Practical Engineering - The Surprising Efficiency of Canal Locks

Short Summary

Main recommendation: canal locks are an efficient, gravity-driven way to raise and lower boats between water levels, and water-saving side ponds can cut the water lost in each cycle. Shipping by water is far more energy-efficient than rail or trucks, and locks let canals overcome the fact that water cannot be laid on a slope. The Panama Canal's new locks, which use three side ponds about the same area as the locks, need only about 40% of the water that a lock without them would require.

Key Points

• Moving a ton of freight by boat takes roughly half the energy of rail and about one-fifth the energy of trucks over the same distance.
• Water is self-leveling, so canals cannot climb hills the way roads or rail can; locks solve this with a reversible, gravity-based lift that needs no external power beyond the water itself.
• Each lock operation drains a full lock of water downstream; on large rivers this usually isn't significant, but with heavy traffic or large locks it could drain a canal or reservoir dry.
• Side ponds recapture water: with a single basin of the same area as the lock, exactly one-third of the water is saved, because water can only flow downhill.
• More basins, or larger basin areas, save more water; a basin area equal to the lock with three basins uses about 40% of the water required without them.

Details Worth Noting

• Concrete instructions: The video describes the lock sequence for each direction. Going up, a boat enters the empty lock, the lower gate closes, water from the upper canal fills the lock until it reaches the upper canal's level, then the upper gate opens and the boat continues. Going down, the boat enters the full lock, the upper gate closes, the water drains into the lower canal until levels match, then the lower gate opens and the boat continues. The video also notes that canals with locks can sometimes be operated by the public themselves.
• The Panama Canal sits about 26 metres (85 feet) above sea level for most of its length, because cutting to sea level would have required an impractically deep excavation through the isthmus.
• The 2016 Panama Canal expansion added water-saving basins to its new locks, which matters because the locks draw from Gatun Lake, a key drinking water source.
• A water-saving formula compares water use with and without side ponds; the video's example uses three basins with a lock-to-basin area ratio of one, yielding 40% of the water needed without them.
• A lock in Hanover, Germany, uses ten basins, reducing lost water by about three-fourths, though its tanks are underground.

Bottom Line

Locks let boats travel uphill and downhill on canals with almost no energy input, and side ponds are the key way to keep that from draining the water supply.