Salvador, J. H. G., Almeda, R., Kanbara, H. and Hato, M.
Mines and Geosciences bureau, North Avenue,
Diliman, Quezon City 1104 Philippines
Fax: (632) 928-8544/
E-mail : [email protected] [email protected]
The Lingayen Gulf area in northwestern Luzon is part of the Philippine northern Luzon Growth Quadrangle. The area is characterized by rapid population growth and expansion of urban centers. This growth changes the landcover and puts a strain on the available resources of the area.
At the same time, the area’s geoenvironmental condition is changing. The 1990 Luzon earthquake caused slope failures and hastened the sediment erosion process. These sediments eventually find their way into the Lingayen Gulf. The earthquake also induced liquefaction particularly in Dagupan area. The 1991 Mt. Pinatubo eruption contributed sediments that will also find their way into the gulf.
Several satellite images from 1972 to 1994 were acquired over the Lingayen Gulf area. These images provide the basic information on the geoenvironmental condition of the Gulf area for about 22 years. These will also be an input into the region’s development plan.
Regional geological interpretation was made on the Landsat TM and JERS-1 images to determine the geological and geomorphological boundaries and lineament zones, chronological changes in the coastal topography and the distribution of coral reefs and mangrovels.
The image documented a regression of about 200 meters along the coastline of Ago, la union and transgression along other parts of the coast. The dispersion pattern of turbid waters was shown. Slope failures in northern Luzon have increased in recent years. Sedimentation of river systems also increased. Mangrove areas are being transformed into fishpond areas.
The Lingayen Gulf area in northwestern Luzon is part of the Philippine Northern Luzon Growth Quadrangle. This Growth Quadrangle, or Northquad for short, is envisioned to become a leading economic zone, which is market-powered and a source of entrepreneurial energy (Batino, 1996).
This area is characterized by rapid population growth and expansion of urban centers. The 1980 data on population densities in the Philippines shows that the Lingayen Gulf area has >300 inhabitants per km2. This value is similar to that in Metro Manila and Cebu. However, please note that the population in the gulf area is expectedly lower than in Metro Manila or Cebu. This growth pushed the land values higher. For example, commercial can run as high as P12,000 per sq. m in La Union and as low as P120 per sq.m Pangasinan. Similarly, residential lots can go to a high of P7,250 per sq. m. in La Union (Batino, 1996).
The growth occurring in the gulf area changes the landcover and puts a strain on the available resources of the area. Already, several resorts and a cement plant are operating in the area (Domingo and Javalosa, 1996). Several mining firms are operating in the Bagulo Miiral District (BMD) to the northeast. One of the latest locators in Malaysia’s national car manufacturer, Proton Wira, which chose Mabini, Pangasinan as the site of its assembly plant. Several other complementary industries like auto components and parts are also planning to set up shops in nearby areas (Batino, 1996). These developments has contributed, in one way or another, to the environmental problem in the Gulf area. These major problems are sedimentation, destruction of important ecosystems, unsanitary waste disposal and improper land use (NEPS and NACIAD, 1984).
At the same time, the area’s geoenvironmental condition is changing. The vicinity of itogon Province is considered to be an area where mass movement or the possibility of it occurring, is high (DNER and NEDA, 1994). The 1990 Luzon earthquake caused numerous slope failures in Banguet and itogon provinces. This, coupled with strong typhoons, hastened the sediment erosion and deposition process. The sediments find their way to the Pangasinan lowlands and eventually into the Lingayen Gulf, both major sources of livelihood in northwestern Luzon. The earthquake also induced liquefaction particularly in Dagupan area. The 1991 Mt. Pinatubo eruption contributed sediments that will also find their way into the gulf. Elsewhere, in La Union, the beachline configuration of the Santo Tomas Spit is changing due to rapid coastal erosion. In particular, there is regression of about 200 meters along the coastline and growth of the spit landform by more than one kilometer southward.
This study is a part of the three-years Philippines-Japan cooperative undertaking by the Philippine Mines and Geoscience Bureau (MGB) under the Dept. of Environment and Natural Resources (DENR), the Nikko Exploration and Devt. Co., Ltd. (NED) and the Earth Remote Sensing Data Analysis Center (ERSDAC) of Japan.
This study is a part of the three-year Philippines-Japan cooperative undertaking by the Philippine Mines and Geosciences Bureau (MGB) under the Dept. of Environment and Natural Resources (DNIR), the Nikko Exploration and Devt. Co., Ltd. (NED) and the Earth Remote Sensing Data Analysis Center (ERSDAC) of Japan.
