The objective of this study was to investigate the risks of runoff and erosion of soils in the Ben Ahmed watershed, it's located in the region of casa-settat, 70 km south-east of Casablanca, and characterized by a semi-arid climate. The study consists of measuring on 1 m2 plot, the volumes of runoff and sediments, under the influence of rainfall generation (60mm/30 min). Soil samples were collected from each plot to determine texture, organic matter and humidity. Results obtained show that the detachability varies between 19 and 34 g/l, infiltrability oscillate between 15 and 37 mm.h-. Pearson correlation test shows that infiltration was negatively correlated with runoff and soil detachability (R=-0.99, R=-0.87 respectively). It‘s significantly correlated with the proportions of sand(R=0.69), silt (R= -0.98) an clay (R= 0.92), however, is weakly correlated with organic matter (R=-0.32). Infiltration and detachability were significantly correlated with humidity (R = -0.99, R = -0.63respectively).