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Posted 11/1/2017

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By Chris Gardner


“ONE DEAD IN WORST FLOOD SINCE 1884” screamed the top of the front page of the August 24, 1933 edition of The Gazette and Daily of York, Pennsylvania in all caps - along with several other headlines about that same devastating flood.

That flood was the primary impetus for the inclusion of Indian Rock Dam in the Flood Control Act of 1936, which authorized the construction of Indian Rock Dam as well as hundreds of other flood risk management works across the country.

Construction on the dam was completed along the west branch of Codorus Creek in 1942 and has been reducing flood risks to York and other downstream communities since then. The U.S. Army Corps of Engineers estimates that Indian Rock Dam has prevented more than $55 million in damages to downstream communities during its lifetime, though the number is likely higher since that primarily takes into account the most extreme high water events.

The project is an earth and rock structure 1,000 feet long rising 83 feet above the streambed, with a side-channel spillway and gated outlet conduit in the right abutment. The normally dry reservoir area can be filled with impounded water to its storage capacity of 9.1 billion gallons before its spillway sees flow, allowing water to move past the dam to prevent too much pressure from building up behind it.

The Flood of 1933 – The Reason Indian Rock Dam Was Built

The powerful flood of 1933 was still on the lips of locals when they came to celebrate the 75th anniversary of the U.S. Army Corps of Engineers completing Indian Rock Dam.

“The 1933 flood caused $4 million in damages, that’s equivalent to $75 million today,” said York Mayor Kim Bracey during Indian Rock Dam’s 75th anniversary commemoration. “More than 800 properties were lost and 3,000 people were left homeless as York was flooded as far east as West Market Street and to the west, Newberry Street.”

Melanie Markowski, nearby Windsor, Pennsylvania said the flood left a big impression on her late mother, who was living in York at the time.

“My mother, told the story always, that the flood waters came and chased them down the street,” “They said people ran down the street, and beat on doors and said ‘Get out of your homes! Get out of your homes, the water’s coming!’ and they came out the front porch and they looked down the street and they started to run because they could see the wall of water coming.”

Markowski and her husband came to the Indian Rock Dam’s 75th anniversary open house to check out the dam that had prevented a repeat of that 1933 storm.
“She always said now this can never happen again,” Markowski said, noting she wished her mother could have come as well. “She was very pleased when they built the dam.”

Several hundred people came out to Indian Rock Dam’s 75th anniversary celebration, which provided the unique opportunity for the public to look inside the dam’s gatehouse – normally closed to the public – and learn about the dam’s history and ask questions of its staff.

Markowski was one of many people that came with a personal connection to the dam and its history.

Erma Henry-Raver said the 75th anniversary event interested her after she read about it in the local paper, so she began looking through her archival trunk for photos and other items related to Indian Rock Dam. She brought along photos from 1945 of her and her family coming to see the new dam when she was a teenager as well as photos of flooding sold as souvenir postcards after the 1933 flood and original newspapers from the flood itself.

“I knew we were going to be here when I got over to her house the other day and she had the contents of the trunk all over the living room,” said her son Tom Raver. “Her family had a farm down towards the Red Lion area and they came in on weekends to the markets downtown so there was their connection because they sold their produce, butter, eggs and stuff at the market downtown and when the flood came in they couldn’t come in. They benefitted from the flood gates too by not being shut out of the market again.”

Tropical Storm Agnes – Indian Rock Dam’s Biggest Test

The dam did its job after being completed in 1942, preventing various potential floods downstream. Thirty years after the completion of Indian Rock Dam, it faced its biggest test when Tropical Storm Agnes brought massive flooding throughout the Susquehanna River Basin. Even with Indian Rock Dam functioning, York still saw significant flooding – though it could have been much worse.

Tropical Storm Agnes brought so much water that it filled Indian Rock Dam’s reservoir with 9.1 billion gallons of water. Water in addition to that 9.1 billion gallons flowed into the concrete spillway and continued downstream where it met with other floodwaters impacting York. 

Jeff Gilbert came to the event at Indian Rock from nearby Shrewsbury, Pennsylvania, but has had a family connection to Indian Rock Dam since it was first built, noting that a portion of his family’s farm upstream of the dam was purchased to be part of the dam’s dry reservoir area before he was born.

For him though, his most powerful memories associated with Indian Rock Dam were during Tropical Storm Agnes. He said that while it had been raining heavily, he and his mother didn’t realize just how significant the rain had been until they saw the lake forming in the reservoir and when they visited his nearby aunt.

“It (Codorus Creek) was literally a lake, and we pulled up to my aunt’s house and she came out in her bath robe and they had been bailing water of her basement and she said ‘Don’t you know that York is in a state of emergency and everything’s closed!,’” Gilbert said. “During the event, we actually came over and we actually watched the water going over the spillway. It was pretty amazing, it looked like Niagara Falls. It was significantly over the spillway, you could see a huge amount of volume coming over.”

Estimates are that the water from the reservoir rose from one to two feet over the height of the side of the spillway, leading excess water to flow into the concrete spillway and downstream.

While water did make it downstream past Indian Rock Dam via the floodway, the dam still held back what would have been 9.1 billion more gallons of potential floodwaters and it is estimated flooding could have been up to 13 feet higher in downtown York had Indian Rock Dam not been there.

Indian Rock Dam Today – Celebrating 75 years, and Counting, of Reducing Flood Risks

Since Tropical Storm Agnes, Indian Rock Dam has continued to manage the flow of the West Branch of Codorus Creek, often largely unnoticed.

Many attendees of the 75th anniversary event were surprised to learn that the dam’s gates were operated as recently as February 2016 to reduce the risk of flooding along Codorus Creek downstream of Indian Rock Dam during a high water event associated with snow melt.

While that event was not one of the more significant ones faced by Indian Rock Dam and its personnel, it did require management of flow downstream to reduce risks. 

Some of the more significant events where water was impounded behind the dam include Hurricane Sandy in 2012, and unnamed high water event in 2013 and Tropical Storm Lee – all of which required holding back billions of gallons of water from downstream. During Tropical Storm Lee, 44.1 percent of the reservoir’s storage capacity was used – meaning just over 4 billion gallons of water was being impounded to reduce risks to York and other downstream communities.
These were just some of the facts and figures that the several hundred attendees at the dam’s 75th anniversary celebration learned about.

While many people have historic connections and memories associated with Indian Rock Dam, Head Dam Operator Steve Young said that in recent years that his team at the dam has been working on forging new bonds with the surrounding community as well.

“What stands out to me at Indian Rock in recent years is how we’re more and more involved with the surrounding community and different people and organizations,” Young said, noting they work closely with the Pennsylvania Fish and Game Commission and the Fraternal Order of the Police on use of land within the dry reservoir and also partner with local environmental and recreational groups as feasible. “It’s not just about Indian Rock Dam. We partner with different groups propose different things and we find ways to work with them.”

Even with that increased connection to the surrounding community, he said he was pleasantly surprised by how many people came out to the 75th anniversary event to learn about the dam and how it reduces flood risks to their communities.

“When this event was first proposed, I had my doubts on the kind of turnout we would get. I thought, well, Indian Rock Dam is a dry project, we don’t have a lake, we don’t have a lot of recreation other than public hunting up in the reservoir and I was wondering what kind of turnout we would get,” Young said. “I was very surprised at the turnout. I was astonished. It makes me feel good that we’re doing something the public appreciates.”

flood risk management Indian Rock Dam