Ingénierie des systèmes d’irrigation et de drainage

In Sub-Saharan countries more than 95% of agricultural practices were laid on rain-fed. Ethiopia is one of the parts of the Sub-Saharan country and its agricultural practice mostly depends on rain-fed farming system. Highly reliance of agriculture on variable rainfall reduces income of farmers which adversely affects economy of the country. The similar climatic variability was happening in the study area in which rain fall doesn’t fulfil the needs crop up to maturity. To address this problem, two years field experiment was conducted at 2015 and 2016 in Misrak Azernet Berbere Woreda, Southern Ethiopia to evaluate the effects of different supplementary irrigation (SI) levels on yield of potato. The experiment laid out in randomized complete block design (RCBD) with five treatments replicated three times. The treatments were:- Rain fed, 100% ET_c (crop evapotranspiration) SI throughout season, 75% of ET_c SI throughout season, 50% of ET_c SI throughout season and 100% ET_c SI starting at flowering stage).The combined yield results show that only rain-fed agriculture through season decreased yield of potato significantly. The maximum yield (45.31 t/ha) was obtained from 100% ET_c Supplementary irrigation throughout season while the minimum yield (24.46 t/ha) was obtained from only rain fed treatment. The yield obtained from 100% of ET_c supplementary irrigation starting from flowering stage was 38.98t/ha which has insignificant yield difference with 100% of ET_c throughout the season (45.31 t/ha). The yields of all supplemented treatments are greater than rain-fed treatment. From these result it can be concluded that supplementing rain fed potato production through irrigation increases yield.

This is the third manuscript of a three-part paper that presents the development and evaluation of a hydraulic simulation model for linear-move laterals equipped with pressure reducing valve (prvs). System description, model assumptions, and specification of the lateral hydraulic simulation problem are discussed in part-one of the paper. Formulation and numerical solution of the lateral hydraulic simulation problem are described in manuscript-two. Results of model evaluation and simulation examples, showing model applications, are presented here. Measured hydraulic data-sets, consisting of lateral pressure head profiles and inlet discharges, were used in model evaluation. The data was obtained through field tests conducted on a linear-move sprinkler irrigation system fitted with prvs. Comparisons of model-predicted and field-measured lateral pressure head profiles and lateral inlet discharges suggest that model performance is satisfactory. Furthermore, potential applications of the model in analyzing prv-set pressure effects on lateral hydraulics and, possibly, in the selection of a suitable prv-set pressure for a lateral with a given parameter combination is shown using simulation examples.

This manuscript presents a hydraulic simulation model for linear-move sprinkler irrigation laterals equipped with pressure reducing valves (prvs). The linear-move lateral considered here consists of a series of arched spans with a specified geometry and multiple outlet-ports. Lateral diameter, hydraulic resistance characteristics, field slope, spacing between outlets, and sprinkler hydraulic characteristics can be constant or variable along a lateral. Lowpressure sprinklers, or spray nozzles, coupled to pressure reducing valves are used in these laterals to achieve controlled application of irrigation water. Depending on their modes of operations, prvs can have a significant effect on lateral hydraulics. Thus, operating modes of prvs are defined and their effects on system hydraulics are described in a companion manuscript. The basic algorithms of the hydraulic computation functionality of the simulation model, presented here, are developed using computational techniques applicable to hydraulic manifolds. However, the algorithms developed as such are modified to account for the particular conditions that prvs impose on the hydraulics of a linear-move lateral. The iterative solution of the linear-move lateral hydraulic simulation problem (which typically involves multiple lateral-wide hydraulic computations) is formulated here as a one-dimensional optimization problem that seeks to minimize the error, between the computed lateral inlet head and the imposed inlet head, as a function of the distal-end nodal head. The current manuscript is part-two of a three-part article and it describes the formulation and numerical solution of the lateral hydraulic simulation problem. Part-one of the article focusses on specification of the lateral hydraulic simulation problem, statement of assumptions, and system description. Part-three presents results of model evaluation and explores potential applications of the model.

This manuscript is the first of a three-part paper that presents the development and evaluation of a numerical hydraulic model for linear-move sprinkler irrigation systems equipped with pressure reducing valves (prvs). Discussions on model development and evaluation are presented in part-two and three of the article, respectively. The current manuscript, on the other hand, focusses on system description, statement of pertinent model assumptions, and the definition of the lateral hydraulic simulation problem and as such it is intended to set the background for the discussions that follow in the companion manuscripts. A concise description of the configuration of the linear-move sprinkler irrigation system, considered in the current study, and its components is presented here. In addition, system attributes that are of particular relevance to hydraulic modeling of linear-move laterals are discussed. Noting that pressure reducing valves are key to achieving a controlled application of irrigation in linear-move systems, the full range of the operating modes of prvs are defined, in the context of irrigation laterals, and their effects on system hydraulics are described. In addition, assumptions that form the basis of the lateral hydraulic simulation model, presented in the companion manuscript, are stated here. Finally, the lateral hydraulic simulation problem is defined and the linear-move lateral is schematized as a branched pipe network, consisting of links and nodes, for hydraulic analysis and simulation.

