The cost and trouble of an innovative, nearly $1 million flood-control effort on a couple of blocks in some of the most flood-prone parts of Shandon has fallen short of expectations.
“The Shandon project has come in a lot higher than we expected,” assistant city manager Missy Gentry recently told City Council. Initial costs forced the city to slash the size of the project by two-thirds, said a city engineer who oversaw the project.
Announced with fanfare in the summer of 2012, the project used underground water retention chambers, which look like egg crates, instead of traditional hard-pipe drainage systems.
Then-city manager Steve Gantt said if the Shandon pilot program succeeded, it could become a template that would reduce the city’s reliance on the traditional pipes.
The pilot project included trying to persuade neighbors to use rain barrels to capture and later release water as another part of nature-friendly drainage.
Gentry and the city’s engineering department say they haven’t written off using underground chambers again.
The start of the Shandon project was delayed in large part because initial bids came in much higher than anticipated.
The bid on the rentention chambers came in at $28 per cubic foot, installed, said assistant city engineer Michael Shue. The city tried again and found a company, Advanced Drainage Systems, that would install similar devices at $9 per cubic foot.
Changing to Advanced Drainage saved $250,000, Shue said.
The chambers are designed to hold storm water and let it seep back into the soil, which reduces water pooling on the surface and has a domino effect on homes downhill of where the chambers are installed, he said.
Still, the 1,000 feet along Amherst Avenue and Maple Street ultimately carried a price tag of $976,000. The improvement has directly benefited about 40 homes, Shue said. That’s far fewer than the 400 city officials initially had wanted to help.
Work finally got started in January 2015, and the two streets were opened to traffic by June of that year, Shue said. “We had hoped to do that a little faster. It’s kind of like working on the old plumbing in your house – it’s always more than you thought,” he said.
Among the troubles installers faced was moving or working around water and sewer lines and electronic cables, Shue said. Sometimes, crews had to move water or sewer lines. That boosted the cost by $75,000, he said.
In other places, narrower retention chambers were used instead of moving more lines.
Future use of the green flood management technique depends on where in the city the chambers are to be installed, as well as other factors.
“It’s good in this situation, but not good in that situation,” Shue said. “If we had a new street, it’s a lot easier because everything gets planned at the same time.”
Older neighborhoods with aging pipes are unlikely to be candidates.
The city might use the chambers again. But there are no immediate plans to repeat the Shandon experiment, Shue said. “It’s certainly more practical than trying to find a vacant lot and putting a detention pond on it.”
Meanwhile, City Hall will start a project late this year to offer 1,000 rain barrels at discounted prices, Gentry said.