Month: November 2020

In the fall of 1905, representatives of the New York State Barge Canal visited Europe on a fact finding tour to see how the new dams (weirs) were working along the canals and river navigation. A stop was made to see the newly built bridge dam at Mirowitz on the Moldau, or today known as Mirejovice on the Vitava River. The engineers were interested in the Vitava as it was very similar to the Mohawk River, and they felt that it would offer a nice comparison to what New York wished to accomplish.

The bridge dam, or what the French called the “barrage mobiles a pont”, was a relatively new system of elevating the weir works above the river channel. Prior to this development, mobile or movable dams were of the trestle type which were attached to a sill in the river channel. By elevating the dam over the river, it was hoped that any floods or ice flows would not damage the structure.

So in 1905 the New York contingent visited Mirejovice to see this new weir. Interestingly, this dam is a mix of the old and new. The five-span-bridge was built to accommodate vehicles and to support the weir works that can be seen in the middle of the span. But to each side you can see the older trestle style needle dam. And in the other photos, you can see the group walking on the heavily stoned river bottom. The group watches from this bank as the weir is deployed.

The other dams along the Vitava were of the trestle type. The only reason that the bridge weir was built was due to the bend in the river and the fear that boats would not be able to line up for the lock while avoiding the piers of the road bridge that had to be built there. So it was decided to combine the two into one.

The Mirejovice weir was heavily promoted in New York during the construction of the Barge Canal as an example of modern construction. It is interesting that today the weir has been replaced while the bridge dams along the Mohawk remain in use 115 years later.

In the collection was a photo of the Horin Lock, which looks like it hasn’t aged a bit over the years.

These photos are from the New York State Archives, Barge Canal Collection 11833.

Michael Riley

The Mohawk River in New York State has been used as a transportation corridor since the beginning of man’s settlement. The river in it’s natural setting was shallow and relatively slow flowing, with the occasional series of rifts or rapids. Along the 120-miles between Rome and the Hudson river there are two waterfalls. The largest of the two is near the eastern end of the river, where the water flows over a 90-foot-high falls at Cohoes. At Little Falls the river flows over a series of rapids that are 45-feet in height. However in the 120-miles between Rome and the Hudson, the elevation change is only 450 feet. This made the river a natural corridor for movement from the east to the west.

This was such a natural pathway that in the 1700s, the Western Inland Lock Navigation Company constructed short canals and locks around the natural obstacles in the river. The falls at Cohoes was simply avoided by making Schenectady the eastern end of navigation. For those interested in the topic of early river navigation, I would suggest Robert Hager’s excellent work; Mohawk River Boats and Navigation before 1820.

The construction of the Erie Canal would change all this. The Mohawk valley route was used but the canal was kept separate from the river by constructing a man-made ditch. In some places this separation might be the width of the canal embankment, but wherever possible, the canal route was kept away from the river so the man-made cut would be protected from floods and ice damage.

The route of the canal returned to the river channel during the construction of the Barge Canal. Instead of avoiding the river, the canal would occupy it in a process called “canalization.” Dams would be constructed to form 12-foot-deep navigation pools, and locks would connect these pools. A major consideration for the engineers was what type of dam would best suit the river since the Mohawk was well known for its seasonal floods.

The Mohawk River has a large watershed that reaches north into the Adirondack mountains and south into the Catskills. From it’s beginnings north of Rome near Boonville, the river flows south to Rome and then turns east in the Mohawk valley. As it flows east, it receives the flow of the 76-mile-long West Canada Creek, which is another south flowing Adirondack foothills river. Just west of Amsterdam, the Mohawk joins with the Schoharie, a river that has it’s beginning near Indian Head Mountain, 93-miles south of its confluence with the Mohawk. With this large watershed, a heavy rain storm or snow melt miles away from the Mohawk valley can cause the Mohawk to quickly rise and flood without much warning. In the winter, large blocks of ice can form in the shallow river waters and when the weather warms in the spring, these ice chunks will begin to float on the rising waters, and create dams that can cause water to backup for miles. When the ice dam finally breaks up, the rushing water and ice flows can easily destroy anything left or built in the river channel.

