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Wind and Rain Interaction in Erosion WIND AND RAIN INTERACTION IN EROSION 2004 Tropical Resource Management Papers, No. 50 (2004). ISBN 90-67S4-843X ISSN: 0926-9495 Financial support for the organisation of the course titeled: "Wind and Water Erosion: Modelling and Measurements" was obtained from the C.T. de Wit graduate school PE & RC, Wageningen, The Netherlands. Financial support for the printing of this publication was obtained from the Stichting "Fonds Landbouw Export-Bureau 1916/1918", Wageningen, The Netherlands. WIND AND RAIN INTERACTION IN EROSION Saskia M. Visser and Wim M. Cornells (eds.) Acknowledgements The idea for organizing a combined wind and water erosion course was bom while 1 visited the Wind Erosion Unit (Manhattan, Kansas) and the National Soil Erosion Laboratory (Purdue, Indiana) as part of my thesis-work. Back in the Netherlands, Ghent University was contacted and preparations started. Thanks to financing of the C.T. de Wit graduate School PE & RC (Wageningen, The Netherlands), the course "Wind and Water Erosion: Modelling ad Measurement" started in September 2003. Young (PhD) researchers with 9 different nationalities came together to discuss and learn more about the interaction between wind and water erosion. I would like to thank Ghent University and the Erosion and Soil & Water Conservation Group of Wageningen University for hosting the course. Special thanks for their contribution to the course goes to the lectures: Ed Skidmore (WERU, Kansas University), Dennis Flanagan (NSEL, Purdue University), Donald Gabriels (Ghent University), Leo Stroosnijder (ESW, Wageningen University), Gunay Erpul, (Soil Department, University of Ankara), Wim Comelis (Ghent University), Michel Riksen (ESW, Wageningen University) and Geert Sterk (ESW, Wageningen University). At the end of the course the idea came up to combine the experiences and ideas of this group of researchers in this special edition of TRMP, for which financing for printing was obtained from the Stichting "Fonds Landbouw Export-Bureau 1916/1918", Wageningen, The Netherlands. Last but not last I want to thank all authors who contributed to this 50' edition of Tropical Resource Mangement Papers. Saskia Faye- Visser Table of Contents Chapter 1 Introduction L. Slroosnijder and D. Gabriels Chapter 2 Commonalities in WEPP and WEPS and Efforts Towards 15 a Single Erosion Process Model D.C.Flanagan and S.M. Visser Chapter 3 Applications of WEPP and WEPS in the Benelux 31 Using WEPP for Single Rainfall Event Prediction in Belgium 33 A.'. Verbist and W. Schiellecatte Predicting the Effect of Tilling Practices on Wind Erosion Activity 43 M.J. P.M. Riksen and S.M. Visser Chapter 4 Upscaling Wind and Water Erosion Models 59 Far from reality? S.M. Visser and J. Palma Chapter 5 The Role of Crust Formation in the Interaction Between 69 Wind and Water Erosion in the Sahel S.M. Visser and J.K. Leenders Chapter 6 Effect of Wind on Runoff 79 G. Erpul, D. Gabriels and D. Norton Chapter 7 The Role of Wind and Water Erosion in Drift-Sand Areas 97 in the Netherlands M.J.P.M. Riksen, D. Goosens and P. D. Jungerius Chapter 8 Effect of Wind-Driven Rain on Transport of Sand by 129 Splash Saltation W.M. Cornells and D. Gabriels Chapter 9 Effect of Slope Aspect on Sediment Transport 143 G. Erpul, D. Gabriels and D. Norton Chapter 10 Wind and Water Erosion in East Africa 157 G.R. Henneman Chapter 11 Farmers' Indicators for Water and Wind Erosion 167 O. Vigiak and J. K. Leenders Chapter 12 Measurement Options for Water and Wind Erosion 183 L. Stroosnijder Chapter 13 The I.C.E. Wind Tunnel for Wind and Water Interaction 195 Research W. M. Comelis, G. Erpul and D. Gabriels Chapter 14 Future Work on Wind and Water Interaction in Erosion 225 Models L. Stroosnijder and D. Gabriels Chapter 1 Introduction L. Stroosnijder & D. Gabriels 'Wageningen University, Erosion and Soil & Water Conservation Group, Nieuwe Kanaal 11, 6709 PA Wageningen; Email: [email protected] 2Dept. Soil Management and Soil Care, International Centre for Eremology, Ghent University, Coupure links 653, B-9000 Gent, Belgium; Email:[email protected] Introduction The 'Tropical Resources Management Papers' (TRMP) series is published by Wageningen UR to disseminate the results obtained by past and present researchers and graduate students in Wageningen research projects on managing tropical and subtropical resources. This 50" publication in the TRMP series is special because it brings together wind and water erosion, students and staff from Ghent and Wageningen universities, and American modeling experts from The National Soil Erosion Laboratory (NSEL), Purdue University, Indiana, USA (WEPP; Water Erosion Prediction Project) and the Wind Erosion Unit (WERU) at Manhattan, Kansas, USA (WEPS; Wind Erosion Prediction System). The classic paradigm is that water and wind erosion have little in common; they occur in different climates at different moments of the year, with water erosion confined to the humid zones during the rainy season and wind erosion