Irrigation Design for Culler s Rotation

Transcription

1 Irrigation Design for Culler s Rotation Wesley Caputo Calla Warren Dustin Till Simon Gregg December 5, Tom Corley Building Auburn University, AL Telephone: FAX:

2 1 Executive Summary In order to select a design that fits the specifications of the Cullers Rotation plot, it was necessary to perform a capital and operating cost analysis to decide which type of irrigation system is most feasible. The implementation options included utilizing water from the nearby pond at Jule Collins Smith Museum of Fine Art, city water, and an adjacent well. After conducting the cost analysis, it was determined that utilizing the nearby well was feasible and substantially cheaper. Due to these circumstances, it was determined that this was the most effective design alternative to pursue. To begin our design, it was important to consider the preliminary components, which include a pump, well casing, main and submain piping, and lateral drip tape. Along with these major components, there were several sub-components that were necessary to consider, including the control box, valve box, fertigation system, and subsequent filters. In this report, all essential components are specified and sized for the optimization of the system. Manufacturers for the sized parts accompany this report as well, including pump, piping, and drip tape. To provide justification for the proposed design, AutoCAD mapping and calculations accompany this design report. 2

3 Contents 1 Executive Summary 2 2 Introduction 4 3 Design Considerations 4 4 Economic Analysis 5 5 Recommindations 6 6 Appendix Calculations Economics Submersible Pump Well Quote AutoCAD Drawing

4 2 Introduction The Cullars Rotation experiment on the campus of Auburn University, started in 1911, is the oldest soil fertility study in the South and one of America s oldest, continuous field crop experiments. The purpose of this report is to design an irrigation system for Cullars Rotation to provide sufficient water for maximum crop yields. This will involve selecting the type of system to be implemented, performing all necessary calculations, and comparing the cost of several alternative systems from economic analysis. The weather in this area is classified as humid. The soil at Cullars is a loamy sand. There are three types of crops being cultivated on this rotation. The total acreage of this plot is 2.1 acres with 0.7 acres being cotton, 0.7 acres of corn, and 0.7 acres of soybeans. The row spacing is 30 in. with a tillage depth of 14 in. The water needed for irrigation will come from an on-site well that is 400 ft. deep with a 6 in. casing that is capable of producing maximum flow of 25 gpm. An aerial photo of Cullars Rotation has been included below (Figure 1) to gain perspective of the area being considered. Figure 1. Culler s Rotation located behind JCSM Arts Center 3 Design Considerations The system that we determined to be the best option for Cullar s Rotation is subsurface drip irrigation. We have selected to use 5/8 8 mil Aqua-Traxx drip tape. The specifications of this tape can be found in the appendix section of this report. The operating pressure is 10 psi and each emitter is rated at a 0.27 gph flow rate with an emitter spacing of 2 ft. The laterals are to be spaced 60 in. apart with one lateral occupying every other row, and buried at least 15 in. There will be 60 rows of laterals in each zone, totaling 6000 ft of drip tape required for each zone. The ACAD map showing the system layout can be found in Appendix. This design will incorporate a valve box that will enable the flow to only one zone while the other two are turned off. Detailed calculations and tables of the design specifications can be found in the appendix 4

5 section of this report. The main components of the design will be discussed in this section. The size of the mainlines were determined by the flushing flow, which is 25 gpm because it was larger than the design flow rate that was calculated for the laterals. The flushing velocity was not to exceed 2 fps. Only 12 of the laterals can be flushed at one time based on the well capacity of 25 gpm. All of the mainlines are to be 2.5 in. Sch 40 PVC. The length of the mainline (not including flush lines) is 1369 ft. The elevation change from the pump to the worst case emitter is 402 ft, with 400 ft of that being the depth of the well and a 2 ft. increase in elevation from the top of the well to the worst case emitter. The total dynamic head required is 462 ft. The pump needs to be 4.5 hp and with a capacity of at least 25 gpm (based on an assumed pump efficiency of 70%). The 30% rule was applied to the 300 ft part of the mainline that feeds the laterals and the lateral for the worst case emitter when determining the head loss. A 5 hp Myers submersible well pump capable of producing 25 gpm was selected for this design. The specifications and the pump curve can be found in the appendix section of this report. This system was designed for the crop that requires the most water, which is cotton, requiring 0.35 in/day and having a 200 day growing season. Only one of the three fields will be allowed to be irrigated at one time. The run time for one zone was determined to be 8 hr/day. For the entire growing season, the system will need to provide 70 in/season to the three zones with a run time of hrs/season. The application efficiency of the system was taken to be 90%. As can be seen in the ACAD map above, there will be one 200 mesh filter located at the well and one located just before the valve box. 4 Economic Analysis This section serves the purpose of comparing our proposed design with two alternative ones, primarily focusing on the water supply method. The 400 ft. deep well will cost $4300 dollars. The 5 hp Myers submersible turbine well pump will cost $ The three reels of drip tape needed will cost $ All of the mainline PVC pipe will have a total cost of $38,250 with $765 worth of fittings. The cost of installation will be $900 and the filtration equipment will cost $500. The operating cost will be $1000 a year based on the price of electricity being $0.11/kWh. Based on these cost, the present value of this system will be $52, based on an annual interest rate of 2%. More details of this economic analysis, including calculations and assumptions, can be found in the appendix. The next option considered is obtaining the water from the city of Auburns water supply. The cost of this water at a pressure of 60 psi is $106/acre-in. The pressure of the water will be used to get the water to the field at the required flow rate, so a pump will not be purchased for this option. Based on the same run time, system layout, and design capacity, the cost of water per year will be $16, The length of time considered is 20 years. The present value of this system will $320,224. The final option considered an electric centrifugal pump located in the pond in front of the Art Museum. It was realized that the pond will not have enough water to supply the desired amount to the field without some external means of refilling the pond, so this option will not be viable for consideration in this system. 5

6 5 Recommindations In conclusion, our proposed design of subsurface drip irrigation using well-water offers more economic feasibility than the other options considered in this scenario. It is recommended that a soil moisture monitor be installed on Cullar s Rotation with a controller for adjusting the irrigation schedule due unforeseen events that may occur to optimize the efficiency of the system. 6

7 6 Appendix 6.1 Calculations 7

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9 6.2 Economics 9

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12 6.3 Submersible Pump 12

13 6.4 Well Quote 6.5 AutoCAD Drawing 13

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