Saturday, Aug. 25 at 5:00 pm
As of this morning, the last 24 hours brought Lake Mendota down 1 inch and Lake Monona up 1 inch. The level of the Yahara River at East Main St. was up 1.8 inches. The Tenney Dam is discharging at 730 cubic feet per second and the County is planning to slow the discharge rate starting this evening. As a result, by Sunday morning the drop in Lake Mendota is expected to slow and Lake Monona is expected to stabilize. The elevation of the Yahara River at Main St. is expected to drop by about an inch. This is good news, but we are not out of the woods by any means.
The next significant chance of rain will occur starting around 4:00 PM Sunday. Low lying areas of the isthmus are now at the same elevation as the elevation of the Yahara River or Lake Monona. What that means is that the puddles in the streets are essentially a back water of the Yahara River or Lake Monona. Storm inlets and pipes are the only way to drain the street. When it rains, instead of water draining into a dry pipe, the water entering the pipe has to push water out. This makes the storm sewer much less efficient. Urban flash flooding is a concern during heavy rainfall and, depending upon the severity, property and vehicles could be flood.
We recommend that vehicles not be parked in the low lying areas of the isthmus. We also recommend that vulnerable properties are protected with sand bags. If flooding of multiple properties occurs, sanitary sewers will be overwhelmed as water from the basements drain into the sanitary sewer system. Therefore, it is very important that properties are protected.
Many areas along Lake Monona, the Wingra Creek, and the Yahara River are experiencing flooding now.
The City is providing sand, sandbags and filled sand bags as we are able. Hundreds of volunteers and the National Guard are assisting.