Rockfall Hazard Rating System(s) in Saudi Arabia – A Review

Slope instability along highways in mountainous areas is not only a major hazard for lives and passing vehicles but also may hinder traffic for long period and thus create significant economic loss. The most common type of slope instability failures in such areas is rockfalls. Many qualitative rockfall hazard rating systems (RHRSs) have been developed across the world. However, the Middle East almost lacks to such systems. For instance, in Saudi Arabia, which has the largest economy in the region, only one system of rockfall hazard rating system (RHRS-SA) has been developed up to now. This paper aimed to critically review this system. Some drawbacks were found in the RHRS-SA. However, the main disadvantage was that the final rating score of risk is not consistent with risk definition. In sum, the remarkable findings of this review can be accounted either for any future modifications for the RHRS-SA or to develop a new rockfall hazard rating system but for a specific area(s) in Saudi Arabia.

DEVELOPING AND SELECTING SLOPE STABILIZATION TECHNIQUES IN MANAGING SLOPE FAILURES

This paper objectives are to; (i) identification of risky slopes (within 4 Provinces in Sumatra including Provinces of Riau, West Sumatra, Jambi and South Sumatra encompassing 840 kms of the “Jalan Lintas Sumatra” highway) based on Rockfall Hazard Rating Systems (RHRS) method; (ii) developing alternatives to stabilize slope hazards, and (iii) selecting appropriate slopes stabilization techniques based on both proactive approach and value engineering one. Based on the Rockfall Hazard Rating Systems (RHRS) method, it was identified 109 steep slopes prone to failure within this highway section. Approximately, 15 slopes were identified as potential high-risk slopes (RHRS scores were calculated >200 points). Based on the proactive approach, seven riskiest slopes ware identified. The preferred stabilization alternatives to remedy most of these slopes are suggested as follow; either (i) a combination of retaining wall and drainage, or (ii) gabion structure and drainage. However, different approaches may yield different results, there are at least 2 main consideration in prioritizing slope stabilization; (i) based on the riskiest slopes, and(ii) the least expensive stabilization alternatives.

Understanding windthrow: Silvicultural implications

Windthrow is a damaging agent that can be of paramount importance in silviculture. Windthrow depends on a number of factors interacting with each other. This paper tries to incorporate windthrow concerns into the silvicultural decision making process by understanding the windthrow process and its interaction with silviculture. The forces involved in the windthrow process are reviewed. The effects of natural factors on these forces are examined and the potential impact of silviculture on these factors is discussed. Some available hazard rating systems are reviewed, trying to underline their applicability in the Eastern Canadian context. Climate affects the severity and frequency of storms. However, wind speed in a particular stand is influenced strongly by local topography. Soil and root characteristics determine the sturdiness of the anchoring system. Many stand-related factors, such as stand height, age, density and stem form, can also exert an influence on the resistance to uprooting. Silviculture can modify the vulnerability to windthrow by acting on these factors. In stands at risk, stripcutting, thinning or the creation of new margins can cause important losses. The impact of stem form also indicates the need for an early control of stand density. Among the hazard rating systems available, the British system seems the most complete but would require some adjustments for use in the Eastern Canadian context. Key words: windthrow, uprooting, blowdown, wind

The applicability of available hazard rating systems for mountain pine beetle in lodgepole pine stands of southeastern Wyoming

Five hazard rating systems for Dendroctonusponderosae Hopkins in Pinuscontorta Dougl. stands were compared under nonoutbreak conditions in the Medicine Bow Mountains of southeastern Wyoming. The applicability of these systems, which were designed in other regions of the United States, to P. contorta stands in southeastern Wyoming was investigated. Thirty-two stands in four different age and diameter categories were sampled and rated by each system. Diameter at breast height did not correlate well with phloem width in any of the stands, as implied by the system of Amman and co-workers. A direct phloem width measurement could further refine this system. Periodic growth ratio, used in both the Berryman and Mahoney systems, did not differentiate between fast- and slow-growing trees. Crown competition factor did not positively correlate with increasing diameter at breast height, as implied by the system of Schenk and co-workers. Stand production ranged from 11.1 to 51.0 g wood•m leaf area−2•year−1, applying a modified system based on that designed by Mitchell and co-workers, indicating very high risk in every stand sampled. Further development and validation of hazard rating systems is necessary for improved analysis of risk to P. contorta stands from D. ponderosae in this region.