Feasibility Study on Underground Drainage and Reservoir System (UDRS)

  • Location: Singapore
  • Location: Singapore
  • Client: PUB, Singapore’s National Water Agency
  • Project status: Complete

Project Overview 

With increased rainfall intensity and land shortage in Singapore, PUB sought to explore the feasibility of underground stormwater conveyance and storage systems to mitigate the impact of rainfall-induced floods. The UDRS comprises three components: underground reservoir caverns (URC), an underground stormwater tunnel system (STS), and a pumped storage hydropower (PSH) system. The UDRS, when implemented, will be a huge undertaking by the Singapore government, holding enough water to supply Singapore’s population of five million for more than four months.

Our role

  • Evaluate the feasibility and develop a conceptual design for a mega stormwater conveyance and storage system (UDRS) for PUB
  • To identify and determine relevant information and potential changes in the following areas
  1. Stormwater management
  2. Water supply
  3. Pumped storage hydropower


  • To mitigate the impact of floods due to climate change and extreme rainfall events of up to a 100-year return period
  • To provide a reservoir storage for significant water supply purposes by maximising space usage
  • To provide electricity storage on a large-scale basis as a source of power generation

Unique features and solutions

  • Underground caverns located within the granite geology found in the central parts of Singapore
  • Large underground cavern storage volume
  • Diversion inlets, drop shafts and/or stormwater link tunnels for collection of excess stormwater from surface catchments
  • Use of 1D-2D hydrodynamic modelling using MIKE FLOOD to identify flood areas and determine the ideal location and dimensions of proposed inlet weirs
  • Use of yield modelling to investigate yield attainable from surface water catchments

Benefits and Achievements


Use of natural underground caverns

Improved Protection

Reduced impact of floods due to extreme weather events


Smoothed output of intermittent generation resources such as solar generators

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