A lot of rain — but maybe not as much as you think — fell Aug. 20 on the shallow, 281-square-mile basin of land that drains into Madison’s lakes Mendota and Monona in Madison, Wisconsin.
Most of the 12- to 15-inch deluge that drenched parts of western Dane County flowed away from Madison toward the Wisconsin River.
Only about 4 inches fell across the lakes’ watershed, but that 4 inches swelled Madison’s lakes enough to flood streets and homes. Even before the rain fell, Lake Mendota was nearly a foot higher than the official maximum. For most of the summer the lake was 8 to 9 inches higher than it should have been in part because underwater plants and delays at a small dam hindered efforts to move excess water downstream.
Staff used ten mechanical weed harvesters to remove over 270 loads of aquatic plants in an effort to increase the water flow out of the chain of lakes. That doubled the flow of water, so more water is leaving the Yahara chain than what’s entering, allowing lake levels to stabilize and lessen the impact of the already flooded areas.