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The West Kowloon flood relieving project comprising a drainage tunnel of 4.9m finished diameter,3.7km long,and a water transfer tunnel of 3.0m diameter,2.8km long was initiated by the Government of Hong Kong Special Administrative Region to reduce flood risk in a dense urban area and at the same time achieve the water conservation objective.The drainage tunnel involves construction of two TBM tunnels through hard rock stratum with a number of transverse fault zones and mixed ground under high ground water table,and the water transfer tunnel involves construction of a TBM tunnel passing through hard rock stratum.Along the drainage tunnel alignment are existing buildings,railway lines,major trunk roads and highway viaducts at a minimal clearance while the water transfer tunnel would pass between existing reservoirs under country park area.The West Kowloon flood relieving project will be implemented under two contracts,namely Lai Chi Kok Transfer Scheme(LCKTS)for the drainage tunnel and the Inter-reservoir Transfer Scheme(IRTS)for the water transfer tunnel.This paper provides an overview of design and planning of the project scheme and the formulation of flood relieving and water conservation strategy.IRTS is at the stage of preparing tender documents while LCKTS contract has already been started in November 2008.This Paper will also discuss the site conditions and constraints,selection of tunnel alignment and TBMs,reference design and construction considerations.