geohazard identification report of the proposed pabahay sa lumad

GEOHAZARD IDENTIFICATION REPORT OF THE
PROPOSED PABAHAY SA LUMAD PROJECTAN NHA-FUNDED PROJECT OF THE LOCAL
GOVERNMENT UNIT OF TALAINGOD,
DAVAO DEL NORTE
by
Beverly Mae M. Brebante
Supervising Science Research Specialist
Mines and Geosciences Bureau – XI
March 2014
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GEOHAZARD IDENTIFICATION REPORT OF THE PROPOSED PABAHAY SA
LUMAD PROJECT- AN NHA-FUNDED PROJECT OF THE
LOCAL GOVERNMENT UNIT OF TALAINGOD, DAVAO DEL NORTE
I. INTRODUCTION
The Philippines has recently been affected by different natural calamities such as
earthquake, landslides, flooding and storm surges that greatly affected the lives of the
Filipinos which include agriculture, economy, livelihood, health and education. This is
attributed to the geologic setting as well as the climatic condition of our country. Taking
these into consideration, the need to conduct scientific studies prior to the commencement of
land development projects is critical in order to identify the natural hazards that may likely
affect the development in the future.
In 2000, DENR issued Department Administrative Order (DAO) 2000-28 entitled
Implementing Guidelines on Engineering Geological and Geohazard Assessment as
Additional Requirement for ECC Applications Covering Subdivisions, Housing and other
Land Development and Infrastructure Projects that was complemented by MGB
Memorandum Circular (MC) 2000-33 which is the Guidelines and Outline/Checklist for the
preparation of an Engineering Geological and Geohazard Assessment Report. These
orders/issuances were formulated in order to safeguard development projects from
geological hazards and avoid the occurrence of another Cherry Hills Subdivision incident
that took place in Antipolo City last August 1999.
As part of their compliance, LGU Talaingod requested the Mines and Geosciences Bureau
Regional Office XI to conduct a paid investigation with OR # 1054422 dated March 12, 2014
within the proposed site for their housing project located in Brgy. Dagohoy, Talaingod,
Davao del Norte
II. GENERAL INFORMATION
A. Location and Accessibility
The municipality of Talaingod is a landlocked municipality in the province of Davao del
Norte. It is bounded by the municipality of Kapalong to the north, east and south and by the
province of Bukidnon to the west. It is approximately 45 kilometers from Tagum City and 122
km from Davao City and is easily accessible by any type of vehicle through the well-paved
Davao del Norte-Bukidnon Highway. The municipality is centered on geographic coordinates
7°37’59” north latitude and 125°34’25” east longitude.
The proposed site is located in So. Paiton of Brgy. Dagohoy and is approximately centered
in geographic coordinates 7°42'9.251"north latitude and 125°37'21.105" east longitude. It is
about 5 linear kilometers north-northwest of Brgy. Dagohoy and 9.3 linear kilometers
northeast of the municipal hall. Accessibility to the site is through the graveled barangay
road and can be reached by any type of vehicle.
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Lake Paiton
So. Paiton
Proposed Tribal
Village
Figure 1. Satellite image of the proposed site (Source: GoogleEarth)
B. Project Description
The proposed site covers a total land area of 5 hectares more or less and is part of the 64,683
more or less defined ancestral domain claim of the Langilan-Ata Manobo Tribe defined by the
Certificate of Ancestral Domain Claim No. R11-CADC-102.
The NHA-funded project – Pabahay sa Lumad - will consist of 102 lots with lot area of about 80
sq.m. more or less and equipped with Tribal Hall, Worship Hall and open space. Beneficiaries
of the project are the indigenous people living near Lake Paiton who will be affected by the
proposed development of the Lake for tourism
purposes. About 900 IPs will be living in the village.
During the inspection, land development was
already initiated and several semi-concrete houses
were already constructed.
Electricity supply will be provided by DANECO will
water needs of future residents is readily available
from a spring and will be distributed to the village
using an electric pump.
Based on the submitted drainage plan of the
project site, drainage system will be installed within
the site and will be directed towards the existing
gullies in the area.
Photo 1. Semi-concrete IP house
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Figure 2
125°37'16.701"E
7°42'14.199"N
125°37'19.284"E
7°42'13.05"N
125°37'16.098"E
7°42'7.024"N
125°37'21.906"E
7°42'6.921"N
III. GENERAL GEOLOGY
A. Tectonic and Geologic Setting
Based on the Simplified Geologic Map of Davao Province of MGB XI, the proposed site is
underlain by Pliocene-Pleistocene Sedimentary rocks composed of well consolidated to
poorly consolidated sandstone and shale with some sequence of conglomerate and pebbly
to conglomeratic sandstone. During the ocular inspection, unconsolidated brown silty clay to
sandy silt to medium –grained sand was the predominant surficial soil material.
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Photo 2 & 3. (Above) unconsolidated medium-grained
sand which mainly underlie the proposed site. (Right)
Rill development along a road-cut which indicates the
alternating resistant and less-resistant sedimentary
layers
Project site
Figure 3
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B. Climate and Vegetation
Climate prevalent in the area based on the
Modified Corona Climate Classification is of
Type IV characterized by rainfall evenly
distributed throughout the year. The
municipality is also located north of the
typhoon belt hence; the occurrence of
typhoon is minimal. Also, the municipality is
naturally protected by its mountain ranges
that act as barriers from the onslaught of
typhoon (PENRO).
Figure 4. Modified Corona’s Climate Classification
The site is presently vegetated with various shrubs and grasses particularly along the
boundaries as land development has already initially started.
