The Schoellkopf Disaster
Aftermath in the Niagra River Gorge
Niagra Mohawk Power Corporation’s (Niagara Mohawk’s) hydroelectric Schoellkopf Station was located in the Niagara River Gorge in the City of Niagara Falls, New York, USA. It was the largest privately owned hydroelectric station in the world. Schoellkopf, actually three adjacent stations: 3A, 3B, and 3C (see Figure 1), consisted of 21 generating units totaling 454,500 rated hp (334,800 rated kW). Stations 1 and 2 were the historic Adams stations located on the Niagara River above Niagara Falls. Station 3A, built 1905–1914, contained units 1–15 (numbered south to north); 13 horizontal 10,000-hp turbines (nine operating at 60 Hz and four operating at 25 Hz with generators rated 8,000 kW and 7,200 kW, respectively), plus two 1,000-hp station service units (see Figure 2). A wall separated the turbine and generator rooms. Station 3B, built 1918–1920, contained units 16–18 (numbered north to south). These were vertical 37,500-hp, 25-Hz machines with generators rated 26,000 kW each (see Figure 3). Station 3C, built 1921–1924, contained units 19–21 (numbered north to south). These were vertical 70,000-hp, 25-hz units with generators rated 52,000 kW each. The hydraulic head was approximately 210 ft (64 m). Power from the 12-kV Station 3A generators was distributed locally via underground cables. Power from the 12-kV Station 3B generators was transmitted on overhead lines to Harper Station located 2.8 mi (4.5 km) east of Schoellkopf. Power from the 12-kV Station 3C generators was transformed to 69 kV and transmitted overhead to Harper Station.
On Thursday, 7 June 1956, starting at approximately 5:10 p.m. and lasting for 15 min, a series of five rock falls from the cliff behind the station estimated at 120,000 tons (109,000 metric tons) destroyed Stations 3B and 3C and damaged Station 3A, resulting in a total loss of power from all units. This article will describe the four major concerns of the aftermath and describe possible causes of the rock fall.
Restoration of Electric Service
The first priority was to restore power to the interrupted customers. The load dispatcher’s office made arrangements to secure power from any possible source, including the Hydro Electric Power Commission of Ontario, Canada (HEPC), which was in the process of converting to 60 Hz and had surplus 25-Hz generation available. Crews at the Huntley Steam Station near Buffalo, New York, were called in to expedite completion of a 25-Hz machine undergoing overhaul. All the replacement power was more expensive than the Schoellkopf power, which caused financial hardship to many electrochemical and electro metallurgical companies.
All 25-Hz and 60-Hz industrial load interrupted was restored by 1:26 a.m. the next morning, 8 June, with one exception. A large portion of the 25-Hz load was not interrupted by the loss of Schoellkopf. Most 60-Hz interruptions were momentary, and some large 60-Hz loads were not interrupted. Some 12-kV, 60-Hz distribution cables serving residential and commercial customers failed. Service to these customers was fully restored by 12:38 a.m. on 8 June.
HEPC supplied 25-Hz power to Gibson Station located 2.5 mi (4 km) north of Harper Station. Bolometer readings indicated that the interconnecting 69-kV transmission lines were overloaded. Early on the morning of 8 June, a project was started to construct a new line between these stations. Material available south of Buffalo for a proposed transmission line was hurriedly trucked to Niagara Falls. Right-of-way was secured in short order. The mayor of Niagara Falls was requested to call a special city council meeting at 10 a.m. for the purpose of granting permission to cross the unused end of the city golf course. The New York City office of the New York Central Railroad was contacted to secure permission to cross railroad land. Permission was secured from a radio station and a private landowner to cross their properties. By noon on 8 June, a field office had been set up at Harper Station, a survey crew was available, design personnel were plotting the line, and a line construction contractor had been engaged. The first pole was set at 1:00 p.m., less than 20 hours after the rock fall. The author can recall being at Harper Station the following week and seeing fire hoses spraying water on an overloaded transformer. At the monthly operating committee meeting following the disaster, the relay engineer reported that all of the various circuit breaker relay operations were correct. He expressed amazement that the two 20-MW Lockport frequency changers had remained in service; on previous occasions during minor system disturbances they had tripped out.
