| dc.description.abstract | The Lake Victoria Basin is facing major ecological challenges that have caused considerable hardship for the population depending on it for their livelihoods and have also reduced the biodiversity of the lake’s flora and fauna. According to ICRAF (2000), more than 80% of the population in the basin is engaged in agricultural production. Deforestation coupled with bad agricultural practices has persistently exacerbated the problem of land degradation in the basin and sedimentation in the lake. As a result, land degradation in prime agricultural areas within the catchments has been attributed to food productivity losses. Assessment on land degradation hazard is therefore deemed essential for soil conservation plans in the basin for sustainable development.
The objective of this study was to identify and map the extent and severity levels of land degradation caused as a result of soil erosion by water in the entire Lake Victoria basin (LVB) in order to support informed decisions for prioritizing and combating land degradation menace in the basin. This study achieved this by fusing geospatial techniques and empirical soil erosion modelling techniques mainly the Revised Universal Soil Loss Equation (RUSLE) Model that looked at five key soil erosion control parameters: vegetation cover, rainfall erosivity, slope factor, soil erodibility and population density data as input variables. The results from modelling were subjected to field assessment in one of the identified hot spots in Bolo area in Kisumu County to gather prove of existence of land degradation hazard.
The output of this study was a land degradation index map which was categorised into five quantile of land degradation severity that is: very low, low, medium, high and very high. This made it easy to visualise major land degradation hot spots which were defined by the very high class as well as overall spatial variability of land degradation severities in the basin’s context. The finding from analysis of results reviled that majority of the basin is experiencing moderate soil erosion but this is shifting towards high.
Major erosion hotspots were found to be areas surrounding the lake namely: areas around Mumias, Bunyore, Kisumu, Kendu Bay, Ahero and south western parts of Homa Bay. The study further noted that the areas experiencing very low degradation were forested areas in the northern parts and towards the eastern sides of the basin. These are areas occupied by the Mount Elgon forests, Kapsabet forest and parts of the Mau forests in Kericho all of which are reserved natural forests.
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This study revealed that the lead contributing factor to soil erosion in the basin and around the identified hotspots was soil erodibility component followed by rainfall erosivity, vegetation cover management, population density and finally slope factor. This contradicted with soil experts rating which ranked slope factor as the main contributor, followed by vegetation cover, soil erodibility, rainfall erosivity and finally population density. Low gravel content of less than 1% was found to influence highly the soil erodibility component as the soils are exposed to easy detachment. High rainfall intensity and depth in the hotspots areas was also a major factor to soil erosion. The other contributing factors were found to be unsustainable agricultural practice in the basin which continually disturbed vegetation cover exposing the top soils to erosion agents.
In conclusion this study acknowledges that the use of the empirical model (Revised Universal Soil Loss Equation model) for assessing soil erosion by surface runoff and its integration with GIS tools proved useful and effective in assessing land degradation in the entire Lake Victoria basin and in achieving the study’s objectives. The study recommends comprehensive catchment level degradation assessment to be undertaken and prioritise the most affected / hotspot areas (Mumias, Bunyore, Kisumu, Kendu Bay, Ahero and south western parts of Homa Bay). The study further recommends capacity building of different stakeholders involved in land reclamation and management activities in the basin. | en_US |
