THE TRANSITION FROM UNCONFINED TO CONFINED AQUIFER IN A RIPARIAN WETLAND ALONG THE WHITE RIVER

In the headwaters of the White River watershed in Mansitee National Forest, Newaygo County Michigan, six groundwater wells were installed in late 2008 as the first step in the initiation of long-term data collection to support water resource management concerns on the National Forest. Four wells form a transect perpendicular to the White River with three of those wells instrumented for hourly water level and temperature data; two piezometers are screened in glacial unconfined sand, one piezometer penetrates through an approximately 8ft (2.4 m) layer of peat that acts to confine the underlying glacial sand, and one piezometer is screened in the surficial peat. Within a 30ft (9.4m) distance the glacial sands transition from a shallow unconfined system to an artesian confined aquifer. This transition is displayed as distinct hydrograph responses, varying vertical and horizontal gradients, and distinct groundwater temperature characteristics. Comparison of hydraulic head changes to corresponding precipitation data show that water levels in the unconfined sand respond significantly to rainfall and snowmelt events. A 1.3 inch (3 cm) rain event generated a 10.6 inch (27 cm) increase in water elevation. Responses in the confined sands are much less than in the unconfined sands, and show a 2.5 inch (6cm) response of the potential surface for the same rainfall event. The horizontal gradient from the unconfined sands to the confined sands changes seasonally, decreasing as the growing season progresses. The vertical gradient between the confined sand and the overlying peat is affected by the seasonal changes in the horizontal gradients, and increases as the horizontal gradient decreases. Groundwater temperatures in the unconfined sands range from 3.9 degrees Celsius (39 F) to 11.7 degrees Celsius (53 F), and in the confined sands temperatures range from 6.7 degrees Celsius (44 F) to 10.3 degrees Celsius (51 F). These data will ultimately form the basis of a long-term hydrogeological monitoring program by which changes that result from resource use , climate change, and other factors can be quantified.