The Cheekeye Debris-Flow Barrier – unique features of a proposed open check dam in Canada

The proposed Cheekeye debris-flow barrier in Squamish, BC, Canada is an open check dam with a very large storage capacity of 2.4 million m3. There are several unique features of the design that deviate from standard international practice, including the very low probability (1 in 10,000 years) design event, the use of a single large structure, the selected construction material, the crest design, and the outlet design. These features were selected for the Cheekeye barrier due to idiosyncrasies of the site specifically, and of debris-flow mitigation in Canada, in general

Quantifying debris-flow hazard and risk based on fan sector

We show how a quantitative estimate of debris-flow hazard and risk can be derived simply from the position of infrastructure on the fan relative to the fan apex and the most likely flow path (e.g., active channel). Fan sectors and the spatial probability of impact in each sector are based on a fan-normalized heat map of debris-flow impacts derived from 146 mapped impact areas across 30 fans in southwestern British Columbia, Canada. As a proof-of-concept, we provide an example for annual life loss risk to an individual who occupies a home in various sectors of a debris-flow fan. The results are comparable to broad findings from quantitative risk assessments completed at 10 fans in British Columbia and Alberta, Canada with similar characteristics. The method presented here is a way to obtain a high-level quantitative risk estimate prior to a detailed site-specific assessment

The Cheekeye Debris-Flow Barrier – unique features of a proposed open check dam in Canada

The proposed Cheekeye debris-flow barrier in Squamish, BC, Canada is an open check dam with a very large storage capacity of 2.4 million m3. There are several unique features of the design that deviate from standard international practice, including the very low probability (1 in 10,000 years) design event, the use of a single large structure, the selected construction material, the crest design, and the outlet design. These features were selected for the Cheekeye barrier due to idiosyncrasies of the site specifically, and of debris-flow mitigation in Canada, in general

Debris Flows, Boulders and Constrictions: A Simple Framework for Modeling Jamming, and Its Consequences on Outflow

International audienceLarge boulders can jam in constrictions, both in canyons and man-made structures (e.g., slit-dams). Boulder jamming occurs stochastically, and partially governs the outflow rate of debris flow material. Explicit hydro-mechanical models of boulder-laden flows are too computationally demanding to study this stochasticity. This study presents a new framework implemented into a numerical program. This program encapsulates basic hydraulic equations and criteria predicting boulder blockage at narrow sections, along with a simple statistical way to compute boulder sizes and numbers. The program applies empirical estimates by experts of the average number of boulders in a deposit to evaluate how equivalent multi-phase flows would interact with a constriction. The model stochastically generates boulders that can obstruct the constriction(s). The program outputs simple descriptions of the upstream flow level over time, as well as the downstream outlet discharge rate and volume. The model is fast (5–30 s per run), allowing uncertainty propagation analyses of interactions between flows, boulders and constrictions. Interaction between both low- and high-risk flows can be quickly evaluated for different scenarios. For uncertainty propagation, we use possibility theory, which accommodates uncertainties relevant to debris flows. The framework gives practitioners a much-needed generalized approach for understanding the long-term behavior of boulder-laden flows through canyons, or for designing engineered structures. Finally, we apply the model to a field case – the design of a proposed North American slit-dam – thence elucidating the design requirements for effective flow control. We found that horizontal bars are necessary for dependably controlling outflow from this structure

Review of the mechanisms of debris-flow impact against barriers

International audienceOur limited understanding of the mechanisms pertaining to the force exerted by debris flows on barriers makes it difficult to ascertain whether a design is inadequate, adequate, or over-designed. The main scientific challenge is because flow-type landslides impacting a rigid barrier is rarely captured in the field, and no systematic, physical experimental data is available to reveal the impact mechanisms. An important consideration in flow-structure interaction is that the impact dynamics can differ radically depending on the composition of the flow. Currently, no framework exists that can characterize the impact behavior for a wide range of flow compositions. This review paper examines recent works on debris-flow structure interactions and the limitations of commonly used approaches to estimate the impact load for the design of barriers. Key challenges faced in this area and outlook for further research are discussed