The state did have some history with building dams in the Mohawk. Small fixed crest dams had been used to supply water to the Erie, such as the dam at Rocky Rift near Indian Castle. was one of these small dams. And prior to this, wing dams had been built along the Mohawk to help boats pass over the riffs. But the canalization of the river would be far beyond anything they had built to date. So they began to look elsewhere around the world to see what had been built and who had success.

One of the ideas they began to study was the movable dam. On a number of rivers, both in Europe and the United States, movable dams had been constructed to improve the navigation of the river by creating temporary navigation pools in times of low water. And the term “low water” is important here. The first movable dams had been designed and built by the French engineer, Charles Antonie Fracois Poiree, in 1834. (Although the bear trap dams built along the Lehigh in Pennsylvania are recognized as the first movable dam, they are built as part of a fixed crest dam, and thus are not a true movable dam.) The Poiree dam consisted of a number of iron frames that were fixed to a foundation on the river bottom. When the natrual river flow was sufficent for boat use, the frames were folded down to layflat on the bottom of the river. When the flow decreased in the summer and the river began to get shallow, men would lift the frames upright, and then lay a wood walkway across the tops of the frames. Once all the frames were raised and the wooden walkway installed, the entire affair looked like a trestle bridge, and thus the name of the dam is sometimes called the trestle dam. However, at this stage there is no dam, just a nice bridge. The dam was constructed by placing in-filling the upstream side of the dam with long narrow boards set vertically. The bottom of the board rested on a sill in the channel bed, and the top leaned against the wooden walkway. By installing board after board, a dam was slowly built up and the water is impounded. The height of the pool depended on the height of the trestle and boards, but these dams were typically three to eight feet in height. In France the boards are called aiguilles or needles, and the name of this type of dam is often called the needle dam. If the pool behind the dam had to be regulated, single or multiple boards could be removed. Once the natural condition of the river allowed use without dams, the needles could be pulled and the frames returned to the river bottom. These types of dams were later modified by French engineers named Boule and Camere, but the basic trestle framework stayed the same. Boule modified the dam by laying the boards horizontally and then joining them into larger gates that could be raised or removed when needed. Camere design a rolling curtain type of dam that looks much like a Venetian Blind.

Slowly the use of the movable dam changed as shipping changed. If the dam was left in place throughout the navigation season, the canalized river could be kept at a set depth. This built consistency into the use of the river. If shippers knows they an always expect a depth a four feet, and that the areas of fast water have been stilled, then shippers can begin to use barges instead of arks. It was only during times of flood, ice, or canal closure, that the dams would be removed.

The period of the mid to late 1800s was a great time of dam innovation, and other movable dams were invented that served the same purpose as the trestle dam, but used a different structural framework. The Chanoine dam used three or four foot wide panels (sometimes called a wicket) that were attached to the river bottom. A man on a bridge or boat would reach into the flowing water with a long hooked pole and lift the panel upright. The panel was supported by a single strut. The idea of the wicket dam was that once the water began to flow over the top of the panel, the water pressure would cause it to trip backwards and release water. Once the water level lowered, the panel would snap back into place. It was found that this self-regulation didn’t work well, so the dam was modified so that all the struts could be released by pulling a level on shore, and the entire dam would return to the river floor. Incidentally, these dams were quite successful, and the last one was replaced recently on the Ohio River.

The engineers in New York State were use to building and maintaining a man-made canal. For the canalization of the Mohawk, the state hired David A. Watt as a “expert designer.” David had co-authored the Improvement of Rivers, a two-volume book that covered the vast field of dam and river navigation topics. He had worked with the U.S. Army Corps of Engineers, and in 1905, he had completed projects in Kentucky and Ohio. David realized that the main issue for the canalization of the Mohawk River was the unpredictable seasonal flooding and ice flows. Early in the Barge Canal planning the trestle dam had been considered, however it was realized that the ice flows would quickly damage or destroy the frames as they lay on the river bottom. However, David had written about another type of movable dam was coming into use throughout Europe, this being the bridge dam.

