The plant covering defacement takes many forms : a rapid physionomic change of the vegetal cover in relation to the over-exploitation through excessive wood cuttings and by overgrazing and an effective receding of the forest thanks to the encroachment of the cultivating lands on the forest domain.

The runoff goes from 0 to 300 mm per year (Streaming coefficient between 0% in the driest years and 25-30% in the most humid ones). However, and most often, it remains inferior to 10%. The soil loss varies in even greater proportions, since it can be insignificant in many cases, to reach a record figure (more than 50 t/ha/year), practically comparable to that of the gullies and the badlands.

In accordance to the plant covering and to the use of the soil, the bare or tilled soil undergoes a stronger erosion than the permanently covered sites. The cork-oak forests in the central Rif, represent the most stable milieu with a streaming of less than 5% and a loss of insignificant rate. The watersheds covered by wheat cultures, with remains of matorral, are also the less eroded ones (<0,9 t/ha). As soon as we go to slopes of wheat monoculture, the specific degradation grows and can reach an average of more than 20 t/ha/year.

The rains of low intensity allow certain water permeation and reduce the runoff on the slopes. On the other hand, episodes of high intensity entail a more important runoff.

The evolved soils having a closed plant cover and dense cultivated plots, record an important permeation. On the other hand, the bare or covered soils with secondary degraded cover undergo a direct superficial streaming.

But water turbidity does not comply with the same factors as the streaming. It is the unceasing rains, responsible for the saturation of the superficial horizon of the soil, that account for the highest turbidity values. Besides, the heavy and brief rains allow moderate turbidity. The coming out of saturation phenomena in the located sites is responsible for the formation of scars that sweep mud materials, in some particular plots. The constitution of rills entails a rapid rise, during a first period and then the tubidity becomes slower after the stabilisation of the rills..

The amount of soil loss is more correlated with the amount of the runoff than with turbidity. That is why it is not always the fields, holding located erosion forms (scars and rills), that represent cases of the most important erosion. Cases of moderate soil loss, despite a strong turbidity correspond to situations of important permeation, with a high impregnation of the superficial horizon. The functioning of the muddy flow process - to the limit of solifluxion - accounts for the strong turbidity, yet the swept mass remains moderate. Still, in cases where a high streaming and a strong turbidity intertwine, we come to rates of specific degradation, that are as important as those recorded in the big gullies. In those cases, erosion becomes disastrous. The load reaches then maximal values.