Impact of land use changes on soil erosion and sedimentation in the Tono Reservoir Watershed using Geowepp Model
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Date
2015-03-02
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Abstract
Sediment delivery from the Tono watershed in the Upper East Region of Ghana is a
major concern in determining the rate of siltation of the Tono Reservoir. As part of a
broader effort to develop a sediment budget for the Tono Reservoir, this study
determined the current volume of silt in the reservoir through bathymetric survey,
mapped land cover changes by maximum likelihood supervised classification of
Landsat images acquired for 1991, 2005 and 2013 and used a process-based watershed
hydrology and upland erosion model, Water Erosion Prediction Project (WEPP), to
simulate hydrology and sediment dynamics for three land-use/land-cover scenarios.
The Geo-spatial interface for WEPP (GeoWEPP) was used to characterize upland
overland flow elements based on their land use/land cover, soil, and slope profiles. A
significant land cover change was observed as shrub land had decreased by 8%, bare-land area had increased by 9.1%, and the Reservoir area had also decreased by 3.7%.
Using characteristics obtained from GeoWEPP as inputs for the WEPP model runoff
fluxes, soil loss rates, and sediment delivery ratio (SDR) for three environmental
scenarios: land-use/land-cover with agricultural lands under fallow tilled management
(Scenario 1), land-use/land-cover with agricultural lands under corn, soybean no till
management (Scenario 2), land-use/land-cover with non-agricultural lands under
shrub-perennial (Scenario 3) were estimated. Over the simulated 29-year period;
runoff depth, soil loss rate and SDR were estimated to be 118.4mm, 22.8 t/ha, and 0.68
for Scenario 1; 94.6mm, 2.8 t/ha, and 0.31 for Scenario 2; and 57.7mm, 0.6t/ha, and
0.92 for Scenario 3. The volume of silt since 1991 to 2013 from the bathymetric results
was 1.62 X 10
5
m
3
of silt per year. This is about 1.74% reduction in reservoir capacity
on annual basis.
Description
A thesis submitted to the Department of Agricultural Engineering,
Kwame Nkrumah University of Science and Technology
in partial fulfillment of the requirements for the degree of
Master of Science in Soil and Water Engineering, 2014
Keywords
GeoWEPP, bathymetry, reservoir, land use change, sediments