The Power of a Curve: Decoding the ecological secrets of a 1,500-year-old Chinese weir

No steel or concrete, yet it forces floodwaters to yield. No electricity, yet it irrigates vast fields of fertile land. For over 1,500 years, the Tongji Weir in Lishui has harnessed the curve to master the waters, a multi-level bridge to balance with nature, and stone-carved rules to safeguard civilization. What ecological wisdom enables this ancient weir to function for over a millennium?