Evaluation of irrigation scheduling at Mubuku Irrigation Scheme
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This research was to evaluate irrigation scheduling at Mubuku settlement irrigation scheme. The rehabilitation of the scheme resulted into the modification of the water delivery systems with improved water conveyance efficiency. Farmers’ current irrigation practice and methods are based on the rated water flows and design data at the time of schemes establishment. All this required to assess the compatibility and suitability of the current irrigation practice/method at the scheme in relation to the new irrigation infrastructures. It was achieved by determining current water application practices, assessing the suitability of the current irrigation schedule and developing a suitable irrigation schedule for the scheme. This research was called out on the divisions 8, 10 and 12 on phase (ii) of the scheme. Calibration of the main canal and secondary canals was done in order to determine their conveyance capacities which involved measuring their cross-section areas and flow velocities using tape measure and flow meter respectively. The climate data for the scheme was generated using climwat software. The crop water requirements were generated using CropWat software. The planting dates were proposed as 18th February and 18th August for the two seasons since most of the farmers plant their seedlings in periods close to those dates. Water performance indicators i.e. water productivity, equity and adequacy were used to access the suitability of the schedule. The current schedules were found to be unfair to the farmers because much water was supplied to the crops in upper fields compared to those located downstream. Farmers in division 8 and 10 irrigate for three hours with a discharge flow of 104 l/s and 96.2 l/s where as farmers in division 12 irrigate once a week for 7 hours with a discharge of 53.2 l/s. Crops in division 8 were receiving excess water which was wasted as run off where as in division 12, they received less water as expected. The water supplied was not meeting the crop water irrigation demands which resulted to water stress. The water application practices was found to be poor in addition to the un-fair schedule. The field ditches were to be large and located at lower elevation points. The proposed schedules will be able to save 30.52 million litres of water for the 3 holdings under study if implemented. This would approximate to 305.2 million litres of water if the schedules were designed for all 30 holdings on phase ii. This amount of water can irrigate 6 holdings of un-irrigated land without extracting water from river Sebwe. This will result to increased crop production since water will be applied to meet crop water demands.