This paper proposes an appraisal of costs produced by water erosion within arable lands strongly exposed to erosion in the catchment area of Tleta, located in the Rif, in the north of Morocco. Adopted methodology is inventive as allows to distinguish the costs according to three severity levels of erosion while taking into account the compensatory contributions, often invisible, of adaptation measures implemented by farmers. The differences between the gross margins obtained in three zones, classified according to the intensity of erosion, are compared two to two. The ensuing losses of benefit for each degree of severity of water erosion are deduced from the discrepancies observed in relation to the slightly degraded zone. The opportunity costs of outstanding lab or resulting from the community mutual aid, identified as a current practice in the basin studied to mitigate the damage of erosion, are also estimated in each zone. The estimates obtained are extrapolated to the whole cereal area of the basin to determine the total cost engendered by water erosion.

Key-words: Economic appraisal, degradation costs, water erosion, benefits loss, soil conservation, erosion cost, Rif, Morocco