Clymans, Wim

Deckers, Jozef

Haile, Mitiku

Heregeweyn, Nigussie

Moeyersons, Jan

Naudts, Jozef

Nyssen, Jan

Poesen, Jean

Vandecasteele, Ine

Ghent University Academic Bibliography

114  22. The sediment budget of May Zeg-zeg catchment and its components  Jan Nyssen1, Wim Clymans2, Jozef Naudts2, Jean Poesen2, Ine Vandecasteele3, Nigussie Haregeweyn4, Jan Moeyersons5, Jozef Deckers2, Mitiku Haile4  1 Department of Geography, Ghent University, Gent, Belgium 2 Department of Earth and Environmental Sciences, K.U.Leuven, Heverlee, Belgium 3 Department of Geology, Ghent University, Gent, Belgium 4 Department of Land Resources Management and Environmental Protection, Mekelle University, Mekelle, Ethiopia 5 Royal Museum of Central Africa, Tervuren, Belgium *Corresponding author. Email: jan.nyssen@ugent.be  An overall approach to assess the effectiveness of soil conservation measures at catchment scale is the comparison of sediment budgets before and after implementation of a catchment management programme. In the May Zeg-zeg catchment (187 ha – Fig. 1) in Tigray, north Ethiopia, integrated catchment management has been implemented since 2004: stone bunds were built in the whole catchment (Fig. 2), vegetation was allowed to regrow on steep slopes and other marginal land (exclosures), stubble grazing abandoned, and check dams built in gullies (Fig. 3; Fig. 4). Land use and management were mapped and analysed for the situation before (2000) and after catchment management (2006) (Fig. 5; Fig 6), whereby attention was also given to the quantification of changes in soil loss due to the abandonment of stubble grazing (Table 1). Sediment yield was also measured at the catchment’s outlet. A combination of decreased soil loss (from 14.3 t ha-1 y-1 in 2000 to 9.0 t ha-1 y-1 in 2006) and increased sediment deposition (from 5.8 to 7.1 t ha-1 y-1) has led to strongly decreased sediment yield (from 8.5 to 1.9 t ha-1 y-1) and sediment delivery ratio (from 0.6 to 0.21). This diachronic comparison of sediment budgets (Fig. 7; Fig. 8) revealed that integrated catchment management is most effective and efficient and is the advisable and desirable way to combat land degradation in Tigray and other tropical mountains.  References Nyssen, J., Clymans, W., Poesen, J., Vandecasteele, I., Nigussie Haregeweyn, Naudts, J., Moeyersons, J., Mitiku Haile, Deckers, J., 2009. How soil conservation affects the catchment sediment budget - a comprehensive study in the north Ethiopian highlands. Earth Surface Processes and Landforms, 34: 1216-1233.  Nyssen, J., Poesen, J., Mitiku Haile, Moeyersons, J., Deckers, J., Hurni, H., 2009. Effects of land use and land cover on sheet and rill erosion rates in the Tigray Highlands, Ethiopia. Zeitschrift für Geomorphologie, 53(2): 171-197. Nyssen, J., Naudts, J., De Geyndt, K., Mitiku Haile, Poesen, J., Moeyersons, J., Deckers, J., 2008. Soils and land use in the Tigray Highlands (Northern Ethiopia).  Land Degradation and Development, 19: 257 - 274. Nyssen, J., Poesen, J., Desta Gebremichael, Vancampenhout, K., D'aes, M., Gebremedhin Yihdego, Govers, G., Leirs, H., Moeyersons, J., Naudts, J., Nigussie Haregeweyn, Mitiku Haile, Deckers, J., 2007. Interdisciplinary on-site evaluation of stone bunds to control soil erosion on cropland in Northern Ethiopia. Soil and Tillage Research, 94: 151-163. Nyssen, J., Poesen, J., Veyret-Picot, M., Moeyersons, J., Mitiku Haile, Deckers, J., Dewit, J., Naudts, J., Kassa Teka, Govers, G., 2006. Assessment of gully erosion rates through interviews 115  and measurements: a case study from Northern Ethiopia. Earth Surface Processes and Landforms, 31(2): 167-185.  Figure 1.  May Zeg-zeg catchment with location of SWC techniques (in 2006) as well as research instrumentation. BW stands for above-ground biomass.   116     Figure 2. Stone bund densities in 2000 (left) and 2006 (right). Position of the 2006 downslope transects for measurement of stone bund density is indicated.   Figure 3. Schematic representation (perspective) of the most common shape of sediment deposition behind check dams in a gully: black dot represents the deepest point, depth (D, m), length (L, m) and width (W, m)   6DWLVch      117   Figure 4. Measured sediment deposition (t) behind check dams in May Zeg-zeg; A, B and C are junctions in the gully system. See Figure 1 for location in the catchment of the gully system with check dams.     B A C 118   Figure 5. Land use maps of MZZ catchment in 2000 and 2006 with photographs of typical land uses in both years.    Figure 6. Relative areas of land use types in 2000 and 2006.  RC68%RA16%EX14%CF1%GR1%HO0.02%Rainfed cropland (RC) Rangeland (RA)Exclosure (EX) Fallow land (CF)Grassland (GR) Housing (HO)WR0.01% CI0.3% HO0.2%GR5%CF0.1%EX22%RA6%RC67%Rainfed cropland (RC) Rangeland (RA)Exclosure (EX) Fallow land (CF)Grassland (GR) Housing (HO)Irrigation fields (CI) Ponds (WR)2000 2006 119  Table 1. Measured mean soil loss rates by sheet and rill erosion (t ha-1 y-1) for each land use category in the MZZ catchment.   MAY ZEGZEG, Tigray, ETHIOPIA187 ha                          2000SOURCES SINKS48%Sheet and rill erosion(cropland) 1277 t y-119%Deposition behind stone bunds20% 503 t y-1Sheet and rill erosion(rangeland)  530 t y-14%Sheet and rill erosion Deposition in exclosures(exclosures) 94 t y-1 311 t y-129% 12%Gully erosion767 t y-110%Deposition in debris fans263 t y-1YIELD(1591 t y-1    8.5 t ha-1 y-1)60% MAY ZEGZEG, Tigray, ETHIOPIA187 ha                          2006SOURCES SINKS66%Sheet and rill erosion(cropland) 1109 t y-150%Deposition behind stone bunds13% 836 t y-1Sheet and rill erosion(rangeland)  212 t y-19%Sheet and rill erosion Deposition in exclosures(exclosures) 149 t y-1 312 t y-112% 19%Gully erosion206 t y-110%Deposition behind check dams170 t y-1YIELD(357 t y-1    1.9 t ha-1 y-1)21% Figure 7. Sediment budgets for MZZ catchment in 2000 (left) and 2006 (right) with computation of sediment sources and sinks. Width of arrows is proportional to sediment masses involved.   120   Figure 8. Sediment budget (sediment production minus sediment deposition = sediment yield) (t ha-1 y-1) for each land unit in 2000 (A) and 2006 (B). Sediment delivery areas (sources) are positive (red) and sediment deposition areas (sinks) are negative (green). (C): changes between 2000 and 2006 with improvements (green) and declines (red), related to decreased sediment input. Gully erosion and deposition behind check dams are not represented.  

The sediment budget of May Zeg-zeg catchment and its components

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The sediment budget of May Zeg-zeg catchment and its components

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