Manggahan Floodway
| Manggahan Floodway | |
 |
|
| Country | Philippines |
|---|---|
| Region | Metro Manila, Rizal |
| Source | Marikina River |
| - location | Pasig City, Metro Manila |
| - coordinates | 14°35′56″N 121°05′25″E / 14.59889°N 121.09028°E |
| Mouth | Laguna de Bay |
| - location | Taytay, Rizal |
| - coordinates | 14°31′30″N 121°08′10″E / 14.52500°N 121.13611°ECoordinates: 14°31′30″N 121°08′10″E / 14.52500°N 121.13611°E |
| Length | 10 km (6 mi) |
 Pasig-Marikina River basin with the Manggahan Floodway shown in cyan.
|
|
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 meters (850 ft). Over 40,000 households are situated along the floodway's banks and these shoreline slums have reduced its effective width to 220 meters (720 ft). Kangkong is cultivated extensively in the floodway as well.
The floodway has only 4 bridges. The 3 bridges within Pasig City are Manggahan Bridge (near Marikina River), Ortigas Bridge (carries Ortigas Avenue Extension) and F.B. Legaspi Bridge. Barkadahan Bridge is the last and only nearest bridge to the lakeshore of Laguna de Bay located at Taytay, Rizal.
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 gastroenteritis 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.
...
Wikipedia