ABSTRACT

As a typical geomorphological process, rock fall is predominantly controlled by slope topography. For many situations, the occurrence of rock falls varies spatially which results in the difficulties of hazard assessment. Efficient hazard assessment of rock falls requires enabling technologies which facilitate topographical analysis. Using LiDAR (Light Detection And Ranging) technique enables us to capture the accurate topographical information of the hazardous area. This paper discusses effect of topography on rockfall process using LiDAR and process modeling. The process modeling of rock falls was conducted using Rockfall Analyst, a three dimensional rockfall analysis tool linked to a GIS system. Both high resolution LiDAR dataset and coarse digital elevation model were used to examine the effect of topography on the rockfall process in terms of rockfall runout, dispersion and energy distribution.

1 INTRODUCTION

As a typical geomorphological process, rock fall is predominantly controlled by the slope topography. For many situations, it is difficult to predict because the occurrence of rock falls varies spatially and temporally. One of the greatest limiting factors in rockfall hazard assessment is the deficiency of high resolution geospatial data related to the delineation of slope topography, rockfall detachment area, rock block geometry, traveling path, runout distance and deposition. The confidence of hazard assessment depends upon the quality and quantity of such data available (Hutchinson et al, 2006). It is necessary to understand the topographic data with a resolution relevant to the scale of morphological features of rockfall process (Glenn et al, 2006).

Conventional survey methods present serious limitations for collecting these spatial datasets and their quantification. Efficient hazard assessment of rockfalls requires enabling technologies which can facilitate topographical analysis. The use of new technologies, such as LiDAR (Light Detection And Ranging) has rapidly increased in the field of geohazard study. It is becoming a standard practice for highly accurate and dense data acquisition (Nagihara et al. 2004; McKean et al. 2004; Bellian et al. 2005; Rosser et al., 2005; Metternicht et al., 2005, Glenn et al 2006). Both ground based LiDAR survey and Airborne LiDAR survey are available nowadays. Ground based LiDAR, such as Optech Ilris-36D, use a reflectorless, time-of-flight laser to capture 3D topographic data, in a high speed, high precision and low cost manner (Rosser et al., 2005). It is capable of capturing detailed topographic information of nearly vertical structures. Airborne LiDAR is suitable for generating high resolution digital elevation model for large area (15 cm vertical accuracy). The high accurate topographic data can help assess the geomorphology, geological settings, structural discontinuities and mechanical characteristics of slopes and rock blocks.

Numerical modeling of rockfall process on fine scale topography can provide insight into the relationship between topography and rockfall behavior (Pfeiffer and Bowen, 1989; Jones et al, 2000; Guzzetti et al, 2002; Agliardi and Crosta, 2003; Dorren and Seijmonsbergen, 2003; Lan et al, 2007; Yilmaz et al, 2008). A three dimensional rockfall program, Rockfall Analyst, was used to simulate the rockfall processes and their spatial distribution (Martin et al, 2006; Lan, et al, 2007).

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