23
Sep

BRIEFER OF THE LANDSLIDE INCIDENT IN BARANGAY TINAAN, CITY OF NAGA, CEBU

Type of Geohazard Incident:  Massive landslide in So. Tagaytay and So. Sindulan and, Barangay Tinaan, Naga City, Cebu.

Date and Time of Occurrence:  September 20, 2018 around 0600H

Impact Area Including Barangays Affected:  Portions of Sitio Tagaytay (crown area) and Sitio Sindulan (toe area) in Barangay Tinaan, Naga City, Cebu. Northeastern portion of the quarry area of Apo Land & Quarry Corporation (ALQC) was also affected.  Artificial damming of Pangdan River caused by the accumulation of landslide debris at the river channel was noted during the aerial survey.

Specific Actions Done by the Regional Office:

As soon as the landslide incident on September 20, 2018 was reported to Regional Director Loreto B. Alburo, two (2) Geologists, one (1) Mining Engineer and one (1) Geodetic Engineer were immediately dispatched to conduct an assessment.  Chief Geologist Al Emil Berador joined the team composed of representatives from OCD, OPAV, DSWD, DPWH and AFP who conducted aerial SAR Flight survey over the affected area.  Subsequently, a meeting was held at the Central Command with the RDRRMC-7 at Camp Lapu-Lapu, Cebu City.

 

 Chronology of Events, Advisories and Communications Made Prior the Landslide Incident:

Date Action Taken Findings/ Observations Recommendations
2007 Based on anecdotal data, a rockfall incident occurred in the vicinity of the landslide area
August 28, 2008 Conduct of 1: 50,000 scale Geohazard Mapping in barangay Tinaan, City of Naga including sitio Sindulan.

 

MGB team provided the Mines and Geosciences Bureau Field Data Sheet to the barangay and was received and signed by barangay councilor Dionisio Basalo on August 28, 2008.

 

(Annex 1)

Barangay Tinaan was classified to have Moderate landslide susceptibility.

 

The team recommended for the relocation of 26 families/ households living at the footslopes of an active landslide area in Sitio Sindulan.

 

No identified relocation site for identified households in sitio Sindulan.

 

In Sitio Taylor Ville, some households were recommended for relocation as the area was identified to have steep slope. A relocation site was identified at Philippine National Railway, in sitio Lower South, barangay Tinaan.

 

Barangay Tinaan was also identified to have High Susceptibility to Flooding.

 

At least 300 households along Pangdan River will be affected in a possible flooding that may reach neck-deep (1-meter) especially during heavy rains.

 

Flooding could be aggravated during high tide when seawater enters Pangdan river.

River bed is already shallow.

Based on anecdotal data (Tuploon Amy,) flooding problem started in 1949.

 

Relocation of residents located at the footslope of the active area in sitios Sindulan and sitio Taylorville

 

Dredging and Riprapping of low-lying river banks.

 

Monitor progress of mass movement (e.g. landslides, tension cracks)

 

Observe for presence of mass movement (e.g. landslides, tension cracks)

 

Develop an early warning device/ system

 

Identify evacuation site

 

Observe for rapid increase/decrease in creek/ river water levels, possibily accompanied by increased turbidity (soil content)

 

Observe for saturated ground or seeps in areas that are not typically wet.

 

Constant communication and updates with barangay Poblacion on geohazard situation.

May 28, 2011 Reported rockfall incident after five days of intermittent heavy to moderate rains in the area
May 31, 2011 Conducted Geohazard Investigation of the reported landslide incident in Barangay Naalad, City of Naga

(Annex 2)

The affected area is along the foot slope of a mountain located across Pangdan river, on the left side of the road (going to Toledo City) in sitio Tagaytay in barangay Tinaan.

 

The rockfall hit four houses at the slope base.

 

The rockfall is attributed to the underlying lithology which consists of inherently porous coralline limestone, the very steep slope, episodes of heavy rainfall prior to the incident. Some residents also reported seeing cracks on the area near the ridge. The overhanging slab left by the recent rockfall still poses an imminent threat to the residents down the slope.

Immediate evacuation and permanent relocation of all 26 houses along the footslope

Observe for presence of tension cracks/ fractures along the ridge area on regular/ daily basis especially during the rainy season.

The present “temporary” relocation site is located on the floodplain of Pangdan River and is susceptible to flooding.

June 1, 2011 MGB-7 furnished a copy of the Incident Report entitled “Geohazard Investigation of the Reported Landslide Incident in Barangay Naalad, City of Naga to the following:

 

The Barangay Chairman of Naalad (Annex 3)

 

City of Naga Mayor Valdemar Chiong

(Annex 4)

 

DENR Regional Executive Director Maximo O. Dichoso,

(Annex 5)

 

MGB Acting Director Leo L. Jasareno (Annex 6)

 

August 19, 2011 Issued Landslide Threat Advisory to Mainit Barangay Chairman Wilfredo Canete

(Annex 7)

High Landslide Susceptibility Rating Observe for and/or monitor presence of mass movement (e.g. landslides, tension cracks). Report situation to the MGB office concerned and the municipality/ city authorities.

