| dc.description.abstract | Flooding continues to be a common environmental hazard in both developed and developing countries. River Nzoia experiences perennial flooding in its lower reaches especially in Budalangi area of Busia county. The mean annual discharge of the River Nzoia is estimated at 1777Mm3 /year. From a physiographic and land use point of view the basin has four distinct zones: a mountain zone, plateau zone, transition zone and lowland zone. The mountain zone is forested but suffers severe land degradation; the plateau zone is the major farming zone. Small scale farming continues in the transition and flood prone lowland areas. The flood prone area is generally flat and swampy. There are two rainfall peaks in the catchment; the first peak comes in the months of April to June, while the other occurs in July to September. Comparatively to other parts in Kenya, the basin receives high rainfalls, whose average annual values vary between 1,000 to 1,500 mm. Several studies (JICA, 1987; JICA, 1992; APFM, 2004; ADCL, 2006) have been carried out in Nzoia basin with a view to characterizing the basin on the basis of climatic data and land use information but none has incorporated landform parameters because geomorphologic studies have not been attempted. River morphometric information is very important in any undertaking to control incidence of flooding in an area. In Kenya Few studies have been carried out on River morphometrics in relation to flooding. This study therefore seeks to analyze the characteristics of River Nzoia basin and how they contribute to flooding of Budalang’i flood plains. The study was guided by the following specific objectives; to examine the drainage basin morphometrics characteristics of the River Nzoia, to determine the influence of rainfall intensity and duration on flooding in Budalang’i flood plains and to assess approaches of managing floods in Budalang’i flood plains. Descriptive research design was used for the study. The target population in this study was drawn from two components of the unit of analysis, namely the geophysical (River Nzoia basin) and the social (households). Simple random sampling technique was used to sample the respondents for the study. A sample size of 71 respondents was sampled from the locations along River Nzoia in Budalang’i flood plains. Interviews and observation were used as methods of data collection. Qualitative data analysis techniques were used to analyze the data where thematic and content analysis was carried out based on the study objectives. The major datasets that were used for this study include Landsat Satellite Imageries, Digital Elevation Data (DEM) and Auxiliary data that included Roads, administrative boundaries, ground truth data for land use land cover classes and topographic map of the area. The study found out that high volumes in upper catchment areas during heavy rains of long rain seasons are at higher velocity due to sudden change of river gradient. This result in higher volumes received at the lower catchment areas known as flood plains (in-flow) against that volume expected to be released to the lake (out flow). This volume difference causes the river to break its normal banks in the lower zones. Land use land cover analysis between 1986-2018 shows that there is an increase in size of the bare ground area which is an indication of wetland degradation and a consequent replacement of wetland vegetation with bare soil that is prone to erosion. Increased farming activities along the Nzoia River has resulted to deforestation in search of cultivation areas increasing the vulnerability of the area to flooding. The rapid expansion of urban centres in the lower parts of the catchment (Rwambwa, Kakamega, and Bungoma) can be said to be a major contributing factor to the annual devastating floods. Based on River morphometry, the study concluded that there is no consistent relationship between relief ratio and basin order in this basin due to high variance in relief on the divide line. However, high relief ratios of above 0.03 are observed as characteristics of upland sub-basins and low value of about 0.01 for sub-basins at the lowlands. This change has explained the flooding phenomena at the lowlands. The computation of bifurcation ratio shows that the values ranged
from 1.5 and 3.4 which are within Strahler’s range. The average value of Bifurcation ratio is 2.2 which is closer to the lower value of 2. Based on bifurcation ratio, River Nzoia basin flows may encounter delayed time to peak and this is a good characteristic for planning and conveying flood forecasts. The drainage pattern of this basin can be classified as fern-shape. This presents a lower concentration time, and it generates higher flow. The major flooding risks that were identified during the study include; Displacement of households, Damage to Farmlands, Damage to Bridges and Roads, Disruption of learning programmes, Economic and Environmental aspects. Approaches to flood management will include both Community non-structural measures and Structural measures for flood control. The study recommends that there is need to undertake further research in land-use land cover changes, river morphometrics and review of the existing flood control and /or mitigation measures | en_US |
