Summary Report

SUMMARY REPORT

RESULTS OF THE MGB GEOHAZARD ASSESSMENT COVERING EIGHT (8) MUNICIPALITIES IN THE PROVINCE OF AURORA

In line with the recent Presidential Directive and NDCC resolutions following the February 17 Southern Leyte landslide incident, and the need to fast track the geohazard mapping program along the eastern seaboard of the Philippines, geologists from the Mines and Geosciences Bureau-Regional Office III (MGB-R3) conducted a geohazard assessment of the barangays in the municipalitIes of Dilasag, Casiguran, Dinalungan, Dipaculao, Baler, Ma. Aurora, San Luis and Dingalan in the province of Aurora.

Each barangay was classified according to their susceptibility to landslide and/or flooding. For landslide susceptibility, the rating parameters are as follows:

High • Presence of active and/ or recent landslides • Presence of numerous and large tension cracks along slope adjacent to the community and that would directly affect the community • Areas with drainages that are prone to landslides damming • Steep/Unstable slopes consisting of loose materials

Moderate • Areas with indicative and/or old landslides • Presence of small tension cracks along slope and are located away from the community • Moderate slopes

Low • Low to gently sloping • No presence of tension cracks

Each barangay was rated into low, moderate or high for flooding susceptibility with the rating parameters as follows:

Low • 0 – 0.5 meter depth of floodwaters

Moderate • 0.51 – 1 meter depth of floodwaters

High • > 1 meter depth of floodwaters

With regards to landslide susceptibility, the barangays assessed include areas that are located on and/or near slopes and riverbanks and have the potential for landslide occurrence. The rating of each barangay presented herein particularly refers to the barangay proper since majority of the population is located there. It should be noted, however, that the rating does not necessarily reflect those of the sitios. These barangays were presented with a Landslide Threat Advisory informing their susceptibility to landslides and the corresponding recommendations particular to the barangay.

The flood susceptibility of the barangays in the seven (7) municipalities was also assessed. Barangays classified with moderate to high susceptibility to flooding are located in identified low portions of the barangay, in topographically low-lying areas and/or near a major river system. These barangays were presented with a Geohazard

2 Threat Advisory informing their susceptibility to flooding and the corresponding recommendations particular to the barangay.

Table 1. Number of Assessed Barangays Municipality/City Total Barangays Number of Assessed Barangays 1. Dilasag 11 11 2. Casiguran 24 24 3. Dinalungan 9 9 4. Dipaculao 25 25 5. Baler 13 13 6. San Luis 18 18 7. Maria Aurora 40 40 8. Dingalan 11 11 TOTAL 151 151

SUMMARY OF THE ASSESSMENT:

A. Municipality of Dilasag

• There are four (4) barangays with low susceptibility to flooding (Esperanza, Masagana, Manggitahan, Ura).

• There are two (2) barangays with low to moderate susceptibility to flooding. The barangay has naturally low-lying areas and portions located near active creeks and river channel (Diagyan and Maligaya).

• There are five (5) barangays with moderate to high susceptibility to flooding (Dikabasan, Dilaguidi, Dimaseset, Diniog and Lawang)

• Riverbank erosion was observed in the active creeks/river and natural channels traversing the municipality.

• Siltation is evident along the active channels traversing the municipality (Pinamacan, Casalukan and unnamed natural channels traversing the municipality )

• The coastal barangays are susceptible to tsunami hazards and storm surges.

• Riverbank erosion was observed in the active creeks/river and natural channels traversing the municipality.

• In terms of landslide susceptibility, barangays located in the highlands has a low to moderate landslide susceptibility. Geohazard threats may increase due to the general nature of the material, and natural and anthropogenic causes which may increase the vulnerability and general condition of the underlying materials.

• There are three (3) barangays where the barangay center has low landslide susceptibility (Masagana, Maligaya and Diniog). These barangays are located in the low-lying portion of the municipality and near the coast. There are no permanent communities in the sitio located in the mountainous areas.

• There are four (4) barangays where the barangay center has low to moderate susceptibility to landslides (Ura, Manggitahan, Dilaguidi and Esperanza). Landslide susceptibility is manifested by the heavy siltation of the natural river/creek channels traversing the barangay.

• There are four (4) barangays with high susceptibility to landslides (Lawang, Dimaseset, Dikabasan and Diagyan). There are recent landslide occurrences and it is also manifested by the heavy siltation of the natural river/creek channels. Creep features are also present especially along Dimaseset and Manggitahan road.

