Flooding

Risk Assessment

As expected, the lakes have mostly dropped a bit (Monona is the critical lake for us at this time). However, Lake Mendota has room to store more water, which is good to have open storage if need be. The extended forecast looks wet, however, the weather makers are likely not thunderstorms, so we are not critical at this time.

We will continue to watch closely the lake levels.

Recall typically 1 inch of rain in the Yahara Watershed typically gets you a 3-inch rise in the elevation of Lake Monona.

Lake Mendota Today

Elevation = 850.69 feet

Change from one week ago = up 0.06 feet

Change from one month ago = up 0.36 feet

Above/below summer maximum: above by 0.59 feet

Above or below 100 year elevation: down 2.11 feet

Lake Mendota Statistics

Surface Area = 9,842 surface area acres

Summer Min = 849.6 feet

Summer Max = 850.1 feet

100-Year Record = 852.8 feet

Lake Monona Today

Elevation = 846.90 feet

Change from one week ago = down 0.13 feet

Change from one month ago = up 0.44 feet

Above/below summer maximum: above by 1.70 feet

Above or below 100 year elevation: down 0.80 feet

Lake Monona Statistics

Surface Area = 3,274 surface area acres

Summer Min = 844.7 feet

Summer Max = 845.2 feet

100-Year Record = 847.7 feet

Further description of numbers above:

Mendota is at 850.69, which is up from 850.63 last week. The summer max by WDNR order is 850.10 (so we are approximately 1 foot, 7 inches over summer max). The 100-year elevation is 852.8, but we can only currently effectively rise to approximately 852.0.

The Historic High on Lake Mendota is 852.74 and was reached on June 6, 2000.

Monona is at 846.90, down from 848.40 last week. The summer max by WDNR order is 845.20 (so we are approximately 1 foot, 10 inches over). The 100-year is 847.7.

The last posted updated Historic High on Lake Monona is approximately 848.40 on September 4, 2018.
Both lakes are likely to continue to rise for another day or so.

The problem low ground elevations in the Isthmus area are at about elevation 848.0-849.00. These areas drain to Lake Monona and/or the Yahara River mostly at East Washington. The closer Monona rises to 847.00, the more ineffective our drainage system in these low areas becomes at addressing high intensity summer storms (1" or more per hour).

Also, if you have sandbags, please review the current sandbag collection plan. It started on Sept. 9 and goes until Sept. 22.

The Engineering Division also has a podcast episode featuring engineers talking about the 2018 flooding event and ways to flood proof your home. Listen on iTunes   and Google Play  , by searching “Everyday Engineering.”