Page plan · 14 pages

Written for: Students and general readers interested in engineering history

1. 1

   Dujiangyan: water control without a dam

   • Dujiangyan is an ancient irrigation system on the Min River in Sichuan, China.
   • It controls floods and delivers water without a dam blocking the river.
   • It has worked for over two thousand years and still serves farmland today.
   • This talk follows its setting, design, operation and lessons.
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   Where the Min River leaves the mountains

   • The Min River rushes down from the mountains of western Sichuan.
   • At the mountain edge it meets the flat Chengdu Plain and slows abruptly.
   • The steep drop gives the river great force and a heavy load of sediment.
   • This location is where the headworks were built.
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   The twin problem of flood and drought on the Chengdu Plain

   • Before the system, the plain suffered floods when the river surged.
   • The same plain could face drought when water did not reach the fields.
   • Farmers needed water spread evenly, not just held back.
   • The challenge was to handle both extremes with one design.
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   Li Bing and the project's origins around 256 BC

   • Tradition credits Li Bing, an official of the state of Qin, with leading the project.
   • Work is dated to around 256 BC.
   • Qin wanted a productive, secure farming base in the region.
   • The project used local materials and the river's own natural behavior.
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   The fish-mouth levee splits the river

   • The fish-mouth levee is a pointed embankment built in mid-river.
   • Its tip faces upstream and divides the Min River into two channels.
   • It acts like a fish's head, parting the current rather than blocking it.
   • Splitting the flow is the first step in controlling the river.
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   Inner and outer channels

   • The split creates an outer channel and an inner channel.
   • The outer channel is the main river and carries floodwater away.
   • The inner channel leads water toward the irrigation canals.
   • Dividing the flow lets the system send water where it is needed.
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   The flying-sand spillway

   • The flying-sand spillway sits along the levee between the two channels.
   • It lets excess water from the inner channel spill into the outer one.
   • Its action also helps push sediment and stones back to the main river.
   • It protects the canals from overflow without gates or a dam.
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   The bottle-neck inlet

   • The bottle-neck inlet is a narrowed opening cut through the mountain ridge.
   • It controls how much water enters the irrigation canals toward the plain.
   • In floods its narrow mouth limits the inflow to the fields.
   • It completes the three-part headworks with the levee and spillway.
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   How the three parts work in a flood

   • In a flood, the high water level sends more flow to the outer channel.
   • The bottle-neck inlet limits what enters the inner channel.
   • The spillway releases surplus water and sediment back to the main river.
   • The three parts work together automatically, with no dam to operate.
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    Annual maintenance traditions at the headworks

    • Maintenance at the headworks is a long-standing yearly custom.
    • Channels are cleared of silt and stones so flow stays balanced.
    • Traditionally this work is done in the dry season.
    • Regular upkeep is a key reason the system still functions.
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    The irrigated plain: from 2.86 to 11.65 million mu

    • Effective irrigated area grew from 2.86 million mu in the early years of the People's Republic of China.
    • By 2025 it reached 11.65 million mu.
    • One mu equals about 666.7 square meters.
    • That is roughly a fourfold increase in irrigated farmland.

    Column chart: Effective irrigated area of the Dujiangyan system. Source: Dujiangyan Irrigation System Nurtures Sichuan's Granary (15 January 2026) · checked 2026-10-10

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    Modern changes, from new canals to digital monitoring

    • The ancient headworks have been joined by new canals extending water reach.
    • Digital monitoring now tracks water conditions across the system.
    • Modern tools support the original design rather than replace it.
    • Old principles and new technology work side by side.
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    Recognition as a UNESCO World Heritage site

    • Dujiangyan is recognized as a UNESCO World Heritage site.
    • The listing honors its lasting value as an engineering achievement.
    • Recognition supports protection of the headworks for future generations.
    • It is also a draw for visitors interested in history and engineering.
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    What engineers learn from it

    • Working with natural flow can replace brute-force blocking.
    • Simple, well-placed structures can regulate a river reliably.
    • Built-in self-regulation reduces the need for constant operation.
    • Regular maintenance is part of the design, not an afterthought.