PhD Theses

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Browsing PhD Theses by Subject "Arusha"

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    Dam safety analysis using physical and numerical models for small dams in Tanzania: the case of Arusha Region
    (University of Dar es Salaam, 2007) Malisa, Johnson
    Different failure modes and causes for the failed earthfill dams in Arusha region have been identified. The resulting extent of embankment damage was observed to be significantly larger where average breach top width was found in most cases more than three times the dam height. Even though, there has not be many small dams that has imposed risk to people`s life in the country to date, the loss resulted from the reported incidents is significant in terms of storage loss, embankment damage, environment and farming system destruction. Most of the existing small earthfill dams in Arusha region have been observed to have significant overtopping potential as a result of inadequate spillway capacity. This has been caused but the inherent uncertainty in the flood estimate method used in ungauged areas where hydrological information is scarce and changes in the catchment characteristics are significant. A method has been proposed and applied toassess and evaluate overtopping potential of a small earthfill dam (s) located in ungauged catchment as well as assessment of damage and danger in the downstream surface erosion resulted into stair-stepped multiple overfalls which finally merged into a single main upstream-migrating headcut. The rate of upstream headcut migration has been evaluated based on measured material properties, hydroulic and dam breach parameters. The important preliminary procedures for dam safety improvement have been highlighted to provide preliminary guidelines in the design, operation and maintenance.