Nanhua Reservoir Naturally Overflowed for First Time This Year After Heavy Rains

Taiwan's Nanhua Reservoir, the second-largest in the south, has naturally overflowed for the first time this year following intense rainfall. The downpour, fueled by the outer bands of Typhoon Mikala and a stationary front, delivered over 205 millimeters of rain to the reservoir's catchment area in just 36 hours. This surge of water pushed the reservoir's levels beyond its capacity, leading to the overflow.

Prior to this event, the reservoir had been operating at high water levels. It had been supplying water to the Zengwen and Wushantou reservoir systems via the Zengwen-Nanhua inter-basin transfer pipeline, while maintaining approximately 2 million cubic meters of flood storage capacity. By Wednesday, the Nanhua Reservoir's storage rate stood at 97.45%. The subsequent heavy rainfall rapidly filled the reservoir, with water levels exceeding 180 meters and initiating the natural overflow, which initially released about 100 cubic meters per second.

As of noon, with 36-hour rainfall exceeding 205 millimeters and continuous inflow from upstream, authorities opened the desilting tunnel on Friday morning to release an additional 100 cubic meters per second, also aiding in sediment discharge. While the rainfall in the catchment area has temporarily subsided, the combined outflow from natural overflow and the desilting tunnel currently totals 165 cubic meters per second. The Sixth Regional Management Office of the Water Resources Agency has issued a warning to residents downstream of the reservoir, urging them to stay away from riverbanks and remain vigilant for their safety.