IJG  Vol.6 No.9 , September 2015
Validation of GLASOD Map for Sediment Sources and Erosion Processes Identification in the Nyumba Ya Mungu Reservoir Catchment
The main objective of this paper is to report on the preliminary validation results of the Global Assessment of Soil Degradation (GLASOD) as a tool for mapping sediment sources in Tanzania. This study was carried out in a well studied catchment, the Nyumba Ya Mungu (NYM) reservoir catchment located in the upstream of Pangani River Sub-basin. Previous studies in the same catchment used quantitative approach that entailed comprehensive sediment sampling programme and numerical modelling to identify sediment sources and erosion processes. Although previous researchers’ findings were satisfactory, the methods used were demanding in terms of resources (time, funding, and personnel) and impractical to a large ungauged catchment. The quest to validate GLASOD map is evident as it was qualitatively developed through collating expert judgments of many soil scientists to produce a world map of human-induced soil degradation at a scale 1:10,000,000. In the current study sediment sources mapped from qualitative method (GLASOD) plus supplement field visit observations and quantitative approaches are compared and discussed in detail. Preliminary results suggest that the paired information on sediment sources, field based data versus GLASOD, for upper catchments or upland locations are more strongly correlated than lower reaches. The results of this study have further emphasized the fact that GLASOD map is satisfactory to depict large regional differences in soil degradation but it is not capable of explaining local degradation. Besides, GLASOD map does not capture erosion processes dynamics compared to comprehensive sediment sampling programme. Notwithstanding, GLASOD map might be a useful tool for sediment sources and erosion processes identification scoping studies in the study area. Based on this study, it is therefore recommended to complement the GLASOD map with field based data for detailed study initiatives.

Cite this paper
Ndomba, P. (2015) Validation of GLASOD Map for Sediment Sources and Erosion Processes Identification in the Nyumba Ya Mungu Reservoir Catchment. International Journal of Geosciences, 6, 972-986. doi: 10.4236/ijg.2015.69077.
[1]   Sonneveld, B.G.J.S. and Dent, D.L. (2009) How Good Is GLASOD? Journal of Environmental Management, 90, 274-283. http://dx.doi.org/10.1016/j.jenvman.2007.09.008

[2]   Ndomba, P.M., Mtalo, F. and Killingtveit, A. (2007) A Proposed Approach of Sediment Sources and Erosion Processes Identification at Large Catchments. Journal of Urban and Environmental Engineering, 1, 79-86. http://dx.doi.org/10.4090/juee.2007.v1n2.079086

[3]   Ndomba, P.M. (2010). Modeling of Sedimentation Upstream of Nyumba ya Mungu Reservoir in Pangani River Basin. Nile Basin Water Science and Engineering, 3, 25-38.

[4]   Mohammadi, T.A. (2011) Proposing a Model for Preparation of the Soil-water Erosion Types’ Maps. Scientific Research and Essays, 6, 3139-3147.

[5]   Oldeman, L.R., Hakkeling, R.A. and Sombroek, W.G. (1991) Global Assessment of Soil Degradation (GLASOD): World Map of the Status of Human-Induced Soil Degradation. United Nations Environment Programme, International Soil Reference and Information Centre, Nairobi.

[6]   Peart, M.R. and Walling, D.E. (1988) Techniques for Establishing Suspended Sediment Sources in Two Drainage Basins in Devon, UK: A Comparative Assessment. Sediment Budgets, Proceedings of the Porto Alegre Symposium, December 1988, IAHS Publ. No. 174, 269-279.

[7]   Minella, J. P. G., Merten, G. H., and Clarke, R.T. (2004) Identification of Sediment Sources in a Small Rural Drainage Basin. Sediment Transfer through the Fluvial System, Proceedings of a Symposium held in Moscow, August 2004, IAHS Publ. 288, 44-51.

[8]   Yanda, P. Z. (1995) Temporal and Spatial Variations of Soil Degradation in Mwisanga Catchment, Kondoa, Tanzania. PhD Dissertation Series No. 4, Department of Physical Geography, Stockholm University, Stockholm, 136.

[9]   Williams, G.P. (1989) Sediment Concentrations versus Water Discharge during Single Hydrologic Events in Rivers. Journal of Hydrology, 111, 89-106. http://dx.doi.org/10.1016/0022-1694(89)90254-0

[10]   Ndomba, P.M. (2007) Modelling of Erosion Processes and Reservoir Sedimentation Upstream of Nyumba Ya Mungu Reservoir in the Pangani River Basin. PhD Thesis in Water Resources Engineering, University of Dar es Salaam, Dar es Salaam.

[11]   Ndomba, P.M. (2013) Validation of PSIAC Model for Sediment Yields Estimation in Ungauged Catchments of Tanzania. International Journal of Geosciences, 4, 1101-1115.

[12]   Molina, A. (2009) A Report on Soil Erosion Processes in the Nile Basin. Consultancy within the Framework of the Nile/FRIEND Project Supported by United Nations Educational, Scientific and Cultural Organization (UNESCO).

[13]   ISRIC, The International Soil Reference and Information Centre (2014) Global Assessment of Human-Induced Soil Degradation. ISRIC-World Soil Information.

[14]   StatSoft, Inc. (2014) Electronic Statistics Textbook (Electronic Version). StatSoft, Tulsa.

[15]   Arnold, J.G., Williams, J.R. and Maidment, D.R. (1995) Continuous-Time Water and Sediment-Routing Model for Large Basins. Journal of Hydrology Engineering, 121, 171-183.

[16]   Wischmeier, W.H. and Smith, D.D. (1965) Predicting Rainfall-Erosion Losses from Cropland East of the Rocky Mountains, Agriculture Handbook, 282. US Department of Agriculture, Agriculture Research Service, Washington DC.

[17]   Williams, J.R. (1975) Sediment-Yield Prediction with Universal Equation Using Runoff Energy Factor. In: Present and Prospective Technology for Predicting Sediment Yield and Sources, US Department of Agriculture, Agriculture Research Service, Washington DC, 244-252.

[18]   Bagnold, R.A. (1977) Bed Load Transport in Natural Rivers. Water Resources Research, 13, 303-312. http://dx.doi.org/10.1029/WR013i002p00303

[19]   Mulengera, M.K. and Payton, R.W. (1999) Estimating the USLE-Soil Erodibility in Developing Tropical Countries. Tropical Agriculture (Trinidad), 76, 17-22.

[20]   Pacific Southwest Inter Agency Committee (PSIAC) (1968) Factors Affecting Sediment Yield in the Pacific Southwest Area and Selection and Evaluation of Measures for Reduction of Erosion and Sediment Yield. Water Management Subcommitte on American Society of Civil Engineers (ASCE), Report No. HY 12.

[21]   Alder, H.L. and Roessler, E.B. (1972) Introduction to Probability and Statistics. Fifth Edition. W. H. Freeman and Company, New York, 373 p.

[22]   Santhi, C.G., Arnold, J.R., Dugas, W.A., Srinivasan, R. and Hauck, L.M. (2001) Validation of the SWAT Model on a Large River Basin with Point and Nonpoint Sources. Journal of America Water Resources Association, 37, 1169-1188. http://dx.doi.org/10.1111/j.1752-1688.2001.tb03630.x