Flash Flood — Waukesha, Wisconsin

1998-08-06 to 1998-08-07 · near Brookfield, Waukesha, Wisconsin

Wider weather episode

A monumental flash flood event ravaged adjacent portions of Milwaukee and Waukesha counties during the afternoon and evening hours. For the northwest quarter of Milwaukee Co., and the northeast/ eastcentral parts of Waukesha Co., it was the second year in row (press headline - "deja vu all over again"). In Milwaukee Co., the damage wasn't as bad as that in June 1997, but for Waukesha Co. it was the worst flooding ever. Here are the details broken down by county: 1) Milwaukee County...The flash flood was the result of 5 to almost 9 inches of rain, between 1330CST (230pm) and 2000CST (9pm), falling on top of 1 to 3 inches that fell the previous two days. Maximum storm rainfall was 8.90 inches in Milwaukee on north 78th Street. A location in northern Wauwatosa came in with 8.40 inches between 2 pm and 9pm, while at 76th and Silver Springs in northwest Milwaukee, 7.12 inches were measured.The flash flooding quickly exhausted the local resources available in the city of Brown Deer, while the Red Cross opened shelters. One-hundred and twenty people in Milwaukee Co. became homeless due to home damage, while another 215 were evacuated. All together, 3517 residential structures sustained damage in the county: 3308 minor, 206 major damage, and 3 destroyed. Five businesses reported minor damage, and 18 major damage. Two private/utility structures had minor damage, and 7 had major damage. These three categories collectively had damage amounts of $20.05 million. There was an additional $2.092 million in damage to the public sector such as road systems, buildings, water control, etc. About 6500 residential and 50 business places lost power due to various outages.One 13 year-old boy was injured as he was swept by flood waters into a culvert and submerged for 15 minutes. Many roads were flooded and closed with water levels reaching 3 to 5 feet. Boats were needed to rescue several people. Highway 45 was closed, while Timmerman Field had minor flooding. A retaining wall in northwest Milwaukee collapsed due to high water levels. The city of Wauwatosa has decided to purchase some of the homes in the Menomonie River flood plain, and the city of Brown Deer will purchase some homes in the South Branch Creek flood plain to mitigate future damage. The Menomonie River in Wauwatosa crested at a record 18.3 feet on August 6th at 2026CST (826pm), about a foot higher than that observed a year ago. It was above flood stage from 1600CST (500pm) on the 6th to 840CST (940 am) on August 7th. The discharge at this location was 12800 cfs, or between a 50 and 100 year flood. Water levels were so high in Wauwatosa that an Amtrack train was halted with 350 passengers on board. Underwood Creek in Wauwatosa crested at a record 13.10 feet, or 2.10 feet above flood stage. It was above flood stage from 1655CST (555pm) on August 6th to 1930CST (830 pm) on the 6th. The synoptic reasons for this flooding can be found in the August 4th entry for flash flooding in Columbia Co. Eastern Walworth and western Racine Co. were persistent atmospheric breeding areas for all the thunderstorms that moved northeast over Milwaukee Co. Interestingly, the atmosphere recovered it's flash-flood potential during the late morning hours (after the Sheboygan County flash flood early on August 6th) as a southwest- northeast orientated surface front sagged south from Washington and Ozaukee counties to Walworth and Racine Counties by early afternoon. 2) Waukesha County...The worst flash flooding of the 1900's struck eastern Waukesha Co. , resulting in large monetary loses, and forcing some residents to decide to move out of flood plains. The worst flash flooding occurred from Brookfield through Elm Grove into New Berlin, and was the result of 6 to almost 12 inches of rain between 1230CST (130pm) and 2000CST (9pm), falling on top of 1 to 2 inches that fell in the previous two days. Maximum storm rainfall was 11.75 inches in Elm Grove at the intersection of North and Calhoun. There was an 11.50 inch report out of Brookfield, while the Brookfield High School registered 8.75 inches. Tragically, 2 teenage boys, ages 10 and 14, died when swirling flood waters swept them into a drainage ditch at 1710CST (610pm) which flowed into Underwood Creek in Elm Grove at Watertown Plank and Sunnyslope Roads. Rescue workers had to put on scuba diving gear to locate one of the boys. Flood waters of 4 to 5 feet covered much of New Berlin, half of Brookfields roads were submerged, and water to a depth of 4 to 7 feet settled in over Elm Grove. In fact, The Mill Place Shopping Center in Elm Grove still had standing water on August 7th. Flooding was so bad at the I-94 and Moreland Rd. interchange that local officials closed that intersection. Rescue workers in boats had to pluck people out of their stalled vehicles in that area. Compounding the flooding problem was the accumulation of raw sewage which backed into many basements. Overall, 2680 residential homes sustained minor flood damage, while 10 had major damage. Thirty businesses suffered minor damage, 20 had major damage, and 2 were destroyed. One utility building sustained minor damage. There was nearly a half-million dollars in damage in the public sector to road systems, buildings, etc. Many roads suffered gravel washouts on the shoulders, while a portion of Blackwolf Run golf course washed away. Many streams and creeks had high water levels for days after the bulk of the flash flood. The Fox River in Pewaukee crested at 12.08 feet at 0100CST (2am) on August 8th, or 2.08 feet over flood stage, and would stay above flood stage through the 10th. The synoptic reasons for this flooding can be found in the August 4th entry for flash flooding in Columbia Co. Eastern Walworth and western Racine Co. were persistent atmospheric breeding areas for all the thunderstorms that affected eastern Waukesha Co.

Source: NOAA Storm Events Database, event_id 5664611. Narrative written by the NWS forecast office that issued the report.