Suitability of SWAT Model for Sediment Yields Modelling in the Eastern Africa - Advances in Data, Methods, Models and Their Applications in Geoscience - page 261

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Suitability of SWAT Model for
Sediment Yields Modelling
in the Eastern Africa
Preksedis Marco Ndomba 1 and Ann van Griensven 2
1 University of Dar es Salaam, Dar es Salaam,
2 UNESCO-IHE, Institute for Water Education, Delft,
1 Tanzania
2 Netherlands
1. Introduction
Sediment yield refers to the amount of sediment exported by a basin over a period of time,
which is also the amount that will enter a reservoir located at the downstream limit of the
basin (Morris and Fan, 1998). The subject of sediment yield modelling has attracted the
attention of many scientists but lack of data, resources and widely accepted methods to
predict/estimate sediment yields are some of the barriers against this direction of research
(Summer et al ., 1992; Wasson 2002; Lawrence et al. , 2004; Ndomba, 2007; Ndomba et al ., 2005,
2008b, 2009; Shimelis et al ., 2010).
The sediment yield model evaluated in this paper is the Soil and Water Assessment Tool
(SWAT). It is hypothesized in the presented study cases that distributed and process based
mathematical models such as SWAT could be a potential tool in predicting and estimating
sediment yield especially at a catchment scale. Application of the distributed and process-
based models could minimize the uncertainty resulting from assuming lumped, stationary and
linear systems. Besides, the SWAT model has particular advantages for the study of basin
change impacts and applications to basins with limited records (Bathurst, 2002; Ndomba,
2007). In principle, their parameters have a physical meaning and can be measured in the field,
and therefore model validation can be concluded on the basis of a short field survey and a
short time series of meteorological and hydrological data (Bathurst, 2002).
SWAT was originally developed by the United States Department of Agriculture (USDA) to
predict the impact of land management practices on water, sediment and agricultural
chemical yields in large ungauged basins (Arnold et al ., 1995). The SWAT model has a long
modelling history since it incorporates features of several Agriculture Research Service
(ARS) models (Neitsch et al ., 2005). The SWAT model is a catchment-scale continuous time
model that operates on a daily time step with up to monthly/annual output frequency. The
major components of the model include weather, hydrology, erosion, soil temperature, plant
growth, nutrients, pesticides, land management, channel and reservoir routing. It divides a
catchment into subcatchments. Each subcatchment is connected through a stream channel
and further divided into a Hydrologic Response Unit (HRU). The HRU is a unique
combination of a soil and vegetation types within the subcatchment. Sediment yield is
estimated for each HRU with the Modified Universal Soil Loss Equation (MUSLE)
(Williams, 1975) (Equation 1).