WorldWide Drilling Resource

Environmental Monitoring by Thomas Kwader, Ph.D., P.G. Why Groundwater is Important to Lakes A lake can also be thought of as a “window into our groundwater”. The water level in a lake is influ- enced by: 1) How much water falls directly on the lake’s surface. 2) How much water drains into the lake from surface creeks, streams, and rivers. 3) How much groundwater seeps into the lake from sediments surrounding the lake’s shoreline and bottom of the lake (i.e. groundwater). (Note: This discussion applies to lakes without a surface water outlet, such as a dam, stream, or pumping system). How much water entering the lake from groundwater depends on many factors, including the size of the lake’s surface drainage basin vs. the size of the lake. The size of the lake may easily be 1/10th, or less than the land area that contributes groundwater to the lake. This land around the lake or drainage basin acts as a large “sponge” storing groundwater which “feeds” the lake 365 days a year. During rainy seasons, the sponge fills up and stores water. The amount of groundwa- ter in the sponge affects the long-term lake level. If groundwater levels are low due to long per iods of l i t t le rainfal l (droughts), the lake levels will begin to fal l rapidl y, espec ial l y in summer months when the evaporation is high and little seepage is contributing to the lake. Healthy high water levels in lakes are best achieved by long periods of steady rainfal l which saturates the ground for many days. These condi- tions tend to fill up the sponge or sedi- ments that makeup the lake’s drainage basin, which in turn, will seep ground- water into the lake for months to come. On the other hand, intense rainfal l events over short periods of time tend to provide much more runoff to the lake; and rapid lake level rises do not main- tain high lake levels for long periods of time because most of the rain occurs as runoff rather than seepage that recharges into the shallow groundwater. In areas where snow accumulates, the amount of winter snowfall also direct- ly affects long-term lake levels and ground- water. This recharge to the sediments occurs as the snow begins to melt. Although we cannot directly impact the amount or duration of precipitation, the understanding of the factors con- tributing to groundwater levels helps us predict future lake and groundwater levels. Tom Tom Kwader may be contacted via e-mail to michele@ worldwidedrillingresource.com ENV 21 WorldWide Drilling Resource ® OCTOBER 2018