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Kenyan citizens living in the lower reaches of River Galana have been suffering from river channel migration and bankline erosion. Lower River Galana reaches could be one of the most complicated areas in terms of channel migration. The river had undergone many channel changes in the especially in the reaches since 1992. It is mainly formed by alluvial deposits, facing riverbank erosion very frequently due to unvarying alteration of river channels. This study aimed at computing the actual shifting along River Galana within Malindi Sub-County for a period of 26years (1992-2018). Time series analysis of river channels extracted from five Landsat images (1992, 1999, 2005, 2013 and 2018) clearly showed that the river channel is under active channel migration and bank line erosion. These activities have been categorized as the main characteristics of River Galana for the study period. They are issues that need urgent measures as they have severe economic and social impacts such as loss of fertile lands (hence low production), settlement displacement and poor infrastructure. The occurrence of channel migration in the area is dependent on various factors such as; bank material, geological factors, topological slope, soil factors among others. Based on the spatial analysis of the considered factors in the research, a migration hotspot zone map was produced which describes the segregation of relative probability of future channel migration and the infrastructure in danger. The impacts analysis showed that many peoples living in the area (section A and section B specifically) have been affected in varying ranges and to some extent, an evacuation was so crucial. The results show that from 1992 to 2018 the highest migration towards south took place at cross section 9 (CS9) (1013.919m) and at CS5 (577.332m) towards north on section A, whereas on section B it was at CS10 (2017.635m) towards south and at CS15 (1008.363) towards north and an ox-bow lake was formed. The total amount of; bank erosion is 642.83ha of land at a rate of 24.72ha a-1 and deposition is 629.59ha of land at a rate of 24.22ha a-1. A channel migration hotspot map showing the areas that are most vulnerable to the areas that are stable. Impacts analysis shows that almost 78% of the respondents are suffering from the River Galana channel migration.
Future studies on impacts of the channel migration in the area can be done using high-resolution data addressing the specific land use and land cover that are affected while providing possible measures of controlling this catastrophe. |
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