1:50,000 Scale Groundwater Resource Mapping and Vulnerability Assessment in the Municipality of Naga, Zamboanga Sibugay [Progress Report]

By Paul Asthor D. Yecyec, Abbygail B. Soco & Merill Jan T. Balignot

INTRODUCTION

The 1:50,000 Scale Groundwater Resource Mapping and Vulnerability Assessment of MGB-IX Geosciences Division commenced on March 12, 2019 in the Municipality of Naga. This is part of the groundwater resource study in the entire Zamboanga Peninsula which will cover 5 municipalities: Naga, Tampilisan, Kalawit, R.T. Limand Titay, for the year 2019. This undertaking conducts well and spring inventory and aims to assess the vulnerability of groundwater resources that will likely be affected by global climate change and potential groundwater pollution. The assessment conducted is vital for the effective and efficient management of groundwater resources for sustainable development.

The program will cover the entire municipality of Naga which is comprised of 22 barangays and will attempt to map-out all major water sources of each barangay. Two major water catchments, which are also referred to as watersheds, are present in Naga. The first one is referred here as Ipil-Naga-Tampilisan Catchment (W1) located on the western part of Naga while the Naga-Kabasalan Catchment (W2) covers the eastern section of the study area. W1 is about 25,000 hectares and is generally the main watershed in the municipality.

To date, 5 barangays which are part of the Ipil-Naga-Tampilisan Catchment (W1) were covered in the inventory. These include Sandayong, Tilubog, Cabong, Guintuluan, and Tipan which are located in the northern extent of the municipality. The areas covered are generally on the mountainous part of Naga which is characterized by its undulating to steeply sloping terrain. Most of these areas are also under a Moderate to High susceptibility to landslide with flooding confined along the main rivers that traverse the area.

The output of this program is a hydrogeologic map or water availability map of Naga with accompanying report.

INITIAL FINDINGS

BarangayHydrogeological
Rock Units
Major Groundwater Source
SandayongBasalt-andesite flow; volcanic breccia and agglomerate of the Zamboanga Volcanic Complex underlie the northern portion of the barangay; The sandstone of the Zamboanga Formation occur to the west and extends to the adjacent barangay, Barangay Tilubog; and the limestone of the Sibugay Formation is present within the eastern and southern portions of the barangay
Groundwater, in this barangay, is commonly tapped through springs. These springs occur in elevations of more than 250 masl. Cavities in limestones, fractures in volcanic rocks and in indurated sandstones, and unconfined highly weathered volcaniclastic layers serve as conduits for groundwater flow. A spring in Purok 4, which has a discharge of 0.6 L/sec, serves as the main source of water for the barangay. This source was developed, and presently provides potable water to the community through Level 2 and Level 3 water distribution systems.
TilubogThe basalt-andesite flows, volcaniclastics, and volcanic breccia of the Zamboanga Volcanic Complex are dominant in the western portion of the barangay; the sandstone of the Zamboanga Formation occurs within the northeast; and the limestone and clastic rocks of the Sibugay Formation occur in the southeast Groundwater in this barangay permeates through unconfined weathered volcaniclastic layers and through fractures in volcanic rocks. It is mainly tapped through springs with elevations of more than 270 masl. A developed source, which taps two springs, is being managed by the barangay and provides potable water to 43 households through Level 3 water distribution system, and to the rest of the community through distributed communal faucets of a Level 2 water distribution system.
GuintuloanThe whole barangay is underlain by the basalt-andesite flows, volcaniclastics, volcanic breccia and agglomerate of the Zamboanga Groundwater springs through fractures in volcanic rocks. These spring sources are tapped by the barangay to provide potable water to the community through Level 2 distribution system. Other undeveloped springs also serve as a Level 1 source of potable water.
CabongThe basalt-andesite flows, volcaniclastics, volcanic breccia and agglomerate of the Zamboanga Volcanic Complex occur in the eastern portion of the barangay; the sandstone, and limestone of the Zamboanga, and Sibugay Formation underlie the western and southern portions of the barangay, respectively. These formations are cut by two parallel, northeast-southwest trending lenses of the Tampilisan MelangeIn this barangay, the groundwater is sourced through shallow wells dug through the sheared rocks of the Tampilisan Melenge. The static water level in inventoried wells is at about 128 masl. A shallow well in Cabong Elementary School was previously pumped to supply potable water to the barangay. However, the pumping operation of the well was stopped due to impractical operational cost. This well presently serves as a Level 1 water source.
TipanThe limestone of the Sibugay Formation dominate the northeastern portion of the barangay while the basalt-andesite flows, volcaniclastics, volcanic breccia and agglomerate of the Zamboanga Volcanic Complex underlie southwestern portion of the barangayThis barangay commonly taps groundwater through springs that usually occur in limestone cavities and volcanic rock fractures. A spring in Purok 2 was developed to provide potable water through Level 2 and 3 water distribution systems in Puroks 1, 2, 3, 4 and 8. Other undeveloped springs in Purok 6 and 9 also serve as Level 1 source of potable water.

LOCATION

Location Map of the Municipality of Naga, Zamboanga Sibugay underlain by SRTM image.

Inventoried groundwater sources in 2016 and 2019.

WELL AND SPRING INVENTORY

  1. Barangay Sandayong
Photo 1. NAG 17 is a spring which is located in Purok 1, Sandayong, Naga, Zamboanga Sibugay. The spring is privately owned by Mr. Alvin Endong and have been used since 1970’s.

Photo 2. NAG 20 is a spring which is situated within the vicinity of Sandayong Elementary School. The spring is utilized for domestic uses of the school.

2. Barangay Tilubog

Photo 3. NAG 22 is a spring which was developed last 2016 and situated along a steep sloping hillside near a gully in Barangay Tilubog. The spring distributes potable water tor approximately 43 houses through a Level 3 distribution system.

3. Barangay Cabong

Photo 4. NAG 24 is a shallow well situated within the vicinity of Cabong Elementary School in Purok 3, Cabong, Naga, Zamboanga Sibugay. The well was developed in 2018 and has been utilized for domestic purposes of the barangay.

4. Barangay Guintuloan

Photo 5. NAG 25 is a spring located along the highway in Purok 1, Guintuloan, Naga, Zamboanga Sibugay. The spring has an average discharge of about 0.01 liters per second and is a Level 1 source of potable for the nearby community.

5. Barangay Tipan

Photo 6. NAG 26 is a spring located in Purok 2, Barangay Tipan, Naga, Zamboanga Sibugay. It was developed through the project of Kalahi-CIDDS and distributes potable water in the barangay, specifically in Purok 1, 2, 3, 4 and 8.
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