Author(s): Joseph H. W. Lee; N. R. Townsend; K. C. Ng
Linked Author(s): Joseph Hun-Wei Lee
Keywords: Urban flooding; Stormwater management; Flood storage; Flow diversion; Underground storage tank; Side weir; Hydraulic transitions; Drainage tunnel; Interception structure; Supercritical spatially varied flow
Abstract: Over the past four decades, changing land use patterns have led to the reduction in upland flood storage capacity and increased lowland runoffs in many parts of Hong Kong. A variety of measures have been developed to protect semi-rural areas, new towns, and metropolitan areas from flooding–including real time warning systems, village polder schemes, river training, stormwater diversion and storage schemes. Many of these flood control schemes share certain characteristics: intense storms and high inflows, tight space constraints and scarce land availability, proximity to densely populated areas and congested underground utilities, and enhanced backwater effect due to coastal reclamation. The design of these flood control schemes often involve complex threedimensional flows: complicated subcritical-supercritical transitions, free surface and surcharged flows, and spatially varied flow at 3D junctions. Such designs can be effectively explored and studied in undistorted physical models supplemented by mathematical model calculations. In this paper, the characteristic hydraulic challenges and solutions of these schemes are illustrated by reference to the Tai Hang Tung Storage Scheme and the Kai Tak Transfer Scheme. These two projects, which are in an advanced stage of construction, constitute the essential components of the West Kowloon Drainage Improvement Scheme.