By Greg Forester, Staff Writer
Princeton Township Committee members received a presentation on the geological history of Harry’s Brook on April 7, given by Dr. Richard K. Olsson of the Princeton Township Flood & Stormwater Management Committee.
Described by Township Committeeman Bernie Miller as “a very technical discussion,” the presentation gave township officials and audience members an overview of the waterway’s history, along with a glimpse of what has happened as Harry’s Brook has flooded, eroded and changed over the years.
”It really depends on how much, how fast and how localized,” Dr. Olsson said about flooding in the areas adjacent to the brook, which flows above ground from the area of Harrison Street and Hamilton Avenue all the way under Route 27, and into Lake Carnegie.
Dr. Olsson — a geologist and professor emeritus at Rutgers University — told committee members how the waterway carries sediments, the small pieces of sand, rock and other materials that usually end up getting deposited in and around the waterway’s floodplain, especially at times when the brook reaches flood stage.
The presentation also included an explanation of how and why streams meander in a snake-like fashion, and carve out an ever-more winding path.
In terms of flooding, Harry’s Brook reaches a state of being completely full every one or two years, according to Dr. Olsson, with slight spillage over the banks.
True flooding occurs at longer intervals. Those flood levels are known by the likelihood of the occurrence, such as a 10-year flood, 50-year flood, or 100-year flood.
For Harry’s Brook a 10-year flood represents floodwaters double the size of Harry’s Brook’s full capacity of water, and a 50-year flood is one having three times the brook’s full capacity. Large-scale flooding of the 100-year type was labeled “catastrophic flooding,” according to the presentation.
During those time periods residential areas surrounding Harry’s Brook and occupying the waterway’s floodplain are likely to be flooded.
April 2007’s flooding, which resulted from a major nor’easter, represented a 100-year flood event for many of the waterways in the area.
While the Township Committee did not take any action following the presentation, members said they appreciated the information.
”I think the members of the Township Committee came away better educated on what causes the problems we have previously seen,” said Mr. Miller.
