A top-down approach to characterise aquifer-river interaction processes

Abstract

The interconnections between groundwater and river systems remain poorly understood in many catchments throughout the world, and yet they are fundamental to effectively managing the quantity and quality of water resources. Many of the techniques traditionally employed by hydrogeologists and hydrologists rely on characterising the groundwater flow systems, topography, geology/aquifer systems, climate and/or the rainfall-runoff processes within a river basin. These studies can provide useful process characterisations that are fundamental to developing a physical understanding of hydrological processes within a specified region. However, in many instances the findings are descriptive and the results are difficult to up-scale to the larger sub-catchment/catchment scale at which water is managed and allocated. Moreover, they may have significant time and cost requirements. An alternative approach is to collate a range of hydrometric data, that for many catchments may already available, and to then analyse data patterns and infer processes from the data without being overly concerned about the details of the physical processes driving the system taking a top-down approach. In this paper the river reaches in the semi-arid Namoi River catchment in Australia were characterised according to three levels of information; namely: (1) presence of aquifer-river hydraulic connection; (2) dominant direction of flux; and (3) the potential for groundwater extraction to impact on river flows. The methods used to characterise the river reaches included an analysis of: (1) groundwater and river channel base elevations using a GIS/database; (2) stream hydrograph data; (3) flow duration data; (4) vertical aquifer connectivity at nested piezometer sites; and (5) paired river and groundwater hydrographs. The data patterns seen in the stream gauging station derived data for gaining, losing and variably gaining-losing river reaches were described together with the general processes that operate in these systems. Subsequently, a map was prepared for the Namoi River catchment river reaches indicating aquifer-river connectivity and dominant direction of flux. The potential for groundwater extraction to impact on river flows was also assessed and found to be a significant issue for the connected aquifer-river systems.