Proposed dams in the Kaliwa River watershed

The Kaliwa Watershed forms part of the Sierra Madre Biodiversity Corridor (SMBC), and has been identified by the Southern Sierra Madre Wildlife Center of the Environmental Studies Institute of Miriam College as one of the SMBC's 14 priority biodiversity conservation sites.[4] It is described as "an important wildlife habitat that contains dipterocarp trees, a wide array of birds, mammals, amphibians and reptiles, some of which are threatened and endemic species."

In 1999 the Kaliwa Watershed, evaluated at the time as "degraded due to anthropogenic pressures", was classified as a protected area under the National Integrated Protected Areas System.[4]

The terrain is generally mountainous, surrounded by slopes > 50%, consisting partly of forested hills and partly of cultivated land, with some slash and burn cultivation (kaingin) areas present. Its elevation is from 220 masl (meters above sea level) to 1,530 masl.[5] A number of small creeks run through the lower slopes, all eventually connecting to the main river.[4]

The Laiban site where the project is supposed to be built is a Barangay of municipality of Tanay in the province of Rizal, east of Metro Manila. It contains he 180 ha Laiban sub-watershed, a microbasin of the bigger Kaliwa Watershed, nestled in the southeastern portion of the Sierra Madre Mountain Range.[4]

Barangays on the site also serve as home to the indigenous Remontado Dumagats.[4]

The other proposed site for the dam and reservoir is further east and downstream on the east-flowing Kaliwa river, located in the Barangays of Pagsanjan in the town of General Nakar and Magsaysay in the town of Infanta. Proposals for the construction of this downstream dam still involves the placement of conveyance tunnels and reservoir areas in the upstream Tanay, Rizal site.[8]

The history of projects on the Kaliwa River watershed began with the conception of the Manila Water Supply III project in November 1979 during the administration of President Ferdinand Marcos. However, instructed the MWSS to look for alternative sites. The MWSS identified the Kaliwa River basin to be the most viable alternative, and began the first World Bank feasibility study on the damming of the Kaliwa river in 1979.[3]

During that time, however, the Philippine economy had gone into rapid decline because Marcos' debt driven deficit spending made the Philippines vulnerable when the United States increased its interest rates in the third quarter of 1981.[9][10][11] The ensuing collapse of the Philippine economy, worsened by the political pressure after the assassination of Benigno Aquino, led to slow development of the Laiban dam project until Marcos was forced out of office and into exile by the 1986 People Power Revolution.[12]

By 1989, the succeeding administration of Corazon Aquino reviewed the project and determined that costs had ballooned so high that the project had to be shelved.[13]

After the administration of President Fidel Ramos took over in 1992, it continued conducting studies for the development of a Kaliwa dam, but these remained just proposals as the Metropolitan Waterworks and Sewerage System was privatized, and concessionaires Manila Water and Maynilad took over the servicing of water in the National Capital Region.[7]

In 2007, the administration of Gloria Macapagal Arroyo was able to get funding for Laiban Dam approved. However, the ZTE broadband scandal forced the project to be shelved.[7]

In 2009, San Miguel Corporation submitted an unsolicited proposal for the building of a dam in Laiban, but public opinion at the thought of higher water rates led to the project once again being shelved in 2010.[7]

Also in 2009, Osaka-based Japanese company Global Utility Development Corporation submitted an unsolicited proposal for what was called the Kaliwa Intake Weir Project, which would have seen the creation of a 7-meter, 550 MLD Weir at the Kaliwa site, instead of a dam.[14] At the instructions of President Aquino, this proposal was explored again in 2017, after the approval of the New Centennial Water Source-Kaliwa Dam Project by NEDA

The New Centennial Water Source-Kaliwa Dam Project was a water project proposed by the Philippine Government in 2012, whose main component was the construction of the Kaliwa Low Dam in Tanay, Rizal, as well as a water supply tunnel, and the attendant infrastructure for these structures.[15] The proposed Kaliwa Low Dam design had a 600 million-liters-a-day (MLD) capacity, and the water supply tunnel has a 2,400-MLD capacity. Had it been built, the Kaliwa Low Dam was expected to ease the demand on the Angat Dam, Manila's sole water storage facility.[16]

In 2015, two consortia were pre-qualified to bid for the undertaking of the Kaliwa Dam project[17] — the SMC-K Water Consortium, which is a partnership between San Miguel Holdings Corp. and Korea Water Resources Corp.; and the Abeima-Datem Consortium, which is a partnership between Albeinsa Infraestructura Medio Ambiento S.A and Datem Inc.[17]

When the project had not moved forward by the time Aquino administration ended, the succeeding Duterte administration decided not to pursue the Kaliwa Low Dam plan. The administration pursued a bigger dam instead, with funds to be obtained through an official development assistance from China.

A second dam further upstream, named Laiban dam, was also proposed under the 2012 version of the NCWS-Kaliwa Dam Project, as part of a larger, integrated system.[18] The proposed system was intended to be built in stages, with the approval of Laiban Dam subject to the success of the Kaliwa Low Dam. As a result, only stage one, involving Kaliwa Low Dam its attendant the water supply tunnel, were actually approved for construction during the administration of Benigno Aquino III.[2] The dam would not be included in the new NCWS plan under the succeeding administration.[19]

The tunnel boring machines for the dam were revealed on June 2, 2021.[24] The project had its groundbreaking on June 29, 2021.[23] Excavation works for the dam is scheduled to begin in December 2021, to be done by a joint venture of MWSS and China Energy Engineering Corporation (CEEC).[25]