Saltwater intrusions in the low-lying coastal areas of South-Western Jutland

Saltwater intrusions in the low-lying coastal areas of South-Western Jutland Rena Meyer* Peter Engesgaard*, Torben O. Sonnenborg^ *University of Copenhagen, Denmark ^Geological Survey of Denmark and Greenland, Denmark Danish Water Forum 30 th January 2017 reme@ign.ku.dk

Introduction SWI Processes Werner et al. (2013)

Introduction Challenges Is the system in steady state? How will it develop in the future? Initial salt content Coastal geology, topography?? DWI 30 th January 2017 Rena Meyer reme@ign.ku.dk modified after Fergusson & Gleeson (2012)

Study Area

Features of the study area: Geology Characteristics: Low lying coastal area, even below sea level Heterogeneous geology + buried valleys Geological model spanning Miocene to postglacial deposits Conceptual model of the geological setting (Jørgensen et al. (2014)) DWI 30 th January 2017 Rena Meyer reme@ign.ku.dk DWI 30 th January 2017 Rena Meyer reme@ign.ku.dk

Modelling approach 1300km2 Heterogeneous Voxel 100x100x5m Geology MODLFOW MODPATH Steady state 1.2 mio cells Multiple objective Regularizatio n Pest calibration of 51 parameters 3D SEAWAT Salt concentration Stage 1 Stage 2 Stage 3 Validation Geophysical (AEM)

Flow & Transport model Geological sections through model domain with interpolated geology Grid specifications: 1.2 mio cells Δx, Δy=200-400m, Δz=5-10m 46 hydrofacies -95m to -100 Postglacial Quarternary Miocene DWI 30 th January 2017 Rena Meyer reme@ign.ku.dk

Flow & Transport model Boundary conditions RCH m/d Boundary conditions: River, drain, recharge, abstraction wells Density-corrected constant head & conc. at the Western coast No flow to the East Quarternary sand & clay W: Coast Density-corrected constant head Constant concentration 35 kg/m 3 W Recharge: Constant concentration 0.1kg/m 3 E: Water divide No flow E Miocene sand & clay No flow = top of Palaeogene

Flow & Transport model Observations Heads: 1100 Discharge: 3 stations C-14 ages : 18 samples, 6 locations, different depth, Quarternary & Miocene aquifers Corrected for dissolution and diffusion Wide range of groundwater ages (hundreds to almost 20000 years)

Simulated discharge 10 3 [m 3 /d] Simulated Modpath ages [years] Simulated head [m] Flow model Results GEUS seminar 25 th January 2017 45 35 25 15 5-5 700 600 500 400 300 200 100 0-5 5 15 25 35 45 Observed head [m] RMS=70m 3 /d 0 100 200 300 400 500 600 700 Observed discharge 10 3 [m 3 /d] 10000 1000 100 RMS=1.55m RMS=2.5ka Rena Meyer 10 10 100 1000 10000 Corrected 14 C ages [years]

SEAWAT model Results Saltwater intrusion for 3 stages: 6000-2000a BP: sea level 0m 2000-200a BP: temporary transgression (sea level +2m) 200-0a BP: dyke protecting areas below sea level (sea level 0m) Salt kg/m 3

Validation Comparison to AEM Simulated saltwater wedge compared to saltwater/freshwater interface delineated from AEM

Conclusion Regional saltwater intrusion model: high resolution, complex heterogeneous geology Flow model fits the observed data well 3 stages simulations: Importance of coastal geology Freshening is still going on steady state is not yet reached Simulated saltwater intrusion fits with observed saltwater/freshwater interface (AEM) Model could be used as a tool to investigate changing conditions on a regional scale DWI 30 th January 2017 Rena Meyer reme@ign.ku.dk

Thank you for your attention GEUS seminar 25 th January 2017 Rena Meyer