Paper No. 9
Presentation Time: 3:40 PM
THE INFLUENCE OF DISCONNECTION ON AQUIFER RESPONSE TO SURFACE WATER TRANSIENCE
SHANAFIELD, Margaret A., National Center for Groundwater Research and Training, Flinders University, Ring Road, Bedford Park, 5063, Australia, COOK, Peter G., National Centre for Groundwater Research and Training/CSIRO Land and Water, Flinders University, Ring Road, Bedford Park, 5042, Australia, BRUNNER, Philip, University of Neuchatel, Rue des Fahys 71, Neuchatel, 2000, Switzerland and SIMMONS, Craig T., School of the Environment & National Centre for Groundwater Research and Training, Flinders University, GPO Box 2100, Adelaide, 5001, Australia, margaret.shanafield@flinders.edu.au
Linkages between surface water flows and groundwater response have important impacts on water resource management decisions, affect the transport of nutrients and contaminants into aquifers, and influence aquatic ecosystems. While a wide body of literature is available to predict aquifer response to surface water variation under saturated (i.e. connected) conditions, a thorough understanding of such responses for partially saturated (i.e. disconnected) cases is lacking. Further, no field methods are available to determine whether the surface water and groundwater systems are connected, in transition, or fully disconnected in any given dataset. Therefore, how possible is it to determine whether a given set of field data can be assumed fully connected for modelling or other analysis? We explore whether changes in the water table in response to transience in surface water levels can be indicative of fully connected, transition, or fully disconnected systems.
This study creates a base case model for a synthetic surface water-groundwater system and establishes the water tables depths for which the channel can be considered fully connected, in transition, and fully disconnected. Aquifer response to a pressure wave travelling down both connected and disconnected channel is then compared under variable channel width, wave duration, aquifer thickness, and conductivity of the clogging layer and aquifer. Under all conditions, the change in total head within the fully connected aquifer is less than or equal to the head of the wave in the channel. However, for the transition and fully disconnected cases, it is possible to produce a predicted change in aquifer water level greater than the change in channel head. The magnitude of this response is highly dependent on variation in wave duration, stream width, and aquifer thickness. The conductivities of the clogging layer and aquifer, as well as wave duration largely control the timing of the aquifer response. Given these results, a set of field data with stream depth and water table measurements in a bore located 10 m from the stream are presented. Can we discern whether the data represent a connected or disconnected system?
