Manggahan Floodway

Manggahan Floodway
Manggahan Floodway in Pasig (2021)
Pasig-Marikina River basin with the Manggahan Floodway shown in cyan.
Location
CountryPhilippines
RegionMetro Manila, Rizal
Physical characteristics
SourceMarikina River
 • locationPasig, Metro Manila
 • coordinates14°35′56″N 121°05′25″E / 14.59889°N 121.09028°E / 14.59889; 121.09028
MouthLaguna de Bay
 • location
Taytay, Rizal
 • coordinates
14°31′30″N 121°08′10″E / 14.52500°N 121.13611°E / 14.52500; 121.13611
Length10 km (6.2 mi)

The Manggahan Floodway is an artificially constructed waterway in Metro Manila, Philippines. The floodway was built in 1986,[1] with the cost of 1.1 billion pesos, in order to reduce flooding along the Pasig River during the rainy season, by diverting the peak water flows of the Marikina River to Laguna de Bay, which serves as a temporary reservoir.[2][3] In case the water level on the lake is higher than the Marikina River, the floodway can also reverse the flow.

By design, the Manggahan Floodway is capable of handling 2,400 cubic meters per second of water flow, although the actual flow is about 2,000 cubic meters per second. To complement the floodway, the Napindan Hydraulic Control System (NHCS) was built in 1983 at the confluence of the Marikina River and the Napindan Channel of the Pasig River to regulate the tidal flow of saline water between Manila Bay and the lake, and to prevent the intrusion of polluted water into the lake.[2]

It has a fully gated diversion dam at its head and was designed with a width of 260 meters (850 ft). Over 40,000 households are situated along the floodway's banks[4] and these shoreline slums have reduced its effective width to 220 meters (720 ft). Kangkong is cultivated extensively in the floodway as well.

The Manggahan Floodway was supposed to function together with the proposed Paranaque Spillway Project, a spillway that would direct flood waters from Laguna de Bay to Manila Bay. However the spillway project was cancelled in 1977 due to budget issues.[5][6]: 61  Ever since the onslaught of 2009's Typhoon Ketsana (Ondoy), and consistently-reoccurring flooding in the metropolis, the Paranaque Spillway project is now being revived,[7] together with the proposed Marikina Dam.[8]

  1. ^ "Background on the Mega-Dike Issue". Leaders and Organizers of Community Organization in Asia. Archived from the original on 2002-08-05. Retrieved 2009-07-21.
  2. ^ a b "Laguna de Bay Masterplan". Laguna Lake Development Authority. Archived from the original on January 29, 2009. Retrieved 2009-07-21.
  3. ^ Alcazaren, Paulo (June 15, 2013). "City Sense: 10 reasons why it floods in Manila". The Philippine Star. STAR Group of Publications. Retrieved October 10, 2014.
  4. ^ Melissa Alipalo (2007-09-21). "Urban poor: small piped water networks help slums in Manila, Philippines". IRC. Archived from the original on 2009-10-26. Retrieved 2009-07-21.
  5. ^ "VERA FILES FACT CHECK: Claim on Cory Aquino scrapping Marcos-era floodway NEEDS CONTEXT". VERA Files. 2020-12-09. Retrieved 2022-09-26.
  6. ^ Japan International Cooperation Agency; CTI Engineering International Co. Ltd.; Nippon Koei Co. Ltd. (October 2020). Republic of The Philippines Follow-Up Study on Parañaque Spillway Project - Final Report (PDF) (Report). Vol. 1: Main Report. Department of Public Works and Highways, Republic of The Philippines. Retrieved 11 October 2022.
  7. ^ Recueno, Aaron (August 9, 2022). "DPWH eyes Parañaque Spillway project to address Metro Manila flooding". Manila Bulletin. Retrieved September 26, 2022.
  8. ^ "DPWH proposes Marikina Dam, Parañaque Spillway to control flooding". CNN Philippines. November 25, 2020. Archived from the original on November 25, 2020. Retrieved September 26, 2022.