Modelling water erosion in the Sahel: application of a physically based soil erosion model in a gentle sloping environment

Water is a major limiting factor in arid and semi-arid agriculture. In the Sahelian zone of Africa, it is not always the limited amount of annual rainfall that constrains crop production, but rather the proportion of rainfall that enters the root zone and becomes plant-available soil moisture. Maximizing the rain-use efficiency and therefore limiting overland flow is an important issue for farmers. The objectives of this research were to model the processes of infiltration, runoff and subsequent erosion in a Sahelian environment and to study the spatial distribution of overland flow and soil erosion. The wide variet y of existing water erosion models are not developed for the Sahel and so do not include the unique Sahelian processes. The topography of the Sahelian agricultural lands in northern Burkina Faso is such that field slopes are generally low (0-5°) and overland flow mostly occurs in the form of sheet flow, which may transport large amounts of fine, nutrient-rich particles despite its low sediment transport capacity. Furthermore, pool formation in a field limits overland flow and causes resettlement of sediment resulting in the development of a surface crust. The EUROSEM model was rewritten in the dynamic modelling code of PCRaster and extended to account for the pool formation and crust development. The modelling results were calibrated with field data from the 2001 rainy season in the Katacheri catchment in northern Burkina Faso. It is concluded that the modified version of EUROSEM for the Sahel is a fully dynamic erosion model, able to simulate infiltration, runoff routing, pool formation, sediment transport, and erosion and deposition by inter-rill processes over the land surface in individual storms at the scale of both runoff plots and fields. A good agreement is obtained between simulated and measured amounts of runoff and sediment discharge. Incorporating crust development during the event may enhance model performance, since the process has a large influence on infiltration capacity and sediment detachment in the Sahel.

[1]  James P. Bennett,et al.  Concepts of mathematical modeling of sediment yield , 1974 .

[2]  Ramesh P. Rudra,et al.  The Roles of Rainfall and Runoff in the Sediment Transport Capacity of Interrill Flow , 1987 .

[3]  A. Mando.  The impact of termites and mulch on the water balance of crusted Sahelian soil. , 1997 .

[4]  Ali Saleh,et al.  Soil roughness measurement: Chain method , 1993 .

[5]  Rattan Lal,et al.  Soil degradation and the future of agriculture in sub-Saharan Africa , 1988 .

[6]  Anita Veihe,et al.  Sustainable Farming Practices: Ghanaian Farmers' Perception of Erosion and Their Use of Conservation Measures , 2000, Environmental management.

[7]  Peter Strauss,et al.  Modelling of event-based soil erosion in Costa Rica, Nicaragua and Mexico : evaluation of the EUROSEM model. , 2001 .

[8]  Robert A. Merriam,et al.  Fog drip from artificial leaves in a fog wind tunnel , 1973 .

[9]  C. R. Umback,et al.  Effects of Wind on Falling Water Drops , 1966 .

[10]  C. Valentin.  Sealing, crusting and hardsetting soils in Sahelian agriculture , 1995 .

[11]  C. Valentin,et al.  Morphology, genesis and classification of surface crusts in loamy and sandy soils , 1992 .

[12]  L. Stroosnijder,et al.  Crust formation on sandy soils in the Sahel I. Rainfall and infiltration , 1984 .

[13]  G. Sterk.  Wind erosion in the Sahelian zone of Niger : processes, models, and control techniques , 1997 .

[14]  Geert Sterk,et al.  Causes, consequences and control of wind erosion in Sahelian Africa: a review , 2003 .

[15]  David C. Goodrich,et al.  Dynamic, Distributed Simulation of Watershed Erosion - the Kineros2 and Eurosem Models. , 1995 .

[16]  Keith L. Bristow,et al.  Water entry into sealing, crusting and hardsetting soils: A review and illustrative simulation study , 1995 .

[17]  Marcel van der Perk,et al.  Simulation of event‐based and long‐term spatial redistribution of Chernobyl‐derived radiocaesium within catchments using geographical information system embedded models , 2003 .

[18]  C. Brandt,et al.  The size distribution of throughfall drops under vegetation canopies , 1989 .

[19]  J. Wallace,et al.  Soil water balance in the Sudano-Sahelian zone: need, relevance and objectives of the workshop , 1991 .

[20]  C. Valentin,et al.  Evaluation of factors influencing water erosion in West Africa using rainfall simulation , 1984 .

[21]  D. Sharon,et al.  The distribution of hydrologically effective rainfall incident on sloping ground , 1980 .

[22]  Bent Hasholt,et al.  Influence of wind speed on rainsplash erosion , 1995 .