Erosion is one of the most dramatic problems arising after land restoration in semi-arid Mediterranean areas. Topsoiling and subsequent hydroseeding are the main practices designed to reclaim motorway embankments, but there is a lack of information about the relationship between the ground cover furnished by the conventional seed mixtures and the erosion rate in the new created slopes. Ground cover and erosion rate were monitored simultaneously on some embankments of the Maresme motorway (Barcelona, Spain) during the first year after reclamation. Under similar geologic, topographic, and climatic conditions, the erosion rate was dependent on the percentage of herbaceous ground cover. Grasses accounted for most of the ground cover. Most of the seeded species did not contribute to the soil protection, and Lolium rigidum was the only grass growing satisfactorily on all the embankments. Legumes were important in autumn with Trifolium repens and Trifolium alexandrinum growing on the northwest- and southeast-facing embankments, respectively. The erosion rate was intolerable where ground cover was <25%, and tolerable where ground cover was> 50%.