Author(s): Anil Kumar, Wong Chin To Louis, Raymond Tai
Linked Author(s): Anil Kumar
Keywords: Flood protection, intake structure, bottom rack, dropshaft, hydraulic modelling
Abstract: The Hong Kong West Drainage Tunnel (HKWDT) meets the major social and business needs by preventing flood damage to the most densely urbanized areas of the Northern Hong Kong (HK) Island. The HKWDT comprises approximately 11km of drainage tunnel with internal diameter varying from 6. 25m to 7. 25m from Tai Hang to Cyberport, about 8km of associated connection adits, 34 no. intake structures and two portals. The majority of intakes are located in the upper catchment intercepting flows from streams, nullahs, box culverts and pipes. The supercritical flow from upstream catchment is diverted to the drainage tunnel through a uniquely designed intake structure focusing on space saving. The intake structure consists of a bottom rack, a bottom rack chamber and connection to a spiral vortex inlet through a link channel, and a dropshaft. An InfoWorks CS model was used for the overall hydraulic design of the HKWDT and to assess the hydraulic performance of the tunnel under a range of rainfall events. However, the InfoWorks CS model has its limitation in assessing the hydraulic behavior of the portals and intake structures. Therefore, physical modelling was used for the hydraulic design of intake structures and portals. Due to the site constraints, two typical intake structures were selected and developed through extensive physical modelling for maximum design discharge. The design of individual intake was developed based upon geometrical similarity using Froude's Law. Furthermore, it was difficult to construct a completely vertical shaft and therefore Computational Fluid Dynamics (CFD) modelling was carried out by using an inclined shaft with a gradient 1 in 200 to assess the hydraulic performance of intake structure. This paper describes the hydraulic design process involved in optimizing the arrangement of the various components of the HKWDT
Year: 2017