But to make more accurate predictions, they must first determine how large an area their model really governs and take seasonal variations into account, said a University of Nebraska-Lincoln water scientist recently. Anne M. Matherne, research hydrologist with the UNL Conservation and Survey Division, speaking in December at a biweekly meeting of the Association for Women Geoscientists held at the division, said traditionally scientists have gathered data on water flow paths for fairly small areas and then applied the model to drainage basins covering many thousands of square miles, which doesn't always produce great accuracy. Her research has shown, she said, that accuracy can be increased when larger areas are modeled and the models are then applied to a given drainage basin. Seasonal variation of the water table can also affect runoff that could lead to flooding, and they need to be taken into account, she said. For example, in upland basins of the ridge and valley country of southwestern Wisconsin, groundwater recharge occurs in the spring from snow melt, causing the water table to be higher at that time and lower the rest of the year, she said.
Heavy runoff is likely in the spring, because the ground is already saturated.
In contrast, in low basins, the water table is higher in the early fall, she said, and heavy runoff is more likely to develop then. Nebraska residents should add state and city sales tax.