Members of Richmond Hill city council got a Cliff’s notes version of a lesson in hydrology at a Tuesday night workshop, as officials discussed Friday’s flooding and ongoing efforts to find solutions.
There, they learned that widening drainage ditches or building more retention ponds likely won’t be of much use and could hurt more than they help.
The discussion came at the beginning of the workshop and after a reported five inches of rain fell in a single hour in Richmond Hill.
That downpour on top of days of rain and a high tide caused flooding in a number of parking lots, streets and subdivisions.
But it also showed some areas previously prone to flooding were spared Friday, which officials showed progress is being made.
Still, council members were told the problem has more to do with low elevation than poor drainage. Much of the structures affected, as well as roads,are lower than FEMA established flood elevations, with some roads as low as 9 feet above sea level while the .
During the workshop, engineers with both EOM, the city’s public works contractor, and Hinesville-based Marcus Sack Engineering, which is conducting a study of the Sterling Creek watershed, spent more than hour on the issue discussing options and explaining Friday’s flash flooding. For starters, Friday’s rain would have extrapolated to a 500-year storm event, according to Sack, who said by contrast Hurricane Matthew in 2016 saw about 11 inches of rain over a 24 hour period and that occurred during a low tide.
What’s more, much of Richmond Hill is in the Sterling Creek watershed, and the city has already spent more than $500,000 on removing obstacles that restricted the creek’s flow.
Sack was hired in 2019 to design a new Sterling Creek bridge, and as part of that effort teamed with Dewberry, Inc., to study the impacts a new bridge would have upstream and downstream.
That study led the city to expand the scope of its efforts to better understand the watershed, which led to an understanding that the city’s options are few and likely to cost tens of millions of dollars – and even then may not work.
During Sack’s presentation, he said any 100 or 500 year “like” event such as Friday’s rain will flood most systems, and the cost in both building and maintaining any system would be out of the city’s reach.
Even raising the elevation of single street would be prohibitive, EOM Engineer Liberto Chacon said, noting Savannah’s project raising a portion of President Street cost $37 million.
What’s more, the permitting and environmental studies required at the state and federal level could take years, and “the engineered solution is working against the power of the Atlantic ocean and extreme rainfall.”
Solutions discussed Tuesday included a storm water pump station, but that would likely cost as much tens of millions of dollars a station to build and run, and is more than the city can afford. They’re also prone to mechanical failure.
The city could also work with property owners in flood prone areas to buy structures and convert them into green space, and Sack said this is usually the most cost effective solution. There are grants available which would cover up to 75 percent of the cost, leaving the city to pay 25 percent.
A third idea is to launch a comprehensive study of watershed, which would cost more than $1 million. Sack said Gwinnett County recently did a similar study that cost $10 million.
In the meantime, the problem isn’t going to go away and will get worse.
Rising sea levels and the increasing frequency of storms which are also becoming more intense are complicating the situation.
In the meantime, officials said the idea is to continue to address drainage through maintenance and the city could
soon hold a series of town hall meetings to inform residents.
As if COVID-19, flooding and other pressing issues of the day weren’t enough, Richmond Hill was hacked by a Russian last week who locked the city out of its computer system using an encryption key and then wanted a $5,000 ransom in bitcoin to get back in, the city said Tuesday night.
Rather than pay the ransom, the city was eventually able to get back in, according to city officials. No personal information of residents was compromised, City Clerk Dawnne Greene said.