Paper No. 2
Presentation Time: 8:25 AM
EXPLORING THE STATE OF CONNECTION BETWEEN SURFACE WATER AND GROUNDWATER USING TRANSIENT STREAM AND WELL DATA
SHANAFIELD, Margaret A.1, BRUNNER, Philip2, COOK, Peter G.3 and GIANNI, Guillaume2, (1)National Center for Groundwater Research and Training, Flinders University, Ring Road, Bedford Park, 5063, Australia, (2)University of Neuchatel, Rue des Fahys 71, Neuchatel, 2000, Switzerland, (3)National Centre for Groundwater Research and Training/CSIRO Land and Water, Flinders University, Ring Road, Bedford Park, 5042, Australia, margaret.shanafield@flinders.edu.au
Two fundamentally different states of connection between surface water and groundwater exist: hydraulically connected or hydraulically disconnected. Because the timing and magnitude of recharge to aquifers differs greatly under connected and disconnected stream systems, the correct determination of this connection status greatly impacts our ability to estimate recharge to aquifers, especially in arid zones. Yet the existing methods of identifying the state of connection have significant shortcomings. Currently, disconnection is identified by showing that the infiltration rate is independent of the water table position or by identifying an unsaturated zone beneath a layer of lower permeability sediment at the streambed surface (referred to as a clogging layer). While the first method is impractical, the second approach is unreliable.
We explore the use of stream and well data in a new method to determine the status of connection between surface and groundwater systems. Initial work on this topic showed that some well hydrograph responses can only be achieved in disconnected systems when the well response is greater than the stream stage variation. However, attempts to uniquely identify the state of connection using realworld data were still unsuccessful, because of the effects of heterogeneity in the streambed and the aquifer. In this work, we use numerical models of hypothetical two-dimensional and three-dimensional channels to explore if and under what conditions the state of connection can be identified from stream and well level data. We generate synthetic observation data using both homogeneous and heterogeneous models. Inverse approaches are then systematically employed to examine the information content of transient stream and groundwater data with regard to identifying the state of connection between surface water and groundwater. Such an analysis allows quantification of the geological and transient conditions for which a unique solution for the state of connection can be identified.
