CFD and Physical Modeling for the Upper Tai Po River Design – An Integration of Ecology and Engineering

Erosion is a primary concern for rivers in upland and hilly areas. Concrete lined channel are frequently used to cope with high velocity, but rising environmental concerns increasingly demand more ecologically friendly designs using more natural substrates. The Upper Tai Po River is such a river in Hong Kong. Its average gradient of 1 in 23 leads to flow velocity exceeding 8 m/s during heavy rainstorms. Recent flooding triggered the decision to increase the river capacity by deepening and widening it.To preserve ecological value, it was decided to line the new channel with gabions, with drops and stilling basins to dissipate energy. The latter had to be designed to suit the hydraulic and topographical conditions of the river. Given the lack of established design guidelines, Computational Fluid Dynamic (CFD) was used to optimize the design, followed by a physical model study to confirm the design and further modify it as needed.