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22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesIDENTIFICATION AND ESTIMATION OF GROUNDWATER INFLOW INTO ABRACKISH LAGOON: FIELD OBSERVATIONS AND MODELING OF SEASONALCHANGES IN DISCHARGEKinza Haider 1 ; Peter Engesgaard 1 , Torben Obel Sonnenborg 2 ; Sabrina Jensen, Carlos Duque 1kha@geo.ku.dk1 Department of Geography and Geology, University of Copenhagen, Denmark; 2 Departmentof Hydrology, Geological survey of Denmark and Greenland, DenmarkDepartment of Geography and Geology, Øster Voldgade 10, 1350 Copenhagen, DenmarkAbstract: Groundwater discharge into a brackish lagoon (Ringkøbing Fjord, Denmark) hasbeen studied using a combination of hydrogeological field investigations and variable-densityflow and transport modeling. A conceptual model of the dynamics controlling the interactionsbetween the more saline lagoon water and fresher groundwater is being developed on thebasis of different tracers with the objective of quantifying where, when, and how muchshallow groundwater discharges to the lagoon. Sampling of groundwater every two months inthe upper 2-3 m have been carried out and EC-depth profiles have been used to estimatechanges in the width of the groundwater discharge zone. Furthermore, temperature as atracer was used to estimate groundwater discharge indirectly. Field observations show thatthe salinity of the lagoon is highest in summer (~ 12 permil), when groundwater discharge islowest and, vice versa, lowest (~ 5 permil) when the discharge is highest (winter). Thisindicates that the forces of the saline intrusion and freshwater discharge are offset in timecreating a dynamic saltwater-freshwater interface (SWI)with maximum and minimum intrusions in the summer andwintertime, respectively. The Hydrogeosphere code wasapplied to simulate the transient conditions in the SWI. Thesimulations are based on the observed dynamic boundaryconditions of hydraulic head on landside and salinity/waterstage in the lagoon. The simulation results compare wellwith field observations: (1) the significant width of dischargezone lies around 20 m depending on the season with amaximum discharge near the shoreline, and (2) themaximum discharge is on the order of a few cm/daydecreasing rapidly off-shore with winter discharge being~15% of that during summer (~0.03 m/d).Key words: Lagoon, groundwater discharge, dynamic,saltwater-freshwater1. INTRODUCTIONFigure 1: Area of StudyThe main objective of this study is to locate, outline and estimate groundwater discharge(GWD) into a brackish lagoon, Ringkøbing Fjord in Western Denmark (Fig. 1). This will helpin closing the water balance of the Skjern river catchment by quantifying one outflowmechanism. The area of study is a bar-built estuary (~300 km 2 ) of controlled salinity (5-12permil) and water level (
22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and Perspectivesincoming seawater. A combination of hydrogeological field investigation techniques wereused to understand the lagoon water-groundwater interaction which include; geophysicaltracers - temperature and electric conductivity, direct seepage meter measurements, andspatial distribution of electric conductivity in the lagoon water. Slugtests were carried out inthe sediment bed of the lagoon at depths up to 12 m to map the local hydrogeology of studyarea. The shallow aquifer system consists mainly of sand with clay lenses up to a depth of 3 m(~13m/d), proceeded by a 4 m thick layer of silty-sands (~5 m/d) and a 5 m thick layer ofclean sands (~22m/d). Below, a clay layer separates the deeper aquifer from the shallow one.2. CONCEPTUAL MODEL AND NUMERICAL MODELINGBased on the field observations onshore and offshore in the study area, a conceptual modelwas constructed (Fig. 2).Landsidehead&lagoonsalinitysinusoidalmodelsequenceZ=12m0masl450m3m7mHeaddhsmodelSsmodel0 50 100 150 200 250 300 350T(d)K13m/dK5m/dK22m/dSalinity0m50minland0.3masl50mWinterSummerSummerWinterx=500mFigure 2: Conceptual model showing geology and field conditions during winter and summerA Hydrogeosphere code (HGS) is used which solves the non-linear coupled densitydependentflow and transport equations. The model domain is a rectangular 2-D vertical crosssection (x–z plane) with 500 m x 12 m extent (Fig. 2). The lagoon boundary is locatedbetween 0-450 m (in x) at 0 m (in z), whereas the rest of the model domain is the main aquifersystem subdivided into three layers with thicknesses 3 m, 7 m and 12 m (Fig. 3) terminatingat impermeable lower boundary of the model (clay layer). The topography of the modelslopes slightly from 0 m to 0.3 m, between 0 – 50 m (in x) at the land side boundary. Thesimulated area is discretized in 261 columns and 75 rows with a graded mesh aroundshoreline (0 m in x) from 0.05 m to 2 m and in the upper 2 m (in z) from 0.05 m to 0.2 m. Theinitial freshwater-brackishwater distribution is based on summer time observations, where thesalinity in the lagoon is highest and the gradient at land side is lowest. In the transient model,two main variables are involved; the hydraulic head at the landside boundary and the salinitychanges in lagoon (in terms of relative concentration). Sinusoidal distributions for both thesevariables are specified in the model with a simulation run time of 10 years. Following the175
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SWIM22 - 22 nd Salt Water Intrusion
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Local Supporting Organizing TeamMar
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Peter StuyfzandKiwa Water Research,
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PrefaceWelcome to the 22 nd Salt Wa
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SUMMARYKeynote Lectures pg 13Coasta
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Groundwater hypersalinization in a
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Hydrostratigraphic Study of Itaipua
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Keynote Lectures
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22 nd Salt Water Intrusion Meeting:
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Effects of sea levelrise and climat
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Hans Sulzbacher 1 ; Helga Wiederhol
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Resistivity [Ωm]0.1 1 10 100 10000
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2. METHODS Figure 1a.
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4. DISCUSSION AND CONCLUSIONSREFERE
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METHODS 51
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DISCUSSION AND CONCLUSIONS
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2. RESULTS, HOW TO GET THERE AND WH
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STUDY OF THE SALTWATER-FRESHWATER I
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4. DISCUSSION5. CONCLUSIONS67
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Hydrogeochemical and isotopicmethod
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Figure 1 Location map of study area
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Therefore, it was clarified that th
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GROUNDWATER HYPERSALINIZATION IN A
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3. RESULTS AND DISCUSSIONS
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Marie Perriquet 1,2 ;Tiernan Henry
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ACKNOWLEDGEMENTREFERENCES234
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1. INTRODUCTION2. EXAMPLE: UPCONING
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Figure 1. Computed density and mole
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Depth (m)22 nd Salt Water Intrusion
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