THE CAUSE OF THE
A new look at the Historic Johnstown Flood of 1889
by WALTER SMOTER FRANK
The article below appeared on pages 63-66 of CIVIL ENGINEERING (May 1988)
in edited form
On May 31,1889, a wall of rushing water three stories high struck the city of Johnstown Pennsylvania. In its wake most of the town was destroyed and over 2,200 people were killed. In lives lost, the Johnstown PA Flood was the worst civil disaster the United States ever suffered. Every state in the nation sent some type of relief, and the people of sixteen foreign countries, including Russia, Turkey, France, Britain, Australia and Germany sent aid. For Clara Barton, the disaster was the first big test for her newly organized American Red Cross.
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Considerable care went into the construction of the new dam. The valley floor was cleared down to the bare rock. The upstream part of the embankment was built up of successive rolled layers of clay and earth, 2 ft thick, which were "puddled" by letting them sit under water for a few days to create a watertight barrier. The exposed upstream puddled ends were then covered with shale and small stone called "riprap" so that the action of the water that would fill the reservoir would not wash against the dam and weaken it. To add weight and strength to the embankment, the core of the dam consisted of shale, earth and small stones while the downstream section of the dam was built up of mostly rock, many weighing over 10 tons. Officially referred to as the Western Reservoir, the site became locally known as the South Fork Dam and was a "mature example of earth and rock dams."
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The completed dam stretched 918 ft across the valley and was over 72 ft high. The earth and rock used in its construction was 10 ft thick at the top and over 220 ft thick on the valley floor. Running under the center of the dam was a huge stone culvert used to discharge water into the South Fork Creek to be fed to the canal via the Little Conemaugh River. The water into the culvert was controlled by five sets of valves and cast iron pipes 2 ft in diameter. In the event that the discharge culvert could not handle water flows during heavy rains, a 85 ft wide spill-way was cut through the solid rock of the hillside near the eastern end of the dam.
In June of 1852, the valves controlling the flow of water into the culvert were closed. By August the reservoir was 40 ft deep. Engineers decided it would be unsafe to fill the reservoir much higher for the first two years. Lack of rain the following year depleted the reservoir. The year after, two small leaks appeared in the dam and the water had to be let out for repairs. The adverse financial impact of these events was followed by the opening of the Pennsylvania Railroad service between Johnstown and Pittsburgh in 1852. With rail service able to deliver goods faster, cheaper and more reliably, the canal was doomed. The State put the whole system up for sale and the railroad purchased it along with the South Fork Dam in 1857.
The dam suffered a major break on June 10, 1862, when the up-stream portion of the stone culvert running under the dam collapsed. There was little damage to property downstream, but a large section of the dam over the damaged portion of the culvert collapsed and was washed away.
For the next thirteen years the dam stood abandoned. The South Fork Creek past through the remains of the downstream section of the culvert which was still covered with eight feet of the embankment, but from there the gap reached up and out till it was almost 200 feet wide at the top.
In 1875 the Pennsylvania Railroad sold the damaged dam and 500 acres of surrounding property. The new owner removed the cast iron valves and pipes and sold them for scrap. In 1879 the property was sold to a Mr. Benjamin Ruff, who wished to repair the dam and create a summer resort.
Ruff's plan was simple. He would fill in the gap and rebuild the dam to its original height. When the lake filled, the excess water could be carried off by the existing spill-way. On October 15, 1879 fifty men were hired and reconstruction on the dam began. Ruff convinced 15 prominent men from the Pittsburgh area that his enterprise would be one of the finest resorts in the country. On November 15, 1879, they were granted a charter under the name of the South Fork Hunting and Fishing Club.
In the meantime the upstream entrance of the remaining part of the culvert was boarded up and any type of fill that could be purchased from local landowners was used, including mud, brush, tree stumps, hay, and even a few wagon loads of horse manure. On December 25, after five days of rain, the repairs to the dam were swept away. Undeterred, work on the breast was resumed in April 1880, but this time with slightly more appropriate methods.
A man who had some experience building railway embankments was employed to supervise the work. A double thickness of hemlock pilings was placed across the culvert entrance. Earth and large stone were dumped into the downstream part of the gap. This embankment was built up until it was high enough to enable a road to be graded out to it. Then rock, clay, shale and earth were hauled out and dumped.
Because the discharge system had been removed and sold for scrap, the water rising in the lake found its way to the stone embankment and started washing away any earth that was mixed with the stone. Hay, straw and cut brush were placed across the upstream face to stop the seepage. Then, earth and clay were dumped over the hay and straw to create the watertight section of the dam.