Photo 4. Looking west, prevailing vegetation within the site
IV. PROJECT SITE SETTING
Physiography
The site is situated on a flattened slope surrounded by rolling to moderately steep slopes
while the western boundary is characterized by very steep slopes towards one of the
tributaries of Daligdigon River. Drainage in the area consists of surface run-off and flows
towards the lower portion at the south and west. The main river system in the area is the
dendritic Daligdigon River which generally trends in a north-northwest-south-southeast
direction and flows towards Si(e)mong River that all drains to Libuganon River. A lake can
also be noted at the northern portion of the sitio which was said to have formed due to the
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blocking of its outflow during the road development.
Photo 5. Looking northeast, these row of houses are
situated 3-4 meters away from the slope edge
Photo 6. Looking south from a peak in So. Paiton
Proper is the Pabahay sa Lumad
Photo 7. Looking north, Lake Paiton
Photo 8. Moderately steep slopes at the eastern
boundary of the property, looking northeast
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Figure 5
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V. IDENTIFIED GEOLOGIC HAZARDS AND RELEVANT FIELD FINDINGS
During the course of the inspection, potential risks were identified by the undersigned.
Among the identified geologic hazards includes slope instability, seismic-related hazard and
rill and gully development.
A. Susceptibility of the Property to Slope Instability
The site is situated on a flattened slope surrounded by rolling to moderately steep slopes
while the western boundary is characterized by very steep slopes towards one of the
tributaries of Daligdigon River. Moreover, the underlying material of the property is
composed of unconsolidated brown silty clay to sandy silt to medium –grained sand
which is easily erodible by surface run-off. During the inspection, rill and gully erosion
was already observed. Some steep cut slopes were also noted at the northern side of
the property proximal to the constructed housing units. Taking into account the geologic
and geomorphic condition of the site, slope instability such as shallow translational slide
is likely to occur in the area.
Sandstone
Siltstone
Sandstone
Siltstone
Sandstone
Photo 9 and 10. (Above)Cut slope at the northern
side of the property. Note the distance of houses
with respect to the slope. (Right) Alternating sand
and silt showing its different resistance to erosion.
The sandstone layer is relatively resistant as
compared to the siltstone layer
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Photo 11. Minor translational slide along the road cut
going to the site
Photo 12. Cut slope at the southern section of the
property to accommodate some of the housing units
B. Susceptibility of the Property to Seismic Hazard
No major geologic structures were encountered during the course of the field
investigation within the project area. However, the Philippines as a whole is situated
on a seismically/tectonically active area. Based on the available geologic data1,
Region XI is traversed by the active Philippine Fault at the eastern side while several
trenches surround Mindanao Island.
Hazards associated with earthquakes include ground shaking, ground rupture or
surface faulting, liquefaction, landslides and tsunami. However, taking into account
the geomorphological and physiographical characteristic of the assessed site, the
seismic-induced hazards that may likely affect the project site is ground shaking,
ground rupture and surface faulting
The intensity of earthquake-induced ground motion is a function of the magnitude of
the earthquake, distance from the epicenter, and the materials through which the
earthquake waves travel. Ground rupture and surface faulting are the physical
displacement of surface deposits or surficial manifestation in response to an
earthquake’s seismic waves.
C. Susceptibility of the Property to Flooding
The area is situated on an elevated area; as such flooding will not be a concern to
the site. However, ponding or localized flooding by surface runoff during extreme
weather condition especially may occur if no proper drainage system is installed.
VI. CONCLUSION and RECOMMENDATIONS
Based on the result of the Geohazard Identification Survey, the possible geologic hazards
identified in the area are seismic-related hazards, landslide and localized flooding.
Generally, the property inspected may be developed; however, this report doesn’t discount
the possibility of these hazards occurring in the future. Dynamic changes inherent in
geological processes make it difficult to give definitive conclusions.
The following recommended measures need to be considered by the developer to proceed
with the project, to wit:
1. Research on the earthquake potential should be undertaken to provide necessary
information for the design of mitigation plans of risks presented by these hazards.
Ground shaking can be mitigated through proper engineering designs of
structures to be built.
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PHIVOLCS Active Fault and Liquefaction Susceptibility Map of Region XI
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2. Since grading and land development have initially started, the modified slopes
should provide natural contours that complement the existing topography and
maintain a natural appearance. Spot grading and the development of small
terraces is the preferred method of terrain modification. The following guidelines
below should be considered by the proponent, to wit:
o Prominent topographic features such as knolls, cliffs, ravines,
should not be graded or otherwise altered,
o Uniform or sharp geometric forms should be avoided,
o Finished contours should appear smooth, rounded and natural,
o Long or wide slopes with a uniform grade should be avoided,
o The crest and toe of regraded slopes should be adequately
blended to prevent sharply defined changes in grade, and,
o A landscaped transition area should be provided between areas
that have been graded for development
3. Proper/Appropriate drainage should also be installed during the development
stage. The drainage system should conform to the natural topography and
existing natural waterway traversing the site. The design of the drainage should
accommodate the maximum historical run-off values of the development site as
well as the surface run-off that may drain towards the area from adjacent
properties.
Nevertheless and in view of the foregoing conclusions on the geophysical environment of the
inspected property, the undersigned is of the opinion that the said project may be allowed to
proceed. This GIR is applicable only to the present development plan of the area. Should
there be any deviation to the original plan and purpose; the developer must undergo further
review by concerned authorities/agencies.
Prepared by:
Beverly Mae M. Brebante
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