Small dam reservoir siltation in the Atlas Mountains of Central Morocco: analysis of factors impacting sediment yield

Since the construction of the first dam, siltation phenomenon has always preoccupied every hydraulic engineer. The problem is widely studied on large dams than on smaller ones even if it has higher impact. Actually, building small dams might be a good option to cope with climate change and improve community resilience in arid areas such as our study area in Morocco. So, well-planned small dams depend immediately on a good understanding of siltation phenomenon linked to water erosion process on the catchment. As known, this process is related to many factors including: rainfall's intensity, runoff, slope, lithology, and vegetation cover upon the whole watershed. The objective of the current study is to identify the most influencing factors that control sediment yield variability in catchment areas. Data of 24 small dams located in western High Atlas and Anti-Atlas Mountains in Morocco are collected and analyzed. Different tools are used, to extract catchment attributes for each reservoir, such as digital elevation models, satellite images, topographic and lithological maps. During a field survey, unavailable sediment yield data are estimated using approximate method. Based on Pearson's correlation and multiple regressions, the relationship between sediment yield and catchment characteristics is studied. The first analysis of Pearson's correlation shows that sediment yield is positively linked to different factors as: catchment area, catchment's shape, drainage density, global slope index, erodibility and sinuosity's degree of the stream. The second analysis of multiple regression with stepwise method shows that only the drainage density, erodibility and global slope index were included in the suggested model with acceptable coefficient of determination (R-2 = 0.85). The results and outcomes of this study will be used to generate thematic maps that will be used as "decision support tool" to better plan small dam projects and mainly to minimize erosion sensitive areas.