MANILA, Philippines ? The Marikina River and other waterways that swelled when tropical storm ?Ondoy? battered Metro Manila on Saturday are clogged not only by illegal settlers but also by subdivisions, aggravating the heavy flooding that drowned many communities, a University of the Philippines geologist said.

?The flood could have been lower and could have risen slowly if there were no constrictions in the waterways,? UP Marine Science Institute professor Fernando Siringan said.

For instance, the badly hit Provident Village and the SM Marikina Mall in Marikina City are actually sitting on flood plains or flat spaces occupied by water when rivers swell, UP engineering professor Guillermo Tabios III also said.

In a forum at the UP College of Engineering yesterday, Tabios presented a study on what happened to the Marikina River Basin on that tragic day.

Disappointing

He said developers should have allotted a space on both sides of the river, at least spanning six times the river?s width, where structures should have been prohibited.

Siringan, one of those who attended the forum, joined an aerial inspection of the metropolis on Thursday to check if there were obstructions in the metropolis? waterways that contributed to the flooding.

What he saw was disappointing. ?We saw many subdivisions whose walls were built on the river itself. So where will the water flow?? he said.

He said this could explain why some elevated areas in Quezon City still experienced flooding as high as eight meters.

But the waterways are not only clogged. They are also already shallow because of accumulated garbage, silt and mud.

?The water had nowhere to flow,? Siringan said.

Siringan also dismissed speculations by many affected residents in Marikina City that the flood was caused by dams which released water, saying there were no dams that could immediately drain into the city.