No rolling or puddling of the earth was done as in the original construction. The deposited material was little more than a colossal railway embankment without the strength or watertightness of the original. Whenever the lake waters reached the top of the repairs, a large wooden flume was used to carry the excess water over the top of the rising embankment.
About a mile upstream from the dam, on what would be the western shore of the lake, a forty-seven room club house was under construction along with some fine Queen Anne "cottages," boat houses and waterfront walkways.
In March 1881, the repaired part of the dam was higher than the bottom of the original spillway and, for the first time, water began flowing through it. By summer the repairs were completed, the lake was stocked with fish and the club house opened.
The road from the town of South Fork to the site reached a point where the top of the dam was only a few yards to its right with the spillway on its left. Since water was now flowing through the spillway and prevented visitors from crossing to the eastern shore of the lake, a bridge was constructed.
The foundation of the bridge consisted of 14 wooden supports 10 ft high at the entrance to the spillway, 99 ft wide at this point. Although the spillway had an average width of 85 ft, there was one area, 175 feet below the bridge, where the width along the bottom was only 69 ft. With these measurements in mind, it would appear that the bridge supports would not affect the discharge of the water. Thus, an array of iron screens to prevent the escape of fish were attached to the bridge supports.
Any traffic going to the club crossed over the top of the dam where the crest was fairly flat and 10 ft wide. If a wagon or carriage was on the breast, and another wanted to cross from the opposite direction, it would have to wait until the other completed its crossing. So, the top of the original dam was cut down 2 ft, giving a road width of 17 feet.
For the next eight years, the South Fork Hunting and Fishing Club was one of the finest summer resorts in Pennsylvania. South Fork, the town from which it drew it's name, was the nearest place of any size. The drive from the South Fork railroad station to the dam was about two miles and visitors were always impressed by the scenic beauty.
Once the dam was reached, drivers would drive out to the center and customarily stop so that the passengers could enjoy the view. To the right, the dam dropped off abruptly and the water that had flowed through the spillway could be seen in the South Fork Creek down in the valley glistening through the top of the trees. To the left the bank sloped only a few yards to the impounded waters which ran on up the valley for two and a half miles.
At the western end of the dam the road turned left, never far from the water, and a mile further on were the main grounds of the club where the width of the lake was nearly a mile. When the water was "up" in the spring, the lake covered over 400 acres and was over seventy feet deep in places.
To all but a few, everything appeared tranquil and safe in the spring of 1889. However, conditions were ripe for disaster.
The lake behind the dam had a perimeter of 7 miles to hold 20 million tons of water, meaning the weight of the repair section was four times heavier than the force of the water on it. A mixture of earth, rock and clay, properly placed, forms a satisfactory material for a dam, but leaks will weaken them over a period of time. A few small leaks had developed at the South Fork Dam, but with the absence of a discharge system, the water in the lake could not be lowered to make the repairs in a proper manner.
The bridge supports, with the iron screens attached to them, were not as innocent as they appeared. The screens ran across the bottom of the bridge supports and reduced the discharge of water to the height of the bars alone by 40%. There was also an array of lighter screens at both ends of the bridge. It was suspected by some that the 99 ft bridge was more of an obstruction than the narrowest point of the spillway.
In the original plans, a spillway depth of 10 ft below the crest of the dam was specified. When the club lowered the crest of the dam 2 ft to widen the roadway, they reduced the capacity of the spillway by one-fifth. In addition, because of the way in which the dam was reconstructed in 1880 and 1881, the repaired section settled until it was at least six inches lower than the ends of the dam.
It is not uncommon for the best earth dams to settle, especially at their centers, the weakest point where the water pressure is the greatest, but with proper maintenance they can be built back up. At the South Fork Dam the part of the embankment which should have been the highest, if only by inches, was the lowest.
On May 28, 1889, a storm started out of Nebraska moving east. When the storm struck the Johnstown-South Fork area two days later it was the worst down-pour that had ever been recorded in that section of the country. The US Signal Service estimated that 6-10 inches of rain fell in 24 hours over the entire section.
During the night small creeks became roaring torrents ripping out trees and debris. Telegraph lines were downed and rail-lines were washed out. Before daybreak the Conemaugh River that ran through Johnstown was about to leave its banks. Fourteen miles up the valley the amount of water entering the lake behind the South Fork Dam was 10,000 cubic feet a minute. The obstructed spillway, however, only carried off 6,000 cfm.
On the morning of May 31, the situation at the dam was serious. The lake had risen over 2 ft during the night and by 7 a.m. was two and a half feet from the top of the dam. Because of the heavy run-off the screens at the spillway became clogged with debris. Every minute 4000 cubic feet of water was building up in the lake. Caretakers attempted to remove the tons of debris that were clogging the screens. By 9 a.m. the water in the lake was still rising an inch every ten minutes. By 10 a.m. the water was less than a foot from the top of the dam.
