Manggahan Floodway
Encyclopedia
The Manggahan Floodway is an artificially constructed waterway in Metro Manila
, the Philippines. The floodway was built in 1986, with the cost of 1.1 billion pesos, in order to reduce the flooding along the Pasig River
during the rainy season, by diverting the peak water flows of the Marikina River
to the Laguna de Bay
which serves as a temporary reservoir. 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.
It has a fully gated diversion dam
at its head and was designed with a width of 260 metres (853 ft). Over 40,000 households are situated along the floodway's banks and these shoreline slum
s have reduced its effective width to 220 metres (721.8 ft). Kangkong is cultivated extensively in the floodway as well.
and other water-borne diseases.
Furthermore, pollution and sediments carried by the floodway will jeopardize the existing and potential uses of the lake. The sedimentation rate of the lake is estimated at 1.5 million m³/year with the Marikina River as a major contributor of silt to the lake through the Manggahan Floodway. Additional pollution comes from the shoreline settlers, living in slums up to 5 rows deep, whose waste goes directly into the floodway.
and dumped one month's rainfall in less than 24 hours, causing the Marikina River system, including the Manggahan Floodway, to burst its banks very rapidly. It is thought that blocked pipes and a poorly maintained sewer system, along with uncollected domestic waste, were major contributory factors in the speed with which the flood waters were able to engulf the surrounding area. The illegal settlers especially were blamed for flooding since their houses reduce the effective width and blocked the flow of the floodway. During the height of the storm, the Marikana River had a flow of about 3000 m³/s (106,000 ft³/s), and the head of the UP National Hydraulic Research Center stated that the floodway could have handled this flow without overflowing if there were no settlers on its banks.
Consequently, in February 2010, President Gloria Macapagal-Arroyo
revoked Proclamation 160 that reserved 20 parcels of land along the floodway for 6700 urban poor families, and ordered the forcible relocation of the illegal settlers whose houses were blocking the waterway to Laguna de Bay.
Metro Manila
Metropolitan Manila , the National Capital Region , or simply Metro Manila, is the metropolitan region encompassing the City of Manila and its surrounding areas in the Philippines...
, the Philippines. The floodway was built in 1986, with the cost of 1.1 billion pesos, in order to reduce the flooding along the Pasig River
Pasig River
The Pasig River is a river in the Philippines that connects Laguna de Bay to Manila Bay. Stretching for , it is lined by Metro Manila on each side...
during the rainy season, by diverting the peak water flows of the Marikina River
Marikina River
The San Mateo - Marikina River is a main river system in Eastern Metro Manila, Philippines. A river stretching from Rodriguez, Rizal, to Pasig City that connects to Pasig River as major tributary near Napindan Area in Pasig City.San Mateo - Marikina River used to be an important transport route...
to the Laguna de Bay
Laguna de Bay
Laguna de Bay is the largest lake in the Philippines and the third largest freshwater lake in Southeast Asia after Tonle Sap in Cambodia and Lake Toba in Sumatra, Indonesia. It is on the island of Luzon between the provinces of Laguna to the south and Rizal to the north...
which serves as a temporary reservoir. 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
Tide
Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the moon and the sun and the rotation of the Earth....
flow of saline water between Manila Bay
Manila Bay
Manila Bay is a natural harbor which serves the Port of Manila , in the Philippines.The bay is considered to be one of the best natural harbors in Southeast Asia and one of the finest in the world...
and the lake, and to prevent the intrusion of polluted water into the lake.
It has a fully gated diversion dam
Diversion dam
A diversion dam is the term for a dam that diverts all or a portion of the flow of a river from its natural course. Diversion dams do not generally impound water in a reservoir...
at its head and was designed with a width of 260 metres (853 ft). Over 40,000 households are situated along the floodway's banks and these shoreline slum
Slum
A slum, as defined by United Nations agency UN-HABITAT, is a run-down area of a city characterized by substandard housing and squalor and lacking in tenure security. According to the United Nations, the percentage of urban dwellers living in slums decreased from 47 percent to 37 percent in the...
s have reduced its effective width to 220 metres (721.8 ft). Kangkong is cultivated extensively in the floodway as well.
Environmental concerns
By carrying flood waters to Laguna de Bay, the Manggahan Floodway lessens flood conditions in Metro Manila but contributes to flooding of the coastal areas of Taguig, Taytay, and other towns in Laguna and Rizal along the lake. Incidents of severe floods became more frequent and lasted longer in these areas since its construction. An unusual large flood occurred in October/November 1986, lasting for 2 months and resulting in high mortality and morbidity rates due to gastroenteritisGastroenteritis
Gastroenteritis is marked by severe inflammation of the gastrointestinal tract involving both the stomach and small intestine resulting in acute diarrhea and vomiting. It can be transferred by contact with contaminated food and water...
and other water-borne diseases.
Furthermore, pollution and sediments carried by the floodway will jeopardize the existing and potential uses of the lake. The sedimentation rate of the lake is estimated at 1.5 million m³/year with the Marikina River as a major contributor of silt to the lake through the Manggahan Floodway. Additional pollution comes from the shoreline settlers, living in slums up to 5 rows deep, whose waste goes directly into the floodway.
2009 Flood
On September 26, 2009, at about 6:00 pm PST, the 50-mph "Tropical Storm Ketsana" (called "Ondoy" in the Philippines) hit Metro ManilaMetro Manila
Metropolitan Manila , the National Capital Region , or simply Metro Manila, is the metropolitan region encompassing the City of Manila and its surrounding areas in the Philippines...
and dumped one month's rainfall in less than 24 hours, causing the Marikina River system, including the Manggahan Floodway, to burst its banks very rapidly. It is thought that blocked pipes and a poorly maintained sewer system, along with uncollected domestic waste, were major contributory factors in the speed with which the flood waters were able to engulf the surrounding area. The illegal settlers especially were blamed for flooding since their houses reduce the effective width and blocked the flow of the floodway. During the height of the storm, the Marikana River had a flow of about 3000 m³/s (106,000 ft³/s), and the head of the UP National Hydraulic Research Center stated that the floodway could have handled this flow without overflowing if there were no settlers on its banks.
Consequently, in February 2010, President Gloria Macapagal-Arroyo
Gloria Macapagal-Arroyo
Gloria Macapagal-Arroyo is a Filipino politician who served as the 14th President of the Philippines from 2001 to 2010, as the 12th Vice President of the Philippines from 1998 to 2001, and is currently a member of the House of Representatives representing the 2nd District of Pampanga...
revoked Proclamation 160 that reserved 20 parcels of land along the floodway for 6700 urban poor families, and ordered the forcible relocation of the illegal settlers whose houses were blocking the waterway to Laguna de Bay.