HYDRAULIC PERFORMANCE EVALUATION OF WATER DISTRBUTION IN GRAVITY IRRIGATION SYSTEM: CASE OF SIRIMA-DUGDADU MEDIUM SCALE IRRIGATION SCHEME, OROMIA, ETHIOPIA

Abstract

The development of irrigation and agricultural water management holds significant potential to improve productivity and reduce climatic volatility in any country. In Ethiopia irrigation development, has been identified as an important tool to inspire economic growth and rural development, and is considered as a corner stone of food security and poverty reduction. While a lot of effort is being exerted towards irrigation development, little attempt was being made toward the performance assessment of already constructed irrigation schemes. Performance assessment is used to identify the present status of the scheme with respect to the selected indicators and will help to identify ‘why the scheme is performing so’ which in turn imply means of improvement. This study was conducted to evaluate the hydraulic performance of off farm left side irrigation canal system of Sirima-Dugdadu Medium Scale irrigation scheme for which no such research conducted before. The evaluation includes, water conveyance, water distribution, operation and maintenance of the system using simple and clear selected performance indicators. In order to proceed to the evaluation, weekly average measurement of discharges was collected for the investigation period of September to December 2016. The discharge measurement was performed at nine measuring stations on branch canal offtake by using SABA universal current meter F1 and three and six inch parshal flumes. Water surface elevation measurement was also conducted along main canal at fifteen measuring location to be used as an input for the calculation of water surface elevation ratio to support for operation and maintenance activity for decision makers. The selected Hydraulic performance indicators for water conveyance and distribution are adequacy (PA), efficiency (PF), dependability (PD) and equity (PE), while the Operation and maintenance based performance evaluation of the system was assessed by parameters like water surface elevation ratio (WSER), effectiveness of infrastructures (EI) and sustainability of irrigated area (SIA). After all available data was collected, evaluation of hydraulic performance assessment of Sirima-Dugdadu left side irrigation canal was performed by using those selected simple and clear performance indicators. From the evaluation, the output result was indicated that the overall average adequacy, efficiency, dependability and equity of the system were 0.788, 0.801, 0.29 and 0.251 respectively. This result indicates, the PA, PE and PD of the system have poor performance, while the PF value of the system was fair. Regarding the operation and maintenance of the system, xi the result of the three parameters, WSER, EI and SIA are 1.01, 0.41 and 0.92 respectively. This result indicates that, the canal carrying capacity was reduced because of siltation and scouring, from initially installed or constructed structures only 41% are functional and 30ha of irrigated area was out of production by irrigation from 400ha initially irrigated. Generally, from the evaluation result assessed by four selected hydraulic performance indicators and three operation and maintenance parameters, this study was proved that, the overall performance of Sirima-Dugdadu left side irrigation system was poor. Therefore, this poor performance was derived partly from the management and operation and partly from the physical structures, so all stakeholders must work together in order to minimize factors that hinder the good performance of the irrigation system.