Analysis and modelling of suspended sediment concentration of rivers in catchments experiencing land cover degradation
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Date
October, 2019
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Abstract
Amongst the issues threatening water security and sustainability is the increasing rate of river sedimentation. Variations in catchment sediment yield results from the variations in its controlling factors such as land use/cover characteristics. Thus, it is crucial that this factor is monitored and managed to ensure sustainability of the resource. However, existing models (statistical) have failed to explore the influence of the land use types. Hence, land cover effect and its associated modifications on the variations in suspended sediment concentration have not been empirically quantified, especially for catchment with heterogeneous land cover classes. In view of this, this research answers the question “To what extent does land use/cover characteristics influence the variations in catchment suspended sediment yield?” The following specific objectives were addressed: (1) to assess the trend and extent of land use /cover changes in the Pra River Basin and their driving forces; (2) to assess the variations in suspended sediment yield of the catchment; (3) to determine the sediment generating areas of the catchment and (4) to assess the relative importance of land use types on the variation of suspended sediment yield and to forecast same. Remote sensing and Geographic Information System techniques, field measurement, data collection and laboratory analysis, and statistical techniques such as Analysis of Variance, multiple regression and correlation analysis were employed for the study. Results reveal that between 1986 and 2018, the Pra River basin had suffered severe land cover degradation resulting from anthropogenic influence. Land use conversion occurred generally from closed and open forest to farmlands, settlement and mining. However, the rate, extent and trend of conversions differed significantly across it sub-basins. Sediment yield of the basin is very high ranging between 13.29 and 215.02 tkm-2yr-1, and differs significantly (p < 0.05) with respect to the contributing drainage basins. Erosion map showed that about 21.3% of the basin comes under severe and very severe erosion risk category. Soil erosion rate varied with land use types in a decreasing order from Mining to Settlement, Farmland/grassland, Open forest and Closed forest. Lower Ofin, Anum, Birim, Twifu Praso, Upper Ofin and Oda sub-basins were identified to be susceptible to high erosion. Model accuracy increased from 60.2% to 76.7% when land cover types were included as predictor variable in the suspended sediment concentration model. This indicates that land cover characteristics play a significant role in explaining the variations in catchment suspended sediment yield. The study recommends that immediate conservation measures and policy implementation must be put in place to restore the ecological integrity of the degraded sub-basins. The need to form district ecological or environmental task force involving officials of water, environment and security agents can be useful in handling respective sub-basin’s environmental threats. This will preserve the water resources for sustainable use.
Description
A thesis submitted to the Department of Civil Engineering, Kwame Nkrumah
University of Science and Technology, Kumasi in partial fulfillment of the
requirements for the award degree of Doctor of Philosophy in Water Resources Engineering.
Keywords
Suspended sediment, Degradation, Land cover, Rivers