Dane County Monitoring Forecasts of Heavy Rain

September 30, 2019
John Reimer, (608) 224-3730
County Executive

Risk of Lake Flooding Significantly Lower than 1 Year Ago; Lakes Running a Foot and a Half Below Last August Levels

Dane County lakes are at a much lower risk of experiencing repeat flooding than a year ago, county officials announced today. While rain is in the forecast once again and there have been several bouts of precipitation in recent weeks, Lakes Mendota and Monona are at least a foot and a half lower today than they were during last year’s flooding.

Levels on Lakes and Monona and Waubesa have come up in recent weeks, but flow rates through the Yahara River are moving along fast enough to bring lakes down ½ inch per day. Essentially, that means the lakes today are near the same level they were on Friday, despite well over an inch of new rain this past weekend.

Of additional benefit, Lake Mendota is 21 inches below 100 year flood levels, affording for a large amount of storm water run-off space for any rains that do fall this week. Mendota will generally rise 1-2 inches for every inch of rain that falls. A year ago at this time, water was moved at a faster rate through the Tenney Lock and Dam because the lake was 19 inches higher at that time than it is now. Lake Monona is currently 16 inches lower than it was during last year’s flooding and as of this morning remains 8 inches below the 100 year flood level. Lake Waubesa is about 5 inches below the 100 year mark.

The projected rate of this week’s rainfall will also help manage storm water run-off. Two to three inches of rain over a 24-36 hour period has a much different impact on lake levels than rains like last August which fell in some cases as fast as two inches an hour.

Should excessive rains fall this week, low lying properties along Monona and Waubesa may begin to experience some water primarily in yards. Should more rain fall than projected, sandbagging would be recommended in areas more prone to flooding issues along the lakes. Based on current forecasts however, it is not anticipated the area will see anywhere near the impact of flooding experienced last August and September.

That said, groundwater levels remain high throughout Dane County. Basement flooding – separate from waters rising on lakes and rivers – is a potential given how saturated the ground remains. Should high rainfall rates persist over the same areas, flash flooding could also be a concern but at this time extensive lake flooding is not projected.

Dane County Land and Water Resources will continue to monitor lake levels through the week.