Ingénierie des systèmes d’irrigation et de drainage

Spate irrigation is form of water management that is unique to arid and semi- arid area where floods are diverted in to cultivated crops by constructing diversion weir across the river. The general objective of the study was Assessments of irrigation efficiency Gobu-I and Gobu-II modern spate irrigation schemes. To achieve the study primary data were collected which includes measurement of soil moisture contents before and after irrigation, measurement of field discharge. The parameters used to compare the efficiencies at the farm field levels were application, storage and distribution uniformity efficiency. The application efficiencies of Gobu-I was 62.75, 72.61 and 77.56% and for Gobu-II was 57.88, 66.12 and 70.14%. The storage efficiencies of Gobu-I schemes were 89.06, 88.71 and 87.8% and for Gobu-II schemes were 90.97, 89.81 and 88.1%. Distribution efficiency for Gobu-I scheme were 92.65, 87.67 and 96.38% and For Gobu-II schemes were 85.05, 89.95 and 95.03% in the head, middle and tail field respectively. Application efficiencies of both schemes were not good because of it’s under limit but storage and distribution efficiencies were good. By strengthening the capacity of DA’s and farmer’s frequent evaluation and follow-up are critical to maintain sustainable performance of the modern spate irrigation schemes.

Water scarcity is among the major limiting factor that affects crop production in which efficient utilization of limited irrigation water is vital. A field experiment was conducted for two consecutive years at Kulumsa Agricultural Research Centre during the dry season based on the objective to determine the effect of moisture stress at different growth stages on yield and water productivity of wheat. Fifteen treatments combined and imposed at four growth stages were used in A Randomized Complete Block Design (RCBD) with three replications. The two years combined result indicated that moisture stress at different growth stages highly significant (P < 0.05) influenced plant height and grain yield of wheat. On the other hand, there was no significant (p > 0.05) variation among treatments on hectolitre weight, total kernel weight, and above-ground biomass. A maximum plant height of 70.5 cm was obtained when wheat is irrigated at the initial and development stages only. The highest grain yield (4.71 ton/ha) was obtained at control treatments where all the growth stage is irrigated which were followed by a treatment in which moisture stress happens only during the late season. On the other hand, the lowest grain yield (2.23 ton/ha) was obtained when wheat irrigated only during the late season, stressing the rest growth stages which leads to a reduction of 52.7% from the control treatment. Generally, the study showed that the grain yield of wheat was highly affected when moisture stress is imposed during the initial and development stages. In addition to this, the highest (4.71 ton/ha) and lowest (2.23 qt/ha) aboveground biomass were obtained at the control and when irrigation was applied only during the late season, respectively. The highest water productivity of 4.56 kg/m3 was obtained when only the initial stage is irrigated. Treatments that received lower irrigation water showed better water productivity especially when moisture stress was not imposed during the initial and development stages. Therefore, in areas where irrigation water is not limited, wheat should be irrigated during all growth stages and if there is limited water resource for irrigation water it could be irrigated only during the initial stages or initial and development stages to maximize water productivity.

The technical performance evaluation of Koga Irrigation Scheme was made in order to identify management practices for implementation to improve the system operation and the performance of the irrigation system. The evaluation was made based on the selected performance indicators such as water application efficiency, dependability of irrigation interval and sustainability of irrigated command area. The results obtained showed that Application efficiency monitored on three farmers’ farm located on different ends of the command ranges from 52.2 to 61.8% at irrigation scheme. Dependability of the schemes evaluated in terms of irrigation interval shows that the schemes irrigate more frequently than was intended. The sustainability of the irrigated area initially planned for development or the actual irrigated area during the design period was 7,004 ha. However currently it is irrigating about 6,200 ha. This shows that the sustainability of the scheme is 0.86 ~ 86%. In conclusion, on farm water loss was revealed in this study. Relatively highest sustainability of irrigation land value is operating and significant proportion of water is lost on farm areas. Therefore, if structures are in place and water users associations are empowered more in order for it to enforce its bylaws; it will augment the efficiency of the scheme exceedingly.