Abhatoo - Centre Nationale de Documentation

The paper describes selected investigations concerning the progress of erosion in various regions of Morocco which were carried out from 1990 onwards by a group of geomorphologists sponsored by UNESCO. It was found that the intensity of erosion, especially in recent years, is linked to fast socio-economic development and incorrect management of the exploitation of natural resources. Extensive grazing, deforestation and expansion of agriculture on frequently unsuitable soils are of great importance here. These activities caused a decrease in the infiltration of precipitation water into the subsoil, thus soils became less humid and ground water resources decrease. Simultaneously increased runoff causes mud accumulation and pollution in man-made water reservoirs, which play an important role in water supply during dry periods.
The first studies in this project were made in the forest of Mamora and in the region of BouKhouali – Tanecherfi (eastern Morocco) in the years 1990-1995. They assessed the process of soil erosion and its intensity. On the basis of the results obtained it was found that type of soil and kind of land use were the main factors influencing the process of soil degradation; these factors being characteristic for individual regions of different climate.
The second set of studies described were carried out in the regions of Tatoft and Benslimane in the years 1996-1999 as a part of the MEDCHANGE (INCO-MED) project in cooperation with Aveiro University. These studies concerned surface flow and erosion rate determined with the use of precipitation simulators. It was recognized that the smallest surface flow occurs in natural oak forests, however this is twice as high when there is grazing in the forest, and four times higher in those areas where trees were cut down and the resulting clearfell areas are used as pasture. Moreover, the studies have shown that the total amount of mineral and organic material which has been eroded depends to a large degree on the intensity of the surface flow, though this relation is not linear. Even scarce plant cover, e.g. matorral (shrubland), n an area being considered is an important factor causing compacting of the soil and retention of the mineral sediment.
The third group of investigations were experiments performed in the region of Sehoul, close to Rabat City in the years 2000-2003 in the project CLIMED (INCO-MED ICA3-2000-30005) in cooperation with Aveiro University and concerning hydrologic reaction and bottom transport.
Erosion connected with rainfall was recognized by means of the hydrologic model LISEM. It was found that the surface flow depends on a low infiltration capacity of the dusty-clayey soils occurring in the drainage area investigated, low soil humidity retention due to the limited thickness of the soil layer or the presence of an impermeable bed and scarce vegetation in wastelands and pastures.