RAINFALL VOL SURPASSES 'ONDOY' / BIG DAMS' OPEN GATES ADD FLOODING

[PHOTO -The volume of rainfall that submerged Metro Manila and nearby provinces yesterday surpassed that of Tropical Storm “Ondoy,” initial reports from the government’s Project Noah (Nationwide Operational Assessment of Hazards) showed.]

MANILA, AUGUST 8, 2012 (INQUIRER) By Leila B. Salaverria - But though the monsoon rains exceeded Ondoy’s rainfall in 2009, the latter still managed to pack more wallop because most of its rainfall came in a shorter period of six hours, said Mahar Lagmay, the project director.

Based on the initial data from Project Noah, there were 472 millimeters of accumulated rainfall from 4:45 p.m. of August 6 to 3:00 p.m. of Auguat 7, a 22-hour period. The data were recorded in Quezon City.

Ondoy’s onslaught dumped 455 mm of rain over a 24-hour period. But 341 mm fell in just six hours.

The monsoon rains, on the other hand, were spread throughout a longer period. This is why the data should be put into perspective, Lagmay said.

Ondoy more intense

“That must be put into perspective. Although the accumulated rainfall was initially more than Ondoy, the amount from Ondoy was compressed in a shorter period, within six hours. It was concentrated during that period, making Ondoy much more intense in terms of rainfall,” Lagmay told the Inquirer in a phone interview.

He added that the data had to be verified by the Philippine Atmospheric, Geophysical and Astronomical Services Administration (Pagasa).

The monsoon rains gave Metro Manila and nearby provinces a near repeat of Ondoy, with many people trapped in their homes because of raging waters and cars stalled in deep floods.

What was different was that there was not even any storm or typhoon to blame for the deluge, just the nameless southwest monsoon.

Pagasa said the southwest monsoon brought heavy rains because it had the lingering effects of Typhoon “Gener” and was enhanced by Tropical Storm “Haikui.” The tropical storm was spotted northeast of Taiwan but was outside the Philippine area of responsibility.

Weather forecaster Glaiza Escullar said Gener had enhanced the southwest monsoon when it was in the country last week.

Before the effects of Gener could wane, Haikui came close to the country and enhanced the monsoon or moisture-laden winds again, thereby causing heavy rains.

Like wet rag

Escullar likened the situation to a wet rag that was drenched in water. Before the rag could be wrung out, it was doused in water again.

As Haikui moved closer to Taiwan, its effect on the southwest monsoon in the country intensified. The peak of the monsoon rains enhanced by Haikui was felt Monday night and Tuesday morning, Escullar said.

Moderate to heavy rains were also felt throughout most of Tuesday and the same may be felt on Wednesday, although it may also start easing up a bit on Wednesday.

According to Pagasa, the downpour would be felt Wednesday in Metro Manila, Ilocos, La Union, Pangasinan, Tarlac, Zambales, Bataan, Pampanga, Bulacan, Rizal, Cavite, Laguna and Batangas.

Landslides and flash floods in mountainous and low-lying areas may occur, Pagasa said.

If no new typhoon, low pressure area or any other weather system would enter the picture, sunnier weather would be felt on Thursday.

Pagasa said data from Project Noah, which is under the Department of Science and Technology, was still subject for verification.

Forecaster Mario Palafox said data from Project Noah came from automatic weather stations and would have to be verified by checking the manual rain gauges of the weather bureau.

“That is subject for verification. The automatic weather station can be susceptible to errors. It may be correct, or the machine could have problems,” Palafox said.

The latest 24-hour rainfall data available from Pagasa as of Tuesday was 323.4 millimeters from 8 a.m. of August 6 to 8 a.m. of August 7, monitored at the Science Garden in Quezon City.

Palafox said the monsoon rains were different from Ondoy’s because the downpour on Tuesday was spread out more uniformly throughout the day.

Abnormal

He also described the monsoon rains as “abnormal” given their heavy volume. There was no storm, typhoon, or even a low pressure area in the country.

“It’s been a long time since we last experienced this kind of rainfall event,” he said.

Palafox also said the rains came intermittently and did not fall down in a single time period because they were caused by the southwest monsoon. These are winds that move around.—With Frances Mangosing, INQUIRER.net

Big dams open gates, add to Luzon flooding By Leila B. Salaverria, Riza T. Olchondra Philippine Daily Inquirer

MANILA, Philippines—Major dams in Luzon kept their gates open to release water on Tuesday as heavy rains from the monsoon pummeled several provinces, contributing to the flooding in large areas in central and northern Luzon.

Ipo, Ambuklao, San Roque, Binga Dams all opened their gates, according to the Philippine Atmospheric, Geophysical and Astronomical Services Administration (Pagasa).

La Mesa Dam, which has no gate, continued to overflow. As of 2 p.m., its water level was 80.55 meters, above its normal water level of 80.15 m.

Ipo Dam had two gates open yesterday, with its water level as of 2 p.m. reaching 100.97, 0.17 m above its normal high level.

San Roque Dam also had two opened gates, taking in much more water. Its water level as of Tuesday afternoon was 282.96 m, 2.96 m above its normal level.

Pagasa warning

Pagasa warned that the Pangasinan municipalities of San Manuel, San Nicolas, Tayug, Sta. Maria, Asingan, Villasis, Alcala, Bautista, Rosales and Bayambang would be affected when San Roque Dam released water from its spillways.

With two gates open, the water level at Ambuklao dam was 751.88 m on Tuesday, just 0.12 m shy of its limit.

Binga Dam had three open gates as of 2:00 p.m. even though its water level of 573.99 m had not reached its normal high water level of 575 m.

By 6 p.m. on Tuesday, Magat Dam also opened one gate as its water level rose to 191.6 m, 1.6 m above its normal high of 190 m.

Pagasa said the Isabela municipalities of Ramon, San Mateo, Aurora, Cabatuan, Luna, Reina Mercedes, Burgos, Naguilian and Gamu would be affected by water from the dam.

Expected to increase Wednesday

Pagasa said the reservoir water elevations of Ambuklao, Binga, and San Roque Dams were expected to increase until at least today, when moderate to heavy rains were expected to fall over their areas.

The water level at La Mesa in Quezon City fluctuated all Tuesday even as it spilled water.

By 6 p.m. Tuesday, the water level was down to 80.44 m or 6 centimeters lower than its level at 4 p.m., according to Manila Water Co. Inc.

The level was 80.53 m at 3 p.m. and 80.60 m at around 12 noon.

The water steadily rose from Monday night to around 8 a.m. Tuesday and then eased up at around midmorning and started going up again, said Manila Water communications manager Jeric Sevilla.

Spill dam

The same was observed on Monday as the volume of rain went from heavy to light and heavy again.

Water at La Mesa receded toward late afternoon on Monday after hitting its maximum level of 80.15 m in the morning.

La Mesa’s water level reached 80.15 m from 2 a.m. to 7 a.m. on Monday after more than two weeks of heavy rain. The water level dropped steadily during the day and reached 80.11 m as of 5 p.m. but started inching up again after 6 p.m.

Being a spill dam, La Mesa does not have to open its gates to ease water levels. Instead its excess water starts flowing out through a spillway after the 80.15-m mark.

Drain to Manila Bay

During the rainy months, a red alert is raised at 79.50 m, according to Sevilla.

Water from La Mesa goes into the Tullahan River, which flows through the northern part of Quezon City, including the Fairview area, as well as the cities of Malabon, Valenzuela and Caloocan. The river drains into Manila Bay.


Chief News Editor: Sol Jose Vanzi

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