Performance Assessment of Diversion Head Work: A Case Study on Abegaz Small-Scale Irrigation Project, in Amhara Region, Ethiopia

Small-scale irrigation systems are crucial for enhancing agricultural productivity in developing regions but often face challenges such as sediment accumulation and inadequate flood management. This study evaluates the hydraulic and structural performance of the Abegaz small-scale irrigation scheme in South Gondar, Ethiopia, focusing on discharge capacity, sediment control, and weir stability. The primary objectives of this research were to assess the hydraulic performance of the diversion weir and associated structures, examine the structural stability and integrity of the weir, and identify maintenance needs and operational challenges affecting long-term sustainability. Through field measurements and analysis of design documentation, we gathered primary and secondary data, which were analyzed using empirical equations to evaluate the weir's current condition. The findings revealed that sediment accumulation raised the riverbed by 0.6 m at the intake, reducing the weir's height from 1.2 to 0.6 m, which impairs its ability to regulate water flow. The diversion weir's discharge capacity was 48.52 m3/s, slightly below the design flood capacity of 50.07 m3/s, indicating vulnerability during extreme flood events. Structural evaluations confirmed the weir's stability. The safety factor for overturning was 1.51 at high flood levels (HFL) and 2.40 at normal pool levels (NPL), exceeding the minimum required value of 1.5. The safety factor for sliding was 1.21 at HFL and 2.96 at NPL, exceeding the minimum required value of 1. Stress analysis at the heel showed maximum stress of 13.85 kN/m2 at NPL, and at the toe, 19.54 kN/m2 at NPL, both well below the allowable limit of 490 kN/m2. Additionally, the eccentricity values were 0.06 m at HFL and 0.078 m at NPL, both less than the permissible limit of B/6 (i.e., 0.425). These findings highlight the need for improved sediment management strategies and potential design modifications to enhance flood resilience. This research offers valuable insights for optimizing small-scale irrigation systems facing sedimentation issues and provides guides for future studies and design improvements.