Accurate surveys of erosion of the Falls of Niagara began in 1842.
From 1842 to 1905, the average rate of erosion of the Horseshoe Falls was 1.16 meters (3.8 feet) per year.
From 1906 to 1927, this rate of erosion was reduced to .70 meters (2.3 feet) per year. This reduction coincided with the large quantity of water being diverted for hydro-electric generation.
Today, through increased water diversion and anti-erosion remedial steps, the rate of recession at the Horseshoe Falls has been reduced to a fraction of what it used to be. Today it is estimated that erosion of the Horseshoe Falls is less than one foot per year. In the future, through remedial efforts and further water diversion that the amount of erosion at the Horseshoe Falls has been projected to be reduced to approximately 1 foot every 10 years.
Remedial work has included:
1) In 1906, approximately 122 meters (400 feet) of crestline of the Horseshoe Falls at the Table Rock was filled in to ensure a more even flow of water over the remaining crestline.
2) In 1941, the submerged Grass Island Weir measuring 443 meters (1455 feet) long was built to ensure the American Falls are guaranteed at least 10% of the water flow.
3) In 1953, the International Control Dam was built to assist in the control the water level flowing over the Falls and to divert water to the hydro intake tunnels.
4) In 1953, the flanks of the Horseshoe Falls crestline at Table Rock and Terrapin Point were deepened to allow for a more even water flow.
Today, erosion of the American Falls is estimated at 3 – 4 inches every 10 years. The water flow which is regulated at a minimum level of 10% of the estimated 100,000 cubic feet per second during the summer (50,000 cubic feet per second during winter) is insufficient to cause major erosion.
The greatest factor affecting the American Falls are the honeycomb type cracks at the crestline in the top dolostone caprock layer. The cracks project to the softer shale layer below. The hydraulic action of the water filtering through these cracks cause them to become enlarged and undermines the softer rock layer below. Combined with the cycle of freezing and thawing during the winter, the rock structure continues to weaken until that portion of the rock cracks apart, causing a rock fall.
The flow of water over the American Falls is insufficient to erode the rock talus at its base.