A group of day laborers were put to work with picks, shovels and a plow and horse on the western hillside. They hoped to cut a trench so the water through it would cut a deeper and wider channel so that the rising waters would not cross over the dam. However, the hillside was 175 ft across and the workman succeeded in making a trench only 2 ft wide and 14 in. deep before hitting rock.
As the water inched upward the fears of some of the observers present were confirmed. It was obvious that the dam "dished a little" at the center where the reconstruction had occurred. As the water rose and started flowing through the small trench on the western hillside, the men and plow were sent to throw up a ridge of earth on the sagging portion of the dam in hopes of heightening it. They made little progress, for even with all the rain the roadway was packed solid.
The workmen on the eastern end of the dam removed the floor boards of the bridge and began ripping out some of the screens and heavy debris. The lake had now grown from its normal 407 acres to 450 acres.
By 11 a.m. the water was even with the sagging center of the dam and started to eat at the small mound that had been thrown up by the plow. Workmen frantically tried to keep the water from breaking through. The water through the trench the plow had cut was running almost knee-deep and its force had widened the trench but had not cut much deeper as hoped. The tremendous weight of the water in the lake forced several serious leaks to develop on the outer face of the reconstructed section. Some of the workmen refused to venture out on the dam.
Around 11:30 a.m. the small mound of earth thrown up by the plow suddenly gave way and the water started over the dam, quickly widening out to 50 ft. Parke, the "resident engineer" at the dam, rushed off on horseback to inform the telegraph operator at South Fork to warn the people in the valley below that the dam might collapse. (Due to the confusion of downed lines and the disbelief of key persons, the message was never taken seriously.)
Around 12:30 p.m. Parke returned and as he crossed the dam he found the water to be running over the center a "good six inches" and about 300 feet across, while the water in the trench had widened to about 25 feet and risen to 20 inches.
The weight and speed of the water over the dam, 123 tons per second, did little damage to the top of the hard packed roadway but it tore at the outer face of the embankment. The force of the water kept washing away the earth and rock, working its way back toward the lake. Not even the heaviest stone could long resist and was soon carried away. By two o'clock, the water had cut a huge step in the very center of the dam. The reconstructed embankment became thinner and thinner. At 3:10pm the entire repaired section of the dam, one witness reported, "simply moved away."
The impounded waters rushed through the opening and tore into the sides of the unprotected original embankment widening the gap a 100 ft on either side. The whole lake, over 20 million tons of water, emptied in 45 minutes. The destruction and death it caused in the valley below would capture the attention of the whole nation and the world.
Investigators subsequently concluded that "the failure was due to the flow of water over the top of the earthen embankment caused by the insufficiency of the waste-way [spillway] to discharge the flood water." But the club and its members were not deemed responsible. The investigators concluded that the original dam had been designed and constructed poorly. The collapse of the culvert in 1862 that caused a break and even the two leaks that had occurred 35 years before were referred to as "slight breaks" in support of this conclusion.
They also concluded that if the original discharge system had been installed and was discharging to its full capacity, if the spillway had not been obstructed, if the dam had not been cut down and even if the dam had not sagged, the water still would have crossed over the dam and caused a failure.
In essence, the investigators concluded that William E Morris, the original designer of the dam who had died, and the original contractors who were also dead, had designed and built a dam without regard to freak storms (that the area had always been known for) and did not provide a large enough spillway.
Based on what was known about the original construction at that time, there is evidence to support this conclusion. However, the original specifications and construction of the dam were not as the investigators believed. The original dam had been designed and constructed in a way that the "most extensive rainfall of the century" would not have caused water to cross over the dam.
Due to the lowering of the dam during reconstruction and the sagging center, the
effectiveness of an emergency-spillway in the area where the trench was cut was
eliminated. The existence of the "emergency spillway" was never revealed to the
investigators. Following are five arguments to support this finding:
In May of 1841, the state had stopped construction for financial reasons. Before work was resumed, Morris was asked to prepare new plans for the dam and specified again that the "waste-way or ways" should not have a width of less than 150 ft.
It is inconceivable that any engineer would approve the completion of a dam with a waste-way width of 69 ft at its narrowest point, when the specifications called for 150 ft.
2. The original construction contact for the Western Reservoir (South Fork Dam) was allotted to James K. Morehead and H. B. Packer on Jan 31, 1840 and called for the "Excavation of earth and rock in wastes ....50,000 yards" (note the term "wastes").
