Monitoring of Hill-Slope Movement Due to Rainfall at Gunung Pass of Cameron Highland District of Peninsular Malaysia

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1 6 Monitoring of Hill-Slope Movement Due to Rainfall at Gunung Pass of Cameron Highland District of Peninsular Malaysia HABIBAH LATEH A, JEFRIZA A, W M MUHIYUDDIN B, BADDRUL TAIB A and YOUNUS AHMED KHAN C A School of Distance Education, University Sains Malaysia, 11800USM, Pulau Pinang,Malaysia B School of Humanities, Universiti Sains Malaysia, USM, Pulau Pinang, Malaysia C Department of Geology and Mining, University of Rajshahi, Rajshahi 6205, Bangladesh habibah@usm.my; jefriza_5500@yahoo.com; Baddrul@pop.jaring.my; younus@ru.acbd Abstract: The theodolite study on slow hill-slope movement at Gunung Pass site of Cameron Highland District of Malaysia was conducted to monitor land movement during rainy seasons of A total of six survey prisms were positioned on the studied hill-slope. Prisms III showed significant down-slope movement of more than 4 m, southward movement of 1.94 m and westward movement of more than 5 m. A good correlation was found between hill-slope movement and rainfall occurrences. Prism III movement was larger than other prisms for the same rainfall amount. All these slow movements took place after the heavy rainfall events in The study significantly found a close correlation between hill-slope displacements and the rainfall amounts during rainy seasons in Finally, the area is unstable and prone to downward movement leading to landsliding. Further study related to the effects of seismic loading either from earthquake or from road traffic on such hill-slope movement is emphasized. Keywords: Gunung Pass, Malaysia, hill-slope movement, rainfall, prisms Introduction: Movement of land is still an unpredictable and is not fully understood. It is impossible to realize these changes without an obvious and consistent record of observable surface phenomena. Landslide is one of the natural land degradation processes that continuously occurring in the hilly terrains. In Malaysia, majority of landslides studies are related to urban land use, especially roads and highways that pass the mountainous or hilly terrains. Improved inventory techniques and surveying methods are strongly needed in order to precisely estimate the characteristics of hill-slope displacement in regions of risk associated to landslide hazard (Peyret et al., 2008). The road between the 23 rd and 26 th km stretches through Gunung Pass of Cameron Highland is on hilly terrain where landslide occurs. Two landslides were occurred in April, 2007 and in December, 2007 at Gunung pass area after heavy rainfall. Slopes can move slowly to produce landslides at the onset of triggering rainfall events. The Gunung Pass slope needs careful monitoring system for any type of movement that may cause further landslide in the area. Slope at Gunung pass site might have some movements inside before failure during the past rainfall seasons in Therefore, the Public Works department of the Malaysian government has installed several prisms with theodolite for monitoring a landslide on the slope. Surveying of surface movement can be performed by several methods. One of the methods is based on instruments such as theodolite, electronic distance meter, or tiltmeter (Angeli et al., 2000). The conventional monitoring using theodolite was used in the present investigation. The other method is based on remote sensing techniques such as Synthetic Aperture Radar (SAR) data with differential information, while some are based on Global Positioning System (GPS) (Gili et al., 2000; Malet et al., 2002; Megawati et al., 2005). # Copyright 2010 CAFET-INNOVA TECHNICAL SOCIETY. All rights reserved.

2 HABIBAH LATEH, JEFRIZA, W M MUHIYUDDIN, BADDRUL TAIB and YOUNUS AHMED KHAN 7 Figure 1: Map of Malaysia (partly) showing study area The present paper unveils some results about the movements of the landslide at Gunung pass site and their relation to rainfall from a monitoring system with theodolitic study. Study Area: The study was conducted in Gunung Pass area of Cameron Highland district (Fig. 1) which is situated near the boundary between Perak and Pahang state. Geographically, Gunung Pass is located on the 26 th km of the highway at latitude N and longitude E. Elevation of the road is 1391 m above the mean sea level while the peak of Gunung Pass reaches 1540 m above mean sea level. The lithology of Cameron Highland consists mostly of Quaternary and Devonian granite and schist (Omar et al., 2004). Gunung Pass is a tropical rainforest covered hilly terrain of Peninsular Malaysia.

