Hydraulic Model Test for the Keelung River Yuanshanzi Flood Diversion Works
Background
Prompted by catastrophic flooding caused by Typhoons Xangsane and Nari in 2000, the Yuanshanzi Flood Diversion Project was launched to enhance overall flood control along the Keelung River. The engineering design targets a 200-year recurrence interval flood Q200, allocating a river channel discharge of $310 m3/s and a diversion tunnel flow of $1,310 m3/s, while maintaining open-channel gravity flow conditions within the tunnel.
Given the complex hydraulic phenomena associated with the intake, diversion tunnel, and outlet structures—which are difficult to capture through numerical modeling alone—the Planning Branch conducted hydraulic model tests during the basic and detailed design phases to validate and refine project designs.
Test Features
Built on Froude scaling principles, undistorted fixed-bed models were established at two distinct scales:
- 1:50 Partial Model: Simulated localized hydraulic phenomena including the river channel, intake structure, and sections of the diversion tunnel.
- 1:100 Overall Model: Simulated the entire diversion system, including the upstream channel, intake, diversion tunnel, and outlet structures.
Testing encompassed steady clear-water trials and quasi-unsteady sediment-laden flow trials to comprehensively assess flow patterns, sediment transport characteristics, and diversion capacities under various design schemes, ensuring compliance with Q200 standards.
Application of Results
Initial basic design trials revealed that both the original design and preliminary alternative failed to reach Q200 targets, as localized pressurized pipe flow occurred in the tunnel, flow conditions in the stilling/sedimentation basin were turbulent, and sediment deposition was observed during sand-bearing tests.
Subsequent detailed design trials confirmed that the optimized design successfully achieved the Q200 objective: delivering a channel discharge of $310 m3/s and a tunnel diversion flow of $1,310 m3/s, with sediment transport dynamics meeting all operational requirements.
The test results provided critical hydraulic validation for the Yuanshanzi Flood Diversion Project, successfully supporting final design execution, ensuring operational performance, and significantly elevating flood security across the Keelung River Basin and Greater Taipei.