Ingénierie des systèmes d’irrigation et de drainage

This research was carried out at steep slope area planted with trees in different elevation terraces. The experiments were conducted at the experimental site at the Chabahar Free Zone. One major disadvantage of trickle systems is the tendency for emitters to clog. A trickle irrigation system was installed in a 50 m long and 20 m wide plot. The hydraulic performance of emitters was based on water flow, uniformity coefficient, application efficiency, and water losses through deep percolation. The flow volumes along the lateral length were fairly consistent and the variation was diminutive under both types suggesting uniform distribution of water. The difference in elevation between upper and lower terraces at the area of study was about 50 m irrigated by drip irrigation system. The system of irrigation has a problem in distribution uniformity of water resulted from initial filling of the pipes and drainage of water after stopping irrigation. Therefore, the lowest terrace receives the highest while the upper terrace receives the lowest amount of water. The problem of a lateral pipe with equally emitters and uniform supply of water is investigated. The flow volumes along the lateral length were fairly consistent and the variation was diminutive under both types suggesting uniform distribution of water. The system achieved rationally high DU, CU, Ea. The CU values for randomly selected laterals with smooth emitters averaged to 81.7% and spiral emitters averaged to 87.4%. The DU values averaged to 75.4% for smooth and averaged to 81% for spiral emitters. The overall Ea achieved were 82.7% and 89.4% for smooth and spiral emitters, respectively. The higher values of CU, DU, and Ea with spiral emitters as compared to smooth emitters suggest that they performed better and could be preferred to achieve uniform water distribution. Water movement below the emission point was more pronounced in the vertical. In most cases, the wetting front followed an axially symmetric pattern. The water laterally moved to about 0.35 m while it moved to a 0.56 m depth. The root zone for many short rooted crops is located in this range hence the percolation losses would practically be negligible under such situations.

A review on mathematical models available in the literature to design and evaluate agricultural drainage hydraulic nets is presented, including open ditch and buried pipe alternatives, for steady state and no steady state soil water flows, homogeneous and stratified soil profiles and smooth and corrugated drainage pipes.

Effective drainage pipe radius effects on drainage performance is considered, based on its perforation density and distribution, as it affects pipe weight bearing strength and pipe deformation intensity. Also, quantitative considerations on perforation density upon water flow resistance into the drain pipe are analyzed.

In this study, irrigation scheduling efficiency of two field crops; paddy rice and berseem fodder, grown in unpuddled sandy loam soil for a typical existing and imposed irrigations has been evaluated using the WINISAREG water balance and irrigation scheduling model that was calibrated and validated using data collected at field experimental plot in Roorkee, India. During the 1st season of each crop, typical irrigation schedules as practiced in the farmers’ field was followed while in the 2nd crop season, a reduced irrigation schedule was imposed aiming for water saving. Water balance components were monitored daily during the crop growth periods. Deep percolation was measured using drainage type lysimeters. Soil moisture content in the root zone was observed using soil moisture profile probe (PR2/6). The crops were provided with all the necessary inputs including fertilizer, pesticide and weeding operations following agronomic practices of the area. The results show that nearly 82-87% of the input water goes to deep percolation during paddy season-1 (continuous irrigation period) while 64%-70% of input water was lost through deep percolation during berseem season-1. Due to the imposed irrigation, the deep percolation has been reduced to nearly 78-80% of input water during paddy season-2 and 42-52% of input water during berseem season-2 besides large input water saving in the crop seasons. The large input water saving was due to alternative irrigation scheduling strategy whose efficiency has been significantly improved. Irrigation scheduling efficiency has been increased from 9.65% to 30.5% for paddy and 23% to 92% for berseem. In particular, comparative irrigation water saving of 64-74% in paddy season and 82-88% in berseem season was achieved with nominal yield penalty. This study shows the possibility of large volume of water saving in water intensive crops such as paddy rice and berseem fields under un-puddled sandy loam soils by considering a reduced irrigation scheduling option.