Suitability of SWAT Model for Sediment Yields Modelling in the Eastern Africa - Advances in Data, Methods, Models and Their Applications in Geoscience - page 279

approaches, , i.e ., field observations and analysis of field-based sediment flow data. It was
observed that the SWAT model could not capture the dynamics of sediment load delivery in
some seasons to the catchment outlet (Ndomba et al ., 2008b). The reach is known to
transport most of the sediment loads delivered from the catchment ( i.e . equilibrium river
reach). The particular study linked the latter problem to model deficiency. The authors
would like to note that it is difficult to compare the model performance objectively as the
quality and quantity of data used are different. Notwithstanding, there is a general
agreement on the performance based on the cumulative sediment yield amount as measured
by a relative error below 20 percent for both (Table 4). It could also be observed that the
catchment size and climate are relatively similar. However, there are differences in
catchment characteristics, i.e . geology, soils type, and topography.

Study cases

Variables Performance indicators Time step

KRC NYM SRC

Daily 68 54.6 38

Calibration, CE (%)

Monthly - 65 82

Runoff Daily 63 68 30

Validation, CE (%)

Monthly - 77.4 81

IVF (%) - 100 104

Daily 66 56 24

Calibration, CE (%\)

Monthly - 83

Sediment
yield rate

Daily 68 - 16

Validation, CE (%)

Monthly - - 80

Relative Error, (RE) (%) 7.5 2.6 0.76

Table 4. SWAT model performance for the 3 study cases, i.e., KRC, NYM and SRC
Note: “-“ not evaluated as a result of missing data .

From the engineering perspective, sediment yield information is critical to estimating the
design life of a reservoir as a result of sedimentation. A lumped spatial and temporal scales
model could serve this purpose. However, if further insights into erosion processes and
sediment sources are sought then finer temporal and spatial scales are important, e.g. , to
evaluate best management practices, effects of land use and effects of land cover change.
Besides, as the overall objective of this paper is to critically assess the suitability of the
SWAT model for sediment yield modeling, various components and/or functionalities were
evaluated. As presented earlier in this chapter, the SWAT model predicted satisfactorily the
cumulative long-term sediment catchment yield, and the performance was measured using
Relative Error (RE) in percent.
The performances of the SWAT model in the study cases and others conducted in
catchments of the Eastern Africa as reported in literatures based on CE and IVF and Relative