STARKVILLE — After an April storm, the city recorded flooding on 30 of its streets. By then, the city’s year-to-date rainfall had almost doubled as city officials and residents alike wondered what could be done.
The city’s response is forthcoming. Tonight, the Board of Aldermen is expected to call for a public hearing on an updated stormwater code.
“I wouldn’t say the storms prompted the changes in the stormwater code, but they certainly expedited it,” City Engineer Edward Kemp said.
The current code was adopted in 2009, well before the current boom in development, which has only exacerbated the flooding situation.
“With the addition of rooftops and buildings and parking lots and these surfaces where water is not able to permeate into the ground, it creates more runoff,” Kemp said. “What we are proposing addresses that.”
There are two major changes in the code. First, a stormwater mitigation system will be required for any new development of a half-acre or more. The old code applied to developments of an acre or more.
The second change requires new developments to provide a system capable of mitigating stormwater runoff for a 100-year storm. The current code requires only systems that can handle a 10-year storm.
There are three basic systems available to developers, Kemp said.
Retention ponds, often used as landscape features, capture run-off from storms. Detention ponds also capture run-off, but hold no water permanently and are empty in dry weather. Finally, there are in-ground systems, which capture and hold the water and release it slowly through graduated piping.
“The basic requirements is that developed properties can’t discharged any more water than what currently exists in their pre-development state,” Kemp said.
Kemp said an effective system relies on several variables specific to the site.
“A lot depends on two factors: the amount of rain and time,” Kemp said. “A 3-inch rain over a day is different than a 3-inch rain over an hour. The systems have to accommodate both.”
Developer Mark Castleberry, who has built projects in Starkville and Columbus, said the code changes could mean significant costs for developers, depending on the project.
“Every site is probably a little different in what you need to meet the code,” Castleberry said. “So it’s hard to calculate. But the very general rule of thumb is that, if you’re going with retention or detention ponds, you need to set aside about 5 percent of your property for a 10-year storm. For a 100-year storm, it goes up to 10 percent of your property.
“If you’re building out somewhere where land is cheap, that’s probably not a big thing,” he added. “But going with the current rate in the city, $1.3 million per acre (for commercial land), that could be a significant cost.”
For smaller developments in densely developed areas, more expensive underground systems will likely be used since ponds might not be an option.
Kemp said he believes developers understand the need for the code changes.
“I think everybody understands the impact of these stormwater events,” Kemp said. “Most people do, at least. For the most part, developers understand the situation. It’s not anything new. From 30,000 feet, there’s nothing really new about what we’re doing that you don’t see in other cities.”
Castleberry agrees, with some reservations.
“Generally, I appreciate and support the city’s need to improve their stormwater plan,” Castleberry said. “There are always costs you have to take on to do projects and this is one of them. The only thing I’d push back just a little on is the question of whether the pendulum has swung too far. I would have favored a system that can handle a 50-year storm. Basically, though, I understand the need to be aggressive in dealing with this. Something has to be done.”
Slim Smith is a columnist and feature writer for The Dispatch. His email address is [email protected].
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