For more than 150 years, humans have tried to limit the geomorphic activity of mountain streams, and the related damage, using torrent control works. Check dams are likely the most emblematic civil engineering structures used in soil conservation programs. Modern mountain societies have inherited thousands of these structures built in upland gullies and streams. To help define their effectiveness and decisions concerning their maintenance or new project designs, a clear understanding of potential effects of check dams on river systems, i.e. their functions, is first needed. The next steps concern quantitative assessments of each function on the flood features and combination of all effects. The present understanding of these sometimes old structures' functions can be complicated because the societal and environmental contexts in which the original structures were built may have changed. To bridge this gap, this paper traces the purposes for which check dams were built, through a detailed analysis of French archives. We first analyze chronologically how each function was theorized and applied in the field. In the nineteenth century, engineers developed a thorough empirical and conceptual knowledge of mountain soil erosion, torrential geomorphology, and sediment transport processes as well as check dam interactions with these natural processes. The second part of this paper synthesizes conceptual descriptions of the check dams' functions, in the light of more than 150 years of experience, with their implication on the features of the structures. The French experience is compared to other countries' pioneering works. Finally, the next steps and remaining research challenges toward a comprehensive analysis of check dams' efficiency in torrent hazard mitigation are presented. This analysis is proposed to remind how, conceptually, check dams may influence geomorphic systems, bearing in mind the knowledge represented in pioneer guidelines and recent works on the subject. Copyright © 2016 John Wiley & Sons, Ltd.

Sediment traps with open check dams are widely used structures in flood hazard mitigation. This paper reviews the literature dedicated to their design. First, the general context in which sediment traps are built and their functions are presented. The second part proposes hydraulic design criteria for classical types with details on the opening shapes and dam crest spillway. The third part details sediment deposition dynamics: its initiation, its controls through the trap basin and open check dam shapes, the effect of hydrographs, and the control of trap self-cleaning. The methods to determine the deposit slope and height are discussed. Finally, a step-by-step design procedure is proposed and future research challenges are highlighted. Field feedback has shown that driftwood can substantially influence sediment trap behavior. A companion paper thoroughly covers the production and transfer of driftwood and the interactions with open check dams.