The greatest sin is to call a man-made disaster an act of heaven.

Build a river mouth like this, and the result cannot honestly be written off as a natural disaster.

The checkpoint is, in effect, a massive unauthorized structure sitting in the river channel. What remains of the channel is forced to scour along the mountain wall. Compete with the river for land, and nature will strike back. Disaster is then not a surprise; it is the design.

The most basic engineering rule for mountain rivers is to give land back to the river and leave a floodway.

A channel that looks like a trickle in ordinary weather does not mean it will only carry a trickle in a storm. What actually decides safety is the flood cross-section required when torrential rain, mountain flood, and debris flow arrive together.

Put large permanent buildings into a river mouth, a valley floor, or a floodway, and the structure becomes a giant obstacle in the channel.

Water that could have spread through a wider section is forced into the remaining opening.

Water level rises.

Velocity increases. Flow concentrates along the mountain wall and the foundations and scours them.

When that happens, the two words “natural disaster” cannot carry all the blame. Nature decides how much water comes. Engineering quality decides how many people die when it arrives.

Engineering that respects mountain flood does not pretend that concrete can conquer a river. It admits that, under extreme weather, a river needs space.

If something must stand in the channel, it should be expendable, quickly rebuildable, and low in human occupancy: a temporary bridge or a simple facility. Major roads, large buildings, and places where people gather should stay out of the floodway.

Where a crossing is unavoidable, use bridges, viaducts, tunnels, and slope works to span the danger — not drop a permanent building onto the path the flood must take.

Across the China–Nepal border, the simple river crossings common in high mountain country rest on a practical idea of risk: better to let a temporary bridge wash away than to stake large numbers of people and large permanent buildings against the flood.

Gyirong Port sits in a China–Nepal border valley at about 1,900 meters — not especially high. If the large buildings had not hugged the valley and occupied the channel, but had been set back upslope, away from the riverbed, the death toll would not have been this high.

The highest standard of engineering is not “man can conquer nature, so build it.” It is knowing where something should never be built at all.

Compete with the river for land, and in ordinary times you gain ground. When the flood comes, nature collects principal and interest.

On that day, writing the whole responsibility as “a natural disaster caused by extreme weather” is not professional engineering. It is using heaven to close the case on a man-made failure.

In just a few months: Typhoon Meisha floods in Guangxi, 159 dead; Gansu rainstorm and mountain flood, 25 dead; another wave of floods and landslides in Chongqing, at least 51 dead.

Suddenly everyone becomes an expert on natural disasters. Of course it was heaven. Who would dare imply that officials should step down, or that General Secretary Xi should answer for it?

When later generations survey the wreckage, do not ask about the torrent. Ask about the people.

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