2011 – Refurbishment of Ambuklao and Binga Hydro Power Dams and Appurtenant Works

 John Grimston, Robin Dawson

The Ambuklao and Binga Hydro-Electric Power Projects are located in Luzon, Philippines and were privatised in early 2008 after public bidding. Ambuklao dam forms an impoundment on the Agno River. The nearest city, Baguio, is approximately 45km or 1.5hrs drive away. The key headworks feature is an embankment central core rockfill dam and reaches a maximum height of some 129 m above the bed of the Agno River. A gated spillway is located at the left abutment, with a steep chute and flip bucket. Binga dam forms an impoundment approximately 20 km downstream of the Ambuklao dam. The rockfill embankment with an inclined clay core reaches a height of about 107 m above the bed of the Agno River. The spillway is located at the left abutment.

Heavy tropical rains and typhoons can cause very high flows in the rivers leading into the Ambuklao and Binga reservoirs. PMF peak flow is 11,600 cumecs. Due to the steep slopes surrounding the reservoir and along the access roads to the Binga Dam, landslides can create a hazard in the reservoir or for emergency access to the dam. There are numerous active faults in the area, including the Abra, Digdig and Philippines Faults (the latter being one of the most active faults around the Philippines). The region around the dams is capable of and has experienced earthquakes with a magnitude of 7.8 on the Richter Scale. This was demonstrated by the 1990 earthquake (7.8 magnitude) and caused minor damage to the dam structures.

The Project owner commenced rehabilitation implementation planning immediately after purchasing the facilities aimed at reactivating the Ambuklao plant’s 75MW capacity (inoperable since 1999 due to reservoir siltation issues triggered by the 1990 earthquake) and increasing it to 105MW. Rehabilitation at the Binga plant will increase capacity from it’s current 100MW to 120MW. The overall rehabilitation works include plant, intakes, associated tunnels, etc. This paper will focus primarily on the dam and spillway related rehabilitation, studies and design including review of the PMF and spillway capacity for both dams, Ambuklao innovative upstream face rehabilitation, Ambuklao spillway studies and rehabilitation and Binga spillway works and reservoir sedimentation studies.

2011 – Refurbishment of Ambuklao and Binga Hydro Power Dams and Appurtenant Works