Geohazard Assessment Report on the Proposed Holiday - MGB-XI

Republic of the Philippines
Department of Environment and Natural Resources
MINES AND GEOSCIENCES BUREAU
Regional Office No. XI
669 Konsuela Bldg., Aurora Quezon Street, Davao City
Tel. No. (082) 222-5601 Telefax No. (082) 221-6535 Email: [email protected]
Geohazard Assessment Report on the Proposed Holiday Oceanview Condotel
at Brgy. Ilihan, Camudmud, Babak District, Island Garden City of Samal
1. INTRODUCTION
A rapid geological hazard assessment was conducted by a technical team led by the
undersigned at a parcel of land in Brgy. Ilihan, Camudmud, Babak District, Island Garden City
of Samal covered by TCT No. T-242592 having a lot size of approximately 20, 771 square
meters under the name of Davao Wess Jay Development Corporation. This undertaking is in
response to the letter request of Mr. Ronald L. Bangayan, President of Holiday Oceanview
Samal, in line with the compliance to the application of an Environmental Compliance
Certificate (ECC) for the proposed Holiday Oceanview Condotel on the said site.
This report presents the result of the rapid assessment which includes susceptibility of the area
to identified geologic hazards. Few recommendations are also stated at the end portion of the
report which should be considered by the proponent before, during, and after the course of the
project to ensure safety and stability on the area.
2. PROJECT DESCRIPTION
The proposed Holiday Oceanview Condotel is composed of three four-storey
residential buildings namely left wing, main building, and right wing connected to each other by
corridors and common veranda. There are 83 consolidated saleable units for the proposed
condotel with a total of 3967.2 sq.m floor area. Other ancillary facilities such an administration
building, lobby, waiting lounge, an elevator, reception, storage rooms, a common comfort room,
an electrical room, and main entrance will be built at the main building with total floor area of
about 2,597.42 sq.m. Open spaces for auxiliary facilities are swimming pools for both kids and
adults, a clubhouse beside the main building, parking lots, driveways and walkways, parks and
playgrounds, gardens, and drainages. A 20m easement from the shoreline has also been
considered on the plan.
3. LOCATION AND ACCESSIBILITY
Holiday Oceanview Condotel is located in Brgy. Ilihan, Camudmud, Babak District,
Island Garden City of Samal. It is approximately centered at geographic coordinates of
7°11'48.15"N, 125°42'37.41"E. It is approximately 7 km NE of the Babak Port and is bounded
by the Davao Gulf to the north where an existing dry dock is and the existing Holiday
Oceanview Subdivision to the south. A perimeter fence has also been established where the
main entrance is at the residential subdivision beside the barangay road.
Geohazard Assessment Report on the Proposed Holiday Oceanview Condotel at Brgy. Ilihan, Camudmud, Babak District, Island Garden City of Samal
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Approximate boundaries of the property as per plotted in Google Earth are as follows;
Point
Northing
Easting
1
7°11'49.65"N 125°42'32.19"E
2
7°11'47.26"N 125°42'32.43"E
3
7°11'48.54"N 125°42'41.37"E
4
7°11'46.70"N 125°42'41.06"E
Figure 1. Satellite Image showing the location of Holiday Oceanview Condotel
The proposed site is accessible by any means of land transportation through the
Samal Island Circumferential Road from the Babak Port for about 5-10 minutes ride going to
Brgy. Ilihan, Camudmud. From the barangay road, a pass through the main gate of Holiday
Residential Subdivision is required to reach the proposed condotel.
Figure 2. Path from Babak Ferry Terminal to Holiday Oceaview Condotel
Geohazard Assessment Report on the Proposed Holiday Oceanview Condotel at Brgy. Ilihan, Camudmud, Babak District, Island Garden City of Samal
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4. METHODOLOGY
A field study was conducted on the proposed site through an open traverse with the aid
of a Garmin 62s Global Positioning System (GPS) device. Two test pits were made to identify
the underlying soil and rock layer. Notable observations on the area and location of test pits
were marked and plotted on the map. Outcrops along cut slopes were also studied and
documented. Moreover, a field test using a geologic scriber was done to estimate the hardness
and strength of soil and rock layer. Few photos were captured on site for documentary
purposes and verification. On the other hand, field data were processed on Google Earth and
ArcGIS v.10 software to overlay satellite images, topographic, geologic, and geohazard maps
to supplement on interpretation. In addition, the site development, detailed topographic, and
drainage plans provided by the proponent were also considered on the analysis.
5. CLIMATE AND VEGETATION
Island Garden City of Samal falls under Type IV according to the Modified Coronas
Classification of Philippine Climate. This type is characterized by a more or less evenly
distributed rainfall throughout the year having no pronounced dry season. Based on the
Koppen-Geiger Classification of World Climate, Davao Region is situated on a Tropical
Rainforest (Af) type of area having at least 60 mm average rainfall per month. Places with this
type of climate is affected by the Inter-tropical Convergence Zone where northeast and
southeast trade winds come together. Average annual precipitation in Samal Island records to
about 2029 mm while its average annual temperature is 25.6 degrees Celsius.
