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Why must water levels be equalized before miter gates can open?

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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.

Miter gates must be operated only after water levels on each side have been equalized because they are designed to withstand the significant water pressure that arises from a difference in levels between adjacent pounds.12

When closed, these gates meet in a V-shape pointing upstream, allowing the pressure of the water to help keep them shut. Because of this structural design, attempting to open them against an unequal water level would be prevented by the immense force exerted by the higher water level against the gate leaves. Unlike vertical lift gates, which can be raised against water pressure, miter gates require the pressure to be balanced on both sides before they can be safely moved into their recesses in the lock walls.12