Turner, J.V., and Townley, L.R. (2004), Determination of groundwater flow-through regimes of shallow lakes and wetlands from numerical analysis of stable isotope and chloride tracer distribution patterns, INTECOL VII: The role of wetlands for integrated water resources management, Symposium 4, Groundwater-surface water interactions in wetlands for integrated water resources management, University of Utrecht, The Netherlands, July.

A numerical model previously developed to systematically examine groundwater flow in vertical section near shallow surface water bodies such as lakes, wetlands, ponds is further developed to include simulation of the distribution patterns of hydrogeochemical and isotopic tracers in relation to the surface water body and the geometry of distribution patterns of the tracers in the groundwater release zone of the lake. Many different flow regimes are identified, however in the modeling, attention is focused on flow-through water bodies, as these are the flow regimes observed in the field validation.

Three lakes on the Swan Coastal Plain of south-west Western Australia are the subjects of field studies where hydrogeochemical and stable isotopes are used to show the flowthrough groundwater flow regime. The flow regimes predicted by the models are shown to occur in three field examples of lakes on the Swan Coastal Plain of south-west Western Australia, confirming the validity of the approach. The flow regime transition diagrams introduced in earlier papers are extended to include consideration of the hydrogeochemical and stable isotopic indices ClL/Cl+ and (1000+¦ÄL)/(1000+¦Ä+) which are the ratios of chloride and isotopic composition respectively introduced into the groundwater release zones of the lakes relative to these parameters in the groundwater capture zone for the lake. Field data from the three field case studies plotted on appropriately configured transition diagrams demonstrates the overall validity of the modeling approach and its underlying assumptions. A dimensional analysis of the solution to flow and isotope and hydrogeochemical distributions inside the model domain indicates nine nondimensional ratios are necessary to analyse the problem, indicating its level of complexity. Due to this, and because the procedure is based on a number of assumptions there may be cases where the procedure might be limited.

It is concluded that there is no better substitute than to use isotopic and hydrogeochemical data in interpreting the interaction between lakes or wetlands and regional aquifers. It is very difficult, to make physical or hydraulic measurements in the field which allow an understanding of lake-aquifer interaction. On the other hand, the natural isotopes of water (2H and 18O) and conservative solutes such as chloride provide clear evidence for groundwater flow pathways.

With the understandings developed in this paper and the field validation of concepts developed in previous papers describing this research, it is possible to predict probable flow regimes for a wide range of surface water bodies and to use the measurements on the flow regimes provided by the isotopic and hydrogeochemical tracers to validate the approach. In an inverse sense, inferences can be made about the aquifer fluxes. The tools and concepts developed are invaluable starting points for the consideration and analysis of other case-specific examples of groundwater- surface water interaction. With this information, decision-making concerning lake and wetland management by water resource and environmental managers can proceed with added confidence.

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Last revised: 17 January 2022