Active Landslide Monitoring and Control in Kundasang, Sabah, Malaysia Kamaluddin Hj.Talib Dept.of Surveying Sci. & Geomatic, Faculty of Architecture, Planning & Surveying, University Teknologi MARA, Shah Alam, Selangor, 40450 MALAYSIA E mail:- khjtalib@yahoo.com Mohd Raihan Taha Professor, Dept.of Civil & Structural Engineering, Universiti Kebangsaan Malaysia, Bangi, Selangor, 43600 MALAYSIA E mail:- drmrt@eng.ukm.my ABSTRACT The town of Kundasang, Sabah and its vicinity has been experiencing an active land movement, a rapid growth in population and agricultural activities for many years. It has been previously established that Kundasang town as a whole is located on a large landslide complex. This landslide complex consisted of a number of individual active land movement and has been identified as the first natural landslide in Malaysia that involved a developed area. This phenomenon is largely due to underground water regime and the geological formation of the land and its affects the stability of the town infrastructure with serious environmental, social and economic implications. Monitoring landslide activities for the area is an active research agenda and the approach of monitoring and control are the key aspects to provide a sound basis for more holistic and sustainable action. The main objective of this paper is to present some ground assessment data of this landslide complex that has been recorded over the past few years. In this study, the application and capability of Global Positioning System (GPS) will be explored to understand the landslide behavior and magnitude in terms of surface displacement. Study implications and its relation to the sustainability of the area will also be discussed that could be a useful tool both for hazard assessment and control. INTRODUCTION The town of Kundasang, Sabah and its vicinity has been experiencing an active land movement, a rapid growth in population and agricultural activities for many years. It has been previously established that Kundasang town as a whole is located on a large landslide complex (Sian and Komoo 2002). These landslide complexes (Fig. 1.0) have been identified as the first natural landslide in Malaysia that involved a developed area. The active movement is largely due to underground water regime (Jamaluddin 2004) and the geological formation (Fig 2.0) of the land (Hassan et.al. 2005) and its affects the stability of the town infrastructure with serious environmental, social and economic implications (Komoo and Salleh 2003).  Figure 1: Landslide complexes (Sian and Komoo 2002)  Figure 2: Geological map of Kundasang (Hassan et.al. 2005 ) From Figure 2, the geological surface of Kundasang area is mainly comprises of Trusmadi formation (57%), Crocker formation (36.4%), Pinosuk gravel (6.36%), Monzodiorite (0.04%) and Alluvial deposit (0.20%)(Fig. 3).  Figure 3: a)Trusmadi formation, b)Crocker formation and c)Pinosuk Gravel (Hassan et.al 2005) From Figure 3, the properties of this geological surface formation are of unconsolidated and loose materials such as sandstone, weathered clasts, angular to sub-angular ultra basic rocks, sub-rounded to rounded granodiotite and with these type of soils characteristics land movement can be easily occurs. The main objective of this paper is to present some ground monitoring data of this landslide complex that has been recorded over the past few years. The exact directions and magnitude of movement are noted. Study implications and its relation to the sustainability of the area will also be briefly discussed. LOCATION OF STUDY AREA The town of Kundasang, Sabah with an area of 61 hectare is situated south of Mt. Kinabalu, 90km east of Kota Kinabalu (capital city of the state of Sabah, Malaysia) along the Tamparuli-Ranau Highway (Fig. 4).  Figure 4: Location of case study: Kundasang, Sabah It is located at an altitude between 1,200m to 1,300m amsl with mountainous climatic temperature of 18oC to 25oC. The population of Kundasang is about 11,000 and governed by Ranau Municipal District Office. ENVIRONMENTAL ISSUES The impact of land movement in this area has given rise to some environmental issues (Taha et.al., 2005) such as slanting tree, cracked retention wall, cracked cement slab, leaning houses, slanting pole, land scar, land hump, road depression and broken road slab (Fig. 5). These issues affect the stability of the town infrastructure with serious implication on the social well being (sustainability) of its inhabitants.  Figure 5: Impact of land movement: a)Slanting tree, b)Cracked retention wall, c)Cracked cement slab, d)Leaning houses, e)Slanting pole, f)Land scar, g)Land hump, h)Road depression and i)Broken road slab Due to this landslide problem, it is found that severe physical exposures are imposed on the infrastructures, housing and living amenities with moderate exposures to the agricultural activities. To understand further the phenomenon of the landslide movement, GPS survey is carried out within K1 landslide complex. RESEARCH METHODOLOGY In this study, the state-of-the-art technology using Global Positioning System (GPS) is utilized (U.S. Army 1996). Using appropriate instrumentation and software, the system can deliver a relative accuracy of measurement at centimeter's level (Rizos 1997 & Talib 2002). In the GPS field observation conducted in this study, six (6) monitoring points (Fig. 6) and two (2) control stations were selected and marked on the ground. Monitoring is based the on Radial Static method (Sickle 2001) using Single Frequency GPS. Fig. 7 shows the flow chart of monitoring using the GPS technique.  Figure 6: Monitoring and Control points mark on aerial photo at K1 Landslide Complex  Figure 7: Flow chart of monitoring using GPS technique RESULTS AND ANALYSES Four sets (interval) of observation were conducted from July 2003 through Aug 2004. The geographical GPS coordinates (f, ?, h) obtained (which is based on WGS84) are transformed to the geocentric system (X, Y, Z) using the following formula (Rizos 1997);  Figure 7: Flow chart of monitoring using GPS technique For analysis purposes, the geocentric coordinates were then transformed to local coordinate system (N, E) (JUPEM 1994) namely Malaysian Rectified Skew Orthomorphic (MRSO). The results are shown in Table 1 to Table 4 below. Taking the difference between the observations (taking the first observation as the datum), the magnitude of the movements of the every monitoring points were determined as shown in Chart 1 to Chart 6, respectively. 
  From the result, as shown in Table 1-4 and Chart 1-6, all the points experiences gradual movement. It can be seen that each point moved in different magnitude and the overall movement (magnitude and direction) of K1 landslide complex is shown in Table 5. 
From Table 5, the individual monitoring points movement varies from 8mm to 576mm and it can be concluded that K1 Landslide Complex experienced horizontal movement (D = v (dX² + dY²) of an average approximately 98mm per year in northerly direction. The largest movement occurred at Point 5 since it is located near to Liwagu River. DISCUSSION AND CONCLUSION GPS surveys for landslide monitoring should gained more popularity as infrastructure and technology improved. In order to provide physical meaning to GPS displacements, the results should be correlated with the hydro-geological and geotechnical characteristics of the studied area and its surrounding (Abidin et al. 2004). In the context of identifying the potential indicators, GPS technology (as conducted and shown in this study) play important role especially in providing analysis of movement. In addition it can provide an early warning system for high risk areas at geohazard areas. The continuing landslide movement in Kundasang, Sabah, has affected the sustainability of the area. Its movement has been established by GPS over the past few years indicating its direction and magnitude. The maximum movement recorded over the past year for K1 Landslide Complex is 98 mm (northerly direction). This data can be used as a guide for local inhabitants and also for the general planning of current and future infrastructure development of the area. A successful outreach program was also conducted in part to share and educate the public and local authorities on the various aspects related to sustainable development on Kundasang. REFERENCES
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