On October 17, 2015, Typhoon Koppu (local name: Lando) brought torrential rains in Luzon island, Philippines generating widespread flooding in numerous places across the island. It also caused landslides and debris flows in the province of Nueva Ecija.
Extensive flooding in Central Luzon were reported, mainly affecting the province of Pampanga. Waters originated north of Arayat then flowed southward to Candaba, Apalit and Hagonoy before draining to Manila Bay. Normally, numerous rivers and streams within a delta should accommodate the water flowing through. Flooding is normal and should be expected, but it should recede fairly quickly as it drains outwards to the sea.
However, this was not the case then in Central Luzon where there was still widespread flooding more than a week after the typhoon made landfall, as we can see above in the Landsat 8 image taken on October 28.
A closer look at the image clearly shows a dike impeding the flow of water westward, constraining the flood within Hagonoy and other nearby towns. Communities west of this dike were spared of the floods, unfortunately, those at the east were severely affected.
What made matters worse was that flood waters draining to the sea were impeded by fishponds that are where delta streams and rivers are supposed to be. The flood waters had to flow through few small channels (white arrows, sediment plumes show where water was discharged to Manila Bay), which clearly could not accommodate the immense volume of water that needed to drain out to the sea. As a result, floods took longer to recede and more people had to endure an extended period of flooding.