Ingénierie des systèmes d’irrigation et de drainage

Extensive effort and huge investment towards irrigation development is being made in Ethiopia. However, little or no attention is given to the monitoring and evaluation of the performance of already established irrigation systems. Consequently, many of the existing irrigation systems are deteriorating in their physical structures, operation and management. Hence, this study attempted to evaluate the performance of water delivery performance and dependability of irrigation interval in Tendaho sugar estate irrigation system in the lower Awash River Valley. Water delivered to canals was measured using flow measuring structure and duration of water delivery while actual irrigation interval was monitored for selected fields. The average values of Delivery Performance Ratio were resulted in 0.36, 0.53, 0.54 and 0.38 for main, primary, secondary and tertiary canals, respectively, and the average value of dependability of irrigation interval was resulted in 1.6 for selected fields. These results of both delivery performance ratios and dependability of irrigation interval reveal that reliability of water delivery during study time was rated under very poor, and the fields waited for long time to get irrigation water. To alleviate the problem and avoid water shortage during dry period, Gate of the Dam should be installed; off-taking canals head and cross regulators must be installed for all canals; regularly repair and calibration should be done for all existing regulators in the Sugar Estate.

Evapotranspiration, which represents a significant amount of moisture lost from a catchment, is an important parameter in the hydrologic cycle. However, it was challenging to determine the quantity due to the non-uniform distribution of meteorological stations and data in adequacy, which can be solved by an interpolation technique. Accordingly, the objective of this study was to estimate the spatiotemporal variability of reference evapotranspiration for the Arjo Dedessa sugar factory and its surroundings. ArcGIS, CROPWAT, and XLSTAT were the materials used. GIS was utilized to map the ETo variability, the XLSTAT2019 software was used to fill in the missing data, and the ETo was calculated using the CROPWAT. The data came from the Ministry of Water, Irrigation, Electricity, and Energy, as well as the National Meteorological Service Agency. Fourteen meteorological stations were identified, and data from 10 of them was selected for study after their quality was verified. The ETo map was created using the elevation and position of each station. Over the whole study area, the ETo values were interpolated using Kriging. The results show that the yearly spatial average daily ETo ranges from 3.67 millimetres to 4.65 millimetres of water depth. Because of the cold climate and heavy precipitation, the ETo value was lower at higher elevations. However, because of the warm temperature, it was higher in low-altitude places. Throughout the year, the monthly ETo temporal distribution has varied. During the summer, daily ETo values ranged from 3.10 to 3.39 millimetres, with a mean of 3.24 millimetres.

Surface irrigation type is one of the most widely used in the world due to its low cost investment. However it is complex methods of applying water to soil, because of extremely difficult to achieve good control over the highly variable nature of the movement of water across a soil surface and its infiltration into the soil over a season. This complexity leads low efficiency of the system because of failure in management and design. In this study, it is attempted to optimize furrow irrigation decision variables at Wonji sugar estate using field experiment and two simulation models. The hydraulic performance of the existing system was evaluated using two systematically selected furrows. Accordingly, an application efficiency of 43% and 25% were obtained. The performance of the system was evaluated as poor due to excess application of water and less management skills of irrigation application. One experimental site was selected at field number of 85 for optimization of decision variables. The field data (before irrigation, during irrigation and after irrigation event) of experimental site (at field number 85) was measured as input for models and simulated using the SIRMOD software and Win SRFR software package. Furrow length of 32m, 48m, and 64m, slope of 0.05%, 0.075% and 0.1%, and flow rate of 3l/ sec, 4l/sec and 5l/sec were analyzed with three replication using volume balance method and two simulation models. Therefore, from the current findings, the optimum decision variables that gave maximum application efficiency and distribution uniformity was slope 0.1%, furrow length 32m,and inflow flow rate 4 l/sec at cut-off time 15.79 minutes. Thus, to improve the performance of furrow irrigation practice, optimal furrow length, inflow rates and cut-off time found by this study could be adopted.