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ABSTRACT: Rockfall along roads can cause significant hazards to human health and infrastructure or interrupt transportation. A section of rock slope on Interstate 70 west, west of Idaho Springs, has been monitored at a daily frequency since March 2018 using a 5-camera photogrammetric system that collects high-definition photos to establish the rockfall MCF trends. An established semi-automated workflow was utilized to produce raw 3D point clouds and locate areas of potential rockfall using change detection. The high frequency of monitoring at this site allows for precise determination of timing and volume of rockfalls and creation of a high temporal resolution database. This database can then be leveraged to analyze trends in rockfall volume and frequency on an annual or seasonal basis. We provide an overview of the workflow applied for database development as well as preliminary results regarding interpretations of variations in rockfall activity. 1. INTRODUCTION According to the US Census Bureau (2023) the US population has expanded from 151 million in 1950 to 331 million in 2020. This growth in population has led to an increased demand for previously undeveloped land, including in relatively hazardous mountainous regions (Thornton et al., 2022). Mountainous regions are prone to rockfall and other geohazards that can have serious repercussions on human infrastructure and health (Abellán et al., 2010; Copons and Vilaplana, 2008; Dussauge et al., 2002). The Colorado Department of Transportation (CDOT) is particularly interested in understanding rockfall trends along critical transportation routes in the mountains. Rockfall can be described as a type of mass wasting event where an individual rock or multiple rock fragments detach from a slope and travel downhill (Cruden and Varnes, 1996; Varnes, 1978). Rockfall generally occurs when blocks detach along existing discontinuities or by sliding and toppling (Hungr et al., 2014). Rockfall can be further subdivided into two categories: primary and secondary. Primary falls occur when a block detaches from the host bedrock, and secondary falls occur when previously detached blocks are moved further downslope (Luckman, 2013). A commonly investigated aspect of rockfall is the mechanism of its triggering and any seasonal trends a site might exhibit. Numerous studies have shown rockfall frequency to follow seasonal trends, likely controlled by weather conditions (Delonca et al., 2014; Matsuoka and Sakai, 1999). The importance of certain conditioning and triggering mechanisms that might be more prevalent in certain seasons can greatly influence these relationships (Krautblatter and Dikau, 2007).
Hollander et al. (Sun,) studied this question.