaarheid van apparatuur, experimenteerruimte e.d. - de aanwezigheid van OBP-ondersteuning - tijdgekoppelde risico's (b.v. weersafhankelijkheid, afhankelijkheid en bereidwilligheid van derden). c. De afspraken die u met samenwerkende organisaties (vraag 8) en/of andere LU-vakgroepen hebt gemaakt, voor zover van belang voor de uitvoering van het project. U wordt verzocht een gedetailleerd werkplan voor de eerste helft van het onderzoekproject te vermelden en een globaal werkplan voor het tweede deel ( inclusief het gereedmaken en de goedkeuring van het concept proefschrift). Indien er nog problemen zijn m.b.t. de beschikbaarheid van voor de uitvoering van het project benodigde personele of materiële middelen, deze hier toelichten. Het formulier dient ondertekend te worden door de voorzitter van de vakgroep en de projectleider.

7 Beets, D., Holocene evolution of the coast of Holland. Marine Geology, 103(1-3), pp Cirkel, D.G., Witte, J.-P.M. & van der Zee, S.E.A.T.M., Estimating seepage intensities from groundwater level time series by inverse modelling: A sensitivity analysis on wet meadow scenarios. Journal of Hydrology, 385(1-4), pp Corwin, D. & Lesch, S., Apparent soil electrical conductivity measurements in agriculture. Computers and Electronics in Agriculture, 46(1-3), pp Eeman, S. et al., Analysis of the thickness of a fresh water lens and of the transition zone between this lens and upwelling saline water. Advances in Water Resources, 34(2), pp Kooi, H. & Groen, J., Offshore continuation of coastal groundwater systems; predictions using sharpinterface approximations and variable-density flow modelling. Journal of Hydrology, 246(1-4), pp Li, G. & Chen, C., Determining the length of confined aquifer roof extending under the sea by the tidal method. Journal of Hydrology, 123(1-2), pp Mulligan, A.E., Langevin, C. & Post, V.E. a, Tidal Boundary Conditions in SEAWAT. Ground water, pp Oude Essink, G.H.P., van Baaren, E.S. & de Louw, P.G.B., Effects of climate change on coastal groundwater systems: A modeling study in the Netherlands. Water Resources Research, 46(May), pp van Meerten, J.J., Kunstmatige infiltratie in kreekruggen, Delft. Vermaas, J.C.J., Kwelscherm voor kreekrug op walcheren, Wageningen. Viezzoli, a et al., Surface water groundwater exchange in transitional coastal environments by airborne electromagnetics: The Venice Lagoon example. Geophysical Research Letters, 37(1), pp.1-6. Voortman, B., De invloed van gebiedseigenschappen en klimaatverandering op de dikte en vorm van regenwaterlenzen in de Provincie Zeeland. Vos, J. de, Raats, P. & Feddes, R., Chloride transport in a recently reclaimed Dutch polder. Journal of Hydrology, 257(1-4), pp Ward, J., Simmons, C. & Dillon, P., A theoretical analysis of mixed convection in aquifer storage and recovery: How important are density effects? Journal of Hydrology, 343(3-4), pp Ward, J., Simmons, C. & Dillon, P., Variable-density modelling of multiple-cycle aquifer storage and recovery (ASR): Importance of anisotropy and layered heterogeneity in brackish aquifers. Journal of Hydrology, 356(1-2), pp Werkgroep Kwelschermstudie, Kwelschermstudie eindrapport, Middelburg.