COMPARATIVE ANALYSIS OF HYDRAULIC PERFORMANCES OF TWO SMALL-SCALE IRRIGATION SCHEMES‟ STRUCTURES: CASE OF TAHTAY TSALIT AND MYCHEW, KOLA TEMBIEN, NORTH ETHIOPIA .

Abstract

Assessment of irrigation performances is very essential in taking different water management strategies. However, the performance of Tahtay Tsalit and Mychew irrigation schemes were not assessed yet and hence, this research was undertaken to compare the hydraulic performance of the two small-scale irrigation schemes mainly using comparative analysis of hydraulic performance indicators. The existing hydraulic structures were identified and evaluated their functionality and for malfunctioned structures the cause and effect of the problem was investigated through field observation and focus group discussions. On top of this, the hydraulic performance of the irrigation schemes were practically assessed using Parshall flume and 90 degree V-notch instruments spatially and temporally. Several factors such as flooding, sedimentation, design problem, damage of sluice gates, abstraction of irrigation water by unwanted plants has been identified in both schemes for malfunctionality of different structures. As a result of this, all flow control gates of the offtake in T.Tsalit irrigation schemes has already stolen and no flow control gates was constructed in Mychew and consequently, farmers are using stone and mud for controlling of water flow which further adds siltation to the canals. According to the irrigation performance standards, there was no any problem in irrigation adequacy, equity, dependability and efficiency of irrigation water in T.Tsalit irrigation schemes. However in Mychew, the adequacy and equity of irrigation water was categorized as poor, while good and fair for dependability and irrigation efficiency respectively. For both irrigation schemes, the average water surface elevation ratio, delivery performance ratio, and delivery duration ratio of the main canal during the monitoring period was less than one, greater than 5% , and 150% respectively. The highest sediment accumulation was observed at head and middle reaches of the irrigation schemes than the tail reaches for both irrigation schemes. Generally, in both irrigation schemes there were a number of irrigation structures which were malfunctioned due to many different reasons and now needs sustainable solution to improve the performance of the irrigation schemes. Hence, it was recommended that Water should be fairly distributed spatially and temporally particularly at Mychew irrigation scheme. Moreover, capacity building and awareness creation to concerned bodies holds the key to bring a difference in irrigation water management in both irrigation schemes.