Using a sprinkler infiltrometer and the GAML model to predict moving sprinkler performance in the field

Kelderman, Simon (2015) Using a sprinkler infiltrometer and the GAML model to predict moving sprinkler performance in the field. [USQ Project]

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Abstract

The Green-Ampt (1911) equation has been regarded as one of the foremost infiltration models. Mein and Larson’s (1971) work extended its use to modelling infiltration under rainfall conditions, known as the GAML model, and Chu (1987) further extended its use to time-varying application rates such as occurs under moving sprinkler systems. However, Chu only demonstrated the efficacy of his work using simple, idealised application patterns that are not seen in the real world. This project, then, sought to extend Chu’s work by testing it in the field using real sprinkler performance data.

Sprinkler performance data, using Nelson brand centre-pivot S3000 sprinkler heads, was collected for the project in the hydraulics laboratory at USQ, Toowoomba. A sprinkler infiltrometer was used in the field to determine modified GAML model parameters, per Chu (1986). A computer program written in Matlab, based on the graphical methods of Chu (1987), used the laboratory sprinkler data and the modified GAML parameters to make a prediction of the runoff that would be generated from a specified time-varying application rate. A mobile sprinkler rig was constructed to deliver the time-varying application rate of water in the field.

A new concept for a sprinkler infiltrometer was tested in the course of the project. Initial work in the laboratory appeared promising but the concept failed to meet expectations in the field, principally due to wind interference. Consequently a small droplet-forming sprinkler infiltrometer was constructed and used for all of the field testing.

The process of determining the modified GAML model parameters was reasonably successful. However, predictions of runoff by the computer model were consistently far larger than that measured. This was believed to be for two key reasons. Firstly, whilst Chu’s (1987) method worked well for simple application patterns, it appeared to struggle with real data and so the predicted runoff by the computer program could only be regarded with suspicion. Secondly, there were significant difficulties collecting all of the runoff from the soil plots in the field. These two reasons for the disparity between predicted and measured runoff meant that this project was not able to conclusively affirm or reject Chu’s (1987) method for applying the GAML model as being suitable for use with real moving sprinkler systems in the field.


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Item Type: USQ Project
Item Status: Live Archive
Additional Information: Bachelor of Engineering (Agricultural) project
Faculty / Department / School: Current - Faculty of Health, Engineering and Sciences - School of Civil Engineering and Surveying
Supervisors: Foley, Joseph
Date Deposited: 06 Jun 2016 23:30
Last Modified: 06 Jun 2016 23:30
Uncontrolled Keywords: Green Ampt, Mein-Larson, Sprinkler, Infiltration
Fields of Research : 09 Engineering > 0999 Other Engineering > 099901 Agricultural Engineering
URI: http://eprints.usq.edu.au/id/eprint/29261

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