Investigating Causes of Failure of Diversion Structure for Irrigation Scheme. (Case Study; May Timket River Diversion, Central zone of Tigray)

Abstract

Small scale irrigation schemes are a key component of the Ethiopian government's food security strategy, Intended to boost agricultural productivity in smallholder farming. Over the past years, numerous schemes have been designed and implemented in the Tigray Region. While some have been successful, others have failed to fulfill their intended purposes. This research focuses on investigating the causes of failure of diversion headwork’s used for irrigation, with specific emphasis on hydrological, hydraulic, and structural design issues. The study centers on the May Timket River Diversion, located in Kola Tembien Woreda. Various data sources were collected and analyzed to identify the primary causes of failure in the May Timket irrigation scheme. ArcGIS was used to delineate the watershed of the study area. Therefore, peak flood discharge was estimated to be 367.66 m^3/s by using the Tekeze Basin method for a 50 year return period. The previous peak flood was 203.18 m^3/s. This difference shows that the causes of failure of the Diversion is mainly due to underestimation of peak flood discharge.in addition there were a problem on material they used; the stone used for masonry is from the river which is rounded and smooth. This makes loose bondage on each other. Therefore the remedial measure to be taken to solve the problem is redesigning the diversion weir based on the new peak flood that found through this study and reconstruct the weir structure using gabion inserted concrete, and gabion inserted hard core to strengthen the structure and protected with proper energy dissipation by constructing stair like structure at downstream of the weir to dissipate energy and downstream scour protection. Strict quality control during construction and regular maintenance are also essential to ensure long term stability and performance.