Reducing runoff by increasing landscaped areas

Résumé

In the Sahel, many water and soils conservation techniques have been implemented within degraded soil areas to reduce their runoff production capacity. However, few are the works that have analyzed the relationships between the landscaping extension area and the importance of the runoff drop generated. The present work aims at fullfulling this lack of knowledge. Experiments were carried out within the Tondi Kiboro catchment (17.7 ha) which is a representative site of the hydro-environmental conditions of Western Niger. In 2007 and 2008, the initial catchment runoff coefficient (no landscaping) was determined using a hydrometric station. In 2010, 3% of the catchment contributory surface (lateritic plateau) was laid out by benches. This proportion was then gradually increased every year to reach 9% in 2016. Thus, it was possible to follow the concomitant evolution of landscaped area and runoff coefficient. The results show that benches play an important role in water retention and flow limitation. Between 2010 and 2016, the runoff coefficient decreased from 43% to 10% though the total landscaped surface remains less than 10%. Since 2012, the runoff coefficient has more or less stabilized around 10% (± 2%). It is thus remarkable that the runoff decrease is not proportional to the dimension of the landscaped surface. Thanks to this work, it was possible to determine an optimal landscaped area that can reduce runoff to a desired level.