Evaluation of Water Delivery Performance and Conveyance Efficiency in Gatto Small-Scale Irrigation Scheme, Southern, Ethiopia

摘要

Irrigation could serve as a viable solution to address the problem of food insecurity by increasing, boosting agricultural production. This research work was conducted to evaluate the performance of Gatto irrigation scheme using some selected performance indicators specifically, water delivery performance, conveyance efficiency and maintenance indicators of the scheme with in the investigation period of October to December 2017. The discharge measurement was performed at twelve measuring points on main canal and eight at two secondary cannels by using VALEPORT automatic current meter and 3-inch Parshall flumes for each selected nine tertiary offtakes from three each at the head, middle and tail end of the scheme. Water delivery performance evaluated with respect to adequacy, equity, efficiency and dependability was focused on variability in discharges of water distribution from head to tail reach and, during the crop season from October to December with overall average value equal to 0.70, 0.44, 0.89 and 0.53 respectively. Thus, the irrigation scheme when compared with Molden and Gates (1990) standards was found under poor condition in adequacy, equity and dependability and under good condition in efficiency. Estimated overall water conveyance efficiencies of the main, first and secondary canals were 86.3%, 77.53% and 73.13% respectively. However, the result found in the scheme was smaller than FAO (1989b) recommended value (95%) and (90%) for lined and unlined cannels with clay soil type. The design depth of water based on the design document was 0.42m nevertheless the actual depth of water in the main canal was 0.26 m due to this the relative change of the water level was 38.1% this greater than 0 value indicates that the intended water level in the main canal has not been achieved due to sediment accumulation in the canal. The result of Gatto small scale irrigation scheme of effective of infrastructures is reckoned to be 57.2 percent and sustainability of irrigation scheme is 88%. Many of the structures are demolished and became dysfunctional because of scouring, sedimentation and silt accumulation. Generally, the performance of the system is poor, it mainly results due to inadequate operation and maintenance provisions and over abstraction of water by upstream users. Therefore, adequate maintenance and other suitable management and operation approaches are required to improve the irrigation system performance. So, all stakeholders must work together in order to minimize factors that hinder the good performance of the irrigation system.