3 8 Monitoring of Hill-Slope Movement Due to Rainfall at Gunung Pass of Cameron Highland District of Peninsular Malaysia Figure 2: a) An installed prism and b) Positions of six prisms at Gunung Pass slope site with xyz reference axes. Methodology: The working method included the measurements of hill-slope movement from the theodolite and collection of rainfall data. The slope movement was then correlated with the rainfall. The seismic loading from seismic activities and road traffic loading on the slope was discussed for further research potential for this area. Measuring Slope Movement: Land surface monitoring system was fully installed for the purpose of monitoring the movement of hill-slope. In the present study, theodolite and prisms were employed to measure the ground displacement. Hillslope movement or landslide monitoring at the Gunung Pass site was conducted during a total of 293 days covering two rainy seasons. Survey nails were placed into the ground as a datum with their positions recorded. Six prisms or target points were then installed on concrete base on the studied slope of Gunung Pass (Fig.2a & 2b). A digital level was used to measure their elevation/heights at high precision. Manual monitoring involved sending a team to the site for readings on prisms. Monitoring was varied in length and intensity. The slope movements in different directions were recorded from March 29, 2008 to January 16, It was assumed that movement of slope was directly related to the vertical and/or horizontal movements of benchmarks or prisms.

4 HABIBAH LATEH, JEFRIZA, W M MUHIYUDDIN, BADDRUL TAIB and YOUNUS AHMED KHAN 9 Figure 3: Average rainfall at Cameron Highland in 2007with the occurrences of two landslides in April and in December. Collection of Rainfall Data: Rainfall data were collected for the year of 2007 including the days of two landslides before the installation of prisms. Again after the installation of prisms for theodolite observation another set of rainfall data was collected. These two sets of rainfall data were then used to correlate rainfall intensities with the two landslide events in 2007 and with the observed movements of hill-slope at Gunung Pass respectively. All the rainfall data were obtained from the station of Ladang Teh Sungai Palas located near the Gunung Pass area. Even no direct seismic data and traffic load data were collected for this study, but it is important to discuss such effects on land movement. The seismic load and traffic load data were being collected for further research in order to assess their effects on the studied slope. Some related discussions are included later in this paper. Results and Discussion: The measured movements of the studied hill-slope land at the Gunung Pass site were investigated with the possible effect of rainfall. The relative movements of the installed 6 prisms (Fig. 2b) are shown in Table 1. Figure 3 shows average rainfall in 2007 at Gunung Pass with two events of landslides. The failures were occurred in the beginning of April 2007 and in December The pattern shows that there was a correlation between rainfall pattern and failure occurrences. After heavy rainfall at March 27th, 2007, the slope became wet and saturated enough and it failed subsequently. Heavy rainfall occurred in the study area during last week of April, 2008 and again during the period of October-December, 2008 that corresponds well to slopemovement in the study area (Fig. 4).

5 10 Monitoring of Hill-Slope Movement Due to Rainfall at Gunung Pass of Cameron Highland District of Peninsular Malaysia Table 1: Measured movements at six different prism locations along x,y and z directions Prisms x(m) y(m) z(m) PI PII PIII PIV PV PVI Data readings of movements were taken from March 29, 2008 until January 16, 2009 and the movement of 293 days is shown in Table 1. The displacement begun in the last week of July 2008 and continued up to the second week of December 2008 with a significant total lateral displacement of more than 7m at the prism III, more than 5m at prisms IV and V. The other displacement were more than 2m at prism VI, more than 1m at prism II and about 0.10m at prism I. Sudden displacements were recorded during the first week of December 2008 (Fig.4b). The graph shows that there was a sudden displacement both in November and December of There was hardly any displacement in May and June, but in July movement started again and continued until the second week of December of Prisms III shows that the most significant movement was 7.38m from the original point. It dropped m downward and moved 1.940m and 5.448m to the south and west respectively (Table 1). Mostly, the recorded displacements took place during the rainy seasons of 2008 when the slope soil materials were saturated enough with the infiltrated rain water. No monitoring system was installed for the previous two landslide events in 2007 and the nature and amount of displacement was not measured. But the past two landslides in 2007 were occurred within the rainy seasons. Hence, it is assumed from the measured displacements for landslide in 2008 that there might have been considerable amount of slope movement in the 2007 events as well as before the final failure of the slopes in the same area. Even though mitigation measures were taken up for the slopes of the study area after the 2007 failure events, they showed continuous movements during two rainy seasons of 2008 with subsequent failure. Further movements are very significant in inducing further landslides in the area and it implies that the slopes may become unstable with any future heavy and prolonged rainfall. There may be other triggering factors like seismic loading from earthquakes and/or from road traffic. Seismic activity and heavy traffic load on the road could be another interesting investigation for which the slope movement may happen in the study area. Malaysia is in the area of low seismic hazard, but consequences may be high if any earthquake happens. Although, the active seismic sources like Sumatra subduction zone and fault that may affect the Malaysian Peninsula area, are located about 300 km away. The Sumatran seismic zone consists of two distinct sources, namely, the Sumatran fault and the Sumatran subduction zone (Mora et al., 2003). The Sumatran fault is a right-lateral fault that has a capability to produce earthquakes with magnitudes not more than 7.8 (Sieh and Natawidjaja, 2000), while the Sumatran-subduction zone is a shallow dipping zone. There is no tectonic plate and the epicenters of the Earthquake within the Peninsula Malaysia and hence it implies that the effect of earthquake on hill-slope movement in Gunung Pass site is smaller than rainfall. But if the slope becomes fully saturated after any prolonged rainfall it is still important to consider even the small tremor from seismic and non-seismic sources like road traffic, especially.

