Postoperation Performance of the Tai Hang Tung Storage Scheme in Storm Events: 2D Hydraulic Analysis and Field Verification: Fid-Bau Portal

Postoperation Performance of the Tai Hang Tung Storage Scheme in Storm Events: 2D Hydraulic Analysis and Field Verification

Lee, J. H. W. / Wong, K. T. M. / Choi, K. W. / Arega, F.

Abstract

The Tai Hang Tung Storage Scheme (THTSS) is an essential part of the West Kowloon Drainage Improvement Project that aims to solve the flooding problem in Mongkok, a congested and densely populated district of the Hong Kong Special Administration Region of China. The heart of the flood detention scheme is a $100,000 - m^{3}$ underground storage tank beneath the Tai Hang Tung Recreation Ground, a triple side-weir system, and transitions to the upstream inlets and downstream channels. During heavy storms, part of the flood flow will spill over the side weirs into the underground storage tank and be temporarily stored; the flow diversion serves to attenuate the flood peaks and prevent downstream flooding. The THTSS was commissioned in 2005, and flow monitoring has been conducted since 2007. The operation of THTSS has essentially resolved the historic flooding problem. Nevertheless, the THTSS performance was put to an extreme test on June 7, 2008, when the highest hourly rainfall on record occurred. The heavy storm led to rapid filling up of the storage tank and minor local street flooding. This storm event suggested the need to use hydrodynamic models to evaluate the performance of the THTSS system. One-dimensional (1D) and two-dimensional (2D) mathematical models have been developed for the THTSS system including the side weir channels and transitions. The complex hydraulics in the triple side-weir system is first studied via a 2D numerical solution of the shallow water equations using a shock-capturing finite-volume method; the flow behavior and weir overflow distributions are compared with laboratory experiments and field data. Measured flood levels in the surcharged system are also studied using a 1D unsteady flow model for key storm events. The calibrated models are used to analyze postcommission performance of the system and to interpret the complex turbulent flows measured during the field survey.