It was my privilege recently to give a talk to a combined meeting of the Pennsylvania Canal Society, the Ohio Canal Society, and the Northern Ohio Chapter of the Society of Industrial Archaeology. The occasion was their annual Fall Tour, which was located in the Pittsburgh area this year.
I chose for my subject the history of the twenty-three sets of dams and locks that make up the Pittsburgh District of the United States Army Corps of Engineers, with particular emphasis on the role of the Dravo Corporation in their development.
I chose to parse the subject geographically (Monongahela Leg, Allegheny Leg, and Ohio Leg) initially, and to then discuss each leg chronologically. Today the “Three Rivers Canal” extends 115 miles up the Monongahela to Fairmont, West Virginia; 62 miles up the Allegheny to Rimerton; and 126 miles down the Ohio to Hannibal, Ohio. Each leg has its own unique characteristics as well as its own unique history.
The Monongahela Leg was the first to be developed. As early as 1818, when construction of the National Road reached Brownsville, it became obvious that navigation improvement would be beneficial between that prospering city and its neighbor, Pittsburgh, about sixty miles downstream. A private firm, the Monongahela Navigation Company, built seven dams and locks by 1881.
A few years later the Corps took over and built eight more, extending the slackwater canal to Fairmont. In the twentieth century the Corps replaced all these dams with nine “modern” dams. More recently they have replaced Braddock with a new dam and are currently doing the same thing at Charleroi.
The success of the Monongahela Leg encouraged the Corps to develop a similar canal on the Allegheny, despite major opposition from timber interests who preferred to float logs downstream in a free-flowing river, unencumbered by locks and dams. The Herr’s Island dam came first, in 1903; by 1939 the canal was complete to Rimerton. All nine dams are fixed crest, with single (56’ by 560’) locks.
The Corps’ first navigation dam on the Ohio, in 1885, was a wicket dam at Davis Island, just east of Neville Island. The wicket dam featured hinged flaps (wickets) that could be raised or lowered to change the depth of the pool behind the dam. Eventually fifty-three dams of this design were built, all the way to the Ohio’s confluence with the Mississippi.
A few years later it became obvious that newer dams with deeper pools and larger locks were required to handle the traffic on the Ohio. In 1922 Dravo built the Emsworth dam a short distance downstream from Davis Island; the old dam was removed. Emsworth actually is two dams, a long one in the main channel between Neville Island and the North Shore and a shorter one in the back channel between Neville Island and the South Shore.
Emsworth was initially a fixed crest dam with two locks, 56’ by 360’ and 110’ by 600’. The larger, commercial lock is sized to permit twelve standard (26’ wide by 195’ long) or nine “Jumbo” (35’ wide by 195” long) barges to be locked through at one time. This combination of locks was replicated at the other five new dams eventually built in the Pittsburgh District.
Dravo followed Emsworth in 1929 with Dashields. This was the first use of circular steel sheet piles for cofferdams. When locks and dams are built in the rivers, the construction site is isolated by temporary dams (cofferdams), then pumped dry to provide a working area. When Dravo built its first dam (#2 on the Allegheny in 1901), cofferdams were built as a pair of braced timber walls, with sand and gravel between them.
In 1930 they persuaded the Corps to allow them to use steel sheet piling instead of timber, a significant improvement in both cost and utility. The next innovation – circular cells – became the standard for construction “in-the-dry”. From 1901 to 1965 Dravo had a continuous series of contracts for either a dam or set of locks on the Ohio River. During this they participated in each of the seventeen major projects in the “modernization” program, building either locks or dam or both’’’’’’.
In 1936 Montgomery Dam was constructed, with vertical lift gates to monitor the flow over the dam crest; Emsworth was retrofitted with vertical gates two years later. Although this capability was quite attractive, operating problems with the vertical gates prompted a switch to tainter gates when the remaining Ohio dams in the Pittsburgh District – New Cumberland, Pike Island, and Hannibal – were built between 1961 and 1975. Tainter gates are circular arcs stiffened by sector trusses meeting at hinge pins.
The Ohio is a unique situation. In early days it was a fine route west eight months of the year, but a bottleneck the other four. It now is a canal nearly one thousand miles long serving as a valuable transportation route carrying eighty million tons per year of coal, grain, petroleum, aggregates, etc. Its future is secure.
The same cannot be said of the Allegheny and Monongahela legs. Volume on the Allegheny peaked at nine million tons per year over twenty years ago; today it is less than five million tons. It is easy to surmise that its future will be limited to recreational traffic, with the possibility the dams will eventually be removed.
The Monongahela leg still carries fifty million tons of freight each year, primarily coal. The combination of society’s attack on fossil fuels and the decline of the iron-making part of the steel industry will undoubtedly reduce this total dramatically; the long-term future of the Monongahela dams is also questionable.
The economic success of southwestern Pennsylvania has benefited greatly from the development of the Three Rivers Canal in the last century and a half. Only the future will tell if it will continue to survive or if we will allow the Allegheny and Monongahela to revert back to their natural states.
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