2019 VRA and Geohazard Updating in La Libertad Municipality, Zamboanga del Norte [Initial Findings]

By Ian T. Demetillo

The VRA and Geohazard Updating of MGB-IX Geosciences Division in the Municipality of La Libertad were conducted on May 2019. La Libertad is part of the targeted municipalities in Zamboanga del Norte which is located on the north-eastern section of Zamboanga Peninsula. It is bounded by the municipality of Rizal to the northeast, southeast by the Province of Misamis Occidental, Dapitan City to the west and municipality of Mutia to the south.

La Libertad is a 5th class municipality in the province of Zamboanga del Norte and is politically divided into twelve (12) barangays namely: La Union, Mauswagon, New Carcar, Singaran, Poblacion, Sta. Cruz, San Jose, New Argao, Sta. Catalina, New Bataan, Mercedes, El Paraiso and La Victoria.

The terrain within La Libertad is characterized by gentle to moderately steep slopes within the immediate vicinity of Poblacion proper. Steeply sloping to rugged terrain is limited within the peak of Mt. Ampiro which stands at 1,532 meters above mean sea level. The study area is situated within the north-western foot of this prominent peak. Major drainage systems within the area and its vicinity exhibit radial to dendritic pattern. Radial pattern is confined within the circumference of Mt. Ampiro turning dendritic toward the low lying areas of Dipolog and Dapitan area. The most prominent river system within the area is Dapitan River which drains the western flanks of Mt. Ampiro and Mt. Malindang. It carries the sediment budget toward Poro River, (locally known as Opao River) and eventually to Dapitan Bay, located northwest.

Initial Findings:

Barangay La Union

La Union is the northern-most barangay in the municipality of La Libertad. It has a total of three (3) Puroks and is bounded by municipality of Rizal to the north and east, Dapitan City to the west and barangay Mauswagon to the south. The area is drain by Potongan River and an unknown intermittent creek.

Field Observations:

  • The barangay is characterized by flat to gently rolling terrain toward the northern, western and eastern limit. Majority of the land area is utilized into coconut and corn plantations.
  • Meandering river of Potongan (northwest-trending) traverses the northern section of the barangay. Meanwhile, an unknown creek is confined on the south-western section of the area, also drain northwest. Apparently, build-up area is absent alongside the waterway.
  • Based on the MGB-IX geohazard map, the barangay falls under low to moderate landslide susceptibility rating. In terms of flooding, a spillway in Purok 1 (northern boundary of La Libertad and Rizal) often experience flooding due to numerous gullies and intermittent creeks upstream. Intense monitoring of the river especially its spillway is highly recommended during extreme weather disturbances.
(Looking south) Partly damaged Potongan River spillway in Purok 1. Inundation within the area depends on the upstream downpour.

Barangay Singaran

Singaran is situated on the western portion of the municipality. It has total of
four (4) Puroks and is bounded by barangay Mauswagon the northwest, San Jose to the south, Dapitan City to the west and Poblacion to the east. The barangay is drain by Dapitan River and numerous developing gullies.

Field observations:

  • The barangay is characterized by rolling terrain toward the southern limit. Eastern limit is interrupted by Dapitan River.
  • Northwest trending Dapitan River traverses the barangay through spillways. This often contributes flood during inclement weather condition. Inundation depends on the upstream downpour that led to the isolation of by passers in and out of the barangay. Boulder-sized rocks within the channel could add up danger to the locals especially during flash flood.
  • Based on the MGB-IX gehazard map, the barangay built-up area falls under low to moderate landslide susceptibility rating. Meanwhile, high landslide area situates on the south where coconut plantation can be seen. On the other hand, flood susceptible areas concentrates along the floodplains of Dapitan River.
(Looking northeast) remnant of the highly damaged spillway across Dapitan River.

Barangay Mercedes

Mercedes is the south-westernmost barangay in the municipality of La Libertad. It has a total of three (3) Puroks and is bounded by barangay San Jose to the north, municipality of Mutia to the south and El-Paraiso to the east. The northwest trending Galay Creek drain on the western section relative to the barangay center.

Field observations:

  • The barangay is situated within a rolling topography within the center (built up area concentrates within the ridge) surrounded by steep sloping hills that plunges toward the natural valley.
  • Based on the actual observation, 2 cases of major mass movement affected the unpaved barangay road; A 10 by 7 meter developing landslide was found in Purok 1 and a 6 by 7 meter landslide was observed along the barangay road near the barangay center. MGB-IX personnel already issued threat advisory for both landslides.
  • Overall, the barangay fall under high landslide susceptibility due to the recurring landslides, critical slope angles, unconsolidated soil types and other factors. Proper mitigating structure, installation of warning signage and active monitoring of the critical areas are highly recommended.
A developing landslide alongside the barangay road in Purok 1. The site is characterized of having thick, unconsolidated clayey to sandy soil.
On-going construction of gabion to alleviate mass movement beside the barangay road.