B. Municipality of Casiguran

• The municipality of Casiguran is generally located at a low elevation. Most of the urban barangays experience flooding due to excessive precipitation, insufficient and inadequate drainage system, back flooding (sheet and coastal floods), overflow from silted natural creek/river channels, constricted natural channels restricting the flow of the river, urban development (elevated roads, increased building and infrastructures), excessive surface runoff and flash floods coming from the mountains.

• There are four (4) barangays with low susceptibility to flooding (Esperanza, Calabgan, Cozo and San Ildefonso).

• There are two (2) barangays with moderate susceptibility to flooding. The barangays are located in a naturally low-lying area and portions located near active creeks and river channel (Brgy. 5[Pob.] and Brgy. 7[Pob.]).

4 • There are three (3) barangays with high susceptibility to flooding. The barangay is located in a naturally low-lying area and near active river channels (Brgy. 4[Pob.], Calantas and Marikit)

• There are thirteen (13) barangays with moderate to high susceptibility to flooding (Brgys. 1, 2, 3, 6, 8 [Pob.], Bianoan, Calangcuasan, Culat, Dibacong, Dibet, Lual, Tabas and Tinib).

• There are two (2) barangays with low, moderate to high level susceptibility to flooding. These barangays have natural high and low elevation areas and are near active rivers and the coast (Ditinagyan and Esteves).

• Riverbank erosion was observed in the active creeks/river and natural channels traversing the municipality.

• Siltation is evident along the active channels traversing the municipality (Casalugan, Amro, Pinamakan (Casiguran), Minanga Rivers and unnamed natural channels traversing the municipality )

• In terms of landslide susceptibility, barangays located in the highlands has a low to moderate landslide susceptibility. Geohazard threats may increase due to the general nature of the material; and natural and anthropogenic causes which may increase the vulnerability and general condition of the underlying materials.

Most of the landslide occurrences are found along the road. The road cuts and exposed toes of the mountain are vulnerable to increased weathering and erosion.

• There are two (2) barangays with low landslide susceptibility (Calabgan and Calantas).

• There are three (3) barangays with portions identified to be of moderate susceptibility to landslides (Cozo, Dibet and Tabas).

• There are two (2) barangays with areas identified to have a high susceptibility to mass movement (Bianoan-near the cemetery, Culat and Ditinagyan-along the road/road cut).

• Barangays with moderate to high susceptibility to landslides are Dibacong and San Ildefonso).

• The coastal areas are also susceptible to storm surges and tsunami hazards.

5 C. Municipality of Dinalungan

• There are six (6) barangays where the barangay proper has low susceptibility to flooding (Abuleg, Ditawini, Mapalad, Nipoo, Simbahan and Zone I). Portion of the barangay located near the creek/river channels are susceptible to moderate to high level floods.

• There are three (3) barangays with low to moderate susceptibility to flooding. The barangays are located in a naturally low-lying area and portions located near active creeks and river channel (Dibaraybay, Paleg and Zone II).

• Brgy. Paleg is susceptible to moderate to high level floods. There are also barangays with identified sitios that have a moderate to high susceptibility to flooding (Dibaraybay-So. Talaytay and So. Bungo, Nipoo-So. Tambalongan; and Zone II-along Bugayong, Talaytay and Dinalungan Rivers).

• Coastal erosion is evident in barangays Abuleg and in Zone II. The coastal areas are also susceptible to storm surges and tsunami hazards.

• Riverbank erosion was observed in the active creeks/river and natural channels traversing the municipality. River piracy and rivers reclaiming its old channels are also evident. Areas not usually flooded experience flooding due to the changing courses of the rivers.

• Siltation is evident along the active channels traversing the municipality. During flood events, the action of water cuts along the old river channels, reclaiming the old channels and eroding the riverbanks along its path. (Bungo, Dinalungan, Abuleg, Talaytay, Dilagdes and Bugayong Rivers and Tambalongan Creek and unnamed natural channels traversing the municipality )

• In terms of landslide susceptibility, barangays located in the highlands has a low to moderate landslide susceptibility. Geohazard threats may increase due to the general nature of the material; and natural and anthropogenic causes which may increase the vulnerability and general condition of the underlying materials.

• There are three (3) barangays with low landslide susceptibility (Abuleg, Ditawini and Mapalad). The areas susceptible to moderate to high landslide are the mountainous portion of the barangay and along the road/road cuts.

• There are two (2) barangays with areas identified to have a moderate susceptibility to mass movement usually located in the mountainous portions of the barangay (Paleg and Simbahan).

