Napindan Hydraulic Control Structure

Satellite image of the Napindan Hydraulic Control Structure along Pasig River

Did you know that Pasig River, the main river of Metro Manila, sometimes reverses its normal flow and instead brings saltwater from Manila Bay to Laguna de Bay? Well, during the summer months of April and May and in times of high tide, the sea level is actually higher than that of Laguna de Bay and thus the flow of water on the Pasig River goes “upstream.” Bet you didn’t know that, huh?

To prevent or lessen the increase of salinity from Manila Bay and pollution from the Pasig River itself from entering Laguna de Bay during these times of reverse flow, the Napindan Hydraulic Control Structure or NHCS was constructed in 1983. The NHCS is found on the confluence of Marikina and Pateros-Taguig rivers with Pasig River. This confluence is also the downstream endpoint of the Napindan Channel, which is the upper part of Pasig River that connects to Laguna de Bay.

Photo of the sluice gates at the Napindan Hydraulic Control Structure

Apart from preventing the reverse flow of Pasig River, the NHCS is also used for flood control. During the rainy season, most of the flooding along the Pasig River area is due to the increased water flow coming from Marikina River. The Manggahan Floodway in Pasig City was constructed to divert much of this water from Marikina River directly into Laguna de Bay. By also closing the NHCS during times of rain, the water is effectively dammed in Laguna de Bay preventing it from flooding the downstream portions of Pasig River.

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Posted on
September 18, 2008
Filed under
Metro ManilaRivers / Waterfalls
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  1. nel reformina wrote on September 28, 2012 @ 07:11AM

    What is the maximum water level of the lake (compared to high tide level of Manila Bay) which the NCHS can “dam” before the water overflows to Pasig River? At this level, how much land area will be under water along the shores of the lake?

  2. Rey A. Mendiola wrote on April 4, 2013 @ 05:05PM

    Today, April 4, 2013, summer months, water level at Laguna Bay is low. The water level to be maintained at the Bay should be measured on June or July months wherein some of the rainwater had filled the bay and no flooding is occuring on the houses near the shorelines.
    During the ’60 to ’80’s, there used to have plenty of fishes in the Bay, and also the “tulya” and “suso”, the food for ducks. When Napindan dam was constructed these shells were gone. Why? One is due to water pollution. The other reason is that during Manila Bay high tide, salt water is mixed with fresh water of Laguna Bay thereby killing some algae or other microbes, our old folk called it “tabsing water”, tabang-asin.
    Also, Laguna Bay should be desilted. During the ’60, when we are swimming at the bay, shorelines are composed of sand and there are lots of “tulya, suso, biya, ayungin, hipon, etc” at a knee deep water and you can see clearly your feet. Now, you can experience knee deep mud or “burak”. What does LLDA officials are doing?

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