TITLE:
Validation of GLASOD Map for Sediment Sources and Erosion Processes Identification in the Nyumba Ya Mungu Reservoir Catchment
AUTHORS:
Preksedis Marco Ndomba
KEYWORDS:
GLASOD, Erosion Processes, Sediment Sources, Soil Degradation, Validation
JOURNAL NAME:
International Journal of Geosciences,
Vol.6 No.9,
September
16,
2015
ABSTRACT: 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.