Why Did Niagara Falls Go Dry in 1969?

Niagara Falls did not entirely go dry in 1969; rather, the American Falls portion was intentionally dewatered by the U.S. Army Corps of Engineers to study the significant accumulation of rocks at its base. This ambitious project aimed to understand the geological stability of the cliff face and determine if efforts were needed to remove the massive talus (rockfall) that had collected over centuries.

The Purpose Behind the Dewatering

For decades leading up to 1969, the American Falls had experienced recurring rockfalls, causing large quantities of debris to pile up at its foot. This debris not only altered the iconic appearance of the falls but also raised concerns about the long-term stability of the cliff and the safety of the surrounding area.

The primary objectives of the dewatering project were to:

• Assess the geological conditions: Engineers needed to get an unobstructed view of the rock formations underlying the falls and the extent of the talus.
• Study erosion patterns: Understanding how the water contributed to erosion and rockfalls was crucial for future management.
• Determine a course of action: Based on their findings, the Corps would recommend whether to clear the rockfall, stabilize the cliff face, or leave it untouched.

How the American Falls Were Temporarily Halted

To achieve the dewatering, the U.S. Army Corps of Engineers undertook a massive engineering feat:

1. Cofferdam Construction: In June 1969, a 600-foot-long cofferdam was built across the Niagara River, diverting the flow of water entirely away from the American Falls and over the Horseshoe Falls. This allowed engineers to access the bedrock of the American Falls.
2. Drying the Falls: Within days of the diversion, the mighty American Falls reduced to a trickle, revealing the bare rock face and the vast amount of accumulated debris at its base for the first time in an estimated 12,000 years.
3. Study Period: For over five months, from June to November 1969, scientists and engineers meticulously studied the exposed riverbed and cliff face. They drilled test boreholes, analyzed rock samples, and mapped the geological structures.

It is important to note that only the American Falls were dewatered. The much larger and more powerful Horseshoe Falls, which carry about 90% of the Niagara River's flow, continued to thunder unimpeded, ensuring the overall spectacle of Niagara Falls remained for tourists.

Discoveries and Outcomes

During the dewatering period, engineers made several key observations:

• Extent of Rockfall: They confirmed the immense volume of fallen rock at the base, estimated to be hundreds of thousands of tons.
• Geological Stability: Detailed studies revealed that while rockfalls were a natural and ongoing process, the overall stability of the American Falls' bedrock was sound.
• No Intervention Deemed Necessary: Ultimately, after thorough analysis, the engineers concluded that major intervention, such as clearing the talus, was not necessary. They determined that the rockfall was a natural part of the falls' evolution and did not pose an immediate hazard requiring significant human alteration. Some minor improvements were made, such as removing loose rocks near Prospect Point.

The dewatering was a significant event, drawing millions of curious visitors who flocked to witness the unprecedented sight of a "dry" Niagara Falls. Public opinion was divided; while some found the exposed rock fascinating, others preferred the majestic flow of water.

Key Facts of the 1969 Dewatering

The End of the Experiment

On November 25, 1969, after the studies were completed, the cofferdam was ceremoniously blasted away, allowing the Niagara River to once again cascade over the American Falls, restoring its full power and beauty. The 1969 dewatering remains a unique and historic chapter in the story of this natural wonder.