Ingénierie des systèmes d’irrigation et de drainage

In this study an overall efficiency of Manushmara Irrigation System, Sarlahi, Nepal is assessed and evaluated with respect to the existing physical environment and irrigation practices. Conveyance and application efficiency are estimated utilizing information from field measurement employing calibrated current meter, soil moisture sensor meter and double ring infiltrometer. The average infiltration rate was found as 6.08 mm/hr. which is moderately low rate generally prevailing in clay loam soil. Conveyance efficiency for network of branch canal system is 67% while that for main canal is 76%. Overall conveyance efficiency for the irrigation system is 51% and Irrigation water application efficiency for the system is 47%. Therefore overall efficiency of the Manushmara Irrigation System is 35.7% which is below average for indicated value for surface irrigation system. It clearly indicates that the water diverted from the source river is not optimally utilized by the irrigation system and needs improvement in to prevent conveyance and application losses of irrigation water. In Nepalese context where majority of irrigation system are surface irrigation system, Evaluation of system efficiency of an irrigation system is important to indicate functional status of the system in terms of utilization of water which help planners and decision makers to take necessary action for the improved performance of the irrigation system.

Water resources were subjected to ever-increasing supply constraints due to extensive agricultural water demand for irrigated lands. Therefore, it is important to develop water-water-saving irrigation strategies to solve the problem. This experiment was conducted for three years to evaluate the effect of furrow irrigation systems on onion yield and water use efficiency at Humbo Woreda. The experiment had six treatments [Appling 100% crop water requirement with Alternate, 100% crop water requirement with Conventional, 75% crop water requirement with Alternate, 75% crop water requirement with Conventional, 50% crop water requirement with Alternate, and 50% crop water requirement with Conventional furrow irrigation] that were arranged in randomized complete block design with three replications. Yield and yield component data were collected and analyzed using Statistical Analysis System at the probability of a 5% confidence level. The experiment result showed that increasing deficit irrigation level significantly affects the yield of onion. Maximum onion yields were obtained under 100% crop water requirement with Alternate, 100% crop water requirement with Conventional, and 75% crop water requirement with Conventional furrow irrigation method without statistical difference. 50% crop water requirement with conventional furrow irrigation and 100% crop water requirement with alternative furrow irrigation were gives maximum water use efficiency of 6.56kg/m3 and 6.11kg/m3 respectively. But 50% crop water requirement with conventional furrow irrigation significantly reduces the yield. Therefore, 100% crop water requirement with Alternative Furrow Irrigation systems is recommended in water scarcity areas to increase water use efficiency without yield reduction.

The future climate, which has a crucial role in any hydrological events that occur within the basin, will have more uncertainty. Due to changing climatic variables, the basin's water balance will become more unpredictable. Not only will climatic parameter changes, but it will also adversely affect the water management within the basin. In this study, an effort has been carried out to compare the future River flow of the Kamala basin and the future water demand of the Kamala irrigation command area. The CROPWAT and AQUACROP model, based on climatic, soil, and crop data, was used to estimate the future Crop Water Requirement (CWR), Irrigation Water Requirement (IWR), and Biomass yield. Since the Hydrological station is absent within the basin, the simulation of the future river flow of the Kamala basin using any hydrological model was unworkable. Therefore, the WECS method is used to forecast the future monthly flow of the Kamala River. The two emission scenarios, ssp245 and ssp585, were conducted based on cropping intensity of 170% and 300%, and IWD for each sub-scenario over 12 months was estimated. For the first sixth months, IWR is increased in the future period as maximum and minimum temperature increases, and the IWR for monsoon season is less required due to increases in precipitation, and again for the post-monsoon season, IWR is increased compared to historical IWR. The highest irrigation water requirement occurred in March under ssp245 and ssp585 and CI 300%. In contrast, October and August have the lowest irrigation water demand under ssp245 and ssp585 scenarios. Based on the finding, the production of the crop with an irrigation system is higher than in a rain-fed system. For paddy, the rain-fed system produced a dry yield of 6.58 tons/ha, whereas the dry yield of the irrigated field has 7.05 tons/ha. The future river flow is insufficient to meet the irrigation water demand in the first five months in the near future under both ssp245 and ssp585 scenarios. The magnitude of deficiency in ssp585 is comparatively higher than in ssp245. Therefore, all of these findings suggest that the crop water requirement of KIP is insufficient in the future to provide a year-round irrigation system.