Hydraulic and operational performance of irrigation schemes in view of water saving and sustainability : sugar estates and community managed schemes In Ethiopia

ABSTRACT The rate of global expansion of irrigated lands has been declining since the 1970s due to the fact that most of the potential for large and medium-scale irrigation schemes has been developed. This rate of decline is also expected to continue in the next decades. As such significant proportion of the expected increase in production would have to be supplied from the existing irrigated and /or cultivated lands. This in turn could be achieved by improving land and water productivity in the existing schemes through ensuring better performance and optimal operation and maintenance. With less than 15% of over 5 million ha irrigation potential developed, irrigated agriculture in Ethiopia remained low. The largest proportion of the developed irrigation in the country belongs to small-scale irrigation by smallholder farmers. While accelerated development of new irrigation, particularly of large and medium-scale schemes is relevant in Ethiopia, performance and sustainability of existing schemes is equally important. The existing irrigation schemes in Ethiopia are generally characterized by overall performance and technical sustainability levels below expectation. The research presented in this thesis evaluates the performance of two large-scale and two small-scale community-managed irrigation schemes located in the Awash River Basin of Ethiopia. The research focussed on hydraulic/water delivery performance in the large-scale schemes and on comparative performance assessment and internal irrigation service utility evaluation in the community-managed schemes. It was found that hydraulic, operational and institutional aspects play a significant role in the overall performance of the irrigation schemes. Major performance challenges were addressed and operational/water management options for improvement were proposed for each case. &nbsp

Modelling and optimization strategies of the main and field irrigation system in Metahara sugar estate, Ethiopia

