Browsing by Author "Mwakalila, Shadrack Sakai"

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Performance evaluation of rain water harvesting For paddy production in Tanzania
(Sokoine University of Agriculture, 1992) Mwakalila, Shadrack Sakai
The major problem inherent of the rain-water harvesting system for paddy production in North-West regions of Tanzania is low runoff efficiency and high rate of loss of stored water due to seepage and evaporation, which result in low yields and sometimes total crop failure. The present research was conducted in Shinyanga region with the objective of assessing the performance of the rain water harvesting system for paddy production. In order to achieve this objective the historical climatic and runoff data together with data from experimental runoff plots were analysed. From historical rainfall data the results showed that: -It is possible to receive 60mm of railfall within 24 hours once every two years and within wet season dry spells of unpredictable length and timing are common -The variations in yearly rainfall is some 25% over a period of 10 years. -At an annual rainfall of 800 mm water deficit in the paddies will amount to 1560 mm The experimental results showed that: -Uncompacted rain catchment with ground slope of less than 5% has an average surface runoff of 30^3 mm per month with mean runoff efficiency of less than 30%. -A compacted rain catchmet with ground slope of less than 5% has an average surface runoff of 66.4 mm per month with mean runoff efficiency between 45% and 60%. - Uncompacted rain catchment with ground slope greater than 5% has an average surface runoff of 66.4 mm per month with mean runoff efficiency between 50% and 65%. -A compacted rain catchment with ground slope of greater than 5% has an average surface runoff of 71.7 mm per month with mean runoff efficiency greater than 65%. -And also the study showed that most of catchments used are large areas of between 10 to 100 km' feeding runoff to ephemeral streams at a runoff yield efficiency of 12%. Therefore from the major findings it was concluded that the rain water harvesting system used in Tanzania has very wide potential but is currently inefficient, mainly due to the low control and inadequate management of the catchment area by the farmers. It is proposed that more research work is required to: quantify the yield benefits attributable to rain water harvesting; establish economically viable design parameters for catchments under different topographical and assess the erosion risks inherent of the system.