Assessment of the Effect of Bench Terracing in El Ogla and El Hadada Watersheds in Tunisia in the Context of Gully Erosion

The study of the erosive manifestation in El Ogla and El Hadada watersheds showed a strong and accelerated erosive dynamic. The aggression of the rains, the unstable nature of the Lower Eocene clays and the pressure of humans on the marginal lands seem to be at the origin of the instability of the slopes. Thus, the preservation of lands requires a colossal effort from the part of the State as well as the peasants. Unfortunately, the majority of developments have been implemented on an ad hoc basis and are far from being implemented comprehensively. In El Ogla and El Hadada watersheds, bench terracing is the most spectacular form of State intervention. It is considered by technicians as the unique solution for all forms of erosion. However, the appearance of forms of failure in various sectors cannot neglect the good functioning of some of them in the stability of the slopes and the reduction of the water slide. The objective of this applied research is to evaluate the behaviour of these benches as an interactive system with the other components of the natural environment based on photointerpretation, field monitoring and the results of the diagnosis of the balance sheet displacement of sediments obtained from the application of the isotopic method of Cesium 137. This assessment of bench terracing is largely based on the Bugeat formula, which seems to be the most appropriate method for determining the suitable dimensions of both height and terrace spacing.