New Mutwal and Torrington Storm Water Tunnels of Colombo Metro


Ministry of Defence and Urban Development+I32

Cost of works:


Period of Activity:

2015 - 2015

The city of Colombo has been repeatedly subject of flooding phenomena due to intense rainfall, insufficient storage, conveyance, and outflow capacity in the Macro-Drainage System. Thus, the Flood and Drainage Management Component of the Metro Colombo Urban Development Project has been set out to regulate the flood safety level of the Colombo Drainage Basin to an acceptable level for a storm of 50 year target return period. The New Mutwal Tunnel and the Torrington Tunnel form part of this governmental program partially funded by the World Bank.

— Project Description:

Geodata Engineering S.p.A. (GDE) has been engaged by Ministry of Urban Development, Water Supply and Drainage of Sri Lanka for the Consultancy Services concerning Review of Conceptual Design and preparation of Bidding Documents for Design and Build Contracts of the proposed New Mutwal and Torrington storm water tunnels. Today there are five main storm water drainage outlets in Colombo basin, namely Wellawatta, Dehiwala, Mutwal Tunnel, North lock, and Ambatale. Of these, the first two are canal outlets directly to the sea and the last two are pumping stations that transfer water into the Kelani river. With the increasing intensity of the peak flow, conveyance capacity of main canals and outfalls are found to be inadequate to cope with the extreme flood peaks. To cope with the infrastructure development needs, GDE’s Client has proposed to introduce two structures, namely the Torrington and New Mutwal Tunnels (NMT) into the existing drainage system to supplement the storm water discharge into the sea. The tunnel internal diameters and alignment axes (horizontal and vertical) have been finalized by Metro Colombo Urban Development Project’s (MCUDP) studies.

— Description of Services:

Following tasks show the contractual activities developed by GDE:

  • Task 1: Review of the available information and submission of the Information Review Report.
  • Task 2: Preparation of Risk Management Strategy and Employer’s Contractual and Technical Requirements (including risk assessment allocation).
  • Submission of Cost Estimate together with a cost comparison, where applicable
  • Preparation of the Bid Documents (including Specification and Geotechnical Baseline Report.

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