A SimulAtion Model For Centre Pivot Irrigation system design and optimiza tion of operation

Abstract

A Simulation Model for Centre Pivot Irrigation System Design and Optimization of Operation (Ph.D Thesis) Osama Osman Ali Osman Abstract: A computer simulation model was developed for the purpose ofthe design and optimization of the operation of centre pivot irrigation system. The model was written in Visual Basic 6.0 Programming Language. The model determines crop water requirement, irrigation scheduling, application rate, irrigation time, and system hydraulic parameters. It also evaluates the performance of the system when supplied with the required data. For verification of the model, field trials were carried out during the period December 2007 - July 2008 at four schemes using centre pivot irrigation systems. The schemes were Ras Al Wadi Al Akhadar Project- north Atbra town, El Bashair Company- south Al Damar town, Tala Company-north Shendi town and the Arab Company for Agricultural Production and Processing in Khartoum area. The schemes were growing alfalfa, except El Bashair company which was growing onion. Crop water requirement was estimated using the modified Penman equation and Penman-Monteith method. The program when supplied with required data can estimate the reference crop evapotranspiration and crop water requirement. The values of May 2008, obtained for reference crop evapotranspiration (ETo) by using the modified Penman equation were 8.7, 8.7, 8.6 and 8.4 mm/day, and by using Penman-Monteith method were 8.9, 8.9, 8.4 and 8.0 mm/day for Ras El Wadi Al Akhdar Project, El Bashair Company, Tala Company and the Arab Company for Agricultural Production and Processing, respectively. The values of April were close to May values, but in January, February and March Pemnan-Monteith gave lower values than modified Pemnan.The values obtained for predicted crop water requirement (ETc) by using the Xlllmodified Penman equation were 10.4, 9.1, 10.3 and 10.0 mm/day. and by using Penrnan-Monteith method were 10.6, 9.3, 10.0 and 9.6 mm/day for Ras El Wadi Al Akhdar Project, El Bashair Company, Tala Company and the Arab Company for Agricultural Production and Processing. respectively. The model determines the irrigation scheduling variables. The total available water in the root zone to be 300, 90, 300 and 345 mm. Readily available water (net depth) was 150, 45, 150, 173 mm. The gross water depth was 230, 69, 231 and 230 mm, irrigation time was 29, 9, 29 and 58 hours and the number oftotal irrigations during the month was found to be 5, 8, 5 and 5, for Ras El Wadi Al Akhdar Project, El Bashair Company, Tala Company and the Arab Company for Agricultural Production and Processing, respectively. The model also determines the system variables. Distance from pivot point to last tower was 380, 405, 332.5 and 468 m, application rate was 100, 48, 91and 42 mm/h, and maximum application rate was 128. 61, 116.5 and 59 mm/h. System capacity was 154, 179, 128 and 123 m3/h. Friction losses were 1.27, 1.43, 3 and 1.0 m for Ras El Wadi Al Akhdar Project, El Bashair Company, Tala Company and the Arab company for Agricultural Production and Processing, respectively. The model determines the coefficient of uniformity of systems, uniformity of distribution and scheduling coefficient. The coefficient of uniformity was 78, 79, 85, 79 and 77%. Uniformity of distribution was 68, 70, 78, 71 and 67%. Scheduling coefficient was 1.47, 1.43, 1.3, 1.41 and 1.49 for Ras E1 Wadi Al Akhdar Project, El Bashair Company, Tala Company, Arab Company for Agricultural Production and Processing and the Arab Company for Agricultural Production and Processing after changing sprinklers, respectively. The model can satisfactorily estimate crop water requirement, irrigation scheduling, system design variables and evaluate the performance of the system. XIV