Water Retention Versus Detention: ‘A Huge Difference’

During Memphis City Council’s meeting Tuesday, Dec. 20, dozens of neighborhood supporters addressed the council about the impact of Lick Creek flooding on their homes.

Among them were Mary Wilder, member of Lick Creek Coalition and a resident of Midtown’s Vollintine-Evergreen neighborhood. She said the Lick Creek detention will alleviate the flooding problem, but not throughout the entire basin because that’s not the way detention works.

“Detention works to alleviate flooding at the points closest to it, so Belleaire, Overton Park, the Zoo, and it should help VECA in that it will slow down the volume of water going into the system,” Wilder said. “You pick up water everywhere you go. And at that size (1 million cubic feet), (the detention basin) should make a significant difference. It really should.”

Because there’s a huge difference in retention and detention, Wilder said. To retain means to hold it, and that’s not what the new parking structure with detention basin underneath will do.

Rather, it will slow the water down before slowly releasing it back into the system at a pace that will allow it to move through the storm water system without causing flooding.

“Retention is that big water feature in front of the city’s development on Crump heading east on the interstate where the old Baptist Hospital used to be,” Wilder said. “There’s a there’s a big fountain blowing all the time. That’s retention. That’s where they’re holding water and actually reusing it, but it also helps with the flooding issue.”

Conversely, detention is typically what happens naturally in the environment, Wilder said.

“It rains, water falls on the forest floor, it doesn’t flood the forest, the trees and the ground suck it up,” she said. “Only in a few areas will it actually create any kind of flooding.”

But in an urban environment where everything’s been paved and has installed roofs, that water doesn’t slow down.

“It comes flying out of the sky and hits the ground and goes flying across the pavement and tries its best it can to get into the storm water system,” Wilder said. “Well, when you get three or six inches in a short period of time, it’s going to cause flooding because we don’t have anything to detain it. We don’t have the trees, we don’t have the grass, we don’t have the green space anymore, we’ve replaced it with hardscape. So, we’re going to hardscape some detention. We’re going to put something underground and catch it for awhile and slow it down because mother nature can’t do it since we took her out of the picture.”

For more of Wilder’s comments, be sure to check out the Overton Square cover story in the week’s The Memphis News, which hits newsstands Saturday.