Stopping the Flow of Water
Water for the Schoellkopf Station was diverted from the Niagara River about 4,000 ft (1,220 m) above the American Falls (see Figure 4). The 4,400-ft (1,341-m) long, 100-ft (30.5-m) wide hydraulic canal extended from the river to the canal basin at Schoellkopf. A 32-ft (9.8-m) high, 32-ft (9.8-m) wide horseshoe-shaped pressure tunnel constructed for Station 3C paralleled the canal. The rock fall broke the lower end of the six penstocks for both Stations 3B and 3C, and water was coming from the ruins in great quantities (see Figure 5).
Operators used hand cranks to close a number of the Station 3A headgates until an emergency generator could be connected to close the remaining ones electrically. The butterfly valves in the Station 3C gatehouse were closed with an emergency generator. The Station 3B headgates could not be closed by any method. Slots were provided in the structure at the top of Station 3B penstocks for stop logs. Only one set of stop logs was available, and a crane was required to set them. The leaf gates separating the pressure tunnel and the hydraulic canal were closed. With no control over water flowing through the three Station 3B 16-ft (4.9-m) diameter penstocks, the velocity increased from an estimated 4,000 ft3/s (114 m3/s) initially to approximately 18,000 ft3/s (514 m3/s) as the tremendous force washed away portions of the rock fall (see Figure 6).
A contractor was engaged to construct a cofferdam at the river end of the hydraulic canal as shown in Figure 4. Due to the high velocity of the water in the canal, estimated at 9 ft/s (2.7 m/s), the cofferdam could not be constructed as planned. To reduce the water flow, open frames were installed in the gate slots of the Station 3B gatehouse, and sheet piling was driven in front of the frames. This reduced the flow to 4,500 ft3/s (129 m3/s), which facilitated the construction of a steel frame and sheet piling cofferdam that was filled with rock. When difficulty was encountered in making the final closure, the pressure tunnel leaf gates in the Station 3C gatehouse were opened to admit water from the tunnel to the canal basin and canal. This reduced the differential head at the cofferdam. The closure was completed on 16 June, nine days after the disaster. The pressure tunnel leaf gates were closed, stopping all flow in the canal except for about 100 ft³/s (2.9 m³/s) leakage through the cofferdam.
Assessing the Damage
The following disaster sequence of events was confirmed by photographs and motion pictures taken by tourists on the Canadian side of the Niagara Gorge. Starting at about 5:10 p.m., a small rock fall occurred south of Station 3C. At approximately the same time, cracks appeared in the south wall of the station and the south wall collapsed. The second fall was much larger and landed on the roof of Station 3C in the vicinity of unit 21. At about the same time, a large crack appeared in the southeast corner of the cantilever crane pit, and a portion of the northwest corner of Station 3B building broke open. The third fall took place substantially behind unit 20 and extended north to the center of the terminal building (see Figure 7). The fourth rock fall extended from the terminal building to the control tower (behind unit 17) that carried the control cables up the bank to the control building (see Figure 8). The fifth and largest fall extended from the control tower to the crane pit (see Figure 9). This did not fall behind Station 3B but was seen to tip forward and fall on the remaining section of Station 3B. The rock fall from the 200-ft (61-m) tall cliff extended for a length of about 450 ft (137 m), being 0–20 ft (6.1 m) thick at the top of the gorge to about 20–60 ft (6.1 to 18.3 m) thick at the bottom. The plane of the fracture was about parallel to Stations 3B and 3C.
The superstructures of Stations 3B and 3C were crushed to the elevation of the generator floor (see Figure 10). Damage to Station 3A consisted of the destruction of the south end of the station building, mechanical damage to two turbine-generator units, destruction of the turbine and generator room cranes, and considerable damage to the generators due to electrical faults and fire.
On 16 July, a general contractor was engaged to remove a sufficient quantity of debris from the crane pit to permit investigation of the extent of the damage to Station 3A. This required the contractor to remove several thousand tons of rock up to 60 ft (18.3 m) high. Many of the pieces weighed in excess of 100 tons (98.4 metric tons). The contractor also scaled the cliff below the control building and removed sufficient debris from Station 3A to permit access of personnel to both the turbine room and the generator room. Personnel were lowered or raised over the cliff in a bucket attached to the cantilever crane. This work was completed by about 25 September.
