The commissioning of Tunnel 4 began today, after the successful completion of all the components of the Angat Water Transmission Improvement Project (AWTIP).   The completion of AWTIP or Tunnel 4 marks another milestone in the MWSS promise of water security for Metro Manila.

The centerpiece of AWTIP is a 6.3 kilometers tunnel with a finished, internal span diameter of 4 meters, designed to accommodate 19 cubic meters per second (m3/s) raw water from Angat Dam.  The tunnel excavation used a modern mechanized double blade tunnel boring technology, at below ground surface depth of 200 meters.  The tunnel is lined with precast concrete with steel reinforcement to ensure structural integrity, and that raw water flows in the long term.

Construction of this Php 3.29 Billion tunnel project started in June 2016 and was completed in June 2020, three (3) months ahead of the original completion date of September 2020.   Completed permanent works include (a) intake structure at Ipo reservoir, (b) new transition basin at Bigte, (c) slope protection works at Ipo Dam, (d) channel connecting Tunnel 4 outlet portal to existing aqueduct 5 (e) interconnection of the new transition basin at Bigte to the existing Transition Basin No. 3, and (f ) the necessary modifications of the existing transition basin No. 3 at Bigte.

The AWTIP is a critical component of the MWSS’  water security program as it mitigates the risk of a partial or total disruption of water supply for Metro Manila.  It will provide redundancy and enable the system’s full design capacity to be restored by allowing the upstream tunnels and downstream aqueducts to be sequentially closed, inspected, and rehabilitated or decommissioned.

Administrator Salamat who visited the project site earlier today said, “I am very pleased to see the completion of Tunnel 4 as it now paves the way for the rehabilitation of the transmission system’s main components that are as old 75 years, in poor condition, and most likely not in compliance with current structural and seismic requirements.   These factors could seriously interrupt Metro Manila’s water supply.  Minor delays due to ECQ restrictions thwarted our best efforts to place on stream the additional 19 m3/s  (equivalent to 1,600 million liters per day) into the delivery system.  We have partially operated the tunnel last April, which solved the summer’s annual water supply problem.  We are currently in commissioning activities and continue to work non-stop.  The 1-month testing period will ensure the performance of each system and the overall system meet the design standards and operating requirements.

The completion of Tunnel 4 is the culmination of the joint efforts of the Philippine Government, with the MWSS as the executing agency and the Asian Development Bank.  MWSS is grateful to ADB for investing in water projects that secure additional bulk raw water transmission to consumers and alleviate the growing demand for water in the service area.  Right after the operationalization of Tunnel 4 is another water security project, a seventh aqueduct known as the Bigte-Novaliches Aqueduct 7 (BNAQ7), to be financed from a loan secured from the ADB.