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How do aqueducts allow canals to cross valleys or other waterways?

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View of Utrecht's Oude Gracht canal lined with historic brick buildings, arched doorways at water level, and boats moored along the canal edge in the Netherlands. — canals and inland waterways The *Oudegracht* (Old Canal), Utrecht, Netherlands.

Aqueducts allow canals to cross valleys or other waterways by serving as elevated structures that carry the canal's water channel across a depression or obstacle.12

Historically, these structures were built using heavy masonry to support the full formation of the canal, which included a puddled clay lining to ensure it remained watertight. Over time, engineering techniques evolved to use lighter and more efficient materials. For example, cast-iron flanged and bolted troughs were later utilized to create a more watertight and manageable channel. In modern engineering, these crossings are typically constructed using concrete reinforced with bituminous sealing to maintain the integrity of the waterway.2

By providing a continuous, elevated path, aqueducts enable canals to maintain their necessary gradients while traversing varied terrain, such as deep valleys or existing rivers, without requiring the water level to drop and rise again.12