Land Use and Land Cover Changes on River Water Quality in Mbagathi Catchment, Nairobi County, Kenya
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Date
2024-10
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Kenyatta University
Abstract
Increase in population, urbanization and industrialization contributes immensely
towards land use and land cover change and decline in water quality in most rivers
such as Mbagathi. This study investigated the significant effect of population growth,
urbanization and industrialization on land use and land cover changes and declining
water quality in rivers, particularly in the case of the Mbagathi River. The main
objective was on determination of the effects of land use and land cover changes on
the quality of water in Mbagathi River catchment from 1990 to 2020. The specific
objectives of the study included (i) determining land use and land cover changes, (ii)
identifying the key drivers of these changes, (iii) determining the levels of selected
water quality parameters, and (iv) determining the effects of land use land cover
changes on water quality. To achieve the first objective, the study employed
classification and analysis of Landsat satellite images of 1990, 2000, 2010, and 2020
using the Google Earth Engine. The second objective was addressed through the
analysis of population and urban development data in relation to the land use and land
cover outputs. The third objective focused on assessment of water quality and was
accomplished by conducting in-situ measurements and laboratory analysis of water
samples collected from the catchment. The fourth objective investigated the link
between land use/land cover and water quality and was achieved through SWAT
modelling using the multi-temporal land use and land cover imagery. The findings of
the classification and analysis process revealed notable changes in land use and land
cover over the study period: a reduction in forest cover from 32% to 14%, a decrease
in grassland from 53% to 30%, an increase in bare ground from 10% to 38%, and an
expansion of urban land cover from 4% to 17%. Key drivers of these changes were
attributed to high population growth, urbanization, inadequate development plans,
proximity to Nairobi town, and land tenure dynamics. The study also observed the
emergence of new settlements around major urban centers like Kiserian, Ongata
Rongai, Ngong, Mlolongo, and Tuala. Analysis within a 3-kilometer radius of these
towns indicated substantial increases in urban areas, reinforcing the influence of
population growth and urban development as primary drivers of land use and land
cover changes in the catchment. Water quality analysis revealed key parameters, with
an average temperature of 20.8°C, a pH of 7.74, an electrical conductivity of 737
μS/cm, total dissolved solids at 371 mg/l, dissolved oxygen at 7.71 mg/l, turbidity at
17.88, total nitrogen at 5.58 mg/l, and total phosphorus at 1.62 mg/l. The study
identified significant differences in water quality among sampling points, particularly
downstream of urban development, which indicated a direct correlation between land
use and land cover changes and water quality. The correlation analysis further
highlighted a strong positive relationship between nitrogen and urban land cover,
demonstrating that as urban land cover increased, so do total nitrogen and total
phosphorus levels. Additionally, an association between bare ground, surface flow,
and sediment yield underscored that increased bare ground contributed to greater
surface flow and sediment yield. Further analysis revealed a strong and positive
significant (p=<0.05) correlation between bare ground and surface flow and sediment
yield. Overall, this study confirmed that land use and land cover changes have a
substantial and adverse impact on water quality in the Mbagathi River, necessitating
comprehensive management strategies to mitigate the effects and support the
achievement of Sustainable Development Goal 6 on water availability and quality.
Description
Supervisors
1. Mary Makokha
2.. Kennedy Obiero
A Thesis Submitted in Partial Fulfilment of the Requirements for the Award of the Degree of Master of Science (Hydrology and Water Resources) in the School of Pure and Applied Sciences, Kenyatta University October, 2024