The Impact of Mega Infrastructure on the Hydrology of Ruiru and Kamiti Rivers

Abstract

Like many other developing nations in Africa, Kenya has seen a significant rise in urbanization. Numerous cities and towns have seen population growth as well as spatial expansion, resulting in enormous metropolitan areas. Metropolitan areas have provided tremendous prospects for growth. Numerous issues and difficulties have been brought on by the fast urbanization in the economic, social, and environmental spheres. One such metropolis in Kenya is Ruiru. Therefore, the goal of this research was to examine how mega infrastructure has affected the hydrology of the Ruiru and Kamiti rivers. Four catchment regions were included in the study area, and they were chosen based on the availability of hydrological data from Water Resources Authority, which was acquired from their offices in Nairobi and Kiambu. On the basis of the Shuttle Radar Topography Mission void filled Digital Elevation Model, the catchment extent was subsequently defined by river gauging station 3BB12 on River Kamiti and delimited using the river gauging station as the catchment outlet. Data sets utilized in the study were Landsat images, google earth images, river flow data, river abstraction records, water production data and rainfall data. Various GIS methods employed to analyze the data included normalized difference built up index, hydrological characterization using the threshold method, change detection, and GIS software. The study period's rainfall data revealed a very slight trend over time. Rainfall did not modify the river flow regime, as evidenced by comparisons to flows that decreased over time. For the time period under research, the supervised classification built up index for the study area increased from 2.8% to 51.8%. However, average flows over this time decreased from 2.2 m3/s to 0.53 m3/s. This demonstrated that altering land use had a discernible impact on river flow regime. It would not have been accurate to draw the conclusion that mega projects had a different impact from "regular" urban growth. This is due to the flow duration curves for the several eras (1958–1987, 1988–2000, 2005–2010, and 2011–2016) displaying a pattern that was consistent throughout, with no aberrant alterations noted in the 10–15 years prior (period of mega projects).