A field experiment was undertaken from 2015 to 2017 G.C., during Gana (from August to December) cropping season to study the effects of in situ moisture conservation and management on yield and yield components of improved maize variety (Melkasa II) at lowland of Bale (Goro and Ginnir districts), southeastern Ethiopian. The experimental design was randomized complete block design (RCBD) using three treatments (flat bed, ridging and furrow with ties, and ridging and furrow without ties (open furrow)) with three replications. The plot size for the treatments was 8 m × 6 m (48 m²). The results revealed that out of the different in situ moisture conservation measures ridging and furrow with ties for Goro District and ridging and furrow without ties (open furrow) for Ginnir district resulted in significantly higher yield improvement over the famers’ practice (flatbed). The highest maize biomass yield of 6.0 t ha^-1 which is 29% higher and grain yield of 5.3 t ha^-1 which is 28% over flatbed was recorded under ridging and furrow with ties for Goro district. Whereas ridging and furrow without ties (open furrow) gave the highest grain yield of 8.8 t ha^-1 (64%) and 11.6 t ha^-1 (28%) for Harawa I and Ebisa of Ginnir district. Moreover, practices of in situ moisture conservation of both ridging and furrow with ties for Goro and open furrow for Ginnir districts resulted in significantly higher plant height, number of ear per plant, ear length, number of kernel per ear (NKPE), biomass, grain yield, thousand kernel weight of “Malkasa II” maize variety. The present study recommended both ridging and furrow with ties and furrow and furrow without ties (open furrow) for mitigation of low moisture at Goro and Ginnir districts, respectively for production of maize.

This study conducted to evaluate the performance of Sanko small-scale irrigation scheme at Basketo Special Woreda, South Nation Nationalities Peoples Regional states. The irrigation scheme includes command area of 120 ha and 600 beneficiaries. The scheme was evaluated using internal and productivity performance indicators. From the analyses of the internal performance indicators, the conveyance efficiency of the main canal was found to be 69.3% and application efficiencies at head (61.6%), middle (63.4%) and tail (46.5%) with average application efficiency of 57.2%. A light soil with high infiltration rates favors deep percolation losses at the top of the fields, resulting in low field application efficiency in tail end part of the scheme. A deep percolation ratio and storage efficiency of the scheme was found to be 42.8% and of 78.5% respectively. Generally overall scheme efficiency of scheme was 39.6%. From the evaluation of productivity indicators, the outputs per cropped area found as at head (84,706 Birr ha-1), middle (220,690 Birr ha-1) and tail (69,686.4 Birr ha-1) and the value of the outputs per command area of scheme was 15,003,276 Birr per command area. The output per unit irrigation supply of irrigation scheme was at head (13.5 Birr m-3), middle (33.95 Birr m-3) and tail (22.12 Birr m-3). Relative water supply and relative irrigation supply; found to be 1.28, which was the same for both since there was no rainfall during study period. From the analysis result, there was lower water use efficiency (WUE) at upper head (23.37 ton/m3) as compared to middle (48.78 ton/m3) and tail (60.22 (ton/ m3) part of the scheme in relation to yield obtained. Based on the evaluation result, highest yield was obtained from at middle part of irrigation scheme and lower yield was obtained from both upper and tail end part of the scheme. The yield reduction in upper and tail part of the scheme was due to over and under irrigation. However, there is still a room for improvement at all system levels. Therefore to reduce over and under irrigate; farmers should get awareness how to use, when to use and how much water used on their fields.

Performance evaluation of irrigation schemes plays a fundamental role in improving irrigation system by identifying where the critical problems occurred. This study was conducted to evaluate the performance of Wosha and Werka irrigation schemes found at Wondo Genet district southern Ethiopia using comparative indicators. Agricultural output, water supply and physical indicators were used as proposed by the International Water Management Institute. The study showed that Werka irrigation scheme has performed better with respect to all agricultural output indicators except output per unit command area. The crop water demands at both irrigation schemes were not satisfied due to the diverted water was inadequate. Physical indicators revealed that irrigation ratio of 0.89 and 0.78 were recorded at Wosha and Werka irrigation scheme, respectively. In addition, water delivery capacity of both irrigation schemes was sufficient. Moreover, the sustainability of irrigated area indicated that the irrigated area of both schemes was expanding beyond the designed command area. Therefore, both irrigation schemes would needs improvement on irrigation water management and expanding high value crops.