Effects of damming on the sosiani river ecosystem: An environmental impact assessment

Abstract

The aim of this study was to analyze the changes in vegetation mosaic and patterns arising from the construction of the Two River Dam found West of Eldoret Town. To accomplish this, it was necessary to study the behaviour of similar species (indicator species) both at the dam and below it. Since the two study areas were within the same agro-ecological zone, the major determining variable in the study was thus the water quantity and quality. The water quality aspect was determined by the quality of industrial effluents discharged into the river after treatment by the two treatment plants (Quarry sewage treatment works and the Eldoret west sewage treatment works) in the town, and the stipulated dilution water as set by the Kenya Bureau of Standards. Agro-chemicals were also considered as chemicals that can affect plants growth. During the study it was found out that the stipulated dilution water from the dam of 5,750 M3/day was not met. Also the two treatment works were inefficient such that the water returned into the river was polluted above the set standards' The riparian vegetation below the dam was exposed to water stress qualitatively and quantitatively. At the dam the vegetation was exposed to all year round high water levels that was relatively unpolluted. The indicator species (Pennisetum clandestinum, Acacia nilotica and Carissa edulis) exhibited in the two study zones significant variations in certain aspects especially biomass and similar characteristics in other observable variables especially height of plants, leaf area index, cover and composition. Explanations were thus adduced to verify the observations and this tallied with other researches done previously (Odingo 1979, Mwendwa 198'4, Karr 1978) though in other areas, The plants were found to have