A saucer in the floodplain
The Lixia River (Lixiahe) region of Jiangsu province is is not a river; it is a vast, low-lying alluvial plain. Geographically, it forms a saucer-shaped depression, with the center of the plain sitting at an elevation of only about 1 meter, while the land surrounding it is higher, at around 4.5 meters. This unique "pot bottom" topography makes the area naturally susceptible to severe flooding. Historically, it was a catchment for waters from the Huai River and the Yangtze River, as well as local rainfall, leading to a reputation for having floods in nine years out of every ten.
To manage this constant water threat across 50,000 square kilometers, engineers constructed a complex water conservancy system. The network includes more than 2,000 flood control gates, thousands of kilometers of levees, and numerous pumping stations. This infrastructure manages floodwater and actively manages and redistributes it. During periods of heavy rainfall or high river levels, the system can divert water from threatened areas to other parts of the network with more capacity, or discharge it into the Yangtze River or the Yellow Sea. The entire system of canals and rivers in the region stretches over 12,000 kilometers.
The digital hydrologist
Coordinating the operation of thousands of gates across such a large area is a massive logistical and computational challenge. Modern flood management in the Lixiahe region, and in other major Chinese river basins, relies on digital twin technology. These are advanced 3D simulations of the entire river basin.
The models are fed a constant stream of real-time data from a wide network of sensors. This data includes rainfall forecasts, upstream flow rates, tidal levels in the Yellow Sea, and current water levels in every canal and holding area. During a potential flood event, the system runs numerous simulations to predict the outcome of different scenarios. By modeling various combinations of gate openings and pumping station activations, the system's operators can identify the optimal strategy to minimize inundation and protect agricultural land and urban centers. These calculations allow for preemptive actions, such as drawing down water levels in certain canals to make space for incoming floodwaters. This shifts from reactive flood defense to a predictive and optimized system of water management.