Publication: Effects of Land Use/Land Cover Change and Rainfall Variability on Hydrological Characteristics of River Ruiru Watershed, Kiambu County, Kenya
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2021-11
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Abstract
Watersheds and their water resources are highly vulnerable to land use/land cover changes and
seasonal rainfall variability as they directly influence basin hydrological characteristics in terms
of water quantity and quality. This study assessed the effects of land use/land cover change and
rainfall variability on hydrological characteristics of River Ruiru watershed in Kiambu County.
The study integrated the use of remote sensing, Geographic Information System (GIS), water
quality sampling, hydrological modelling and statistical methods to collect and analyse the
collected data. Results of land use/land cover change analysis indicated that built-up areas,
annual crops and perennial crops (tea and coffee) increased by 3.068%, 35.848% and 11.493%
respectively between 1976 and 2017. However, it was observed that perennial crops increased
gradually between 1976 and 1995 but declined by 1.94% between 1995 and 2017. Grassland,
shrubland and forestland declined by 7.48%, 13.25% and 29.79% respectively between 1976 and
2017. Consequently, Soil and Water Assessment Tool (SWAT) model simulation results
indicated that the land use/land cover changes that occurred in River Ruiru watershed between
1984 and 2017 had effects on the quantity of river discharge and water quality for drinking
purposes. Surface runoff (SURQ), lateral flow (LATQ) and groundwater contribution to
discharge (GWQ) increased from 30.25mm/yr, 8.48mm/yr and 9.95mm/yr to 181.25mm/yr,
11.44mm/yr and 10.66mm/yr respectively. Moreover, the nitrates in surface runoff (NO3SURQ),
nitrates in lateral runoff (NO3LATQ), Organic Nitrogen (N.ORG) and Organic Phosphorus
(P.ORG) increased from 0.05kgN/ha/yr, 0.06kgN/ha/yr, 5.77kgN/ha/yr and 0.87kgP/ha/yr to
1.47kgN/ha/yr, 0.19kgN/ha/yr, 70.60kgN/ha/yr and 8.86kgP/ha/yr respectively. In additions,
findings from the study indicated that temporal rainfall variability had effects on the quantity of
river discharge and water quality of River Ruiru. Based on regression analysis, the correlation
between the observed and predicted value of dependent variable indicated an association of
R=0.972 between temporal rainfall variability and quantity of river discharge hence showing a
strong positive linear relationship. Similarly, Pearson’s correlation analysis results showed that
temporal rainfall variability was strongly and positively correlated to NO3, N.ORG and P.ORG
with R=.695, p<.001; R=.781, p<.001 and R=-.780, p<.001. Furthermore, results from a paired
sample t-test indicated that pH, turbidity, Dissolved Oxygen (DO), electrical conductivity and
Total Dissolved Solids (TDS) had higher mean during wet season (M=8.40, M=79.00, M=51.20,
M=87.00 and M=54.20) than in dry season (M=6.80, M=11.60, M=43.40, M=73.00, and
M=45.40). The difference for these water quality parameters between dry and wet seasons was
significant (P=0.003, P=0.034, P=0.005, P=0.013 and P=0.014). Moreover, findings from the
study indicated that DO, TDS, electrical conductivity, total phosphorus and total nitrogen values
were within World Health Organization (WHO) and National Environment Management
Authority (NEMA) recommended values. However, the results for the total coliforms and E. coli
indicated that River Ruiru was severely polluted with faecal organisms. In conclusion, land use
and land cover changes and temporal rainfall variability have affected the quantity of river
discharge and water quality in River Ruiru watershed. As such, remedial actions to address the
hydrological effects of land use/land cover change and temporal rainfall variability both by
national and county governments are required.
Description
A Thesis Submitted in Fulfilment of the Requirements for the Award of the Degree of Doctor of Philosophy (Hydrology and Water Resources Management) in the School of Pure and Applied Sciences of Kenyatta University, November, 2021
Keywords
FORESTRY, AGRICULTURAL SCIENCES and LANDSCAPE PLANNING::Landscape planning::Nature conservation and landscape management