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Regional/Global Environment
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Geoenvironmental Monitoring of the Lingayen Gulf, Northwestern Luzon, Philippines Using Remote Sensing Technology
3.0 Results and Discussions
Brief statements of interpretation results are given below:
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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).
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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).
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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).
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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).
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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).
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The distribution of coral reef communities in Pangasinan remain essentially unchanged. However, mangrove areas are being converted to fishpond areas (MGB & NED, 1995 & 1996).
4.0 Conclusion
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.
5.0 Acknowledgments
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.
6.0 References
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Batino, C., 1996. Investing in Philippine Growth Areas: Northwestern Luzon and the Cordilleras. Business World 9th Anniversary Report. 5-12.
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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.
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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.
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Duna, B. G., 1963. Preliminary Report on the Geology and Mineral Resources of La union Province. BMG internal Report.
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Japan Meteorological Agency monthly Precipitation Report from 1981 to 1994.
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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.
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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.
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National Environmental Protection Council and National Council on Integrated Area Development, 1984. Ecological Profile of Pangasinan.
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US National Oceanic and Atmospheric Administration Monthly Precipitation Report from 1970 to 1980.
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