Liu Yan segmented grain route to cut losses

Grain grown in the south had to reach the Tang capital at Chang'an by water, a route passing through the Grand Canal, the Bian and Yellow rivers, and finally the Wei river, each with distinct current speeds, depths and hazards. The most dangerous stretch, the Sanmen Gorge on the Yellow River, was notorious for whirlpools and submerged rock that regularly capsized boats and drowned crews and grain alike, no matter how boats were built for the calmer stretches elsewhere on the route.

Moving grain the entire distance in the same boats end to end meant either building every boat sturdy enough for the worst stretch at the cost of efficiency everywhere else, or accepting losses at the dangerous points as an unavoidable cost of the lighter, more efficient boats used on the rest of the route. Neither compromise actually solved the underlying mismatch between one vessel design and several genuinely different water conditions.

Segmented the route into legs with purpose-built boats and hub transfers, portaging at Sanmen Gorge, so no boat faced conditions it wasn't built for.

Each leg could be optimized for its specific conditions, avoiding compromise designs.

Transferring cargo at hubs allowed using the most efficient boat for each stretch.

Portaging around the Sanmen Gorge eliminated the deadliest hazard entirely.

Purpose-built fleets reduced losses, enabling record grain deliveries.

When a route or process has genuinely different conditions, segment it and use purpose-built equipment per segment, rather than forcing one design to survive the worst case.

The reformed system is recorded as moving on the order of 1.1 million shi of grain a year to the capital, with historical accounts specifically noting that not a single unit of grain was lost to sinking under the new system — a sharp contrast to the losses direct, single-boat transport had suffered at Sanmen for generations.