The present study aims to document the changes that occurred over the Lingayen Gulf area using remote sensing technology. The satellite-based images will provide the basic information on the geoenvironmental condition of the Gulf area for a span about 22 years, form 1972 to 1994. The information obtained will be an input into the region’s development plan.
1.1 Location and Accessibility
The Lingayen Gulf area in NW Luzon can be accessed via the North Expressway through private vehicles or by public utility buses. Air fights to San Fernando, La Union is available. Sea ports are present in San Fernando, La Union and Currimao in llcos Norte.
1.2 General Topographic and Geologic Setting
Generally, the Lingayen Gulf area comprise the lowland area. This lowland is composed essentially of quaternary alluvial deposits and several limestone units. To the NE is the highlands of the BMD where igneous rocks intrude undifferentiated older rocks. In between the gulf area and the BMD are the shale, sandstone and limestone units.
The Sto. Tomas spit, located along the coast of La Union, is about two km at its widest portion and eight km long tapering gradually to the south. The Sto. Tomas Spit is probably formed by the action of south-flowing longshore currents. The Aringay-Pugo River on the NE is probably the source of quaternary materials that make up the spit (Duna, 1963).
1.3 Drainage and Climate
The Agno River is the largest river flowing into the Lingayen Gulf. The total length of the river is about 270 km and the area covered by its drainage reaches 7,640 km2. it flows through the mountain areas east of itogon Province characterized by deep valleys and rugged topography. It ten flows through the lowlands of Pangasinan before emptying to the Lingayen Gulf in the west.
The Study area has a type I climate. The dry season starts in November and ends in April. The rainy season is from May to October. The total annual rainfall in La Union is 2,409 mm. Typhoons and monsoons usually accompany the rainy season. The precipitation data from the US National Oceanic and Atmospheric Administration (NOAA) (1970 to 1980) and the Japan Meteorological Agency (JMA) (1981 to 1994) measured in Dagupan shows a high 2,659 mm monthly rainfall in July 1972. This was due to a major typhoon at that time.
Several satellite images, Landat TM, MSS and JERS-1 OPS images, from 1972 to 1994 were obtained Table 1 shows the summary of the images used.
|Landsat MSS||125/49||18 November 1972|
|Landsat MSS||125/49||10 May 1976|
|Landsat MSS||125/49||21 February 1979|
|Landsat TM||116/49||31 January 1988|
|Landsat TM||116/49||03 December 1989|
|Landsat TM||116/49||02 April 1993|
|Landsat TM||117/49||27 April 1988|
|Landsat TM||117/49||24 may 1992|
|Landsat TM||117/49||11 March 19494|
|JERS-OPS||91/273, 274||06 November 1993|
|JERS-1 SAR||91/273, 274||07 May 1993|
Table 1 – Summary table for the datasets used
False color composites were prepared from these available data. Each of the images were enhanced and geometrically corrected to a 1:50,000 map. Several interpretations were made on the processed images.
- A regional geological interpretation was made on the 1993 TM images to determine the geological and geomorphological boundaries and the lineament zones.
- A photogeomorphological interpretation map of the Agno River Basin with special emphasis on identifying landslide concavities was also made.
- A maximum likelihood classification was applied to the 1988 and 1993 TM images to identify open area, soil, weathered areas or barren ground areas before and after the July 1990 earthquake.
- A photogeological interpretation was made on the 1972 to 1993 images to document the extent of flood deposits in the Agno River Basin. The images were compared with each other to assess the trend.
- These images covering the Sto. Tomas Spit and an additional 1946 aerial photographs were superimposed. The changes in the configuration of the coastline over time were interpreted from the superimposed images.
- The distribution of coral reef and other reef communities were mapped from the images.
3.0 Results and Discussions
Brief statements of interpretation results are given below:
- The regional geological interpretation shows that landslide occurs in several areas irrespective of seemingly high resistance or medium resistance rocks. Most landslides occur mostly in mountainous or high relief areas, irrespective of lithology (MGB & NED, 1996).
- The distribution of the barren ground is on mountainous areas near drainage systems making it reasonable to believe that these are landslide areas. The classification statistics show that barren ground areas increased from 2.7km2 in 1988 to 5.6 km2 in 1993 after the earthquake. Sediments from these areas will find themselves mostly in the Agno River Systems that will empty in the Lingayen Gulf (MGB & NED, 1996).