 

Observe for saturated ground or seeps and sunken or displaced road surfaces. Report situation to the MGB office concerned and the municipality/ city authorities.

 

For relocation/ evacuation of 20 households on foot/midslopes where mass movement is active.

September 13, 2011 Issued Landslide Threat Advisory to Barangay Cabungahan, City of Naga, Cebu

(Annex 8)

Low Landslide Susceptibility Rating Observe for and/or monitor presence of mass movement (e.g. landslides, tension cracks). Report situation to the MGB office concerned and the municipality/ city authorities.

 

Observe for saturated ground or seeps and sunken or displaced road surfaces. Report situation to the MGB office concerned and the municipality/ city authorities.

September 14, 2011 Furnished copy of the Result of the MGB-7 Flooding Assessment and Mapping (1:10,000 scale) to the following barangays in the City of Naga:

-North Poblacion (Annex 9)

-East Poblacion (Annex 10)

-Colon (Annex 11)

 

Barangay North Poblacion: 1 sitio was found susceptible (low) to flooding

 

Barangay East Poblacion: 1 sitio was found susceptible (low) to flooding

 

Barangay Colon: 2 sitios were found susceptible (low) to flooding

Result of the MGB-7 Flooding Assessment and Mapping (1:10,000 scale) of barangay Colon, Naga City

(Annex 12)

Result of the MGB-7 Flooding Assessment and Mapping (1:10,000 scale) of the barangays in Poblacion, Naga City

September 13, 2011 Furnished copy of the Result of the MGB-7 Landslide and Flooding Assessment and Mapping (1:10,000 scale) to Barangay Mainit Chairman  Wilfredo Canete

 

Issued a Landslide Threat Advisory informing the susceptibility of the sitio to landslides

 

(Annex 13)

 

1 sitio was found to be located on and/or near slopes and have potential for landslide occurrence. This sitio was classified as having a very high/ critical landslide susceptibility.

 

Sitio Upper was identified to have High Flood Susceptibility Rating

See Result of the MGB-7 Landslide Assessment and Mapping (1:10,000 scale) of barangay Mainit in Naga City, Cebu (Annex 14)

 

See Result of the MGB-7 Flooding Assessment and Mapping (1:10,000 scale) of barangay Mainit in Naga City, Cebu (Annex 15)

September 13, 2011 Furnished copy of the Result of the MGB-7 Landslide Assessment and Mapping (1:10,000 scale) to Naalad Barangay Chairman Sandra Canalita

 

(Annex 16)

Sitio Crossing was found to be located on and/or near slopes and have potential for landslide occurrence. The sitio was classified as having high landslide susceptibility. See Result of the MGB-7 Landslide Assessment and Mapping (1:10,000 scale) of barangay Naalad in Naga City, Cebu (Annex 17)
September 13, 2011 Furnished copy of the Result of the MGB-7 Landslide Assessment and Mapping (1:10,000 scale) to Tinaan Barangay Chairman Zosimo M. Panilag

 

(Annex 18)

Sitio Tapon was found susceptible to flooding. The sitio was classified as having high flood susceptibility. See Result of the MGB-7 Flooding Assessment and Mapping (1:10,000 scale) of barangay Naalad in Naga City, Cebu (Annex 19)
November 27, 2017 Issued Geohazard Threat Advisory to Naga City Mayor Kristine Vanessa Chiong (Annex 20)  
August 13, 2018 Issued Geohazard Threat Advisory to Naga City Mayor Kristine Vanessa Chiong (Annex 21)  
August 22, 2018 Issued Geohazard Threat Advisory to Mayor Kristine Vanessa T. Chiong

 

(Annex 22)

“We trust your discretion in the immediate and appropriate pro-active intervention on this matter. Together, let us work for a safe citizenry and zero casualty in the Province”
August 29, 2018 Conducted Geological Investigation/ Assessment on the cracks/ fissures in linestone within Apo Land and Quarry Corp. (ALQC) Tenement in sitio Tagaytay, barangay Tina-an, City of Naga, Cebu

 

(Annex 23)

 

Fracturing of the materials is a natural phenomenon. It happens and will always happen in different locations and elevations and at different rates and scales, and with or without mining operations, and with or without vegetation.

 

 

Continuous monitoring of the extensometers to monitor the movement of the

crack/fissures.

 

Frequency of monitoring may be made at closer observation intervals in the coming days.