The main spillway as it existed then and does now, is a quadrant of a circle 310 ft down the center, an 85 ft average width, with a maximum height of 52 ft on the hillside and 20 ft on the dam side. Noting the contours of the hill and the way the spillway fans out as it reaches up, it becomes apparent, even today, that the removal of earth and rock in this waste could not have exceeded 34,000 cu yd. The remaining 16,000 cu yd was consumed excavating the emergency spillway on the western hillside which was only 175 ft across.
3. All observers, including Parke, in the vicinity of the dam before the break, stated that water started flowing through the western hillside before it started over the dam. Parke claims that his men were responsible for this because they had dug and plowed down the western hillside "no more than knee deep," or about 14 inches. Yet later testimony revealed that the dam sagged at least 6 in. and 2 ft of height was taken off the top of the dam to make the road wider; however, there was no need to cut the 175 ft hillside down to make the road wider.
If the western hillside was not meant to be lower than the top of the original dam, they would have had to dig down at least 30 in. when water was already flowing over the dam. Remember, Parke himself, in a letter to the ASCE in June 1889, stated that when he crossed to the western side (when water was running over the center of the dam at a depth of a "good six inches") he found the water in the trench to have risen to a depth of about 20 inches. Even if no attempt was made to dig or plow the western hillside down, the water would still have started through there before it started over the dam which sagged at least six inches and had been cut down two feet.
Ironically, the area where the trench was cut was 175 ft across and so level that
workmen could cut a trench in less than an hour that caused water to flow through it. Only
superb engineering could have created this situation (the top of the dam that the club
reconstructed was not that level). Also, Parke, not knowing that the hillside was an
emergency spillway constructed over rock, was amazed that the flow of the water through
the trench did not cut a deeper channel. In addition, on the outlet side of the trench,
the escaping water never touched the constructed portion of the dam which could have
weakened it. Here, too, superior engineering was evident.
In 1889, the average altitude of stations 1 and 1 + 50, where the flow of water through the trench could not have affected the level, is 1,610.24 ft. The average altitude between stations 2 and 10 on the dam (eliminating the washed out section) is 1,610.76 ft. To get a roadway width of 17 ft, 2 ft of embankment was taken off between stations 2 and 10. Add the 2 ft and the average altitude on the dam would be 1,612.76--this gives a higher altitude of 2.52 ft above the hillside stations of 1 and 1 + 50 where there was no need to take off two feet when the club made the road wider.
There is no doubt that there had been an emergency spillway in and around stations 1 and 1 + 50 at least 70 ft wide and at least 3 ft deep (the missing 0.48 ft can be explained by noting the contours of the landscape between station 0 and 1.) This area slopes into the area of stations 1 and 1 + 50 which could have easily been filled by erosion during the 37 years from the date of construction until the break. Even one year after the '89 break, P.E Brendlinger from the ASCE investigated the site and could find "but slight traces" of the trench that had been 20 in. deep and 25 ft wide.
5. On the eastern end of the dam where the only altitude measurement was taken (station 10+50), where there would have been no need to cut down the dam to make the road wider since the northern side of the road is the natural hillside, the altitude is 1,613.34. Since no cutting down would have occurred there, and since only 4 ft of puddled dam construction was needed on the lake side, the chances of subsidence would be minuscule. Therefore, at least 1,613.34 ft had to be the altitude of the original construction since the ends of the original dam would not be lower than the center. Ironically, 1,613.34 is almost exactly 10 ft above the bottom of the main spillway (1,603.4 ft), just as Morris specified in 1839 and 1841. That would have left an emergency spill-way on the western hillside over 3 1/2 ft deep and over 70 ft wide--wide enough to have carried off the waters of a storm greater than the one of 1889.
If the reconstruction of the South Fork Dam had been rebuilt to the original
specifications and construction, the disaster of May 31, 1889, would never have occurred.
Granted; a break like the one in 1862, when the culvert collapsed, could have caused great
damage. However, the South Fork Dam as originally designed by Morris and constructed by
Morehead and Packer would not have had water pass over it--the worst possible thing that
can befall an earth and rock dam--the unquestionable cause of the 1889 Johnstown disaster.
This is a view from what remains of the breast of the dam today looking toward the buildings in the far background (the white area on the hillside), where once the clubhouse sat at the water's edge.
This is a view of what remains of the breast of the dam today while standing on the east section looking across (the washed out portion) to what remains of the west section.
The above article appeared on pages 63-66 of CIVIL ENGINEERING (May 1988) in edited form.
For more information--links below.
Johnstown Flood Museum (Special thanks for the use of the two black & white photos.)
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