6 • Brgy. Nipoo is susceptible to moderate to high landslide. So. Talaytay in Dibaraybay is included in the areas with high susceptibility to landslide or mass movement.

• The lowlands of barangay Ditawini is a possible landslide debris accumulation zone. Ditawini at present is heavily silted and floodwaters had increased turbidity (uprooted trees and debris accompanying the floodwaters forming temporary dams along the river channel).

D. Municipality of Dipaculao

• There are thirteen (13) barangays with low susceptibility to flooding (Laboy, Buenavista, South Poblacion, Ipil, Lobbot, Maligaya, Mucdol, Borlongan, Dianed, Ditale, Gupa, Mijares and Puangi).

• There are six (6) barangays with low to moderate susceptibility to flooding.. There are portions of the barangays which are located in a naturally low-lying area and portions located near active creeks and river channels (Dinutunan, Dimabuno, North Poblacion, Diamanen, Diarabasin and Sapang Kawayan).

• The six (6) barangays susceptible to moderate to high level floods has portions that are located naturally low in the barangay and are usually adjacent to active creeks and rivers and the coasta l area (Bayabas, Lipit, Calaocan, Dinadiawan, Salay and Toytoyan).

• The coastal areas are also susceptible to storm surges and tsunami hazards.

• Siltation is also evident along the active channels traversing the municipality. During flood events, the action of water cuts along the river channels and eroding the riverbanks along its path.

• In terms of landslide susceptibility, barangays located in the highlands has a low to moderate landslide susceptibility. Geohazard threats may increase due to the general nature of the material; and natural and anthropogenic causes which may increase the vulnerability and general condition of the underlying materials.

• There are seven (7) barangays with low landslide susceptibility (Mijares, Toytoyan, Dinadiawan, Ditale, Gupa, Maligaya and Dibutunan). The areas susceptible to moderate to high landslide are the mountainous portion of the barangay and along the road/road cuts. There are portions in the mountainous

7 portion of barangay Gupa where creep, a form of slow movement landslide, is evident.

• There are six (6) barangays with areas identified to have a moderate susceptibility to mass movement usually located in the mountainous portions of the municipality (Mucdol, Borlongan, Calaocan, Dianed, Sapang Kawayan and Salay).

• Two (2) barangays are identified with a moderate to high susceptibility to mass movement (Diarabasin and Dimabuno).

• Brgy. Diamanen has a high susceptibility to landslides. The barangay is located within an old landslide area. The rivers traversing the barangay are heavily silted and the river channel is already higher than the level of the road.

E. Municipality of Baler

• Brgy. Reserva has a low susceptibility to flooding in most area of the barangay. There are purok that are susceptible to moderate to high level floods. These are usually adjacent to active river channels (ex. Malupa River) and identified low- lying portions of the barangay.

• There are seven (7) barangays with low to moderate susceptibility to flooding. The barangays are located in a naturally low-lying area and portions located near active creeks and river channel and the coast (Poblacion Barangays 1,2, 3, 4, 5, Sabang and Zabali).

• Barangay Buhangin has moderate susceptibility to flooding especially the purok located near Bugnoyas and Pudoc creeks. Those located along the Aguang River are susceptible to high level floods. Brgy. Calabuanan also has a moderate susceptibility to flooding. Most of the floodwaters are overflow from the major rivers draining towards Aguang River and floodwaters coming from the highlands of Ma. Aurora.

• There are two (2) barangays (Suklayin and Pingit) that have a moderate to high susceptibility to flooding. These barangays are generally located at a low elevation.

• Brgy. Obligacion has a high susceptibility to flooding. Malupa and DIkildit rivers contribute to flooding and back flooding in the barangay.

• The coastal barangays are susceptible to tsunami hazards and storm surges.

• Riverbank erosion was observed in the active creeks/river and natural channels traversing the municipality.

8 • Siltation is evident along the active channels traversing the municipality. During flood events, the action of water cuts along the old river channels, reclaiming the old channels and eroding the riverbanks along its path.

• In terms of landslide susceptibility, barangays Zabali and Pingit have a moderate susceptibility to landslides. The threat may increase due to the general nature of the material and natural and anthropogenic causes which may increase the vulnerability and general condition of the underlying materials. The PAGASA road in So. Digisit in Brgy. Zabali has active landslide surfaces. From the Mariano L. Sindac Elementary School, an active landslide surface is present.

