ESTIMATION OF UNLINED CANAL SEEPAGE AND VALIDATION OF EMPIRICAL EQUATIONS UNDER DIFFERENT CANAL SIDE SLOPE IN-THE CASE OF OMO KURAZ II SUGAR ESTATE, SOUTH ETHIOPIA

Abstract

The Omo Kuraz II irrigation scheme in Southern Ethiopia suffers from significant irrigation water loss along the tertiary canal, which exacerbates water scarcity issues. This study quantified seepage losses within the Omo Kuraz II Sugar Estate, focusing on the impact of canal side slopes and comparing various equations for estimating seepage from earthen canals. Tools used included electric current meter for inflow-outflow measurements, staff gauges for water level monitoring during ponding tests, and perforated pipes for piezometric surveys of groundwater levels along the canal bank. The evaluation underscored the strengths and limitations of empirical methods against actual field data, providing insights into the effectiveness of different equations for predicting seepage rates and improving irrigation management practices. The findings indicated that the average seepage loss observed using inflow-outflow, ponding and piezometer survey method in tertiary canals 7-13 was 9.46, 5.52 and 3.01 while in tertiary canal 10-5, it was 11.40, 6.43 and 3.52 and in Tertiary canal 13-3 it was 6.54, 4.50 and 2.69m3/m/day, respectively. The study revealed significant seepage losses, estimated to range from 3.69 to 10.91m³/m/day. Considering the scheme's extensive tertiary canal network, totaling 127,846.75 meters, the annual total seepage loss is projected to be substantial, ranging from 2,358.77 to 6,974.04m³/year. The investigation of seepage losses began by examining selected tertiary canals, revealing that canal 7-13 exhibited greater seepage loss compared to canals 10-5 and 13 3. This difference was attributed to the side slope of the earthen canals, with canal 7-13 having a gentler slope of 1:1.5, while canals 10-5 and 13-3 had steeper slopes of 1:1. The study found that gentler slopes resulted in an increase in seepage by approximately 41.3% to 67.7% due to the increased surface area and longer flow path of water along the slope allow more time for water to infiltrate into the soil compared to steeper slopes. Additionally, the Indian equation was identified as the most reliable for estimating seepage, despite underestimating losses by -52.46%. It provided estimates closer to observed values than other equations, which significantly overestimated losses. This suggests the Indian equation may be more suitable for the hydrological conditions of the Kuraz II irrigation scheme. The key beneficiaries of these findings include the Omo Kuraz I, II and III sugar factories and the Ethiopian Sugar Industry Group, as improved seepage estimation will enhance water resource management