Angat Dam

Dams have been an influential part of human development for thousands of years. However, it was only in the last century, and increasingly in the last 50 years, that technological advances have enabled the construction of large dams. These are important reservoir structures for various communities for these structures help people to have water to drink and provide water for irrigation, improving navigation, creating a reservoir of water to supply industrial uses, generating hydroelectric power, creating recreation areas or habitat for fish and wildlife and containing effluent from industrial sites. The ability of dams to reduce flow variability means that water can be regulated, mitigating droughts and, to varying extents, controlling floods.

Angat dam, a famous concrete water reservoir embankment hydroelectric dam in the Philippines was built in order to supply water to Metro Manila. It was a part of the Angat-Ipo-La Mesa water system. The reservoir supplies about 90 percent of raw water requirements for Metro Manila through the facilities of the Metropolitan Waterworks and Sewerage System and irrigates about 28,000 hectares of farmland in the provinces of Bulacan and Pampanga.

Fig 1.0 Angat-Ipo-La Mesa Water System

The figure above shows how water is being supplied from Angat reservoir up to the Manila Water and Maynilad Water distribution systems which supply 90 percent of water in the east and west zones of Metro Manila.

The project is located at Barangay Tibagan, Bustos, Bulacan, served by the Angat River. The dam area is bounded by Umiray River in the northeast, the Kanan River in the southeast, and the Marikina River in the south. The main dam is about 18 meters above sea level. Among the 2.5-meter high, six-span dam’s main features are easily deflatable and inflatable rubber body, resistance to sedimentation, economical and having auto-deflation system. The dam has a normal high water level of 210 meters, according to the Philippine Atmospheric, Geophysical and Astronomical Services Administration (Pagasa). It has three gates opening a total of 1.5 meters to gradually release water that had accumulated due to incessant rains during typhoons. Despite of supplying potable water it also produces energy to Metro Manila and nearby areas, its capacity for the main auxiliary powerhouse is 200,000 KW. Surrounded by lush greens, this place is also ideal for fishing, boating and hunting.

The dam was originally built in 1926 until steel sector gates were installed in 1967 on top of the regulator dam for the purpose of generating irrigation water, power supply and domestic water supply. The design capacity of the dam is 850 million cubic meters. The construction cost of the dam is Php 315.344 million and was being funded by the Philippine government, it runs 50 kilometers upstream from the Bustos Dam as a fixed type river weir. The method of design was based on hydrological modeling using the Water and Energy Budget-Based distributed hydrological model (WEB-DHM). In fact the AARD, Angat Afterbay Regulator Dam formerly known as Bustos Dam is the longest rubber dam in Asia at 79 meters and the second largest in the world.

With its construction, the Bustos Dam’s height was increased by 2.5 meters and later renamed Angat Afterbay Regulator Dam, increasing the service area of the Angat-Maasim Rivers Irrigation System (AMRIS), which operates the AARD from 25,000 hectares in 1927 to 31,485 hectares in 20 towns in Bulacan and Pampanga benefitting 20,562 farmers.

At the beginning of the operation of the dam, a disastrous event in 1967 took place in Angat Dam when Typhoon Welming hit Central Luzon. As a successful bidder, Engineering Construction Inc. has garanted a contract by NAWASA to construct a tunnel covering a distance of seven kilometers, passing through the mountain, from the Ipo river up to Bicti. The plaintiff corporation already had completed the first major phase of the work, namely, the tunnel excavation work. Some portions of the outworks at the Bicti site were still under construction. As soon as the plaintiff corporation had finished the tunnel excavation work at the Bicti site, all the equipment no longer needed there were transferred to the Ipo site where some projects were yet to be completed. When Typhoon Welming hit Central Luzon, passing through Angat Hydro-electric Project and Dam at lpo, Norzagaray, Bulacan. Strong winds struck the project area, and heavy rains intermittently fell. Due to the heavy downpour, the water in the reservoir of the Angat Dam was rising perilously at the rate of sixty centimeters per hour. To prevent an overflow of water from the dam, since the water level had reached the danger height of 212 meters above sea level, NAPOCOR caused the opening of the spillway gates. Due to the negligent manner with which the spillway gates of the Angat Dam were opened, an extraordinary large volume of water rushed out of the gates, and hit the installations and construction works of ECI at the lpo site with terrific impact, as a result of which the latter's stockpile of materials and supplies, camp facilities and permanent structures and accessories either washed away, lost or destroyed.

