Structures for controlling debris flows and debris floods have been used for decades throughout the world. These are typically rigid structures such as check dams, diversion berms, catchment basins, or debris breakers or racks. Most often a combination of structures are used to help control the destructive power of the event by limiting velocity and erosive potential. The use of flexible-net systems has become more common for retaining debris and dewatering a flow.
These debris flow barriers are normally constructed in-channel, perpendicular to the flow direction. A simple gully net is often sufficient for narrow spans (e.g. less than 15 m), whereas a post and net system is required for wide channels or open-slope applications.
Where standardized guidelines exist for the design and application of rockfall catchment fences, there are very limited resources for flexible-net debris flow barriers. Any existing guidelines are based on design criteria for rigid structures and are not fully transferable. Completely absent is standardized testing methods. This is partially due to the difficult task of creating reproducible debris flow events in an appropriate test setting but also to the fact that every debris flow barrier must be designed based on highly variable site-specific parameters that have a much greater impact on the design than for rockfall.
Each system is designed based on information provided by the field engineer regarding the physical characteristics of the material, the site geometry and the nature of the debris flow event. This evaluation on a site-to-site basis is the only way to arrive at a technically correct solution and safe system. Some of the major design parameters are: