TY - BOOK

T1 - Large scale hydrogeological modelling of a low-lying complex coastal aquifer system

AU - Meyer, Rena

PY - 2018/3

Y1 - 2018/3

N2 - Aquifers in low-lying coastal areas are vulnerable to saltwater intrusion because of the naturally low head gradient, high groundwater abstraction rates and intensive land use. The problem is expected to intensify in future because of increasing freshwater demand concomitant with population and economic growth and relative sea level rise as a consequence of climate change. Numerical modelling provides a tool to better understand groundwater systems and make predictions on system behaviour in response to future stresses to support sustainable water management and to mitigate the risk of saltwater intrusion. In this thesis a new methodological approach was developed to combine 3D numerical groundwater modelling with a detailed geological description and hydrological, geochemical and geophysical data. It was applied to a regional scale saltwater intrusion in order to analyse and quantify the groundwater flow dynamics, identify the driving mechanisms that formed the saltwater intrusion to its present extent and to predict its progression in the future. The study area is located in the transboundary region between Southern Denmark and Northern Germany, adjacent to the Wadden Sea. Here, a large-scale saltwater intrusion reaching up to 20 km inland is observed. The 1300 km2-sized area is characterized by a complex glacially deformed geology with buried valleys and post-glacial changes in hydraulic conditions. Lying in the direct foreland of the Scandinavian Ice Sheet during the late Weichselian, it was impacted by high hydraulic pressures. The post-glacial sea level rise partly flooded the area. A few centuries ago humans started to reclaim large areas from the Wadden Sea, established dikes and drains to protect the land from flooding and to keep the water table below the surface. It is unknown how the saltwater intrusion developed to its present extent and how it will affect the aquifer system in the future. To enhance our understanding of this phenomenon and investigate the system in a physically realistic way, flow and advective transport models together with inverse modelling were used to find optimal parametrization schemes that accommodate hydrogeological heterogeneities. Subsequently, density-dependent flow and transport modelling of multiple salt sources was successfully applied to simulate the formation of the saltwater intrusion during the last 4200 years, accounting for historic changes in the hydraulic system, and its progression in the upcoming 200 years. The variety of observation data was beneficial to constrain parameter estimates, to analyse uncertainties and their impact on water balance predictions and to evaluate the saltwater model. The simulations proved to be successful in gaining insight into 1) the features of the studied regional flow system that comprises both human alternations to the hydraulic system and the specifications of the (hydro)geological setting and 2) the driving forces of the saltwater intrusion both in the past and future. The application of a similar approach is recommended to saltwater intrusion problems on regional scale in other similarly affected areas.

AB - Aquifers in low-lying coastal areas are vulnerable to saltwater intrusion because of the naturally low head gradient, high groundwater abstraction rates and intensive land use. The problem is expected to intensify in future because of increasing freshwater demand concomitant with population and economic growth and relative sea level rise as a consequence of climate change. Numerical modelling provides a tool to better understand groundwater systems and make predictions on system behaviour in response to future stresses to support sustainable water management and to mitigate the risk of saltwater intrusion. In this thesis a new methodological approach was developed to combine 3D numerical groundwater modelling with a detailed geological description and hydrological, geochemical and geophysical data. It was applied to a regional scale saltwater intrusion in order to analyse and quantify the groundwater flow dynamics, identify the driving mechanisms that formed the saltwater intrusion to its present extent and to predict its progression in the future. The study area is located in the transboundary region between Southern Denmark and Northern Germany, adjacent to the Wadden Sea. Here, a large-scale saltwater intrusion reaching up to 20 km inland is observed. The 1300 km2-sized area is characterized by a complex glacially deformed geology with buried valleys and post-glacial changes in hydraulic conditions. Lying in the direct foreland of the Scandinavian Ice Sheet during the late Weichselian, it was impacted by high hydraulic pressures. The post-glacial sea level rise partly flooded the area. A few centuries ago humans started to reclaim large areas from the Wadden Sea, established dikes and drains to protect the land from flooding and to keep the water table below the surface. It is unknown how the saltwater intrusion developed to its present extent and how it will affect the aquifer system in the future. To enhance our understanding of this phenomenon and investigate the system in a physically realistic way, flow and advective transport models together with inverse modelling were used to find optimal parametrization schemes that accommodate hydrogeological heterogeneities. Subsequently, density-dependent flow and transport modelling of multiple salt sources was successfully applied to simulate the formation of the saltwater intrusion during the last 4200 years, accounting for historic changes in the hydraulic system, and its progression in the upcoming 200 years. The variety of observation data was beneficial to constrain parameter estimates, to analyse uncertainties and their impact on water balance predictions and to evaluate the saltwater model. The simulations proved to be successful in gaining insight into 1) the features of the studied regional flow system that comprises both human alternations to the hydraulic system and the specifications of the (hydro)geological setting and 2) the driving forces of the saltwater intrusion both in the past and future. The application of a similar approach is recommended to saltwater intrusion problems on regional scale in other similarly affected areas.

UR - https://soeg.kb.dk/permalink/45KBDK_KGL/fbp0ps/alma99122372046605763

M3 - Ph.D. thesis

BT - Large scale hydrogeological modelling of a low-lying complex coastal aquifer system

PB - Department of Geosciences and Natural Resource Management, Faculty of Science, University of Copenhagen

ER -