County Grounds Flood Basins Finally Ready for Action

Six years in the making, massive detention basins are finished, and Village should be safe from floods.

Two interconnected floodwater detention basins started six years ago on the County Grounds in Wauwatosa are finished, the Milwaukee Metropolitan Sewerage District announced Tuesday.

The flood basins together will hold approximately 315 million gallons of water. By comparison, the Deep Tunnel system stores 521 million gallons, MMSD spokesman Bill Graffin said.

However, the basins are not designed to work as the Deep Tunnel does. Rather than collecting and storing water during any rain or snowmelt, they will fill only when their single feeder, Underwood Creek, reaches the level of a 1 percent probability, or so-called 100-year, flood event.

A 17-foot diameter tunnel from that level on the creek bank runs for one-half mile, cutting under the DNR Forestry Center woods, and leads into the basins, Graffin said. During a severe flood on Underwood Creek, the tunnel can be opened to capture the flood crest for several hours, mitigating flooding downstream, especially on the Menomonee River as it passes through the Village area of the city.

The basins are also intended to relieve flooding further downstream in Valley Park in Milwaukee, also known as Piggsville.

The tunnels are also not intended to hold water for any length of time should they fill in a flood. As soon as floodwaters on the streams receded, the water in the basins would be released slowly into the Menomonee.

"If the basins fill to capacity, it will take four days for them to empty," Graffin said.

Back-to-back severe floods that inundated scores of Tosa homes and State Street businesses in 1997 and 1998 led the City of Wauwatosa to seek assistance from MMSD in protecting against future floods.

The MMSD embarked on a flood study of the entire Menomonee River watershed and brought forward a plan that called not only for the basins on the County Grounds but also for lowering the floodplain in  and surrounding it with levees.

For that part of the watershed project, more than 60 homes and more than a dozen businesses were purchased and demolished, and Hart Park was nearly doubled in size.

The Hart Park project was finished several years ago, but it was intended to function along with the detention basins. Had a very severe flood event occurred before the basins came online, the Hart Park levees might not have held back the tide.

Now that the basins are ready, the Village should be safe from the kind of flooding that twice turned State Street into a navigable waterway more than a decade ago.

On July 22 of last year, parts of State Street flooded again in massive rains that inundated large areas of metro Milwaukee. But it was determined that none of the water outside the Hart Park levees was either river water or backups from storm sewers. It was surface water that came from the sky so fast it couldn't get into the storm sewers fast enough.

MMSD has published a 2010 year in review video that offers some astonishing footage for those interested in reliving that event.

Spencer A Hoyt June 08, 2011 at 01:24 PM
In the plans to obtain approval for these "Flood Basins" MMSD, politicians, developers and others showcased these basins when not flooded would be utilized as open spaces with public access. They even had renderings of well manicured soccer fields with goals/nets and all sorts of activity taking place within the basins. Jim, Can you share with us any follow up to these original comittments? Thanks in advance for your time and consideration! I know Patch can do it! God knows Wauwatosa Now aint...
jbw June 08, 2011 at 09:17 PM
Yes, thank you for the information. We seem to have a lot of those 100-year events, don't we? Perhaps the estimates are little too optimistic.
Jim Price June 08, 2011 at 10:23 PM
Hi, Spencer. I was involved in the detention basins project from the beginning (in a non-journalistic capacity) and yes, I remember there were some plans put out in the beginning that looked very different from what we see today. It's been so long I don't remember the details – but I know people who do. Will look into it.
Conservative Digest July 21, 2011 at 01:14 PM
Thus is a disastrous waste of money. We could have done a lot more for a lot less by sealing the sanitary sewers so we don;t get backups in basements all of the time, I have 9. Go back in history and the cementing or channelizing of Underwood creek pushed by Dick Bachmann and others caused most of the problems, We could have bought a few more houses, built some dikes and saved some money,


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