Barangay New Argao

New Argao is located in the central section of the municipality. It has a total of three (3) Puroks and is bounded by barangay Poblacion to the north, El- Paraiso to the southeast, San Jose to the west and Sta. Catalina to the east. The barangay is drain by Dapitan River, Napilan, Singaran and Lunguna Creeks.

Field observations:

  • The area is typified flat to undulating terrain on the center and steep toward the valley of the surrounding waterways.
  • Several minor rivers and creeks surround the barangay. Relative to the barangay hall, south-eastern section has confluence of Napilan and Singaran creek. These creeks then merge with Lungunan Creek and finally drain toward Dapitan River. (extensive floodplain)
  • Flooding concentrates within the floodplains of the above-mentioned river (floodplains in these areas have short expanse due to confinement of the surrounding hills; except for Lungunan-Dapitan River confluence). In 2018, a flash flood destroyed 9 houses beside the riverbank of Lungunan Creek in Purok 2. Flood level reached up to 4 meter high.
  • Generally, (except for the barangay center) the barangay fall under high landslide susceptibility rating. This is due to the abrupt change of slope angle especially in Purok 2 where 2 households presently reside. Constant monitoring and installation of warning signage are highly recommended. Note that MGB-IX personnel already issued threat advisory for the critical areas in the barangay.
(Looking NNW) Remnants of the built-up area after the flash flood, beside Lungunan River.

Barangay El-Paraiso

El- Paraiso is the southern-most barangay in the municipality of La Libertad. It has a total of four (4) Puroks and is bounded by barangay New Argao to the north, municipality of Mutia to the south, Mercedes to the west and La Victoria to the east. The area is drain by Dapitan River and Singaran Creek.

Field observations:

  • The area topography is typified flat to gently rolling in the central section while rugged toward its edges.
  • The major river of Dapitan drains the north-eastern limit of the barangay while Singaran creek (headwater of Lungunan Creek) drains from the center up to the northwest section toward New Argao. Southwest from the barangay center has presence of intermittent creeks that eventually drain toward Lungunan Creek.
  • Northwest trending Dapitan River traverses the barangay through spillways and hanging bridge. This often contributes flood during inclement weather condition affecting 7 households in Purok 1. Inundation depends on the upstream downpour that led to the isolation of by passers in and out of the barangay. Boulder-sized rocks within the channel could add up danger to the locals especially during flash flood.
  • The spillway across Dapitan River, (primary access for four-wheel vehicle) was destroyed by flood in 2018. For the meantime, the hanging bridge served as the primary access, in and out of the barangay. Intense monitoring of these rivers especially its spillways is highly recommended during extreme weather disturbances.
(Left) A jeepney crosses the spillway in 2017. (Right) Damaged spillway after the flood in 2018.

Barangay Sta. Catalina

Sta. Catalina is located in the central section of the municipality. It has a total of three (3) Puroks and is bounded by barangay Poblacion to the northwest; New Argao to the west, La Victoria and New Bataan to the east. The area is drain by Dapitan River and headwater of Potongan River.

Field observations:

  • The northwest trending Dapitan River traverses the western limit of the area. Meanwhile, headwaters of Potongan River drain the northern limit.
  • Generally, barangay Sta. Catalina fall under low landslide susceptibility rating due to its flat to gently rolling topography. High landslide susceptible areas can be found on the western and eastern limits toward the valleys of Dapitan River and Potongan River headwater respectively.
  • Based on the actual observation, developing rills are present within the unpaved Sta. Catalina-La Victoria barangay road. This is merely due to the absence of drainage system and concrete road. Thus, adequate drainage system and proper road access are recommended.
The newly relocated barangay center of Sta. Catalina is situated within a flat terrain.

Barangay New Bataan

New Bataan is located on the south-western section of the municipality. It has total of three (3) Puroks and is bounded by barangay Sta. Cruz to the north, La Victoria to the south, Sta. Catalina to the west and Province of Misamis Occidental to the east. The barangay is drain Balubuhan River and Sibakan Creek.

Field observations:

  • The barangay center including its built-up area is situated within a northwest trending ridge surrounded by sloping hills.
  • Relative to the barangay center, the southern limit is drain by Balubuhan River while northern limit is drain by Sibakan creek. Both creeks are headwaters of Potongan River which flow in a northwest manner.
  • The spillway across Bulubohan River, (primary access from La Victoria) is inaccessible during heavy rains. Inundation depends on the upstream downpour that emanates from the surrounding gullies. Thus intense monitoring is highly recommended during extreme weather disturbances.
A spillway between La Victoria and New Bataan. Inundation along the area depends on the upsteam downpour.

Barangay Sta. Cruz

Sta. Cruz is located in the eastern section of the municipality. It has a total of four (4) Puroks and is bounded by municipality of Rizal to the north, barangay New Bataan to the south, Sta. Catalina to the west and Province of Misamis Occidental to the east. The barangay is primarily drain by Potongan River.

