On November 11, 2020, Typhoon Ulysses brought devastating winds and very heavy rainfall to CALABARZON. Already the third typhoon to hit the region in a span of only one month, next after typhoons Quinta and Rolly, and after several severe tropical storms such as Siony and Tonyo, Ulysses brought severe flooding and many landslide incidents in the region. In preparation for the upcoming typhoons, Rolly and Ulysses, quarry and crushing plant operators in CALABARZON were directed by this Office to intensify self-monitoring measures in their quarry area and siltation control facilities. Preventive measures were made to be taken even before the typhoons to avoid possible accidents/incidents that might affect the environment and the safety of nearby communities. Among these measures was the possibility of the temporary stoppage of quarry operations.

The Department of Science and Technology – Philippine Atmospheric, Geophysical and Astronomical Services Administration (DOST – PAGASA) recorded rain precipitation of 153 mm on the day of the landfall—6% higher than the expected level of rainfall in the entire month of November. It caused the water level of the Marikina River to reach up to 22 meters above mean sea level (MSL) as measured in the river monitoring station in Marikina City, and eventually inundation of low-lying areas in Rodriguez and San Mateo, Rizal.

The flooding in CALABARZON and the National Capital Region caused by Typhoon Ulysses was largely influenced by the oversaturation of the vast land of Sierra Madre. This was already the case even before the said typhoon entered the Philippine Area of Responsibility due to Typhoon Rolly and Tropical Storm Siony. It led to more surface run-off along the headwater of Wawa Dam reaching the lowland, specifically the low-lying areas of Montalban, San Mateo, and Marikina City. Evidence of this was the overflow of riverine water destroying several houses situated along the river embankment in Sitio Wawa and Sitio Esse in Brgy. San Rafael. No active quarrying activities can be located upstream of the dam, but the overflowed water brought silts and debris along roads and structures thereat.

Because of the preventive actions taken, quarry operators and permit holders within the Marikina river basin reported that no landslide nor ground movement occurred within their contract areas. Surface run-off was contained within their respective siltation control facilities. Their established and operationalized catchbasins and settling ponds had the purpose of containing surface run-off from their quarry and crushing plant areas and remained intact with no signs of overflow during and after the typhoon.

As stated from the previous reports from this Office regarding the flooding of San Mateo, Rodriguez, and Marikina City due to Monsson Rains in August 2018 and Tropical Storm Ondoy back in 2009, quarrying, in general, has minimal impact on the flooding characteristics of the Marikina River Basin. In the mentioned municipalities, flooding, erosion, and siltation will occur within the basins and adjacent low-lying areas particularly during an intense and prolonged downpour with or without quarrying operations. This is because quarrying is only a fraction of land disturbance inside the Marikina Watershed. Quarry operations cover only 278 out of the 53,500 hectare-total drainage area of the Marikina Watershed/River Basin (UP NFRC data). Other land developments contribute to siltation and flooding of the Marikina River System, particularly the growing urbanization of the area. An increased number of establishments and subdivisions generally increases the size and frequency of floods through reduced percolation, reduction of groundwater flow, increase the surface run-off, and increase the flood height downstream, exposing the communities to greater flood hazards.

This Office continues to conduct regular monitoring of all National and LGU issued contracts/permits in the Rizal province through the Multi-partite Monitoring Team of each contractor/operator/permit holder. Compliance with their commitments under the Environmental Protection and Enhancement Program (EPEP), Safety and Health Program (SHP), and Social Development and Management Program (SDMP) is thoroughly checked to ensure that the measures of siltation control, slope stabilization, and reforestation among other parameters are implemented and complied with.

 

Areas within the vicinity of Wawa dam.

Kasiglahan Village located near the confluence of Main Marikina Wawa River and Tanag River

Surface run-off at the quarry area of Montalban Millex Aggregates, Corp. (MMAC) was contained within the catch basin.

Stable slope with no major soil erosion observed along the embankment of Kaybibit River Adjacent to Hardrock Aggregates, Inc. in Antipolo City


By : Engr. Patrizia S. Benedicto             |          19 November 2020