At its core the bridge dam takes the trestle dam and turns it upside down. Instead of mounting the frames to the river bottom, the frames are suspended from an overhead bridge where they are safe from the ice flows and easier to maintain. The French had built a bridge dam at Poses on the Seine River in 1885. This dam combined the hanging frames with the Camere curtain dams. This dam was unique enough to be given a fair amount of press in the American papers. Watt knew about this dam but he focused on a new type of bridge dam that had been built at Mirowitz on the Moldau [Vitava] River in the Czech Republic. The similarities of the Moldau and the Mohawk is striking, and for Watt, the Mirowitz dam was just what he needed.

The Mirowitz bridge dam was a mix between a roadway bridge and a dam. It’s appearance was of a typical truss-type bridge with five spans. The dam components, which were were long steel beams and plates, hung off the bottom of the road-deck. These were attached to the bridge along the downstream side, and could be lowered or hinged down, so that the lower part of the bean rested on a concrete sill in the river channel. With these supports in place, the large plates that created the dam were lowered. The navigation pool was regulated by either allowing the water to flow over the top of the plates, or by lifting individual plates so that water could escape. Interestingly, or oddly, this dam was a hybrid of this new hanging bridge dam, and two sections of a Poiree trestle dam. And, among all the dams along the Moldau, the dam at Mirowitz was the only bridge dam. The rest were very large trestle dams with Boule gates. The Moldau dam was only used because it was thought that a new road bridge, and a new dam, would be too difficult to navigate around as Mirowitz was located on a long bend in the river. This one bridge dam at Mirowitz [Mirejovice] was often cited by Watt and others as the example for the new dams that would be built along the Mohawk.

Watt would need to build eight bridge dams along the Mohawk between Schenectady and Fort Plain. In this construction alone, he would be doubling the total number of bridge dams in use around the world. These dams would certainly be in the public’s eye as each dam consisted of a multi-span truss bridge, structures that would be very visible to those traveling through the valley on the New York Central Railroad and the main highways ran along the river. Their successes (or failures) would be on view for all to behold, especially those politicians who used the railroad to travel to Albany. It was a gamble for Watt and the state.

Construction began in 1906 and for the most part, all the dams were finished by 1913. The only exception was at Lock 8, where the contractor ran into quicksand and couldn’t complete his contract. For the most part, all the structures are alike, although each was adapted to fit into the environment. All the dams between Scotia and Amsterdam use three truss-type-spans as the river was naturally wider east of the confluence with the Schoharie Creek. All the dams between Tribes Hill and Fort Plain have two truss spans. The dam at Tribes Hill (at Lock 12) has two very long spans in order to minimize ice damming.

The vertical beams that hold the steel plates operate as pairs. First the frames are lowered into the river channel to rest upon a concrete sill. Each pair of frames holds two steel plates, and these can be raised or lowered as needed. Typically the lowered and larger plate remains in place all season long, and the upper and smaller plate is moved to adjust the navigation pool and flow of water. These two plates was an Watt innovation and a notable change from the dam at Mirowitz which used one large monolith plate. By splitting the plate into two, excess water could be released from the mid-point in the dam face. If the water was released under the plates, the flow would create scour in the river channel.

The frames and plates were raised and lowered by using a large mechanical winch. When first designed, this winch was driven by a steam engine and boiler that was moved along rails that circled around the outside of the bridge. Steam engines were used as electricity was not available to most of the rural dams, and the winch was designed to be powerful enough to raise the dam even if the frames and plates were deployed. The platform that supported the winch was cantilevered out from the bridge on all sides, and these cantilevered beams were also used to support the dam components. This left the inside of the bridge open for possible use as a highway bridge, although when first built, there were no plans to use any of the bridge dams in this manner.

