Browsing by Author "Nyenza, Eleuter Tosumsindo Sagimembe"

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    Rainfall erosivity in Tanzania
    (Sokoine University of Agriculture, 1995) Nyenza, Eleuter Tosumsindo Sagimembe
    A study was conducted with the main aim of making an iso-erodent map of Tanzania. The specific objectives/steps in this study were, first, to collect rainfall data from a few selected meteorological stations;second,to select erosivity index for calculating the erosivity of storms; third,to model the erosivity using easily available rainfall parameters; fourth, to extrapolate the model to a large number of rainfall recording stations;fifth,and last, to map the erosivities.Eleven meteorological stations were selected for studying and modelling erosivity. Using EI3U indexz (Wischmeier and Smithz 1958) daily erosivities of 10 217 storms from the stations have been calculated using information obtained from the charts of daily recording raingauge.Average monthly erosivities have been found. Ten-year averages have been used in order to portray long term trends. A highly significant correlation between daily amount of rainfall and erosivity has been observed. A multivariate linear prediction model has been obtained for predicting more easily monthly erosivity. The model is based on available rainfall parameters of average monthly total rainfall, average number of days per month Receiving rainfall of at least one millimetre,and the average maximum daily rainfall of the month. The prediction monthly model erosivities has 347 of used been stations to calculate mean from all over the country; the mean annual erosivities of the stations have been obtained by summation of the mean monthly erosivities .The rainfall parameters fed in the model have been averaged for a period of at least ten years. The mean annual erosivities of the stations have been entered in the map of Tanzania which has been drawn at a scale of 1:7 000 000,and an iso-erodent map has been obtained. Areas of high erosivity have been found to be associated with areas of high rainfall. Highest risk areas have been found to be in Rungwe/Ileje districts in the Southern Highlands of Mbeya region where erosivity values of up to 2105 joules per hectare have been observed. Other potential risk areas include the areas around Mt.northern Tanzania,Western parts of in Kilimanjaro Lake Victoria r and Eastern parts of Lake Tanganyika. Other areas include some areas of Ruvuma region, especially the eastern parts of Lake Nyasa, the Zanzibar Island, and the coastal areas. Low risk areas have been found to be the central regions of Dodoma and Singida and some areas bordering these regions, and some parts of Kilimanjaro region particularly in Same district where erosivity values as low as 176 joules per hectare have been observed.An erosivity map shows in generalr the areas where concerted efforts needed to conserve natural resources may be required (high risk areas) .Knowledge of potential erosivity is important for development planning.