Investigations of the damage to Station 3A show the turbines for units 3–15 suffered little if any damage; one casting on unit 2 turbine was cracked and unit 1 turbine was badly damaged. The turbines for units 2–15 were found to be outside the slide area and resting on good foundations. The turbine gates had remained partly open, thereby allowing the units to run for a considerable period of time, which caused considerable damage to the generators. It was also found that all the penstocks were intact and that no movement between the penstocks and the station wall had taken place. The governors, except for units 1 and 2, suffered only minor, if any, damage. The generators for units 1 and 2 were damaged beyond reasonable repair (see Figure 11). Generators for units 3–15 (except unit 12) were damaged but could be repaired economically by rewinding (see Figure 12). The stator for unit 12 was torn loose from its anchorage and overturned (see Figure 13).
From time to time, inspections were made of the remains of Stations 3B and 3C. These stations moved toward the river with a turning radius inside the Station 3A generator room. This movement appears as much as 20 ft (6.1 m) at unit 21 where the greatest movement took place. It apparently took place more or less as a unit with cracks appearing between some of the units, particularly at the construction joints between units 18 and 19 and between units 20 and 21. It also appeared that the plane was at a considerable depth so that any reconstruction would require excavation for new foundations. Access to the wheel pits of units 18–21 showed that these pits contained considerable quantities of fairly small rock and that the machinery in this area was not particularly damaged. Access to the inside of the scroll case for unit 21 showed that the scroll case with the distributor and wicket gates were intact as a unit. Measurements with a level showed that all these units plus unit 17 were inclined slightly from the vertical. This angle was approximately 5° on unit 21 and considerably smaller on the other units. The inclination was not in the same direction on all units, i.e., on units 19 and 21 it was to the southwest, on unit 20 to the northeast, and on unit 18 slightly to the west. Unit 16 was not accessible for inspection because one of the largest rocks destroyed at least the upper part of the generator. The penstocks of the units were broken at the lower end, and the Johnson valve of unit 21 was broken (a Johnson valve is used to control the flow of water in large pipes). The other Johnson valves were not accessible. Because rehabilitation of Stations 3B and 3C would require a complete dismantling of the remaining machinery, excavating for a new foundation at an unknown depth, and complete new construction with much new machinery, it was decided to abandon Stations 3B and 3C.
Table 1. Station 3A units in commercial operation
|Unit Number||Estimated Date||Actual Date|
|6||30 December 1956||20 December 1956|
|7||30 December 1956||21 December 1956|
|9||30 December 1956||4 January 1957|
|10||30 December 1956||5 January 1957|
|11||1 March 1957||14 March 1957|
|14||1 July 1957||3 May 1957|
|13||1 June 1957||6 June 1957|
|5||1 September 1957||8 June 1957|
|15||1 August 1957||27 June 1957|
|4||1 October 1957||1 July 1957|
|12||1 March 1957||1 August 1957|
Partial Restoration of Station 3A
As investigations progressed, it was decided to rehabilitate part of Station 3A. The elevators were returned to service on 20 October following replacement of some elevator shaft structural steel and repairs to the exterior stone wall. A crane from Niagara Mohawk’s Riverside Station in Albany, New York, was rehabilitated and installed in the generator room and was ready for service on 13 October. A crane for the turbine room was purchased secondhand, rehabilitated at the factory, installed in the turbine room, and was ready for service in November. Work was started on dismantling and rewinding the least damaged generators, units 6, 7, 9, and 10, using Niagara Mohawk crews under the direction of a General Electric Company erector. Next, Niagara Mohawk crews rewound unit 11, and General Electric Company personnel rewound units 13–15. Pole pieces from the rotors of these units were sent to the General Electric repair shop in Buffalo to be checked and repaired as needed. A new stator was ordered for unit 12, and new 60-Hz generators were ordered for units 4 and 5 to replace the 25-Hz units. The turbines for all of these units required only a general cleanup and scraping of the babbitt bearings. The governors and related equipment were cleaned, and minor repairs were made. A new wall was built to close the south end of Station 3A.
As repairs were completed, the units were placed in commercial operation as shown in Table 1. Units 6 and 7 were subsequently shut down during repairs to the canal basin cofferdam and returned to service on 3 January 1957.
Two secondhand 60-Hz generators were located in Dallas, Texas, and installed on units 3 and 8 to replace the station service generators.
