The history of the aqueduct

The Dalsland Canal was completed between 1864 and 1868. Construction was overseen by the renowned canal builder Nils Ericson. Due to the soil conditions in Håverud, it was not feasible to build a normal lock system at the site. The rock was too loose, the current too strong and the slope too steep. So Nils Ericson came up with the brilliant idea of building an aqueduct instead. Werner Ericson, his son, was the foreman.

The aqueduct was manufactured by the renowned firm Bergsunds Mekaniska Verkstad in Stockholm. The sheets where put together on land, with the heavy chute hauled into place above the river.

The aqueduct consists of a freely suspended bridge, where the water is channelled through a 33.5-metre long sheet metal chute above the river. The sheet metal is joined together by 33,000 rivets.

The aqueduct was manufactured by the renowned firm Bergsunds Mekaniska Verkstad in Stockholm. The sheets where put together on land, with the heavy chute hauled into place above the river.

At the time the Dalsland Canal was constructed, Håverud was the point on the channel which presented the biggest obstacle to an uninterrupted waterway. It was the site of a ravine, surrounded by rocky beaches. Through this narrow valley, flanked by steep slopes, a gateway was formed through which the Håverud current tumbled down a fall of almost nine metres, before flowing into Lake Upperudshöljen.

For obvious reasons, constructing a canal here, in the trapped current between the high rock walls, was associated with extensive costs and technical challenges. As a result, Major Liliehöök recommended construction of a railway over Håverudsedet, as opposed to a canal.

There was really only one satisfactory solution to the equation of creating a navigable channel through the Håverud fall, which was, in some way, to lead the canal over the fall itself. Colonel Nils Ericson proposed an aqueduct made from sheet iron.

 

Construction

The aqueduct was constructed in the shape of a box, open at each end. The lateral panels, in which the bearing capacity is extended, are arched at the upper edge to a height of 10 feet (around 3 metres) at the centre, and 6.5 feet (around 2 metres) at the ends. The sides and base consist of ¼ inch (6 mm) English plate, while the foot and top flanges use ½–5/8 inch, 12.5–15.5 mm plate – simple at the ends and increased to triple in the middle. The top flanges also serve as a footbridge or tow path, with rails at the edges.

To provide reinforcement and make the structure more taut, a skeleton of iron reinforcements was placed externally along the sides and base, comprising two differently constructed systems which alternate with each other. One consists of an angle bar under the base, on which a reinforcement of the flat bar is placed, in the form of an inverted truss, and another angle bar securely riveted on each lateral panel, right over the first, deflected at the top and base flange, and at the angle against the latter, reinforced with a triangular filler plate. This type of reinforcement is placed across the full length of the aqueduct, at intervals of three feet (0.9 metres). Every fifth reinforcement deploys the other construction, which involves an angle bar under the entire base and on the sides, similar to the previous one, however, the inverted truss under the base is replaced by a securely fastened plate at the angle bar, with plates also securely fastened to the sides at the angle bar. These filler panels are reinforced by an angle bar running around the sides and base, securely fastened at the edge, and another which runs under the base and past the angles, and applied on the other side of the plate, opposite the previous one.

Reinforcements of this type are used at intervals of 15 feet, or around 4.5 metres. Under all of the base reinforcements, parallel with the longitudinal direction, two flat bars run in order to stabilise the vertical position. At both ends of the Aqueduct, the sides are further reinforced by sealants, which are vertically affixed to the angle bar. Inside the Aqueduct, level with the water’s surface, runs a timber moulding affixed by bolts, which serves as a fender.

The aqueduct is connected at both sides by brickwork. Dilatation (expansion/contraction), the detrimental effects of which for normal bridges are easily prevented through mobile intermediate landings, presented an issue in this case, as the sealant between the iron and the brickwork also needed to be mobile. This is resolved in the following way: At the eastern end, where the Aqueduct meets the pier before the recess in lock no. 6, there are two vertical oak beams securely bolted to the wall, and a horizontal oak beam recessed and securely bolted to the retaining wall of the abutment. An intermediate layer of thick coarse cloth has been inserted between the beams and the walls. The beams are hollowed out, to enable the lateral panels to be inserted into the vertical beams, with an angle bar fixed to the horizontal beam under the base plate. The opening of the vertical beams is sealed with leather strips, one of the edges of which is securely pegged along the beam, with the other edge clamped securely to the side panel by the securely screwed timber moulding.

The opening along the horizontal beam needs to be filled with sawdust, behind which a small gear is inserted. A sheet iron cover prevents the sawdust from being washed away. The rolls under the base flanges of the sides are of the same type usually found on iron bridges. The base plate is supported by three upset and inverted rail sections, securely riveted to the plate in a series on small rolls – two under each rail section – and fixed to the bearing blocks.

As the western end of the Aqueduct rests steadfastly on the abutment, mobile sealing was not required. The transition from iron to brickwork is enabled through oak beams in this case as well, to which the plate is nailed.

The Aqueduct can be filled to a depth of 5.5 feet (1.6 metres), which corresponds to a mass of around 5.580 centner, (237.150 kg). Factoring in its own weight of 1.500 centner (63.750 kg), the structure bears an evenly distributed load of 7.080 centner (300.900 kg).

With regard to detailed engineering and execution, the Aqueduct was produced by Bergsunds Mekaniska Verkstad, Stockholm.

 

Securing in place

The abutment foundations were simple, as the walls could be placed directly onto rock. At the east end, retaining walls were cut and erected straight into the rock. At the west end, a small existing rock under the water’s surface provided the foundation for the abutment. This was easy to access, by ensuring the water fell to exactly the level required by keeping the floodgates to the mill open, while the abutment foundations and other masonry work was in progress nearby.

The process of hauling the Aqueduct was not as extensive as had been anticipated. The depth and strong current of the river made it difficult to provide support between the abutments, so the Aqueduct had to be assembled on land and then hauled into position. A protruding rocky outcrop located on the eastern side of the channel, opposite the western abutment, came to good use. A provisional abutment made of timber piles were erected here, stretching out into the current, with a distance of just 50 feet (15 metres), approximately, to the western abutment of the Aqueduct.

The Aqueduct was then riveted together, resting on eight-inch circular timber, whose rolls could accommodate its full length. The rolls comprised five rows of long logs placed on a bracing banking engine. The reinforcement skeleton under the base, which was supposed to be in the way, was not secured until the Aqueduct had been hauled over, with the vertical position of the sides maintained meanwhile through bars which were fixed inside the Aqueduct. The area inside the western abutment would not allow for more than one-half of the length to be assembled at one time. Consequently, the eastern half of the aqueduct was firstly riveted together and then hauled out and spliced in several stages, until the end reached over to the opposite shore. Two Betancourt windlasses provided enough strength for this procedure. But the biggest challenge remained: to get it into place. Blasting was carried out in order to make space for a rolling platform, which was formed using diagonally positioned beams, like a regular pane. In order to simultaneously bring about rotation and forward motion on the Aqueduct, the rolls were placed beneath on this platform, obliquely, under the ends of the structure, or approximately perpendicular to the path which it was intended to follow. Two six-disc pulleys and windlasses were required for this procedure. Once the end had reached about halfway to the middle, the Aqueduct was assembled into its full length and hauled into place.