Spatial and temporal aspects of the transition from connection to disconnection between rivers, lakes and groundwater

A changing groundwater table can affect the flow regime between surface water and groundwater. Quantitative approaches are required to understand how such changes influence the flow regime. While in a fully connected regime changes in the groundwater table are related linearly to changes of the infiltration rate, in a disconnected regime the infiltration rate is essentially independent of such changes. However, transitional regimes between connected and disconnected regimes also exist and we identify different transitional pathways. We illustrate how hydrological parameters determine the pathway of transition and show that spatial variations of the infiltration flux through a surface water body strongly depends on these different pathways of transition. Moreover, the spatial distribution of seepage through a surface water body is shown to depend on the state of connection. We also show that the transition from a connected to disconnected flow regime may require a significant drop of the groundwater table. The study demonstrates that the transition zone may be of greater importance than is usually acknowledged. A comparison of lakes and rivers reveals that the latter are less likely to disconnect in response to a decrease of the regional groundwater table. We relate this behavior to differences in the build-up of a groundwater mound in 2D and 3D. Finally, we carry out some simple transient simulations for 3D systems to analyse the transient behavior of surface water groundwater interaction in the context of disconnection. We show that the state of connection is a critical variable in the dynamics of infiltration in a non-steady system.