It was decided to supply the water for Station 3A through the pressure tunnel and close off and drain the hydraulic canal. The canal was drained by constructing a short connection from the canal to an existing shaft that emptied into the tailrace tunnel for the Adams Stations. (This shaft was also used to drain the pressure tunnel.) This work was completed by Niagara Mohawk personnel on 25 September 1956. The canal had not been dewatered since its initial construction in the 1850s. Similarly, the canal basin had not been dewatered since it was constructed in 1904–1906. The canal and basin had been enlarged over time using underwater blasting. As a result, the bottoms were rough with many large rocks. It was thought that the underwater blasting had opened seams in the adjacent rock that may have allowed water to leak from the basin to the high bank. Therefore, the bottom and sides of the basin were cleaned and lined with reinforced concrete. An attempt was made to grout the rock bottom prior to placing the lining, but this attempt was abandoned when grout forced into a hole would come out through other holes some distance away. A steel frame and sheet piling cofferdam filled with a sandy material was constructed at the upstream end of the canal basin lining to separate the basin from the hydraulic canal (see Figure 4). When water was admitted to the canal basin on 14 December, the cofferdam showed signs of failure. Therefore, the basin was drained on 26 December, the cofferdam was reinforced and filled with crushed stone, and water was readmitted on 2 January 1957.
Studies showed that using the pressure tunnel to supply the canal basin turned the basin into a surge tank and that the shutdown of more than four units would cause the water to spill over the top of the forebay. The use of the old ice run or the Station 3B penstocks was abandoned when a test release of about 1,000 ft³/s (28.6 m³/s) down the unit 17 penstock showed water would come into the south end of Station 3A. The width of the spillway constructed at the south end of Station 3C varied from 119 ft (36.3 m) at the canal basin to 50 ft (15.2 m) at the high bank. The excavation was principally through earth down to bedrock with minor rock excavation required to maintain an elevation at the crest of 1 ft (0.3 m) above the canal basin water level. The spillway walls were lined with concrete, but the bottom was left unlined except for the area in the vicinity of the crest. A contractor started construction on 15 March 1957, and the last concrete was poured on 19 July. During construction of the spillway, station operators were instructed to maintain low basin water levels and, in the event of a major loss of load, to sound an alarm to enable personnel to exit the work area.
The bottom of the abandoned hydraulic canal was filled with ash from the city incinerator and layered with crushed stone. The upper fill was debris from the city’s urban renewal project. The railings and lampposts on the four concrete arch bridges carrying city streets over the canal were removed, and sand was placed under the arches. Steel truss bridges carrying two city streets over the canal were also removed.
Possible Rock Fall Causes
Rock falls in the Niagara River Gorge are not uncommon. During the 20th century, rock falls completely changed the crest of the American Falls and the crest on the United States side of the river at Whirlpool State Park. The geology of the area is a dolomite cap over layers of shale and sandstone. Over the centuries, Niagara Falls has receded by the force of falling water eroding the shale and causing the dolomite cap to collapse (see Figure 14).
Although the exact cause of the Schoellkopf disaster has never been determined, two possible causes have been mentioned.
One possible cause may have been from the effects of an earlier earthquake; minor earthquakes in western New York are rare but not unknown. Dr. Austin C. McTigue, a nationally known seismologist and chair of the Canisius College Physics Department in Buffalo, New York, was of the opinion that Schoellkopf was destroyed by an earthquake. Dr. McTigue said it was just another release of the elastic strain in the earth in the area. Any energy released must necessarily be the result of an elastic adjustment in the vicinity. He theorized that there was a definite pattern with earth disturbances stretching from Anna, Ohio, to as far north as Messina, New York, and Toronto, Ontario. Dr. McTigue pointed out that the Schoellkopf station was not subject to erosion or erosion-like forces found at both the American and Horseshoe Falls.
A second possible cause may have been from the effect of the procedure used to try to stop water leaking through the gorge wall behind Stations 3B and 3C. As noted earlier, the hydraulic canal and canal basin were unlined and may have been leaking water to the high bank. When the canal was drained, the water table dropped so low that the wells in the vicinity used by some commercial businesses for air conditioning went dry. This showed that the unlined canal was a major source of groundwater in the area. In addition, the cliff behind Stations 3B and 3C was honeycombed with the tailraces of former industries located at the top of the cliff that used mechanical power in their manufacturing processes (see Figure 15). Niagara Mohawk engineers decided that the best way to stop this leakage was to place a grout curtain along the high bank behind the two stations. This curtain would be 300 ft (91.4 m) deep starting at the south end of the Station 3A concrete forebay and extend to the south end of Station 3C (see Figure 16). Work started at Station 3A in May 1956 with a survey party laying out the location and vertical angle of the grout holes and Niagara Mohawk crews performing the boring and grouting. As work progressed, the leakage of water slowed. Although this work had not been completed at the time of the rock fall, it may have changed the hydraulic pressure in the rock behind the grout curtain.