Field observations:

  • The area is located within a ridge and topography is typified gently rolling, interrupted by northern and eastern slopes toward its watercourse.
  • Northwest trending drainage system parallels the ridge within area. Potongan River drains on the northern limit while an unknown creek (headwater of Balobohan River) drains the southern limit. These river bodies are confined within steep sloping hills, so it does not affect the residential area.
  • Built-up area concentrates within the ridge and above the natural ravines. These houses are made up mostly of concrete mixed with light materials.
Present drainage alongside the barangay road. Adequate drainage system is then recommended.

Barangay New Carcar

New Carcar is situated on the east-central section of the municipality. It has a total of three (3) Puroks and is bounded by municipality of Rizal to the north and east, Sta. Cruz to the south and Mauswagon to the west. The barangay is drain by Balobohan and Putongan Rivers.

Field observations:

  • The barangay is situated within a northwest trending ridge, interconnected with the southern barangay. Its topography is typified to have gently rolling terrain interrupted by northern and eastern slopes toward its watercourse.
  • Northwest trending drainage system parallels the ridge within area. Potongan River drains on the northern limit of the barangay while Balubohan River drains the southern limit. These river bodies are confined within steep sloping hills.
  • The spillway across Bulubuhan River is inaccessible during heavy rains. 2 hours of inundation have been observed thus, intense monitoring upstream is highly recommended during extreme weather disturbances.
Erosion is manifested by exposed roots near the spillway of Balubohan River.

Barangay Mauswagon

Mauswagon is located on the north-central section of the municipality. It has a total of seven (7) Puroks and is bounded by barangay La Union to the north, Poblacion to the south, Dapitan City to the west and New Carcar to the east. The barangay is drain by Potongan River and an intermittent creek.

Field observations:

  • The topography of the barangay is typified flat to gently rolling that plunges toward the river and intermittent creek on the eastern and western limit, respectively.
  • The north-northwest trending Balubohan River delimits the eastern section of the barangay from the neighbouring New Carcar. Meanwhile, an intermittent creek trending northwest traverses the central part and eventually drains toward Dapitan River.
  • Majority of the built-up areas are made-up of concrete materials. Generally, the barangay fall under low landslide susceptibility rating based on the MGB-IX geohazard map.
Rescue equipment s of Barangay Mauswagon

Barangay Poblacion

Poblacion is situated in the central section of the municipality. It has a total of six (6) Puroks and is bounded by barangay Mauswagon to the north, Sta Catalina to the southeast, Singaran to the west and New Carcar to the northeast. The barangay is drain by Dapitan River, Balubohan River and intermittent creeks.

Field observations:

  • The topography of the barangay is typified flat to gently rolling that plunges toward the river and intermittent creek on the east and west, respectively.
  • Dapitan River traverses the western limit of the barangay through spillway (Poblacion-Singaran spillway). This repeatedly contributes flooding during inclement weather condition wherein, inundation depends on the upstream downpour that led to the isolation of by passers in and out of the barangay. Boulder-sized rocks within the channel could add up danger to the locals especially during flash flood.
  • The barangay is the center for businesses in the municipality. Some of the major infrastructures include, Municipal Hall, Public Market, gymnasium, etc. Other built –up are predominantly made-up of concrete materials. Adequate drainage system is recommended within the area.
Confined drainage system adjacent to the barangay center.

Barangay La Victoria

La Victoria is the north-easternmost barangay in the municipality of La Libertad. It has a total of three (3) Puroks and is bounded by barangay New Bataan to the north, El-Paraiso to the west and Province of Misamis Occidental to the east. The barangay is drain by Dapitan River and Bukiran Creek.

Field observations:

  • The barangay is within a northwest trending ridge, interconnected with the northwest barangay. The topography of the barangay is typified rolling to rugged as it plunges toward the headwaters of Dapitan River to the west.
  • West of the barangay has confluence of Bukiran creek and other intermittent creeks. These creeks eventually drain toward the northwest trending Dapitan River (major river in the municipality). This repeatedly contributes flooding during inclement weather condition. Since the area is situated on the foot slope of Mount Malindang, floodwater emanate from this point. Hence, flood monitoring system for Dapitan River is recommended in this area.
  • Based on the MGB-IX geohazard map, the central portion of the barangay fall under low to moderate landslide susceptibility rating. Meanwhile, south-western limit have very steep slopes toward Dapitan River valley, making it highly susceptible to landslide.
The handover of flood and landslide flyers to the officials of Barangay La Victoria.

Barangay San Jose

San Jose is located on the south-western section of the municipality. It has a total of three (3) Puroks and is bounded by barangay Singaran to the north, Mercedes to the south, New Argao to the east and Dapitan City to the east. Portions of Piñan River and Longonan River drain the area.

Field observations:

  • The area is typified to have rolling to steeply sloping terrain toward southwest, relative to the barangay center.
  • Northern section of the barangay is drain by northwest trending Piñan River (portion only) which has wide floodplain. Meanwhile, Lungunan Creek drains on the eastern limit which eventually merges with Dapitan River.
  • Generally, barangay San Jose fall under moderate to high landslide susceptibility rating due to its rolling to rugged topography. On the other hand, high flood susceptible area concentrates within the floodplains of the above-mentioned river.
he handover of landslide and flood flyers to the Secretary of Barangay San Jose

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