Signature Projects

This project encompasses the detailed design, manufacturing, construction, and turnkey delivery of the Zhongzhuang Regulating Reservoir Weir, covering the main weir structure, gates, and ancillary facilities including a fish passage. Throughout the entire construction process, Nan Dao Engineering maintained strict control over construction quality and schedule, ultimately delivering a high-performance hydraulic structure capable of flood control, sediment discharge, and water supply regulation. The weir incorporates nine tilting movable gates, each standing 5.16 meters in height — the first large-scale tilting weir structure of its kind on domestic waterways. The gate operation employs a dual mechanism: hydraulic pressure raises the gates when water storage is required, while the gates lower by their own weight during typhoon flood events to maximize discharge capacity. This design ensures safe operability even during power outages caused by typhoons, significantly reducing operational risk. The project also features a fish passage tailored to the local ecosystem, balancing flood control and water supply functions with the preservation of river ecology.

Portions of the former Zhongzhuang riverbed had long suffered from illegal sand and gravel extraction, followed by backfilling with soil and waste materials, resulting in adverse environmental impacts on the surrounding area. Additionally, the upper reaches of the Dahan River frequently carry large volumes of suspended sediment during typhoon and heavy rainfall events, causing raw water turbidity at Shimen Reservoir and Yuanshan Weir to rise sharply beyond the treatment capacity of downstream water purification plants. As a result, the Taoyuan and Banxin districts have faced recurring water supply crises. In response, the Water Resources Agency, Ministry of Economic Affairs, planned the construction of a regulating reservoir in the abandoned riverbed, with an effective storage capacity of 4.92 million tonnes. The reservoir regulates the surplus flow of the Dahan River, serving as a backup water supply system during periods of excessively high turbidity caused by typhoon floods, while simultaneously rehabilitating the former riverbed and creating a quality aquatic environment.

The weir operates in two modes depending on hydrological conditions. Under normal conditions, the gates are raised to divert clear water into the regulating reservoir for storage, while the impoundment creates an expansive lake landscape in the weir zone. During typhoon flood events, the gates are lowered to increase the river's flood conveyance cross-section, preventing bank scour from elevated water levels; the weir can also operate in coordination with Shimen Reservoir for hydraulic sediment flushing, effectively reducing reservoir siltation. During Shimen Reservoir sediment flushing operations, this project provides 6.2 days of backup water supply and, through joint operation with the reservoir, supplements water supply by 24,000 tonnes per day. When raw water turbidity remains excessively high following typhoon floods, clear water from the regulating reservoir can be diverted to water treatment plants, effectively resolving turbidity-related supply disruptions and significantly reducing the risk of water outages in the Taoyuan and Banxin districts. Through the joint sediment flushing mechanism, the project contributes to extending the operational lifespan of Shimen Reservoir and promoting its sustainable use. During Typhoon Dujuan in 2015, the coordinated flushing and flood discharge operation removed 550,000 cubic metres of sediment in a single event, saving over NT$300 million in dredging costs — a compelling demonstration of the project's long-term economic value.