Debris Basin and Deflection Berm Design for Fire-Related Debris-Flow Mitigation

Debris flows are hazardous because of their poor predictability, high impact forces, and ability to deposit large quantities of sediment in inundated areas. To minimize the risk to developments on alluvial fans, debris-flow mitigation structures may be required. This study reviewed the state of practice for the design of two types of debris-flow mitigation structures: basins and deflection berms. Published guidelines for these structures are rare, and there appears to be little standardization. Recommended design improvements, particularly for fire-related debris flows, include incorporating several recent developments in debris-flow mitigation design, reducing subjectivity, and enhancing the technical basis for the designs. Specific shortcomings of existing design methodologies include techniques for predicting debris-flow volume, specifica-tions for berm geometry, impact loading considerations, and lack of flexibility in outlet works design, among others. Proposed solutions and guidelines for these issues are presented.