A "wet microburst" -- a rapid downdraft of a thunderstorm --  in a matter of minutes caused an estimated $2 million in damage in Casper after it overwhelmed the city's storm sewer system and flooded streets on July 3, 2009.

Since then, little has changed.

The city has no way to provide consistent funding for a storm sewer system and it needs to create one to pay for $46 million worth of capital improvements over the next 20 years, or otherwise watch history repeat itself, public services director Andrew Beamer said at council's work session Tuesday.

The city is responsible for the repair, maintenance and capital projects of its storm sewer system. The U.S. Environmental Protection Agency and the Wyoming Department of Water Quality also set requirements for the quality of water that enters the North Platte River.

Residents have the responsibility to pay for it, Councilman Bob Hopkins said.

"I think it's only fair, that by living in the city, that something that is a requirement for a city to have and one of the things you live in the city for, should become part of your utilities," Hopkins said.

In 2013, the city commissioned the storm sewer plan and recently contracted with Civil Engineering Professionals, Inc., to implement it, according to the agenda for the work session.

CEPI engineer Tom Brauer said Casper's storm sewer system has 135 miles of pipe, 4,300 catch basins, 860 inlets and outlets, 1,900 manholes, three lift stations, and more than 50 acres of water detention areas.

Most of the pipe -- some of which is seven feet in diameter -- is concrete, but there are areas where it is too small. Some pipe is clay tile between 50 and 60 years old.

The storm sewer system is not as big as the sanitary sewer system with its 316 miles of pipe, 7,201 manholes, and 11 lift stations, Brauer said.

But there's an even bigger difference than size.

Residents and businesses pay for the sewer system at rates based on their use.

Casper has no such dedicated funding source for its storm sewer system.

The city has allocated annually $500,000 from the Optional One-Cent Sales Tax for storm sewer improvements, but cut that to $0 for the new fiscal year. The city also has contributed $78,000 to $104,000 a year for operations in recent years.

The best way to create a steady money source would be to create a Storm Water Utility enterprise funding method, just like the city does for sewer, water and solid waste by setting rates based on usage, Brauer said.

So a storm water utility would be a fee-based system, and not a tax, he added.

Other municipalities have set rates for their storm water utilities based on the amount of water-impervious space on a property.

Sidewalks, driveways and structures are impervious, and the water that falls on them -- unlike grass and soil -- goes into the storm sewer system, Brauer said.

He applied data and mathematical models to determine what property owners would pay. For example, the most common residential lot in Casper is about 8,000 square feet, and about 2,800 square feet of that is impervious. That rate would be $5.50 per month. Smaller lots would pay $3.30 and larger lots would pay $7.70 a month, he said.

The fee structure would raise annually $2,114,000 for capital improvements and $214,000 for operations and maintenance.

State law says local governments can create storm water utilities. Cities can create them by an ordinance and then putting the matter to the public for a vote, he said.

However, Brauer and council members would like to see the law changed so local governments can pass the ordinance and have the storm water utility put into place without placing the measure on the ballot.

Council members informally voted to support Rep. Pat Sweeney who wants to talk with other legislators about making that change. Sweeney told council Cheyenne and Gillette have similar issues.

On a personal level, Councilwoman Amanda Huckabay said she'd rather pay $5.50 a month instead of having the city pay another $2 million in a flash flood.

Chris Walsh said improving and maintaining a storm sewer system isn't as noticeable as painting the walls in the city garage, but it's far more important. "This is what a government is for."

However, he anticipates people won't like paying for it, he said. "There will be a backlash."

Dallas Laird said people will still perceive the fee as a tax, and may balk at voting for it unless the city can do a good job educating people about it.

Charlie Powell asked how he could convince his neighbors to support it because he and they live in south Casper where the water starts flowing and would not be victims of a failed storm sewer system and flooding.

Brauer responded the issue comes down to what is good for the community and not just individuals.

"There's a 'greater good' component that you would hope," he said. "It's like helping out your neighbors -- in the old days it was moving cattle and cutting hay, and today it's maybe a storm water (system)."