The current study deals with Modelling and optimization strategies of both main andfield irrigation system at Metahara Sugar Estate, located in Ethiopia. The method offield irrigation is surface (furrow) with dominantly gravity conveyance and distributionsystems. Surface irrigation accounts for 70% of total irrigated land around the world. Inmany of these irrigated areas, water is becoming a scarce resource. Still the efficiencywith which water is being used in agriculture particularly in surface irrigated systems isgenerally low. The performance of large-scale irrigation schemes world wide has beendisappointing with reduced water productivity. There are significant water losses inconveyance, distribution and in the field. There is a need to quantify water losses inorder to decide on measures to be taken in order to minimize it and improve theproductivity of water.The operational performance level of most irrigation schemes in developing countriesdrastically dropped in time. The causes are one or more of low management inputs,financial constraints or lack of professional and technical human resources to deal withthe problems. Performance assessment in such schemes helps to identify the causes offailures and areas of focus to improve the performance level. Similarly, the fieldirrigation performance (efficiency) in most surface-irrigated schemes in developingcountries is low due to either deep percolation losses or tail run-offs. The cause is eitheror both of lack of knowledge of the relationships between the parameters affectingperformance or little awareness on the significance of optimization.In the current study of Metahara Sugar Estate irrigation scheme, five core elements canbe identified. First modelling the inflow at the main intake using DUFLOW; secondperformance assessment of the main irrigation system with the help of some selectedperformance indicators; third performance evaluation of the existing field irrigationdesign and management practices; fourth management based optimization strategies ofthe main irrigation system and fifth management strategies to optimize the performanceof the field irrigation system.The average annual water abstraction measurements by the Estate and Ministry ofWater Resources (MoWR) show a difference of 22% which became a source of conflicton the water fees to be paid for the government. The difference of 22% in waterabstraction corresponds to 50.6 Mm3 annually. With an irrigation water fee of US{dollar} 0.34per 1,000 m3, the difference accounts for US{dollar} 17,200 annually. On the other hand, thevalue of irrigation water at Metahara Sugar Estate has been estimated to be US{dollar} 0.068per m3 while the cost of water is US{dollar} 0.00034 per m3. This water cost nearlycorresponds to 0.61% of the net annual benefit. This cost is very small as compared to areasonable cost level of up to 5% to be paid for water management. Without givingspecial attention to the benefit derived from water, the cost of water paid annually mayseem high. However, simple economic comparison proved that the present cost ofwater at Metahara Sugar estate is very low compared to its value.Modelling the inflow at the main intake has been carried out with three main objectives:first, to prepare a kind of operation rule of the intake to assist the gate operators; second,to evaluate the abstraction measurement of the two parties by simulation and commenton the reliability of the measurements; third, to give a more reasonable Q-H relation at both gauging stations. The operation rule has been prepared on monthly basis to makeit easier and it gives the required control sluice gates adjustments for both irrigation andoff-irrigation hours. The existing stage-discharge relationship used by the Estate hasbeen evaluated using DUFLOW simulated Q-H relations at the gauging site. Thesimulated Q-H relation produced at the gauging station of the MoWR can be used as animmediate check and revision of Q-H relation they are using.Performance assessment of the main irrigation system has been done with the help ofsome selected performance indicators. The selection of indicators was based on theirsignificance and whether they can be evaluated within the scope of this study (limitedfield data and time in this case). Upon getting ideas on the performance level, somequalitative strategies (management based strategies) have been dealt with that can helpto improve the performance level.The performance of the existing field irrigation management practices (furrow inflowand cut-off time) has been evaluated by simulation with the SIRMOD III model underthe existing field configuration. The model was first calibrated using Manning'sroughness coefficient 'n' as a calibrating parameter, and validated using data collectedin the field. It has been found out that the existing management practices do not takeinto account the different water holding capacities and infiltration characteristics ofsoils at Metahara Sugar Estate and not suitable for all soil classes. As such there is aneed to determine optimum field irrigation practices for each soil type. In optimization,for each soil class inflow times that can maximize the application efficiency has beendetermined making sure that the requirement efficiency is between 95-100%.It has been concluded finally that the water abstraction measured by the Estate more orless agrees with the simulation results. Moreover, the technique of measurement,sedimentation, backwater effect of structures on downstream of the gauging station andweed growth on canal sides have been identified as the major causes for possible overestimation of water abstraction measurements of the MoWR. The performanceassessment has shown that there is fair annual water supply to fields. However, there isa problem in matching the supplies and demands in time. Hence, shortage occurs insome months while there is somewhat excess supply in some other months.Sedimentation of conveyance and offtake structures has been identified as the majorcause for failure in optimum performance of the main system. It has also beenconcluded that the existing typical (theoretical) furrow inflow time of 60 minutes is notoptimal for all soil classes. It results in substantial deep percolation losses withconsequent low application efficiencies in medium to light soils

Hydraulic and operational performance of irrigation schemes in view of water saving and sustainability : sugar estates and community managed schemes In Ethiopia

The rate of global expansion of irrigated lands has been declining since the 1970s due to the fact that most of the potential for large and medium-scale irrigation schemes has been developed. This rate of decline is also expected to continue in the next decades. As such significant proportion of the expected increase in production would have to be supplied from the existing irrigated and /or cultivated lands. This in turn could be achieved by improving land and water productivity in the existing schemes through ensuring better performance and optimal operation and maintenance.With less than 15% of over 5 million ha irrigation potential developed, irrigated agriculture in Ethiopia remained low. The largest proportion of the developed irrigation in the country belongs to small-scale irrigation by smallholder farmers. While accelerated development of new irrigation, particularly of large and medium-scale schemes is relevant in Ethiopia, performance and sustainability of existing schemes is equally important. The existing irrigation schemes in Ethiopia are generally characterized by overall performance and technical sustainability levels below expectation. The research presented in this thesis evaluates the performance of two large-scale and two small-scale community-managed irrigation schemes located in the Awash River Basin of Ethiopia. The research focussed on hydraulic/water delivery performance in the large-scale schemes and on comparative performance assessment and internal irrigation service utility evaluation in the community-managed schemes. It was found that hydraulic, operational and institutional aspects play a significant role in the overall performance of the irrigation schemes. Major performance challenges were addressed and operational/water management options for improvement were proposed for each case