F. Municipality of San Luis

• There are thirteen (13) barangays with low susceptibility to flooding in the barangay proper; with low-lying areas and/or communities adjacent to river/creek channels and the coast susceptible to moderate to high level floods (Brgys. 1, 2, 3, 4, Real, Dibalo, Diteki, Ditumabo, Nonong, L. Pimentel, San Jose, Dibayabay and Dibut)

• There are two (2) barangays with low to moderate susceptibility to flooding. The barangays are located in a naturally low-lying area and portions located near active creeks and river channel and the coast (Bacong and Dikapinisan).

• There are two (2) barangays with moderate to high susceptibility to flooding (Dimanayat and San Isidro). In Dimanayat, the floodwaters are coming from the highlands, the sand/gravel bars forming at the coastlines are indication of high turbidity. San Isidro is affected by the overflow from Dimanibong, Diteki and Ditumabo Rivers.

• Brgy. Zarah has a high susceptibility to flooding. Flooding is influenced by active rivers and creeks traversing the municipality.

• The coastal barangays are susceptible to tsunami hazards and storm surges.

• Riverbank erosion was observed in the active creeks/river and natural channels traversing the municipality. Areas not usually flooded experience flooding due to the changing courses of the rivers.

• In terms of landslide susceptibility, barangays located in the highlands has a low to moderate landslide susceptibility. Geohazard threats may increase due to the

9 general nature of the material, and natural and anthropogenic causes which may increase the vulnerability and general condition of the underlying materials.

• There are six (6) barangays where the barangay center has low landslide susceptibility (Ditumabo, Nonong, Zarah, L. Pimentel, Dikapinisan, Dibut). Zones of moderate to high susceptibility to landslides are located in the mountainous portion of the barangay.

• There are two (2) barangays where the barangay center has low to moderate susceptibility to landslides (Real and Dibalo) and with areas identified to have a moderate susceptibility to mass movement usually located in the mountainous portions of the barangay.

• Brgy. Diteki had been affected by landslides during the 2004 disaster that hit the municipality. Artificial damming is possible upstream of Diteki River, the downstream portion of the river is a possible landslide debris accumulation zone.

• Brgy. Dimanayat has a moderate to high susceptibility to landslide and is a possible landslide debris accumulation zone. During flood events, the barangay is on the path of the waters coming from the highlands. The floodwaters are usually turbid with accompanying rocks, boulders and uprooted trees. Rock debris and uprooted trees may accumulate along the river bed forming temporary dams.

G. Municipality of Maria Aurora

• There are twenty three (23) barangays with low susceptibility to flooding (Brgy. 1, Brgy. 4, Dimanpudso, Bannawag, Punglo, Debucao, San Leonardo, Bayanihan, Wenceslao, Villa Aurora, Dianawan, San Juan, Alcala, Bangco, Quirino, Diaman, San Joaquin, Bazal, Diaat, Decoliat, Ramada, Galintuja and Suguit). There are portions and sitios of the barangay that are susceptible to moderate to high floods especially the agricultural areas and those adjacent to the active river channels.

• There are five (5) barangays with low to moderate susceptibility to flooding. (Bagtu, Florida, Dikildit, Baubo and San Jose). There are portions of the barangays which are located in a naturally low-lying area and portions located near active creeks and river channels. In Brgy. Dikildit, there are portions that are susceptible to moderate to high level flood.

• The two (2) barangays in the poblacion (Brgys. 2 and 3) have a moderate susceptibility to flooding. Malupa, Diaat and Pacugao rivers influence flooding in the barangays. Overflow from the river and possible breaching of the protective dikes and natural terraces will be of great influence to flooding. Surface runoff coming from the nearby barangays also contributes to flooding.

• There are seven (7) barangays with moderate to high susceptibility to flooding. The areas of the barangay located adjacent to the active natural river channels have a high susceptibility to flooding. (Sta. Lucia, Diome, Dialatnan, Kadayakan, Sto. Tomas, Sto. Cristo and Malasin).

• Siltation is also evident along the active channels traversing the municipality. During flood events, the action of water bring with it debris from the mountainous areas, cuts along the river channels and erode the riverbanks along its path. River widening is an active process.

• In terms of landslide susceptibility, barangays located in the highlands has a low to moderate/ moderate to high landslide susceptibility. Geohazard threats may increase due to the general nature of the material; and natural and anthropogenic causes which may increase the vulnerability and general condition of the underlying materials. Most of the areas with high susceptibility to landslide and mass movement are the roads/highway especially in the mountainous areas. Heavy rains, nature of the underlying materials, seismic and anthropogenic causes are the main triggers of mass movement.