 

Subject site must be closely monitored during times of heavy rainfall and longer rain periods

 

Conduct a comprehensive study in the area

 

For ALQC to conduct an IEC to allay the concerns of the residents

 

Maintain close coordination and open communication with LGUs

 

August 29, 2018 Furnished a copy of the “Geological Investigation/ Assessment R: Cracks/ Fissures in Limstones within Apo Land and Quarry Corporation (ALQC) Tenement in Sitio Tagaytay, Barangay Tina-an, Naga City, Cebu” to ALQC Quarry Leader Engr. Romeo P. Igot.

 

Transmittal letter signed by Atty. Gerardo V. Mahusay, In-charge of the Office of the Regional Director at the time.

 

(Annex 24)

 

August 29, 2018 Furnished a copy of the “Geological Investigation/ Assessment R: Cracks/ Fissures in Limstones within Apo Land and Quarry Corporation (ALQC) Tenement in Sitio Tagaytay, Barangay Tina-an, Naga City, Cebu” to Naga City Mayor Kristine Vanessa Chiong.

 

Transmittal letter signed by Atty. Gerardo V. Mahusay, In-charge of the Office of the Regional Director at the time.

 

(Annex 25)

 

September 4, 2018 A copy of the above-mentioned report was again furnished to the Office of the Mayor.

 

The transmittal letter was signed by

MGB-7 Regional Director Loreto B. Alburo.

 

(Annex 26)

 

“Based on the technical report, the manifestation of the assessed cracks/ fissures in the subject site is a natural phenomenon and is not related to the mining operation within the ALQC Tenement in Sitio Tagaytay, barangay Tinaan, Naga City…”
September 13, 2018 Sent Threat Advisory to the Office of Naga City Mayor at the onset of Typhoon Ompong

 

Email sent at 12:58 p.m. (Annex 27)

 

Another email sent 1:52 p.m. (Annex 28)

 

Attached Advisory dated Sept 12, 2018 (Annex 29)

September 18, 2018 Conducted a Follow-up Investigation Assessment on the cracks/ fissures in limestone within Apo Land and Quarry Corp. (ALQC) Tenement in sitio Tagaytay, barangay Tina-an, City of Naga, Cebu.

 

The Joint investigation was conducted together with barangay officials in Tinaan, Representatives from LGU-Naga, ALQC Representatives, among others.

 

(Annex 30)

Found new, long and wider cracks and are found near a community of 7 residential houses, near the NGCP Tower.

 

(See Report: Annex 30)

Immediate and forced of all residents near the area as discussed with representatives from ALQC and LGU-Naga during the conference. LGU Naga to call for the attention of NGCP regarding the status of the tower at Sitio Tagaytay.

 

Continuous monitoring of the ground cracks identified by ALQC.

 

Continue the monitoring of the subject site especially during times of heavy rainfall and longer rain periods.

 

Plotting of the cracks and fissures in topographic map should be continued.

 

Detailed structural and geotechnical maps of the ALQC tenements should be made and should be made available.

 

Always maintain close coordination and open communication with LGU-Naga City. ComRel or company representatives may be assigned to update and feedback, from time to time, the LGU Naga City, concerning this matter.

 

For the LGU Naga to use geohazard maps provided by the MGB for their disaster management planning.

 

 

September 18, 2018 Conducted an exit conference with LGU-Naga (represented by CENR Officer of Naga), ALQC-Naga Representatives. Recommended the immediate evacuation of the residents in sitio Tagaytay in barangay Tinaan, City of Naga.

 

This recommendation resulted to zero casualty of the residents in sitio Tagaytay.

September 19, 2018 MGB-7 received a copy of the letter from the City Administrator addressed to NGCP.

 

“This is to inform you that the City Government, in coordination with the Mines and Geosciences Bureau, and APO Land Quarry Corp (ALQC) are currently monitoring the ground cracks/ fissures found in sitio Tagaytay, barangay Tinaan, City of Naga Cebu were towers are situated…”

 

(See Annex 31 and 32)

September 20, 2018 UNFORTUNATE LANDSLIDE INCIDENT IN TINAAN, NAGA, CEBU.
September 20, 2018 MGB7 Geohazard Flash Report

 

(Annex 33)

 

RELATED DOCUMENT/S:

Results of the MGB-7 Rapid Field Assessment of Landslide/Flood Prone Barangays in Naga City, Cebu (Annex 34)

 

 SPECIFIC ACTIONS TO BE DONE BY THE MGB CENTRAL OFFICE:

1 To review & reassess the geohazard maps.

  1. Determine the causes of the landslide.
  2. Check the safety of the quarry operation whether there are lapses on the implementation of the safety program & three-year Development Work Program
  3. Determine the completeness of the assessment of the tension cracks investigation, including why the tenor of the letter assuring that no impact to the community
  4. The assessment of the safety of the surrounding communities from the impact of the quarry operation in 15days

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