There had been some rock movement prior to the 7 June 1956 rock falls. In 1941, an inspection was made of the draft tube on unit 21 due to uneven wear between the turbine runner and the seal ring at the top of the draft tube. The bottom of the draft tube dispersion tube was found to be misaligned, an indication of possible rock movement. At a later date, the Johnson valves were found to be distorted and could not be operated in their normal fashion. A condition known as “rock squeeze,” the inward movement of the walls in the turbine pits over a period of time, caused problems at the Adams and Rankine Stations.
On the morning of the rock falls, water leakage from the cliff behind Stations 3B and 3C was increasing, and water was flowing across the unit 21 generator floor. Ceramic tiles were popping off the restroom walls, and glass was falling out of some Station 3C windows. Crews were placing sand bags and using squeegees to keep the water away from unit 21 generator at the time the first rock fall started. Of the 40 men in the station, 37 escaped through the north end of Station 3A. Three men exited the south end of Station 3C. Two were picked up by a launch from the Maid of the Mist, a tourist boat company. The third was washed into the river and drowned. It is remarkable that only one person lost his life in the catastrophic rock falls suffered on 7 June 1956.
In 1921, Niagara Mohawk’s predecessor, The Niagara Falls Power Company, was issued Federal Power Commission (FPC) License No. 1 to divert 20,000 ft³/s (667 m³/s) of water from the Niagara River for 50 years. In 1950, a new treaty between the United States and Canada increased the allowable diversion (actually specifying the amount of water that must flow over the falls rather than specifying the maximum diversion). Within a year, Canada proceeded with construction of the Sir Adam Beck Station No. 2 at Queenston, Ontario, to take full advantage of the 300 ft (91.4 m) head at the end of the Niagara Gorge, and 60-Hz power generation began in 1954. Development on the U.S. side was delayed by a curious clause in the treaty that required the U.S. Congress to determine the developer. The House of Representatives passed a bill to permit a consortium of five private power companies to do the development, but public power proponents in the Senate delayed any action until after the Schoellkopf disaster. In 1957, the Power Authority of the State of New York (PASNY, later New York Power Authority) was awarded a 50-year license. Construction of the Niagara Power Project began in 1958, and 60-Hz power generation started in 1961.
The Schoellkopf and Adams Stations were shut down on 30 September 1961, and Niagara Mohawk surrendered its FPC license. These stations were subsequently demolished.
A rate schedule dated 15 August 1957 (and withdrawn 30 September 1961) specified that 132,816 kW of the power from the Schoellkopf and Adams Stations were for use by 17 electrometallurgical and electrochemical companies (plus the National Biscuit Company’s shredded wheat cereal plant). The rate for this power was US$2.23 per kW per month of demand; there was no energy charge. Because this power was expected to be used around the clock, the charge for a 30-day month (720 hours) was equivalent to a total cost of US$0.0031 per kWh. These (and other companies) later became eligible for an allotment from PASNY known as “replacement power.”
The author would like to acknowledge the valuable assistance of Roy W. Cotton in the preparation of this article. Mr. Cotton was employed by The Niagara Falls Power Company and its successor, the Niagara Mohawk Power Corporation, in the Western Division Engineering and Law Departments from 1939 to 1982 and as a consultant from 1982 to 1997.
For Further Reading
B. Gawronski, J. Kasikova, L. Schneekloth, and T. Yots, The Power Trail: History of Hydroelectricity at Niagara. Buffalo, New York: Western New York Wares.
E. D. Adams, Niagara Power. New York: Niagara Falls Power Company, 1927.
T. J. Blalock and C. A. Woodworth, “25-Hz at Niagara Falls, end of an era on the Niagara Frontier, part 1,” IEEE Power Energy Mag., vol. 6, no. 1, pp. 84–90, Jan./Feb. 2008.
T. J. Blalock and C. A. Woodworth, “25-Hz at Niagara Falls, end of an era on the Niagara Frontier, part 2,” IEEE Power Energy Mag., vol. 6, no. 2, pp. 78–82, Mar./Apr. 2008.
R. Berketa. (2012, 13 Feb.). Schoellkopf Power Station disaster, a history. Available Online.
J. Paradise. (2012). Schoellkopf Power Plant disaster. Available Online.
CGM Systems, Inc. (2005). Niagara Falls geography. Available Online.