As noted, most of the work was complete by the spring of 1913. In March of that year, the dams at Tribes Hill and Yosts (Locks 12 and 13) had been lowered to allow the dredging contractors to get an early start to the dredging season since the State was very eager to get the new canal completed and the old Erie abandoned. Unknown to all, a large winter storm was dumping inches of rain across the mid-west. In Ohio it is known as the “Storm of 1913”, and it’s flooding caused so much damage as to put the Ohio and Erie Canal out of business. In New York the storm headed east along the Mohawk Valley, catching the Barge Canal contractors unaware. As the flood waters rose, the construction wood, buggies, wagons and derricks was swept up. As the water began to rise, the locktenders at 12 and 13 decided to pull up the top steel plates but left the lower plates and frames in place. As the debris from the contractors sites along the river washed downstream, it began to collect and pile up on the plates and frames. These debris dams impounded the water to a greater depth then the dam was designed for. The resulting flood created stresses caused the plates and frames to twist and bend, the chains to break, and the supporting members in the bridge to buckle. Heroic measures were taken by the locktender forces to clear the dams, but the damage was done.

It was very apparent to everyone that the dams had some major issues. If the dams were not raised prior to flooding, they were impossible to raise. The dams are constructed to that the pressure of the water helps to seal the dam to the sill, much like a miter lock gate uses the water to help seal the gate closed. If any debris collects on the plates and frames, they become impossible to raise. Any adjustment has to take place prior to the flood waters reaching the dam. And, as they discovered in 1913, the bridge structure was strong enough to handle the immense pressure of the flood waters.

To salvage the dams all the bridges were given a additional, and sometimes a fourth, truss. In all cases, the downstream truss was twinned to add rigidity. (The dam at Scotia was built after 1913, and it was built with single, but stronger trusses.) The cantilevered sections were especially weak and these were strengthened. To help to reduce the weight on these cantilevered members, the heavy steam powered winches were replaced with lighter electric winches. On the original design, these winches ran on a track that circled the dam, much like a child’s Christmas train running around the tree. This was modified to that all the lifting points and winch were along the downstream side of the dam. The State made most of these modifications very quietly. In addition to all these repairs, the dam at Rotterdam Junction was modified to serve as a road bridge. Later in 1927 the dam at Tribes Hill would be also used as road bridge.

The next test of the dams was during the fall storms of 1938 when much the same flooding occurred. It was feared that four of the dams would fail, but they held, likely largely due to the work done after the 1913 floods. Of course, the last major event was in 2011 when Hurricane Irene and Tropical Storm Lee brought damaging floods to the valley. Although the storms resulted in damages over 50 million dollars, the dams held.

There were other bridge dams built as part of the Barge Canal project. At Herkimer a single span bridge dam was built in 1918 to replace a Poiree Dam that was first built there in 1910. At May’s Point in Seneca County, a single span bridge dam forms a navigable pool for Lock 25. On the Genesee arm of the canal at Rochester, a single span bridge dam was used to create the pool that creates the Rochester harbor. This dam was replaced in 1926 when the power company took control of the works and replaced the dam with a taintor gate dam. The last bridge dam was built in 1927 at Rocky Rift on the upper Mohawk. This was a smaller three span truss dam. The 1927 dam replaced a fixed crest and Boule trestle dam that was difficult to control.

The bridge dam fell quickly out of favor for the reasons seen here. They are difficult to operate under poor conditions, and once debris begins to build up on the frames and gates, they are impossible to open. The dams along the Mohawk might be the last of their kind, although two other bridge dams are still in use. The Emergency Swing Dam at Sault Ste. Marie, and the Camere dam on the Red River north of Winnipeg, are close cousins in the bridge dam family tree. All these are engineering landmarks.

I wanted find out if the bridge at Mirowitz (today’s it is Mirejovice) was still is use. The bridge is still in place, however the dam components have been replaced with a type of roller dam. I was able to grab a view of it off of Google Earth.