Groundwater Model of the Seeland Aquifer
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Amt für Wasser Office des eaux und Abfall et des déchets Bau -, Verkehrs- Direction des travaux undErreur Energiedirektion ! Nom de publics, des transports despropriété Kantons deBern document et de l’énergie inconnu. du canton de Berne Erreur ! Nom de propriété de document inconnu. GROUNDWATER MODEL OF THE SEELAND AQUIFER Dr. Fabien Cochand Rolf Tschumper Prof. Philip Brunner Prof. Daniel Hunkeler Neuchâtel, le 19.07.2019 Table of contents 1 Introduction ................................................................................................................................... 1 2 General consideration.................................................................................................................... 1 2.1 Previous studies ........................................................................................................... 1 2.2 Seeland aquifer ............................................................................................................ 2 2.3 Model geometries ........................................................................................................ 3 2.4 Simultaneous field measurements ............................................................................... 5 2.5 General modelling methodology ................................................................................. 5 3 Model development ....................................................................................................................... 6 3.1 Model mesh development ............................................................................................ 6 3.2 Steady-state model boundary conditions ..................................................................... 6 3.2.1 River BCs ................................................................................................................ 6 3.2.2 Fixed GW head BCs and well BCs ......................................................................... 7 3.2.3 Lateral inflow BCs .................................................................................................. 7 3.2.4 Recharge from rainfall ........................................................................................... 10 3.3 Transient model boundary conditions ....................................................................... 11 4 Steady-state model ...................................................................................................................... 13 4.1 Calibration procedure ................................................................................................ 13 4.2 Calibrated value of the hydraulic conductivity .......................................................... 14 4.3 Reproduction of groundwater heads .......................................................................... 15 4.4 Water balance ............................................................................................................ 16 4.5 River-aquifer interactions .......................................................................................... 18 4.6 Uncertainties .............................................................................................................. 19 5 Transient model ........................................................................................................................... 21 5.1 Calibration procedure and initial conditions ............................................................. 21 5.2 Transient reproduction of the groundwater heads ..................................................... 21 5.3 Minimum, mean and maximum maps ....................................................................... 25 5.4 Summary of model weakness or uncertainties .......................................................... 25 6 Model applications ...................................................................................................................... 26 6.1 Pumping test at the Gimmiz pumping station ........................................................... 27 6.2 Sugar factory pollution .............................................................................................. 30 6.2.1 Advective behaviour of the contaminant ............................................................... 30 6.2.2 Transport model ..................................................................................................... 32 7 Model improvement and conclusion ........................................................................................... 33 8 References ................................................................................................................................... 34 9 Appendices .................................................................................................................................. 36 Table of figures Figure 1: Seeland geology (from WWA (2004)) ......................................................................... 3 Figure 2: Model area and boundaries ........................................................................................... 4 Figure 3: Model mesh .................................................................................................................. 6 Figure 4: Implemented BCs ......................................................................................................... 8 Figure 5: Lateral inflow calculation: (a) Monthly mean precipitation and monthly mean calculated PET, (b) Net precipitation and (c) Monthly mean lateral inflow ........................................... 9 Figure 6: Soil types within the Seeland (left) and percentage of agriculture (right). ................. 10 Figure 7: Implemented temporary pumping wells ..................................................................... 12 Figure 8: Pilot points and measured GW heads used to calibrate the model. ............................ 13 Figure 9: Calibrated hydraulic conductivity .............................................................................. 14 Figure 10: Observed vs. simulated GW head scatter plot .......................................................... 15 Figure 11: Observed vs. simulated GW head errors at observation wells ................................. 16 Figure 12: Simulated river-aquifer interactions ......................................................................... 18 Figure 13: Relative uncertainty reduction calculated by PEST ................................................. 20 Figure 14: Observed transient groundwater head observation wells ......................................... 23 Figure 15: Weakness areas of model ......................................................................................... 26 Figure 16: Gimmiz pumping test hydrographs .......................................................................... 28 Figure 17: Observed vs simulated drawdown ............................................................................ 29 Figure 18: a) Expected particle tracking using observed groundwater head contours (KELLERHALS+HEAFELI, 2018) and b) small-scale simulated particle tracking ............................ 31 1 Introduction According to articles 39 to 41 of the cantonal law for water use (WNG) the Office for Water and Waste of the canton of Berne (AWA) is in charge to collect the fundamental information for the use and the conservation of any surface and subsurface water. To fulfil this aim: The hydrogeological archive (SousSol) and available datasets (Blaue Berichte, local studies, HydroPro, WAWIKO, …) are of great value. This Information should be better evaluated and documented for the public. Updated information of groundwater must be provided in an easy way to involved parties and interested people, in particular departments and responsible persons. The most important information must be provided to the public as thematic maps in the Geoportal of the Canton Bern and must be updated. Monitoring the ongoing situation of the groundwater table in a quantitative and qualitative way according to the Wasserversorgungsstrategie 2010. In order to achieve general objectives described above, a groundwater flow FEFLOW model of the Seeland aquifer was developed. This report presents the technical development and results of the Seeland aquifer model. The model development is based on the preliminary study entitled “GROUNDWATER MODELLING TASK OF THE SEELAND AQUIFER - PRELIMINARY STUDY - 12.05.2017”. In this report, we will focus on technical modelling aspects and some key points will be repeated. 2 General consideration 2.1 Previous studies Numerous geologic and hydrogeological studies have been dedicated to the Seeland aquifer. The first comprehensive hydrogeology study of the Seeland can be found in WEA (1976) (WEA is now AWA) and includes a strategy for a sustainable groundwater resources management. Another 1 report (WEA 1989) is dedicated to the interactions between the aquifer, the former Aare and the Hagneck Canal. To date, the most comprehensive general studies is WEA (1998). Other studies investigated more specific aspects; Jammet (2011) investigated the interactions between the Hagneck Canal, the aquifer and the pumping wells of Gimmiz during different pumping conditions, Wanner and Böhi (2011) carried out a pumping test at Gimmiz and Jordan (2000) developed a 2D Feflow model of the northern part (north of the Hagneck Canal) of the Seeland aquifer to determine the capture zone of the Worben pumping well. Before this study, WEA (1998) developed also a numerical