to the more arid zones during the dry season. However, at the onset of the rainy season in semi-arid environments, high intensity rainfall is often preceded by strong convective winds and the processes of wind and water erosion occur almost simultaneously at the same location. Further, there is growing evidence of interaction between the two processes. In Australia and the West African Sahel, rivers draining inland towards desert regions bring vast amounts of sediment to semi-arid regions; when dry, these sediments may be vulnerable to wind erosion. In this way, water erosion of soils in the more humid margins of deserts is an important source of sediment for dust storms in semi-arid areas (McTainsh et al., 1992). On a smaller scale, the processes of wind and water erosion control crust formation and the dynamics of the fine particles. Under the influence of water, specific crusts that mitigate wind erosion are formed. Cultivated fields are the source of fine particles that will be eroded by wind and deposited elsewhere, where they result in more crust development and, in turn, in more runoff and erosion. So, the interaction between wind and water erosion plays an important role in fertility management in traditional agrosystems (Rajot and Valentin, 2001; Visser, 2004). The interaction between wind and water erosion also affects mass transport. Though wind is a factor that has important roles in water erosion processes, very few studies have been done on the effect of wind on raindrops and overflow characteristics (Erpul et al., 2004). In wind-driven rains, the wind velocity and direction are expected to affect not only the energy input of the rains, but also the shallow flow hydraulics, because impacting raindrops induce changes in micro relief. Significant aspects of the erosion processes in situations where wind and rain occur simultaneously are still imperfectly understood. In his wind tunnel study, Comelis (2002) showed that the particles transported due to wind-driven rain traveled higher and longer than particles saltating in rainless wind. Despite the many differences in the processes of wind and water erosion, there are also many similarities. Air and water are both fluids and thus air behaves in many ways like water. Sediments are detached by the same lift forces and so both fluids have to overcome the same resistances to stress. Sediment transport, whether by wind or by water, is dependent on the transport capacity of the fluid. When the flow is hindered by obstacles, this capacity decreases and selective deposition will occur: the coarser sediment is deposited first, and the finest sediment last. The similarities between the processes result in commonalities in the models describing the processes of wind and water erosion. II Chapter 1 There has been substantial effort in research and development of models of water erosion, and since the 1980s the number of publications on wind erosion has been rising sharply. However, so far the interrelationship between wind and water erosion has not attracted much interest, even though these interactions are an important component of the continuous land degradation in semi-arid environments. Furthermore, despite the clear commonalities, so far there has not been a single model that describes/predicts both the processes of wind and water erosion; neither has there been worldwide collaboration between the experts in the two research fields. To redress this, the idea was bom to bring together Ph.D. students interested in the commonalities between wind and water erosion in a 2-week postgraduate course under supervision of the Wageningen 'Production Ecology and Resource Conservation' Graduate School. The long-standing collaboration between the universities of Ghent and Wageningen made it easy to assemble a team of Dutch and Belgian students. The lecturers from Ghent and Wagenmgen were augmented by lecturers from Purdue and Kansas State universities. One week of the course was in Ghent and one in Wageningen. The students contributed their recent research experience in the form of case studies, and the lecturers contributed results from previous projects. The course was so successful that at its conclusion it was decided to combine all the experience and ideas into this special 50* TRMP publication. The book starts with a discussion in chapter 2 on the commonalities of WEPP and WEPS, two physically based models on water and wind respectively, developed in the USA. Their applicability outside the USA is discussed in chapter 3 and the possibilities for upscaling field-scale models to the region scale are described in chapter 4. Chapters 5 through 9 highlight the various aspects of the interrelationship between wind and water. How African farmers recognize the presence of wind and water erosion is described in chapter 10. Chapter 11 discusses the various techniques for measuring wind and water erosion separately, and chapter 12 describes the use of a wind tunnel to investigate water and wind interaction.
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