Water erosion is a critical issue for Morocco, especially in its semi-arid regions, where climatic and edaphic conditions only allow erratic soil formation and vegetation growth. Therefore, water erosion endangers human activity both directly (loss of arable land, landslides, mudflows) and indirectly (siltation of dams, river pollution). This study is part of the Kingdom’s effort to assess the risk of water erosion in its territory. It is dedicated to the Bin El-Ouidane dam water catchment, one of the biggest water storage facilities in the country, located in the High Atlas Mountains. The poorly developed soils are very sensitive to erosion in this mountainous area that combines steep slopes and sparse vegetation cover. The calculation of soil losses is carried out with the RUSLE model and corrected by estimating areas of deposition based on the unit stream power theory. This method produces a mean erosion rate of around 6.3 t·ha ^-1·y ^-1, or an overall annual loss of 4.1 mln t, consistently with the siltation rate of the dam. Primary risk areas (erosion rates > 40 t·ha ^-1·y ^-1) account for 54% of the total losses, while they cover only 7% of the catchment. This distribution of the soil losses also shows that the erosion risk is mainly correlated to slope, directing the means of control toward mechanical interventions.

The stream power is one of the important river variables which is used in morphological analysis. Therefore, the stream power determines both erosion and deposition. This research examines the stream power, instability and morphometric changes of the channel using the annual geomorphic energy (AGE) in Haji Arab River in Buin Zahra (Qazvin Province). The AGE is calculated by integrating the relationship between the excess specific stream power and discharge using a flow duration curve. The AGE values for each reach should be either positive or negative. Therefore, according to the differentials in AGE values, depositional and erosional reach are determined. In this paper, the results of the AGE method were compared with the rapid geomorphic assessments (RGA), including the channel stability indicators (CSI) model and OSEPI index. Also, the RHS method based on the field works was used to identify depositional and erosional geomorphic landforms. Comparing the results of the AGE with rapid RGA indices, shows that results of the OSEPI are more consistent with the erosional and depositional status of the reaches, based on the AGE. Spatial variations in lithology and structure, when combined with the course of the Haji Arab River indicate that channel morphometry locally reflects geological factors that have caused slope differences in different reaches. The calculated AGE values at different cross-sections have significant variability, reflecting characteristic local variation in bed slope, cross-section geometry and bed-sediment composition.