The Bicol River Basin


Posted at Oct 23 2009 03:40 PM | Updated as of Oct 25 2009 09:35 AM

This is the map of tributaries and flood-prone areas around the Bicol River basin from Pagasa’s Flood Forecast Branch. The text below the map gives general information about the Agno River Basin and its environs.

Fast Facts:

  • Location: Bicol Peninsula
  • Draining area: 3,771 sq. km.
  • Encompasses:
    • Central portion of Camarines Sur
    • Northern portion of Albay
    • Portion of Camarines Norte
      • Medium-sized basin, Southern Luzon


  • Annual water runoff: 5,100 cubic meters
    • Starts from Mayon Volcano (4,421 m elevation) and goes in a northwestward direction
  • Average annual rainfall:
    • 2,000-3,600 mm in southwestern section of basin
  • Tropical cyclone passages, northeast monsoon and orographic effect: flood-producing rains in the basin from May to February
  • Storm surges associated with slow-moving typhoons: causes flooding from the sea in the alluvial plain near the mouth of the river or over San Miguel Bay (Bicol)
  • Flood target areas:
    • Central part of basin: from Baao lake to Bato lake
    • Alluvial plain (extends from Naga City to the river mouth or over San Miguel Bay)

Connecting water ways and nearby mountain ranges

  • Principal tributary: Sipocot River (Bicol)
    • This river cuts through mountainous terrain and has a steeper slope
    • The Bicol River widens to more than 1,000 meters across after joining Sipocot River before discharging water into the San Miguel Bay (Bicol)
  • East of river basin: chain of volcanoes
  • West of river basin: highlands and lowhills
  • Bicol Plain: between Eastern Bicol Cordillera and Ragay Hills (Bicol)
  • Water run off from Mayon Volcano:
    • Regulated through:
      • Bato lake
      • Buhi lake
      • Baao lake
    • Stream-flow reaches the mainstream of Bicol River

Source: Pagasa Flood Forecast Branch