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Over the past decades, rapid urbanization and global climate change has resulted in a significant increase in flood risks in the urban areas of Hong Kong. In the early 2000s, the Drainage Services Department proposed an innovative "Upstream Interception" scheme, namely The Hong Kong West Drainage Tunnel (HKWDT) to improve the flood protection standard for the western areas around northern Hong Kong Island. The engineering challenge was how to effectively intercept and transfer the supercritical (high speed) flow from the steep, natural watercourses located in the densely populated Mid-Levels district to the drainage tunnel located about 100 m below ground. The challenge was overcome by the development of a compact bottom rack and vortex-intake system to stably decelerate the supercritical approach flow, with efficient energy dissipation, for smooth conveyance of flow from a high elevation to the deep, drainage tunnel and discharge to the sea. Through a combination of theory, heuristic design, and physical model tests, both spiral shaped and tangential vortex intakes have been designed. Since the commissioning of HKWDT in 2012, with its vortex-flow intake system, the HKWDT has successfully protected the downhill urban areas of Hong Kong Island from flooding. [ABSTRACT FROM AUTHOR]