A repair design for the Lake Forrest Dam finally is gaining “momentum” with a preferred option after three years of talks, according to the head of a homeowners association working with the cities of Atlanta and Sandy Springs.

But repairs would take a minimum of two years. Meanwhile, a recently filed emergency response plan shows the reason the state Safe Dams Program is pushing for those repairs. In a worst-case failure, the lake behind the dam would flood a huge section of Chastain Park within seconds, submerge such major roads as West Wieuca under five feet of water, and flow for miles both upstream and downstream on Nancy Creek.

A worst-case-scenario failure of the Lake Forrest Dam could flood a huge section of Chastain Park and Nancy Creek, as shown in blue on this map contained in an Emergency Action Plan filed with the state Safe Dams Program by the city of Sandy Springs.

The fatal potential of such a flood is why the state classifies the 60-year-old earthen dam as “high-hazard,” which is not a judgment of its condition — though there is no question it indeed needs repairs.

But work on a solution has dragged on since 2009 due to the dam’s location directly under the 4600 block of Lake Forrest Drive, right on the Atlanta-Sandy Springs border, which makes for complicated ownership and liability issues. Both cities, several individual homeowners, and a larger lake-owning group of homeowners called the Three Lakes Corporation all have repair responsibilities, according to the state.

Neal Sweeney, the current head of Three Lakes Corporation, said there is no specific timeframe for agreeing on a repair option, but there is a sense of urgency, as the state could take the owners to court to mandate a fix.

“Nobody wants to be in a position where all of a sudden we’re under the gun of some enforcement action,” Sweeney said.

In recent years, Sandy Springs has taken the lead on studying repair options, splitting the cost with Atlanta. The work included removing the fish from the lake and lowering its level by 12 feet. City-hired engineers say the dam has several problems that could cause collapse: trees growing on its slope, a corroding pipe inside it, and an inability to handle the flow of water from a major rainstorm.

Last fall, engineers presented the Sandy Springs City Council with two repair design options: an upgraded version of today’s dam, known as the “full pool” option for restoring the lake, or a new, smaller dam built farther upstream. Either option could cost roughly $7 million and take years to complete: nine to 12 months of design and permitting, and 15 to 18 months of construction, possibly including the closure of Lake Forrest Drive during work.

Since then, city of Atlanta officials also reviewed the design options, according to Department of Watershed Management spokesperson Rukiya Campbell. Now, both cities say, they’re working with homeowners — around the lake as well as downstream — to get support for one of the designs to move forward with further engineering and public review.

Sweeney said that Three Lakes Corporation has been “very actively cooperating” with both cities over the past eight to nine months, receiving useful expert advice. The current discussions are on “nitty-gritty stuff” like state environmental permitting and the possible construction impacts, he said.

The homeowners “absolutely” prefer the “full pool” design to restore the lake, with the other option as “just a non-starter for us.”

“Needless to say, going from lakefront property to what now looks like a wide, dirty creek” is not popular among the homeowners, he said, so the “full pool” is the way they want to go.

Another question still hanging: Will the homeowners have to pay a share of the repairs costs?

“That’s yet to be determined. Our position is, we shouldn’t be responsible for fixing Lake Forrest [Drive] or fixing the watershed,” Sweeney said, adding that some homeowners are willing to help in other ways, such as donating property easements for construction.

To read the Emergency Action Plan for the dam filed with the state, click here.

Editor’s note: The Reporter Newspapers has published a series of articles about “high-hazard” dams in our communities. Previous installments have looked at the location and condition of the 11 local “high-hazard” dams; the cost of maintaining these dams and the long process of repairing them; concerns about the lack of emergency plans in case of a dam failure and an overview of recently filed plans; and how the state inspects the structures.