The local floods caused by Hurricane Irene were indeed historic.
The enormous volume of water in the Schoharie Creek set records Monday and probably exceeded the 100-year-flood level, said Jerry Butch, a hydrologist with the U.S. Geological Survey. Preliminary numbers gathered from river gauges show the Mohawk River in Schenectady County was slightly below the 100-year-flood designation.
The Hudson River in the Albany area was also just below 100-year-flood level, he said.
“The event was so large we are still determining [the final numbers],” Butch said Wednesday.
Hydrologists don’t like to refer to flooding events as a 100-year flood or a 500-year flood.
They would rather describe a 100-year flood as a high-water event having a 1 percent chance of happening in any year. It’s a way of describing the probability that a given flood exceeded 100 years of water volume records.
“There is a common misunderstanding,” Butch said. “Just because you have a 100-year flood, doesn’t mean you are safe for 99 years,” Butch said.
“You could have them two years apart,” Butch said.
Whatever the description, flooding from Irene, which had been downgraded to a tropical storm by the time it hit this region, set water volume records on the Schoharie Creek and was near record levels on the Mohawk and Hudson rivers.
“I can’t recall in the 32 years I have been with the USGS having 40 USGS gauges experience peaks of record [levels] from one event,” Butch said.
The 40 record flows came from rivers and creeks in eastern New York on Sunday and Monday from Essex County south into the Catskills. U.S. Geological Survey crews were in the field throughout eastern New York this week checking gauges to verify readings.
More than 13 inches of rain fell in the Catskills, with much of the water draining into the Schoharie Creek, said Raymond O’Keefe, meteorologist-in-charge at the National Weather Service in Albany.
The gauge at the Schoharie Reservoir reached 1,137.73 feet above sea level, surpassing the record of 1,136 feet set in January, 1996, O’Keefe said.
At the gauge in Burtonsville near the borders of Schoharie, Montgomery and Schenectady counties, a record creek level of 15.3 feet was recorded, surpassing the old record of 12.08 feet set on Jan. 20, 1996, according to preliminary records.
“All that water is pouring into the Mohawk River,” O’Keefe said.
The flooding devastated farmland, roads and businesses along the Schoharie Creek.
The Schoharie Creek empties into the Mohawk River, where the flooding also caused large-scale damage and property losses.
The extensive flooding along the Mohawk this week was almost identical to the flooding seen in June of 2006 when several days of heavy rain brought the river over its banks, O’Keefe said.
He said the fact that a tropical storm was able to track so far into upstate New York is in itself unusual.
“This is a rare event,” O’Keefe said. “For the areas hit with record flooding it was catastrophic.”
He said preliminary data from Tropical Storm Irene show the Mohawk cresting at 226.22 feet above sea level in Schenectady. This is the 11th highest reading on record but some 6 feet below the record of March 20, 1914.
The National Weather Service is using a new gauge at Freemans Bridge for its readings on the Mohawk in Schenectady rather than a gauge upstream on the Gateway Bridge, O’Keefe said.
He said the Freemans Bridge gauge was just installed last December. He said readings may be higher on the Mohawk near Schenectady’s Stockade area in light of how much flooding occurred there. Some residents of the Stockade said they have never seen flood waters this high in their neighborhood.
The Hudson River was also running extremely high, thanks to water entering from both the Mohawk from the west and the Hoosic rivers from the east. The Hudson was at 27.05 feet above sea level at Troy on Monday and called at “major flood stage” by the weather service. The Hudson at Albany was also at major flood stage at 15.4 feet above sea level. The record for Albany is 21.71 feet established in 1857, O’Keefe said.
The top wind gust from Tropical Storm Irene recorded at Albany International Airport was just 51 miles per hour. Wind gust of 59 miles per hour in Glenmont and 56 miles per hour in Scotia were recorded on Sunday during the peak of the storm.
The highest rainfall recorded in the Capital Region was 10.28 inches in Delanson in Schenectady County. The rainfall levels ranged from 4 inches to 8 inches through most of the region, OKeefe said.
In Saratoga County, rainfall measurement from the storm ranged from 6.75 inches in Gansevoort and 6.60 in Saratoga Springs to 2.94 inches in Corinth, according to preliminary storm numbers complied by the National Weather Service.