Assessment of Land Cover Changes in the Micro-Catchments of the Nyando River Basin within the Lake Victoria Basin, Kenya

Abstract

The Nyando and Awach river catchments serve as vital headwaters draining into the Winam Gulf of Lake Victoria, an ecosystem increasingly threatened by sediment and nutrient loading. Despite its crucial role in regional hydrological stability, this region has undergone immense, largely unregulated anthropogenic pressure, leading to suspected widespread environmental degradation. The lack of long-term spatial data on the nature and level of land cover conversion constitutes a major barrier to formulating effective conservation strategies. To address this gap, this study quantified the extent, magnitude, and spatial dynamics of Land Cover Change (LCC) to assess the actual scale of environmental degradation. LCC was quantified through a time-series analysis of LANDSAT TM/ETM satellite imagery (1995, 2000, 2006, and 2012). A comparative micro-catchment classification (Uninterfered, Interfered, and Intervened sites) provided the environmental sampling framework. Images were processed using a Hybrid Supervised Classification approach to delineate four key thematic classes: Vegetation, Built-up Land, Water, and Open Land. Change detection matrices were then generated to calculate the absolute change, rate of change and conversion pathways. The results revealed significant vegetation decline in the Nyando catchment, characterized by a net loss of 54.2% of vegetative cover over the 17-year period. This loss corresponded with a marked increase in Open Land (≈41.5%) and Built-up Area (≈14.3%). The dominant conversion pathway, accounting for approximately 40.9% of all change, was the direct transformation of Vegetation to Open Land, signifying widespread, non-conservative agricultural expansion in the highlands. However, the Awach catchments registered comparatively lower net change, largely due to the replacement of indigenous forests with commercial plantations, which concealed ongoing ecological degradation. The significant expansion of exposed Open Land critically increases the risk of soil erosion and intensifies runoff, posing a serious threat to the hydrological stability of the basin and contributing to sediment loading in Lake Victoria. Urgent policy interventions focused on mandating soil conservation practices, regulating settlement expansion and immediate rehabilitation of riparian zones are necessary to reverse these detrimental trends and ensure the sustainable use of basin resources.