Lake Montclair, dam restored to meet new state flood standards

If Montclair has a 100-year storm, the spillway will be able to accommodate it.

Lake Montclair was lowered to just 20 feet this past summer, leaving residents who are used to summer swimming and boating on high and dry.

The lake’s spillway, an area designed for lake water to spill over the top of a dam in the event of a heavy rainstorm- needed to be fixed. The spillway needed to be widened and deepened and a cutback protection wall was installed underground  – as Lake Montclair also underwent changes to meet the state standards for dam safety regulations.

The repairs come after the state recently changed the “maximum probable precipitation” standards, an estimate to how much rain could fall during a massive storm such as a hurricane.

The values from the 1970’s were 28, 33, and 37 inches of rainfall in 6, 12, and 24 hour time brackets. A study was done by the state and the numbers were updated in 2016 to 26.3 and 30.1 inches for 6, 12, and 24 hour periods based on historical data. Lake Montclair did not meet the new standards.

The updated standards help to ensure the dam doesn’t burst during periods of heavy rain.

The Montclair Property Owners Association also had to widen and deepen the lake and also installed a cutback protection wall – a big concrete wall designed to stop erosion so the lake doesn’t drain into the spillway, said Justin Field, with MPOA.

With the repairs complete, it took about three weeks for the water levels to return to normal.

Maintaining the spillway is a big deal for the surrounding area, Field explained. Lake Montclair is part of the Powell’s Creek watershed, which, according to the Prince William Conservation Alliance, “begins near Independent Hill and flows past the Prince William landfill on Route 234, then on to  Montclair, where it meets the dam that forms Lake Montclair.”

If the dam were to break, that would spell disaster for nearby neighborhoods.  

“There are almost 400 occupied structures that would be damaged, flooded – Route 1 would be affected, I-95 would be affected, all the way out into the Potomac River. So that’s the importance of good upkeep on our dam which we do, and then making sure our spillway met all the requirements that it needed to meet.”

Richard Arvin, Chairman of the Montclair Lake Management Committee, is one of a group of volunteers who manage the maintenance and ecology of the lake. Arvin has lived near the lake for about 15 years.

Many residents complained while the lake was dry. One of the fears from residents was that fish would be killed.

That didn’t happen.

“We did not have a fish kill. We didn’t kill anything off.” Arvin said. Arvin explained that they had discussed the impact to wildlife with the Department of Game and Inland Fisheries and they weren’t concerned.

With the low lake level, he also said it was an opportunity to get some projects done that they wouldn’t have been able to do otherwise.  The association repaired swim platforms, added new fish, held a lake clean up, and a lot of residents repaired their docks. “So there [were] some advantages,” Arvin said.

They also found a sunken pontoon boat at the bottom of the lake.

Despite the inconvenience for those who wanted to enjoy the lake, Field said summer was the best time to close the lake. The warm weather was a benefit because of the backfill material that needed to dry out.

He also explained they didn’t want to risk running into delays during colder weather that would cause the project to go into the next summer. This way, they figured they could just affect one season of recreation rather than several.

“We bit the bullet, understanding it was going to be an inconvenience but the summertime was the best time for us to do it, get it done, so we that could enjoy [one] compliance with the new state regulations, and then just have our lake back next summer for a full recreation season.” Field said.

This should be the last time the lake will be lowered to this extent. Other than the annual lowering of around three feet that happens near Thanksgiving, Field said they don’t foresee the lake to be lowered to anything near the level it was lowered during this project.

The 108-acre lake sinks 54 feet at its deepest point.