- Coarse sediments flowing down the river systems are deposited as alluvial fans and floodplain deposits. The chronological changes in the distribution of these sediments flowing down along the Agno River systems were examined from the 1972 to 1993 images. The analysis shows a high sediments deposition in 1972 than in any other year. The precipitation data from the US NOAA (1970 to 1980) and the JMA shows that high rainfall contributes to high sediment deposition along river beds (MGB & NED, 1996).
- The field survey in 1995 shows that the height of the river bed upstream of the Agno River rose by about 1.5 meters. The same field survey shows that the back of the Ambuklao and Binga Dams were heavily silted. Personal communication with geologists from the Cordillera Administrative Region states that the high sedimentation occurred after the July 1990 earthquake (MGB & NED, 1996).
- The Net effect on the coastline’s configuration derived from the 1946 aerial photograph, the 1976 MSS, the 1994 TM and the superimposed images is an erosion of about 200 m on the west side of the spit. The affected a local baranggay. It also shows an approximately 1.176 m growth of the spit’s in 48 years. This growth is believed to be related to increased sedimentation caused by typhoons and the July 1990 earthquake. Furthermore, the eroded sediments on the west coast may have been transported and deposited on the southern and thus contributing to its growth. We believe that at present, the Sto. Tomas Spit continues to grow (MGB & NED, 1996).
- The distribution of coral reef communities in Pangasinan remain essentially unchanged. However, mangrove areas are being converted to fishpond areas (MGB & NED, 1995 & 1996).
The foregoing results and discussion briefly show the geoenvironmental condition of the Lingayen Gulf over the last 22 yeas. Further up to date data will hopefully improve the documentation process and will make the monitoring more effective.
Specific results can be summed up in the following statements:
Slope failures and sedimentation of river systems can be documented by satellite systems. Slope failures in northern Luzon have increased in recent years. Sedimentation of river systems also increased. These phenomena can be related to the effort of the 1990 Luzon Earthquake. High rainfall is also a factor especially in increased sedimentation. The sediments from these two processes find their way into the Agno River and eventually to the sea, thus contributing to he sedimentation of the Lingayen Gulf.
The change in the beachline of the Sto. Tomas Spit in La Union is due to rapid coastal erosion and associated sedimentation. In particular, the Sto. Tomas spit was eroded by about 200 m along the western coastline and grew by more than one km southward. It is believed that the spit continues to grow southward. These grow processes are believed to be related to the increased sedimentation caused by intense typhoon and the 1990 Luzon earthquake.
The coral reef communities in Pangasinan remain essentially unchanged in spite of the the development around the area. However, mangrove communities have already been affected and changed to fishpond areas.
The authors wishes to acknowledge the whole-hearted support of the management and staff of MGB, NED and ERSDAC. Funding for this study was provided by ERSDAC.
- Batino, C., 1996. Investing in Philippine Growth Areas: Northwestern Luzon and the Cordilleras. Business World 9th Anniversary Report. 5-12.
- Department of Natural Resources and the National Economic Development Authority, 1994. Identification of Sources of Siltation Affecting the Major River Systems of Region I, 76 pp.
- Domingo, E. D., Javelosa, R. S., Kanbara, H., Shimazaki, Y. and J. H. G. Salvador, 1995. Coastal Geoenvironmental Issues in the Lingayen Gulf Area, Northwestern Luzon, Philippines, ITIT International Symposium on the Geological Aspects of Sustainable Development in Coastal and Offshore Ares of East and Southeast Asia, 3-4.
- Duna, B. G., 1963. Preliminary Report on the Geology and Mineral Resources of La union Province. BMG internal Report.
- Japan Meteorological Agency monthly Precipitation Report from 1981 to 1994.
- Mines and Geosciences Bureau and the Nikko Exploration and Development Co.’ Ltd 1995. Joint Study on Application Techniques of Remote Sensing Date for Monitoring Coastal Environment and Resources in the Philippine Archipelago, First Phase.
- Mines and Geosciences Bureau and the Nikko Exploration and Development Co.’ Ltd. 1996. joint Study on Application Techniques of Remote Sensing Data for Monitoring Coastal Environment and Resources in the Philippine Archipelago, Second Phase.
- National Environmental Protection Council and National Council on Integrated Area Development, 1984. Ecological Profile of Pangasinan.
- US National Oceanic and Atmospheric Administration Monthly Precipitation Report from 1970 to 1980.