SAN JUAN RIVER, Metro Manila, Philippines
The San Juan River is one of the tributaries of Pasig River. It borders the Tullahan River in the north, the Marikina River basin in the east, and Pasig River in the South. The River originates south of La Mesa dam as the San Francisco River and changes its name to San Juan River after joining the Mariablo River at about 7.3 km from the river mouth. Five tributaries, namely: Talayan Creek, Diliman Creek, Salapan (Ermitanyo) Creek, Maytunas Creek, and Buhangin Creek feed into the main channel that eventually drains to the Pasig River.
The entire San Juan River basin including its tributaries has a catchment area of 90.4 sq. km, comprising the lower half of Quezon City, the municipality of San Juan and parts of Mandaluyong City, Pasig City and Manila City. Of the total area, about 78sq km is located in Quezon City.
The basin is characteristically a Central Plateau Lowland or Guadalupe Formation Lowland. Central Plateau Lowland was formed during the Pleistocene period (2,000,000 years ago) by great volcanic eruption. It has elevations ranging from 20m to 40 m at the south of Pasig River. Going northward, the çlevation increases, reaching 70m in Quezon City and over lOOm in the Novaliches area. Hence, most of Quezon City has a rolling terrain while the Municipality of San Juan has predominantly gentle slope except for the flat areas scattered along the western parts of the municipality where the slope ranges from 0% to 1% only.
The basin lies on a solid foundation of compact Pleistocene Guadalupe Tuff Formation (adobe) overlain by Quaternary (Holocene) alluvium. The Guadalupe Formation consists of massive to medium bedded, fine-grained vitric tuff and welded volcanic breccias (rocks) with subordinate amounts of tuffaceous, fine to medium grained sandstone. Southwest towards the direction of Pasig River where the topography is generally flat, the surface area is mostly covered with alluvium. This river floodplain deposit consists of loose to granular sand, silt, clay loam and granular clay.
In the 1940’s, the San Juan River basin was mostly paddy fields and wooded/bamboo areas. Development was limited to the San Juan, San Francisco and Kamuning-Cubao areas only. However, with the urbanization of Metro Manila, the paddy fields and wood areas gradually vanished and gave way to residential buildings, commercial and business establishments and factories. At present, approximately 90% of the area is classified as urban, although mostly of low density. The remaining 10% are unoccupied area or open spaces.
(Department of Public Works and Highways, CTI Engineering Co., Ltd. in association wlth Nikken Consultants, Woodflelds Consultants, Inc.and Basic Technology and Management Corp.)