An Irrigation Tank for Harvesting Rainwater in Semi-arid Savannah Areas : Design and Construction Practices in Ghana/West Africa

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Water as a limiting factor in agricultural production in semi-arid Savannah could be developed on a small scale by constructing self-reliant irrigation tanks (micro-dams) that directly catch and store rainwater from prepared catchment, having less impact on the environment. The tank could also be a core of village-level rural community to encourage agricultural activities as well as farmers' communication. The paper describes the design and construction practices of a prototype irrigation tank for harvesting rainwater in Ghana. Topographical survey and geotechnical investigation at the project site provided data for the appropriate location and design of the micro-dam. Representative soil samples from soil profiles to the parent material showed that the subsoil condition was suitable for the foundation structure and as core material. Prudent and meticulous construction process of the irrigation tank proceeded with the removal of organic materials from the surface soil before starting the embanking. Apart for filter materials, clay core and rock materials were appropriately identified near the dam site and mined for the embanking process to cut down on the cost of construction of the dam reservoir. Embanking was implemented in two phases in order to release floods smoothly through the central watercourse route zone and the spillway section of the dam in the event of rains during the construction period. A steel pipe (draw-off pipe) appropriately fitted with an anti-seepage collar and a spindle fitted valve was laid in the transverse of the dam body, for withdrawing water from the reservoir to the farmland. Due diligence was taken in the design and construction of the spillway structure. Design flood discharge was taken on 100-year flood discharge from a viewpoint of sustainable water source development. With the installation of soil tensiometers within the farmland, the soil moisture status is monitored in order to help optimally decide the timing and amount of water supply from the irrigation tank and therefore to increase crop yield while increasing water use efficiency. With the aid of an automatic water level sensor and an automatic rain gauge, the time-varying reservoir water level and rainfall are also monitored for future research use.
日本雨水資源化システム学会の論文

An Irrigation Tank for Harvesting Rainwater in Semi-arid Savannah Areas : Design and Construction Practices in Ghana/West Africa

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