The River in the Sky-Over and Under/In and Out -- Brooks Aqueduct NHS, Brooks AB CAN - Alberta Heritage Markers on Waymarking.com

The second of three panels overlooking the Brooks Aqueduct and the modern irrigation canal that replaced it, this panel shares the history of how the Aqueduct crossed the CPR tracks with an ingenious inverted siphon that passed under the RR tracks before going back up to aqueduct height - all without a pump.

RIVER IN THE SKY

[photo]
Water going into the siphon (main) and the siphon under construction

[inset]
[photo]
A close-up of the wooden forms and rebar in place, ready for the concrete to be poured.

[photo]
Building the intake to the aqueduct, 1914.

[photo]
a shot of the intake canal in the spring of 1918 empty (inset) and the outlet in 1915 (main)

OVER AND UNDER

Getting the water in and out of the Aqueduct wasn’t the only challenge. As it marched across the valley it would run smack into the CPR tracks. The Aqueduct as planned was not high enough for trains to go under it. In the construction required to lower the train tracks would be terrifically expensive. The engineers decided and inverted siphon that would take the water from the Aqueduct under the tracks and bring it back up to the continuation of the Aqueduct on the other side was the solution.

The siphon is just a large pipe. The pipe narrows gradually from a diameter 12 feet 8 ½ inches (3.8 m) at the point where it meets the Aqueduct, to a diameter of 9 feet 9 inches (2.9 m) when it passes under the railway tracks. This narrowing increases the water’s speed. The water has to flow faster to keep up with the water forced along at higher pressure behind it.

Then the siphon gradually increases in diameter until it meets the shell of the Aqueduct on the other side. Water spreads back out and the flow rate slows down to what it was when it entered the siphon from the Aqueduct shell on the other side of the tracks.

Train went over, the water went under, and the Aqueduct continued its march across the valley.

HOW DOES THE SIPHON WORK?

Daniel Bernoulli was a member of a Swiss mathematical family who lived in the 1700s. Bernoulli’s principle states that a change in the pressure of a flowing liquid will always be accompanied by a change in its speed. Bernoulli noted that the energy per unit mass of a liquid at one point in its flow will always be equal to the energy per unit mass at another point.

Giovanni Battista Venturi, also living and working in the 1700s, described that phenomenon when flowing liquid encounters a narrowing in the pipe. As the area of the liquid decreases, the pressure on the liquid drops in the liquids speed increases.

This is what happens when the water in the Aqueduct flows into the siphon. The siphon’s pipe is narrower than the Aqueduct’s shell. There is less water area, which means less pressure, making for faster flowing water. A measurement of energy per unit mass taken at a point in the Aqueduct, and at a point in the siphon, would come out the same.

IN AND OUT

The Brooks Aqueduct was just one part of the irrigation system that brought Bow River water to farmers in the Eastern Irrigation Section. Water traveled down an earthen canal on its way to the Aqueduct, and then carried on in an earthen canal when it left the Aqueduct on the far side of the valley. Both canals were wider than the Aqueduct.
At the intake on the Aqueduct’s western end the engineers designed a 150 foot (45.7 m) long sloped and graded structure gradually narrowed to direct the water into the Aqueduct. The engineers wanted to make the transition as smooth as possible to reduce the waters frictional losses as it moved from the water canal into the narrower Aqueduct. If the transition is too abrupt water swirls and forms eddies. This causes it to lose additional energy to friction because the water molecules are bouncing around into each other more. They wouldn’t have enough energy left to keep moving along fast enough through the Aqueduct.

The engineers had an easier task at the Aqueduct’s eastern end. Frictional loss was not a concern here. They designed a simple rectangular box as the outlet structure. It was just 30 feet (9.1 m) long and had the same width as the bottom of the canal. The engineers placed a 21 inch (53.3 cm) high baffle wall for 14 feet (4.2 m) in a stream and causing side worlds that would erode the canal’s banks."

Type of Marker: Cultural Sign Age: Historic Site or Building Marker Parking: very easy Placement agency: Eastern Irrigation District and partners

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Date Logged Log User Rating   07/24/2019 Benchmark Blasterz visited it