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Accueil du site → Master → Kenya → 1992 → Soil erosion and its impact on surface water reservoirs a case study of Nguu Tatu catchment north-east of Mombasa district Kenya

University of Nairobi (1992)

Soil erosion and its impact on surface water reservoirs a case study of Nguu Tatu catchment north-east of Mombasa district Kenya

Kitheka, John Utu

Titre : Soil erosion and its impact on surface water reservoirs a case study of Nguu Tatu catchment north-east of Mombasa district Kenya

Auteur : Kitheka, John Utu

Université de soutenance : University of Nairobi

Grade : Master of Science (MS) 1992

Résumé
This is a study on soil erosion and its impact. on small reservoirs located in the Nguu Tatu catchment situated in the northern parts of Mombasa District, Kenya. The main objective of this study is the determination of the types, patterns and rates of# soil erosion within a sub-humid tropical Nguu Tatu Catchment and especially the assessment of the impact of soil erosion on reservoirs water quantity and quality. The methodology applied on this study involved three major approaches namely catchment erosion survey, measurement of water and suspended sediment discharge and finally reservoir sedimentation survey. Catchment soil erosion surveys involved the determination of rates, patterns and magnitude of soil erosion within the catchment by use of hills] ope plot experiments, slope traverses and benchmarks employing the use of erosion nails. Measurement of stream flow and corresponding suspended sediment concentration provided information on sediment discharge. The reservoir sedimentation survey involved the establishment of transects across the reservoirs as well as digging holes into the deposited sediments in order to establish rates of reservoir siltation. In this study, it has been established that high rates of soil erosion occurs in this small catchment area experiencing a combination of arid and semi-arid type of climate. The predominant t.ypss of soil erosion was found to be gully/rill erosion and sheetwashoccurring on sideslopes and in localities surrounding the reservoirs that have been highly degraded. It was also found that - 1 ABS’l’RACT This is a study on soil erosion and its impact :: on small •. ,.reservoirs located in the Nguu Tatu catchment situated in the northern parts of MombasaDistrict, Kenya. The main objective of this study is the determination of the types, patterns and rates of# soil erosion within a sub-humid tropical Nguu Tatu Catchment and especially the assessment of the impact of soil erosion on reservoirs water quantity and quality. The methodology applied on this study involved three major approaches namely catchment erosion survey, measurement of water and suspended sediment discharge and finally reservoir sedimentation survey. Catchment soil erosion surveys involved the determination of rates, patterns and maqn’i tude of soil erosion within the catchmen-t by Lise of hills] ope plot experiments, slope traverses and benchmarks employing the use of erosion nails. Measurement of strenm flow and corresponding suspended sediment concentration provided information on sediment discharge. The reservoir sedimentation survey involved the establishment of transects across the reservoirs as well as digging holes into the deposited sediments in order to establish r at es of reservoir si 1tat ion . In this study, it has been established that high rates of soil erosion occurs int.his small. catchment area experiencing a combination of arid and semi-arid type of climate. The predominant types of soil erosion was found to be gully/rill erasion and sheetwash occurring on sideslopes and in localities surrounding the reservoirs that have been highly degraded. It was also found that - 1 the flashy characteri.sti.cs of the ephemeral flows in the catchment coincides with very high sediment transport rates. The .a’nnual sediment production rate was found to be highly variable on seasonal basis. The rates of gully and rill erosion were measured to be in the range of 0.24 m3/m2 to 1.39 m3/m2• The mean sediment transport rates in the catchment is 5,957 tons/yr. The mean soil erosion rate in the catchment was measured to be 0.7 cm/yr which is equivalent to sediment production rate of 2,979 tons/km2/yr. Factors that were found to influence soil erosion rate in the catchment are mainly rainfall characteristics (Rainfall amount and intensity), slope gradient and length I surface runoff depth and percentage, ground cover and rock /soil type.

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Page publiée le 12 décembre 2014, mise à jour le 9 mars 2018