Nearly a month’s worth of rain fell on the Lehigh Valley in 3 days. Here's what it did to the watershed.
BETHLEHEM, Pa. — On average, the Lehigh Valley sees about 3.6 inches of precipitation during April.
But that was nearly the amount of rain — officially, 3.2 inches — measured at Lehigh Valley International Airport’s weather station Friday through late Sunday.
- The Lehigh Valley got 3.2 inches of rain Friday through late Sunday
- That's almost the amount the region normally gets in all of April
- The drenching caused a rapid rise of the Delaware River
Some areas got even more.
CoCoRaHS, or the Community Collaborative Rain, Snow & Hail Network, is a volunteer network of backyard weather observers who send measurements directly to the National Weather Service.
Here were some of those numbers:
- Palmerton, Carbon County: 3.40 inches
- Bowmanstown, Carbon County: 3.50 inches
- Lehighton, Carbon County: 3.61 inches
- Hilltown, Bucks County: 3.34 inches
- Jim Thorpe, Carbon County: 3.35 inches
- Shillington, Berks County: 3.68 inches
Some parts of New Jersey got nearly 8 inches of rain in the same time frame, leading to flood warnings extended through 8 p.m. Tuesday.
It was a deluge of water for a three-day period, and for areas south of the Lehigh Valley, more than the monthly rainfall totals in 13 of the past 18 months.
How the system dropped so much rain
On Sunday, a counterclockwise-spinning low-pressure system was moving up the coast. The Lehigh Valley was on the western side of the low, which meant heavy rainfall and cool northerly winds.
It also wasn’t the only storm system to factor into our forecast.
The pattern was a double-barrel low — weather parlance for double trouble. One system was over the Ohio Valley and transferred its energy to the secondary low riding up the eastern seaboard.
That’s why precipitation was so widespread on Sunday.
By 6 p.m. Monday, the National Weather Service’s Middle Atlantic River Forecast Center was forecasting flooding at 14 river forecast locations across the Mid-Atlantic region.
"The biggest takeaway for me was the fact that the vast majority of the period between Friday afternoon and Sunday was a slow and steady soaker."EPAWA meteorologist Bobby Martrich
"The biggest takeaway for me was the fact that the vast majority of the period between Friday afternoon and Sunday was a slow and steady soaker," EPAWA meteorologist Bobby Martrich said.
But Martrich was quick to note the weekend played out as expected.
"I figured on a widespread 2-3 inches-plus as a grand total for both events over most areas, and that was generally the idea for the Lehigh Valley," he said. "But some areas across New Jersey got hit a lot harder than that."
The impact on the watershed
The weekend drenching caused a rapid rise of the Delaware River, especially in Riegelsville at the northern tip of Bucks County.
A gauge measured water levels at just over 5 feet on Saturday morning, but projected the river would crest around 16.8 feet about 2 p.m. Tuesday.
At that level, the river is considered to be in the "action" stage — about 5 feet below flood stage.
During such events, rainwater hits pavement and impervious surfaces and flows into drains, picking up pollutants such as oil, road salts, fertilizers and much more. Those pollutants flow into nearby water bodies, where they can harm wildlife and even contaminate drinking water.
On Friday, during a wet well draw down, workers at Lehigh County Authority’s wastewater treatment plant fished something unusual out of the water.
A baby American alligator was found embedded in a clump of material screened out before entering the plant along the Lehigh River, off Union Street.
“This alligator was embedded with only its tail sticking out a boulder of this horrible grease and motor oil and diapers and fat,” said Barbara Miller, who was involved in the rescue.
Treatment plant Manager Gary Saunders said draw downs are usually done before heavy rain is expected.
"We turn our pumps on high or higher than normal and we pull the level in the pipeline that leads into the plant," Saunders said Tuesday. "That increases velocity and tends to flush any debris that's been settling in the pipe.
"The stuff that came up that the alligator was caught in is typically grease — it's mass blocks or chunks of grease that form in the pipelines.
"When that comes up during a storm, especially with the initial flush and higher velocities that come through we get inundated very quickly and it could clog things up and cause other problems."
Saunders said his team tries to simulate waterflow ahead of time to get debris out before storms hit, but said LCA is doing "all kinds of stuff" to prevent untreated water from going into a bypass line and out into the river.
"We try to avoid that at every cost," he said.
According to NOAA, those pollutants are known as nonpoint source pollutants and among the most significant threats to aquatic ecosystems in the country.
As the water runs over through the watershed and pollutants wash directly into waterways, the contaminants can infiltrate groundwater and concentrate in our streams and rivers before being carried down the watershed and into the ocean.