IMPACT OF RIPARIAN ZONE DEGRADATION ON FLOOD OCCURRENCE AND MANAGEMENT IN THE NAIROBI RIVER BASIN, NAIROBI CITY COUNTY, KENYA

Abstract

The Nairobi River basin riparian zone is critical to the ecological and hydrological stability of Nairobi City County, Kenya. However, growing urbanisation, pollution, and deforestation have reduced its ability to manage floods. The degradation of the riparian zone has increased the frequency and severity of flooding in the city, demanding a thorough investigation into the role of the Nairobi River basin riparian zone in flood management. This study sought to assess the degradation of the riparian zone over 30 years (1991-2021), determine the relationship between degradation and flood occurrences, and recommend long-term mitigation solutions. The hydrological cycle theory, which elucidated how alterations in land use and climate patterns disrupted natural water flow dynamics, exacerbating flood risks, guided the research. A correlational research design was applied in the study. A sample size of 373 individuals was chosen, comprising government officials, NGOs, and local inhabitants, using simple random and selective sampling methods. Data collection tools included surveys, interviews, GIS, and remote sensing technology. Inferential statistics were employed to identify correlations and significance levels, with data analysis conducted using SPSS version 25. The Nairobi River basin riparian zone has deteriorated significantly during the past 30 years, with the built-up area expanding from 80.2 km² in 1991 to 275.5 km² in 2021, mostly due to urbanisation and encroachment. The study found a significant positive connection (r = 0.72, p < 0.05) between riparian vegetation degradation and the frequency of floods. 52% of respondents reported annual floods, and 37% reported biannual floods. Deforestation, pollution, and unregulated construction activities significantly influenced flood occurrences (p < 0.01). Reforestation, riparian buffer zones, and improved waste management are key sustainable mitigation techniques that significantly lower flood risks (p < 0.05), according to regression analysis. Community engagement and policy enforcement were also cited as crucial to successful implementation. To conclude, the degradation of the Nairobi River basin riparian zone is significantly linked to rising flooding. The report suggests that Nairobi City County undertake stringent riparian zone management methods, like as afforestation and buffer zone enforcement, as well as include flood mitigation strategies into urban design frameworks.