• There are nine (9) barangays with low landslide susceptibility (Dikildit, Dialatnan, Punglo, Baubo, Bazal, Diaat, San Leonardo, Bayanihan and San Joaquin). Sitio Dimanibong in Dikildit has a low to moderate susceptibility to landslide. In Baubo, there is a portion with high susceptibility to landslide near the school.

• There are nine (9) barangays with low to moderate susceptibility to mass movement usually located in the mountainous portions of the municipality (Galintuja, Decoliat, San Juan, Dianawan, Suguit, Dikildit, Sto. Tomas, Wenceslao and Brgy. 3).

• In barangay Diome, most of the identified areas with moderate to high susceptibility to landslides are along the road/highway.

• So. Bilao (Diaman) and So. Yang-ya (Kadayakan) are areas with high susceptibility to landslides.

• The present location of Brgy. Villa Aurora has a low to moderate susceptibility to landslides. The tributaries of Cabatangan River traversing the barangay are actively eroding the creek/riverbanks bringing with it rock debris from the highlands. There are areas that are prone to landslide damming. The Cabatangan River has a very high turbidity during flood events. Barangays

11 influenced by the Cabatangan/Malupa rivers are possible landslide debris accumulation zone.

H. Municipality of Dingalan

• There are two (2) barangays with low susceptibility to flooding in the barangay proper. The barangays are located at a generally high topography area (Tanawan and Caragsacan). In Caragsacan, there are natural creeks/rivers that are susceptible to flash flooding confined to the natural channel.

• There are four (4) barangays with low to moderate susceptibility to flooding. The barangays are located in a naturally low-lying area and portions located near active creeks and river channel and the coast (Paltic, Ibona, Butas na Bato and Poblacion).

• There are four (4) barangays with moderate to high susceptibility to flooding (Umiray, Matawe, Aplaya and Dikapinisan). The floodwaters are coming from the highlands, overflow from the rivers. Flashfloods along the rivers traversing the barangays are common.

• Brgy. Davildavilan has a low, moderate to high susceptibility to flooding. There are naturally high and low-lying areas in the barangay.

• The coastal barangays are susceptible to tsunami hazards and storm surges.

• Riverbank erosion was observed in the active creeks/river and natural channels traversing the municipality. Major river systems are agent of debris flow which usually accumulate at the low-lying barangays of the municipality and usually adjacent the rivers. The following barangays are possible landslide debris accumulation zones: Davildavilan, Paltic, Poblacion, Dakapanikian and Aplaya.

• In terms of landslide susceptibility, the barangay center of the barangays located in the highlands has a low to moderate landslide susceptibility. Areas identified to be with high susceptibility to landslides are the mountainous portions. Geohazard threats may increase due to the general nature of the material, and natural and anthropogenic causes which may increase the vulnerability and general condition of the underlying materials. The major factors that trigger landslides are heavy rains, earthquake and fault movements related.

12 • There are six (6) barangays where the barangay center has low to moderate landslide susceptibility (Aplaya, Dikapanikian, Poblacion, Ibona, Tanawan and Caragsacan).

• There are five (5) barangays where the barangay center has moderate to high susceptibility to landslides (Butas na Bato, Matawe, Umiray, Paltic and Davildavilan).

• Artificial damming is possible upstream of Davildavilan, Paltic, Subsob , Langawan and Pisok Rivers, the downstream portion of the river is a possible landslide debris accumulation zone. Other natural channels that contribute to flooding are Umiray, Malakawayan and Dingalan rivers and numerous creeks such as Imulat and Kailugan.

• During flood events, the barangays on the path of the waters coming from the highlands are usually vulnerable. The floodwaters are usually turbid with accompanying rocks, boulders and uprooted trees. Rock debris and uprooted trees may accumulate along the river bed forming temporary dams.

It should be noted that these susceptibility ratings were arrived at as of this field assessment. However, the rating could advance (e.g., from low to moderate, and moderate to high) based on the present and historical accounts of the flood /landslide susceptibility in the municipality. Hence, the MGB constantly recommends strict and continuous monitoring of the barangays, continuing information and education campaigns on disaster preparedness, disaster risk management and mitigations; and strengthening of the Barangay Disaster Coordinating Council.

The matrices of the municipalities included in the assessment are included in the compact disc as an attachment to this report.

MGB-RIII Assessment Team

Carolyn V. Sacdalan Clarissa G. Villanueva Senior Science Research Specialist Senior Geologist

Rick Rodell C. Luis Senior Geologist

Noted by:

Noel B. Lacadin OIC, Geosciences Division