UTILIZING SOIL MOISTURE AND WATER TABLE DATA FOR ASSESSING GROUND WATER RECHARGE

Quantifying ground water recharge remains one of the seminal problems in hydrologic research and evaluation. Recharge varies spatially and temporally and is one of the most difficult, complex, and uncertain hydrologic parameters to quantify in the water budget. Monitoring changes in soil moisture content at multiple depths in the unsaturated zone and changes in the water table elevation provide a continuous record of the recharge process and a means to quantify temporal and spatial recharge variability.

In this study hourly field measurements of soil moisture content and water table elevation were collected at two sites, a clear cut and a coniferous forest site, within the Trout Lake basin of northern Wisconsin. Collectively, the data provided a means to identify which precipitation and snowmelt events recharged the ground water system and as such were used collectively to assess the temporal and spatial variability of ground water recharge from September 1999 – May 2001. Analysis of the data allowed for a better understanding of the compounding and often countering climatic and physical factors (e.g., rainfall timing, intensity, and quantity, snowmelt, soil moisture conditions, properties of the soil and sediment, types of vegetation present, ground temperature) that inevitably control the recharge process within this basin.

Recharge was primarily limited to a few isolated events (snowmelt, spring rains, a large summer thunderstorm) for the period of study, with recharge at the clear cut site almost double that at the conifer site. The results highlight the magnitude of recharge variability and the impacts of land cover change on the recharge process. Collectively, the two datasets provided a comprehensive means to track each recharge event from infiltration at the ground surface to percolation through the unsaturated zone down to the water table.