Another tragedy happened occurred in 1978 that lasted for twenty one hours during the height of the Typhoon Kading, at that time NAPOCOR opened simultaneously all the three floodgates of the Angat Dam. wherein they open the three floodgates simultaneously from 1 meter to 8 meters at the first hour, until all floodgates were opened to the maximum of 14 to 14.5 meters by six hours of the same day. These acts of NPC resulted in the inundation of several towns in Bulacan near Angat Dam. Hardest-hit was Norzagaray, Bulacan.

Fig. 2.0 Map of Angat Sub System

The figure shows Norzagaray as one of the municipalities that were analyzed that will be greatly affected by the release of water from Angat dam’s spillways. About 100 Garayenos died and millions of pesos worth of properties including houses, farms, plants, working animals were destroyed. Eleven people were filed against the electric corporation in the Regional Trial Court of Malolos. NPC stressed out that there was very little opening of the spillways, ranging from 1 meter to 2 meters. But from midnight or from the first hours of the day that the tragedy happened the opening of all the three spillways started at 5 meters and swiftly went as far up as 14 meters. What made the situation worse was that the opening of the spillways was made at the unholy hours when residents were asleep. The plaintiffs all testified that they were never given any warning that the spillways would be opened to that extent.

The series of typhoons affected the structure until Bay 1 sector gate finally gave way in September 1990 after Typhoon Iriang carried away the structure 250 meters downstream from its original post. The agency has undertaken temporary rehabilitation works in the dam using their own budget and through funding assistance from the World Bank. Although it was rehabilitated, the result of the works of the agency seem to be not satisfying enough to ensure that the structure can resist the effects of natural calamities that’s why rehabilitations were been entrusted to Kurimoto, LTD., Osaka, Japan.

At present, the Manila Waterworks and Sewerage System will assess the structural condition of the 44-year-old Angat Dam for there was a fear that the dam was being damaged by the past earthquakes. Western Marikina Valley Fault could trigger movement on the fault lines beneath the dam and its dikes according to the experts. If those were damaged, the flood would affect not only areas near the Angat River but extend both upstream and downstream into the flood plain of the Pampanga River, that would be a devastating sight for some cities and towns in Bulacan, Pampanga and Metro Manila, the latter home to more than 15 million of the country's 98 million population. Recently, China had announced that they will provide the Philippines P5.3 billion for the Angat Water Utilization and Aqueduct Improvement Project which involves the construction of an additional 9.9 kms to Aqueduct 6 and an interconnection facility that would ensure water flow from Angat Dam to La Mesa Dam in Novaliches.The project aims to ensure water supply for Metro Manila's 15 million residents and reduce the 394 million liters of wastage.

As an assessment in the case of 1967 event, it cannot be pretended that there was no negligence or that NAPOCOR exercised extraordinary care in the opening of the spillway gates of the Angat Dam. Maintainers of the dam knew very well that it was far safer to open them gradually. But the spillway gates were opened only when Typhoon Welming was already at its height. In my own view, since NAPOCOR knew the coming of the typhoon four days before the tragedy took place, for me a possible solution to the problem is that action could have been taken as earlier as possible, when the water in the reservoir was still low. At that time, the gates of the dam could have been opened in a regulated manner and it could have been prevented the incident of having an extraordinary large volume of water that was being unleashed out of the gates of the dam.

