Towards two-dimensional infiltration measurement in complex and variable soil environments

Skehan, Ned (2016) Towards two-dimensional infiltration measurement in complex and variable soil environments. [USQ Project]

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Abstract

The measurement of the infiltration rate in soil science has traditionally been a reasonable, but qualitative assessment of the physical characteristics of the soil. Monitoring how the infiltration rate changes over time gives insight into how the physical characteristics such as soil structure, changes. Quantifying this change is useful when assessing how mine site rehabilitation soils settle in the years following the burial of mining waste rock. The actual technique for measuring the infiltration rate is currently done as a point measurement, which is statistically unreliable for an average reading when the environment has a high level of variability within its physical characteristics. It was theorised that Electrical Resistivity Tomography (ERT) has the capability to quantify the infiltration variability that exists in complex soil environments which contains features including mining waste rock, textural variations, and structural anomalies such as varying degrees of compaction. This research investigated the use that a time lapsed measurement of soil moisture change over a two-dimensional transect has when attempting to track a wetting front through a soil profile. The project is broken into two distinct stages, developing a methodology for tracking a wetting front and applying the method to a variable soil to assess the accuracy. The first stage involves creating software protocols and inversion corrections that allow measurements of soil moisture to be corrected for time due to the ERT measuring in a successive technique with a specific order. As these corrections are developed and the order of measurement is known, the soil moisture across a two-dimensional transect can be measured repeatedly at a known time interval, allowing the quantification of the soil moisture rate of change, or the infiltration rate at every point along that transect. Once this method is developed, it is replicated on a variable soil, which contains a large buried rock, a textural change and a compacted region.

An irrigation system was developed to deliver the equivalent of an 8mm/hr rainfall event, and this was run while the ERT ran continuously, collecting a two-dimensional image of the profile every 60min. For the experiment on a variable profile, an anthropogenic soil was made, with buried features such as a rock, logs and a compacted section, with a texture change as the overburden. The same experimental procedure was then applied to this profile. Due to Terrameter malfunction an older model Terrameter SAS4000 was used to collect the variable profile data sets, which provided complications in analysis.

It was found that the ERT does have the capacity to locate stochastic variability in the underground pedology and geology, but does not deliver an infiltration rate accurate enough for scientific research. This is due to the ERT measuring at fixed depths, 13cm apart. The inversion software offers an improvement to this 13cm depth increment, however a lack of data density from the ERT prevented this improvement from being useful. Although the infiltration rate itself could not be parameterised explicitly from the data into minimum, maximum, and average infiltration rates, it was possible to identify that approximately 10% of the 5m wide irrigated section had a very high (relative to the profile) infiltration rate, while approximately 38% had a low rate, with two categories in between.


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Item Type: USQ Project
Item Status: Live Archive
Additional Information: Bachelor of Engineering (Honours) Major Agricultural Engineering project
Faculty / Department / School: Current - Faculty of Health, Engineering and Sciences - School of Civil Engineering and Surveying
Supervisors: Bennett, John
Date Deposited: 23 Jul 2017 23:20
Last Modified: 23 Jul 2017 23:20
Uncontrolled Keywords: infiltration rate; qualitative assessment; soil science; structural anomalies; two-dimensional infiltration; complex and variable soil environments
Fields of Research : 09 Engineering > 0905 Civil Engineering > 090599 Civil Engineering not elsewhere classified
URI: http://eprints.usq.edu.au/id/eprint/31480

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