Spatial scale impact on daily surface water and sediment fluxes in Thukela river,South Africa |
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| Institution: | 1. World Agroforestry Centre (ICRAF), West and Central Africa, BP 16317, Yaoundé, Cameroon;2. Dept. Environment, Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (I.N.I.A), Ctra. de A Coruña 7.5, 28040 Madrid, Spain;3. World Agroforestry Centre, West and Central Africa, Sahel Node, BP E 5115, Bamako, Mali;4. World Agroforestry Centre, Nairobi, P.O. BOX 30677-00100, Kenya;1. CSISA-MI Project, CIMMYT, Dhaka, Bangladesh;2. Geographic Information System, International Crop Research Institute for the Semi Arid Tropics (ICRISAT), Patancheru, Hyderabad 502324, India;3. Department of Agricultural Economics and Agribusiness, Louisiana State University, Baton Rouge, LA 70803 – 5604, USA;4. Research Fellow, Social Sciences Division, International Rice Research Institute (IRRI), Philippines;5. Social Sciences Division, International Rice Research Institute (IRRI), Los Baños, Philippines;1. The United Graduate School of Agricultural Sciences, Tottori University, 1390 Hamasaka, Tottori 680-8553, Japan;2. College of Agriculture and Environmental Sciences, Bahir Dar University, P.O. Box 1289, Bahir Dar, Ethiopia;3. Arid Land Research Center, Tottori University, Tottori, Japan;4. International Platform for Dryland Research and Education, Tottori University, Tottori, Japan;5. Center for International Affairs, Tottori University, Tottori, Japan;6. Faculty of Life and Environmental Science, Shimane University, Shimane, Japan;7. Institute for Soil, Climate and Water, Agricultural Research Council, Pretoria, South Africa;8. Faculty of Civil and Water Resource Engineering, Bahir Dar Institute of Technology, Bahir Dar University, Bahir Dar, Ethiopia |
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| Abstract: | The on- and off-site effects of soil erosion in many environments are well known, but there is still limited understanding of the soil loss fluxes in downstream direction due, among other factors, to scarce and poor quality. A four year study to (i) evaluate water and sediment fluxes at different spatio-temporal scales and (ii) interpret the results in terms of processes involved and the controlling factors, was conducted in Thukela basin, South Africa. Five hierarchically nested catchments; namely microcatchment (0.23 km2), subcatchment (1.20 km2), catchment (9.75 km2), sub-basin (253 km2) and basin (29,038 km2), were used in addition to fifteen (1 m2) microplots and ten (10 m2) plots on five locations within the microcatchment. The results showed 19% decrease of unit-area runoff (q) from 3.1 L m?2 day?1 at microplot to 2.5 L m?2 day?1 at plot scale followed by steeper (56%) decrease at microcatchment scale. The q decreased in downstream direction to very low level (q ≤ 0.26 L m?2 day?1). The changes in q were accompanied by initial 1% increase of soil loss (SL) from 18.8 g m?2 day?1 at microplot to 19.1 g m?2 day?1 at plot scale. The SL also decreased sharply (by 39 fold) to 0.50 g m?2 day?1 at microcatchment scale, followed by further decrease in downstream direction. The decrease of q with spatial scale was attributed to infiltration losses, while initial increase of SL signified greater competence of sheet than splash erosion. The decrease of SL beyond the plot scale was attributed to redistribution of the soil on the hillslope and deposition on the stream channel upstream of the microcatchment outlet. Therefore, erosion control strategies focussing on the recovery of vegetation on the slope and stabilisation of gullies are recommended. |
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| Keywords: | Erosion mechanisms Multiple nested catchments Sediment fluxes Water quality |
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