Last week's flash flood on Indian Creek hit 100-year flood level; council clears way for $400,000 study; city will figure out tiger dams

The flash flood that hit Indian Creek last week reached the status of a 100-year flood, Dave Elgin, the city's public works director, told the City Council this week.

The council gave Elgin and Ken DeKeyser, the city's storm water management engineer, the go-ahead to contract with the Army Corps of Engineers to conduct a $400,000 feasibility study for Indian Creek and its entire 93 sq. mi. watershed.

Elgin and City Manager Jim Prosser told the council it earlier had put money aside for the study, $200,000 of which will be paid by the Corps and $200,000 by the city. Other jurisdictions in the watershed, to date, have not agreed to participate.

DeKeyser noted that the Corps had completed an earlier “reconnaissance” study of the creek and watershed in 2004, concluding that a more thorough feasibility study was needed.

The feasibility study must be completed before any federal money is made available to remedy problems in the watershed, DeKeyser explained to the council. The Corps' expertise, he added, is needed before anyone contemplates the construction of levees or berms along the creek.

DeKeyser said the Corps is ready to start the study, which he said would be complete in a year or two.

In the meantime, the city will place backflow valves in storm sewers to prevent creek water from pushing out sewers, he said.

The council had plenty of questions about the city's temporary flood-protection system of water-filled bladders called tiger dams. Indian Creek's flash flood last week overwhelmed the dams, causing them to float.

DeKeyser and Elgin said the dams were deployed last Wednesday as much as an exercise for the city's public works crews as anything. A continued deluge of rain, though, prevented the crews from having time to redeploy the tiger dams to higher ground, they said.

DeKeyser suggested that the city hold a training exercise next spring along the creek in the Sun Valley Neighborhood so crews can work on the best place to put the tiger dams.

The tiger dams and a second temporary system, sand-filled wire baskets called Hesco barriers, were purchased by the council with the intent of using them along the Cedar River not Indian Creek. The Hesco barriers take more time to set up than tiger dams and so weren't used along Indian Creek, Elgin and DeKeyser said.

Council member Justin Shields said he had fielded numerous complaints from people who had sewer backups in their basements as a result of last week's heavy rain.