In the case of 1978 tragedy, NAPOCOR should have minimized the openings of the spillways much earlier as possible to prevent having too much large collection of water at the dam that made them to forcibly increase the height of the opening of the spillways and they should have opened these in a gradual manner in order to avoid unleashing of large amount of water in a short period of time for the communities around it wouldn’t be able to prepare for the coming of an unexpected flood to their place. In our perspective, typhoon in 1990 is not only the reason in the failure of the Bay 1 Sector gate, the soil condition underneath the dam also contributed to it’s failure. For me, one of the solutions that I’ve thought in order to minimize the occurrence of this kind of incident is by studying and applying the proper grouting techniques that could be a remedial tool in various applications such as strengthening soil structure around a dam or reducing water flow through the ground by means of seepage through grout pump and injecting cement grout to fill voids or fractures in the dam foundation. It helps in order to improve the stability of rock foundations, provides pre-construction site improvements, stops rock slabbing, rectifies sinkhole problems, repairs fractures in dam foundations, controls soft-ground settlements and arrests foundation settlement.

As a conclusion, NAPOCOR is liable for all of these tragedies, they are making decisions even without thinking of the possible events that may occur in compensation of what they have done. They don’t even focus in consulting weathering agencies in order to monitor the present as well as the future condition of our weather. Weather in our country is one of the major factors that contributes in affecting the conditions of our dams. It was concluded that this factor should be seriously analyzed as earlier as possible in order for the water related agencies as well as the department concerned on the environment to be prepared and well equipped to avoid unfortunate circumstances that may occur in the operation of our dams.

For our recommendations, one of these is that the government should develop better program of national public awareness. The public is generally unaware of the benefits dams bring to their community and to the Philippines as a whole. They are similarly unaware of the effect a dam failure could have on them, through flooding and the potential for loss of life or property and the loss of the goods or protection supported by the dam. Nowadays in the country, many houses are built in dam failure flood inundation zones. Zoning board are unaware of this when they develop zones, also the developers are unaware of it when they construct within this zone, and home or property owners buy in this zone completely unaware of what the consequences might be should the dam fail. A national and local focus should be placed on increasing public awareness of dam safety to increase consciousness of the need to purchase flood insurance.

Another is that the government should develop national dam rehabilitation and repair program for those persons who are in charge of operating Angat dam. It is difficult for many of these personnels to find the funding necessary to undertake rehabilitation work when necessary. Often times, vital repairs are neglected, and these dams are subject to further deterioration due to lack of funds and neglect. Deterioration can lead to dam failure. These types of disasters can cause great destruction and loss of life.

New technological equipments should be purchased including state-of-the-art computer systems and software, new equipment to aid in engineering analysis, video inspection cameras to inspect conduits through dams, laptop computers for use in the field to complete inspection reports and other correspondence, surveying equipment; a four-wheel drive vehicle on which to mount a survey unit, and a TV-VCR to review conduit inspection videos. These equipments could make fast access to necessary data and monitoring of the present condition of the dam.

Number of dam inspection should increase. Helicopter should be use to reach some remote dams for inspections and to reduce travel time to other dams for inspections. Improvements into dam inventory databases could greatly help in identifying the present water volume and improvement of telecommunication for confirming important data and current condition of the dam. Dam safety research should be made for it would lessen the risk of the past unfortunate experiences of the dam to happen again. Dam inspector training program should be maintained and improved for it would enhance the knowledge of the inspector to dam safety engineering and safety techniques.

Policy makers should be educated about on the importance of dam safety. It cannot be emphasized enough how important dams are to the nation’s economy and to the safety and well being of citizens. Policies concerning everything from public safety, to homeland security, to energy, to flood control should take into consideration the maintenance and rehabilitation of dams. Education of lawmakers at all levels is an important part of the future National Dam Safety Program.

References

Angat Dam. In Wikipedia, the free encyclopedia. Retrieved from http://en.wikipedia.org/wiki/Angat_Dam

Angat dam, dike sit on fault line. Retrieved from http://balita.ph/2012/07/26/angat-dam-dike-sit-on-fault-line-feature/

Investigation on dam foundation grouting process. Retrieved from http://pwri.go.jp/eng/ activity/pdf/reports/h.satoh.061107.pdf Acreman, M., F.A.K. Farquharson, M.P. McCartney, C. Sullivan, K. Campbell, N. Hodgson, J. Morton, D.
Smith, M. Birley, D. Knott, J. Lazenby and E.B. Barbier Wingfield. 2000. Managed flood releases from reservoirs: Issues and guidance. Report to DFID and the World Commission on Dams. Wallingford,
UK: Centre for Ecology and Hydrology, 88p