6 HABIBAH LATEH, JEFRIZA, W M MUHIYUDDIN, BADDRUL TAIB and YOUNUS AHMED KHAN 11 Conclusion: Figure 4: a) Average rainfall at Cameron Highland from March 29th, 2008 to Dec 30th,2008; b) Observed total displacement at Prisms I-VI Surface movement of hill-slope at the Gunung Pass site of Cameroon Highland of Peninsular Malaysia has been measured using theodolite. Theodolite studies during the year of 2008 revealed that the significant total movement was 7.38m at Prism III from the original point. It also dropped vertically downward more than 4m along the slope. This area with prism III has moved more than 5m laterally westward. All these major movements took place after the heavy rainfall events in The study observed a close correlation between hillslope displacements and the rainfall amounts during rainy seasons in The two landslides were occurred at the same place before possibly because of the considerable amount of movements of slope after heavy prolonged rainfall in Therefore, the area is found to be in an unstable condition and prone to landslides. Acknowledgement: The authors would like to acknowledge the financial support from Universiti Sains Malaysia. The authors also extend their acknowledgement to the Public Works Department and MTD Construction Sdn Bhd for installing prisms and the Department of

7 12 Monitoring of Hill-Slope Movement Due to Rainfall at Gunung Pass of Cameron Highland District of Peninsular Malaysia Irrigation and Drainage (DID) for providing rainfall data. Finally, the authors gratefully acknowledge the comments and suggestions from reviewer Professor G T Thong of Nagaland University, India. References: [1] Angeli, M.G., Pasuto, A. and Silvano, S., (2000) A critical review of landslide monitoring experiences. Engg. Geol. v55, pp [2] Gili, J.A., Corominas, J. and Rius, J., (2000) Using Global Positioning System techniques in landslide monitoring, Engg. Geol., v55, pp [3] Malet, J.P., Maquare, O. and Calais, E., (2002) The use of Global Positioning System techniques for the continuous monitoring of landslides application to the Super-Sauze earth flow (Alpes de Haute-Provence, France). Geomorphology, v43, pp [4] Megawati, K., Pan, T-C. and Koketsu, K., (2005) Response spectral attenuation relationships for Sumatran-subduction earthquakes and the seismic hazard implications to Singapore and Kuala Lumpur. Soil Dynamics and Earthquake engineering, v25, pp [5] Mora, P., Baldi, P., Casula, G., Fabris, M., Ghiotti, M., Mazzini, E. and Pesci, A.,(2003) Global Positioning Systems and digital photogrammetry for the monitoring of the mass movements: application to the Ca di M alta landslide (Northern Apennines, Italy). Engg. Geol., v68, pp [6] Omar, S., Jeber, F. M. and Manor S.,(2004) GIS/RS for landslides zonation in Pos Slim Cameron Highlands district, Peninsula Malaysia. Disaster Prevention Management, v13, pp [7] Peyret, M., Djamour Y., Rizza, M., Ritz, J.F., Hurtrez, J.E., Goudarzi, M.A. Nankali, H., Chery, J., Le Dortz, K. and Uri, F., (2008) Monitoring of the large slow Kahrod landslide in Alborz mountain range (Iran) by GPS and SAR Interferometry. J. Engg. Geol., v100, pp [8] Sieh, K. and Natawidjaja, D., (2000) Neotectonics of the Sumatran fault, Indonesia. J. Geophys. Res., v105(b12), pp.28:295 32