Townley, L.R. (2000), The importance of dynamic exchange between groundwater and wetlands: what the models tell us, In: Invited Symposium entitled "The range of significance of ground water to wetland water and chemical budgets", at Quebec 2000 Millennium Wetland Event and INTECOL's VI International Wetlands Conference, co-sponsored by the Society of Wetland Scientists (US) (SWS), the International Peat Society (IPS), International Mire Conservation Group (IMCG) and INTECOL, Quebec City, 6-12 August.

Wetlands can be classified as recharge, discharge or flowthrough water bodies, depending on the spatial distribution of flux across the interface between the water body and underlying aquifer. Modeling of steady groundwater flow in two and three dimensions allows this classification to be explored in great detail, as a function of wetland and aquifer geometry, however much more interesting results can be obtained by modeling transient flows. Some wetlands cycle, for example, between recharge, flowthrough and discharge regimes. Periodic fluctuations are often used by hydrologists to study aquifer properties near tidal rivers and estuaries. However in many parts of the world, seasonal climatic variations can also be well approximated by a combination of long-term average and sinusoidal fluctuations. The response of aquifers near wetlands can therefore be approximated by a combination of steady and sinusoidal responses. New modeling results are provided based on analysis of periodic flows, which are driven by sinusoidal variations of recharge and/or boundary conditions in time. the results can be visualized by animation of streak lines, analogous to plumes of smoke from a chimney in a periodic wind. Seasonally varying exchange between groundwater and wetlands has implications for water quality in both the wetlands and the underlying aquifers.

[This paper was kindly presented by Dr Don Rosenberry of USGS on behalf of the author.]