Figure 3. Climate Map of the Philippines
6. SITE GEOLOGY
6.1 TOPOGRAPHY
The proposed site is situated near shore characterized by a gently sloping to flat
beach. Landwards, a cut hillslope ranging from moderate to steep was observed where
Geohazard Assessment Report on the Proposed Holiday Oceanview Condotel at Brgy. Ilihan, Camudmud, Babak District, Island Garden City of Samal
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some portions has been applied by structural mitigation such as retaining wall and weep
holes. Seaward, slope gradient is low where waves are generally calm.
Retaining wall
w/ weep holes
Proposed Condotel
Photo 1. General topography of the proposed site
6.2 HYDROLOGY
No river systems were observed in the area and groundwater recharge is low.
However, surface runoff drains toward Davao Gulf at the north.
6.3 LITHOLOGY AND STRUCTURES
The area is underlain by a fossiliferous limestone with fossilized corals, shells, and
other marine organisms. It is slightly porous but is generally indurated, hardly penetrated
by finger but moderate by a scriber. Some outcrops show moderately jointed rocks
particularly on the east portion of the property. Other than that, there were no local faults
noted in the area.
Photo 2. Fossiliferous limestone rock layer seen in an outcrop
6.4 SOIL
Soil layer is composed of very thin white sandy soil with fragments of marine
organisms about a cm thick but gradually thickens to about a meter near shore.
Geohazard Assessment Report on the Proposed Holiday Oceanview Condotel at Brgy. Ilihan, Camudmud, Babak District, Island Garden City of Samal
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7. ASSESSED GEOLOGIC HAZARDS
7.1 FLOOD
The area is vulnerable to coastal flooding especially during unusual high tides and
storm surges although there were no reported incidents of such. This assessment was
deduced because of the area’s geomorphology. No river systems were observed in the
area thus riverine flooding is unlikely to occur however surface runoff is a significant
contributing factor to flooding especially when combined with coastal flooding.
7.2 LANDSLIDE
Landslide susceptibility of some areas with engineering mitigation has downgraded
from high to moderate however areas with cut slopes and no installed mitigation still
remains high. Abrupt change in slope gradient affects the stability of slopes on the area.
Nevertheless, weep holes were observed on the retaining walls about 1m spacing just
sufficient to drain seepages. Rockfall is likely to occur on the east portion of the property
due to vertically cut slopes.
7.3 SEISMIC-RELATED HAZARDS
Ground shaking is minimal on the area due to intact limestone rock layer however
varies depending on the magnitude and proximity of the earthquake’s epicenter. On the
other hand, liquefaction is unlikely due to thin sandy soil layer and insignificant amount of
groundwater. Moreover, localized earthquake-induced landslide typically rockfall is likely to
occur on jointed rocks.
7.4 GROUNDWATER AND SINKHOLE
No springs or caverns were observed on the area except for very small cavities on
some portions of the rock layer thus low susceptible to sinkhole. The area is at low
groundwater recharge and the underlying rock is relatively permeable thus development
may cause some groundwater contamination especially on the area near shore. Sewages
and waste disposals should be contained properly.
8. CONCLUSIONS AND RECOMMENDATIONS
The proposed Holiday Oceanview Condotel is situated on a suitable geologic condition
as per current site investigation involving geologic and geohazard assessment. However,
considering the density of the proposed buildings and facilities as per site development plan, a
detailed study such as an Engineering Geological and Geohazard Assessment Report
(EGGAR) targeting slope stability analysis, drainage and water outflow analysis, and a
foundation analysis considering the bearing capacity of the ground should be conducted to
ensure stability. Nevertheless, report should also contain the proposed structural mitigating
Geohazard Assessment Report on the Proposed Holiday Oceanview Condotel at Brgy. Ilihan, Camudmud, Babak District, Island Garden City of Samal
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measures and other modifications, maps including cross sections, data acquired and tests,
documentary photos, and other relevant data.
Furthermore, drainage systems such as storm pipes and canals should maintain
allowable gradient to avoid backflow. Thus maintenance, monitoring, and clearing are needed
for the drainage facilities. To avoid coastal and groundwater contamination, a 20m easement
from the coastline should be maintained. Moreover, waste disposal should be properly done
thus dumping is not allowed in the area. Sewage facilities should be contained properly
considering that limestone is relatively permeable and soluble thus a detailed study on the
location and design of the facility is necessary. Construction of slope protection such as
retaining walls with weep holes, rock bolts, soil nails, and nets are of great help for the stability
of steep cut slopes. Installation of breakwalls and seawalls along the coast can also lessen the
impact of storm surges but requires a detailed study.
9. PHOTO DOCUMENTATION
Photo 3. A jetty along the west side boundary of the
property
Photo 4. A boundary marker (mohon) on the northwest
portion of the property
Photo 5. Test pit excavated to identify underlying
lithology
Photo 6. Coralline Limestone excavated from a test pit
Geohazard Assessment Report on the Proposed Holiday Oceanview Condotel at Brgy. Ilihan, Camudmud, Babak District, Island Garden City of Samal
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Photo 7. Vertical cut slopes with lush vegetation
Photo 8. Overview of the proposed site looking
northwest
Photo 9. View of the main road from the residential
subdivision to the condotel
Photo 10. Retaining wall with weep holes on a cut
slope
Photo 11. Closer view of the wall
Photo 12. Cut slope near the steps connecting the
subdivision and condotel
10. ATTACHMENTS
Topographic Map Showing the Location of Holiday Oceanview Condotel
Prepared By:
Capter John M. Tubo
Geologist
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