The city has nearly completed the Big Creek levee flood control project and now has set its sight on a new project — the Lincoln Draw, which runs from north of Interstate 70 through the center of town.
The surrounding area is subject to extensive flooding, and it is for this project that the stormwater utility fund was established in 2011, said Toby Dougherty, Hays city manager. Previous studies have been done, but the project never was completed due to issues such as funding.
A part of the draw is Lincoln Tunnel, a 6-foot diameter tunnel built in the 1930s. It carries water underground for approximately a mile in town.
“It’s in pretty decent shape,” said Steven Walters, stormwater specialist for the city.
He said they walked through it a few weeks ago for an inspection.
There are some areas where the tunnel has been repaired or lined. The tunnel walls are made of double-lined vitreous clay blocks. Each layer is 4 inches thick, Walters said.
The tunnel now contributes to the flooding because it isn’t large enough to carry the volume of water required. Walters said the tunnel probably did work for a few decades, but all of the homes and streets built up in the surrounding areas have created more impervious surfaces, creating more water runoff and fewer grass and soil surfaces where the rain could soak in.
“You’re increasing the amount of water that is introduced into the system and the speed it is introduced into the system,” he said.
Stormwater ordinances were introduced in the 1990s which require developers to make sure pre-development and post-development flows are the same for flood events.
“The tunnel would need to be somewhere in the neighborhood of 10 times bigger than what it currently is,” Walters said. “The tunnel is not something we can address with the current funding of the stormwater utility in a time frame we are comfortable with.
“There’s a lot of things to look at and consider.”
Approximately 100 properties are located on the Lincoln Tunnel. The walls of the basements of some homes located in its path curve around the tunnel.
To dig out the tunnel and make it open would be cost prohibitive, Walters said. He estimated it would cost $75 million to excavate and reconstruct the channel.
The water that drains into the creek bed already exceeds what the tunnel was intended to handle, he said.
City staff believes building multiple detention basins in the watershed, downsizing culverts, building up existing embankments and easement acquisition will alleviate the issues.
“We have to plan better than we’ve done in the past,” Walters said. “You don’t want to make the situation worse.
“It’s great and wonderful to have all of this new (construction) north of I-70, but we’ve still got all this property which has a potential to flood.”
The project will not address FEMA floodplain designation.
Portions of a separate 1989 study by the Corps of Engineers can be used for planning, but engineering models have changed, and the city has grown substantially. Mayor Eber Phelps said in 1989, the concentration of the study was growth on 27th Street.
Commissioner Henry Schwaller IV said they have to do something to alleviate the problems.
The Hays City Commission approved pairing with the U.S. Army Corps of Engineers to pay for an engineering study of the draw at its regular meeting Thursday.
The city’s cost of the study will be $332,000, and the final engineering and construction city cost estimate will be $1,447,268, with the total cost of $3.5 million.
The project will allow for continued development within the watershed and reduce flood risk below 19th Street, Walters said. There would be minimal long-term maintenance liability.
The project would be funded through the stormwater reserve fund.
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