PENNSYLVANIA

Professor, team probe flooding risks in Conemaugh watershed

By JOSHUA BYERS, 

The (Johnstown) Tribune-Democrat

August 7, 2021

JOHNSTOWN, Pa. (AP) —

Scientific measuring devices have hung suspended in the Little Conemaugh River at the base of the former South Fork Hunting and Fishing Club dam, tracking the rise and fall of water levels for four years, and Christopher Coughenour has diligently recorded the readings.

The earthen dam has sat in ruins since the breach in May of 1889 let loose 20 million tons of water into the valley, destroying much of Johnstown. It’s now part of a historic landmark.

Not much has been done to study the local watershed and flooding that occurs within it since that disaster.

That’s where work begins by Coughenour, a University of Pittsburgh at Johnstown natural sciences assistant professor, and some of his colleagues and students.

“No modern hydrological study has been done,” he said, “at least not in the public domain.”

There are about 200 square miles of drainage that eventually flows into the Conemaugh River, which runs west toward Pittsburgh from the point where the Stonycreek and Little Conemaugh rivers meet in downtown Johnstown. Coughenour said his interest concerns direct runoff into the Little Conemaugh River sub-basin, which covers roughly 55 square miles of drainage.

Coughenour and his team are trying to figure out how much water can enter that watershed before the rivers rise and flood. They’ve also studied the recurrence intervals, which are the average expected times of discharge of high volumes of water.

By doing that, he said the research will provide insight into what happened in 1889, as well as the level of risk for a major weather-related event Johnstown faces today. Coughenour said that’s beneficial because often the Federal Emergency Management Agency and insurance companies use that sort of information to gauge vulnerability.

The point of the study is to determine the actual return period for an event such as the 1936 Johnstown flood, which was the largest discharge on record at the time, with 28,000 cubic feet of water per second passing through the valley. The Johnstown flood of 1977 beat that record by nearly double, with 40,000 cubic feet per second.

Tracking water data

The professor and team have monitored the river to record a variety of empirical data since 2017.

The group used a staff plate with inches and feet measurements for sight readings and a water logger for temperature and pressure analysis. The pressure reading is converted to height and measured as the hydrostatic pressure, which provides the stream’s “stage.”

Ideally, Coughenour’s team collected data four to five times per year.

That information was then used to create a stream rating curve, which is combined with NEXRAD – a special Doppler radar – to produce the watershed response data.

“What we’re trying to figure out is, ‘How much input does the watershed take before the stream rises?’ ” Coughenour said.

The team used what he called the unit hydrograph approach. That shows how the watershed responds to one unit of excess precipitation.

‘A lot of knowledge’

Surprisingly, Coughenour said, the best data during the study came from 2020, although the discharge measurements, calculated by gathering velocity readings against the width and depth of the stream, couldn’t be done because of COVID-19 restrictions.

Despite the setback, the pandemic didn’t really affect the project otherwise. Utilizing discharge data from previous years, the study’s integrity remained intact.

“I thought it was an amazing experience and opportunity,” UPJ alumnus Anthony Taylor said. “I gained a lot of knowledge.”

Taylor was one of the students who helped Coughenour with the research. He was tapped as a freshman by the professor to lend a hand because of his interest in hydrology, and helped until he graduated in 2019.

“It was an unforgettable experience,” Taylor said.

One aspect of the work that stood out to him was having to invent a cable-way system in order to collect velocity data on the river with a weighted device.

Because the study was conducted in a national historic site operated by the U.S. National Park Service, the group couldn’t permanently alter the area. That meant no digging for poles to set up a pulley system. So the team had to get creative.

Sharing the findings

Coughenour said they fabricated a system and temporarily mounted it to a tree.

Collecting this data allowed the team to determine the discharge of the river.

However, all of this is complicated by the hilly topography of the region and shifting weather patterns. There’s also the issue with calculating snowfall and a rapid melt, which Coughenour said his team didn’t do because that’s another factor entirely.

Taylor said he learned a lot by contributing to the project, and one aspect that stood out was how quickly the river changed based on precipitation. He added that he’d like to see the research expanded on.

The study was submitted for publication in June and he should find out in August or September if it was picked up.

Coughenour said, ultimately, all the data he and his team collect will be given to the National Park Service and will also be publicly available.

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Online:

https://bit.ly/3A460xa