Impacts of Amelioration on Sodic Soil Hydraulic Conductivity and Potential Consequences for Deep Drainage in the Lower Burdekin, North Queensland

Lucy Reading (2010). Impacts of Amelioration on Sodic Soil Hydraulic Conductivity and Potential Consequences for Deep Drainage in the Lower Burdekin, North Queensland PhD Thesis, School of Civil Engineering, The University of Queensland.

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s41382316_PhD_abstract.pdf s41382316_PhD_abstract.pdf application/pdf 9.82KB 5
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Author Lucy Reading
Thesis Title Impacts of Amelioration on Sodic Soil Hydraulic Conductivity and Potential Consequences for Deep Drainage in the Lower Burdekin, North Queensland
School, Centre or Institute School of Civil Engineering
Institution The University of Queensland
Publication date 2010-05
Thesis type PhD Thesis
Total pages 265
Total colour pages 23
Total black and white pages 242
Subjects 09 Engineering
Abstract/Summary Groundwater tables are rising beneath irrigated fields in the Lower Burdekin in North Queensland, Australia. The soils where this occurs are predominantly sodic clay soils with low hydraulic conductivities. Many of these soils have been treated by applying gypsum or by increasing the salinity of irrigation water by mixing saline groundwater with fresh river water. While the purpose of these treatments is to increase infiltration into the surface soils and improve productivity of the root zone, it is thought that the treatments may have altered the soil hydraulic properties well below the root zone leading to increased groundwater recharge and rising water tables. The objective of this thesis is to assess the potential for sodic soil amelioration treatments to increase soil hydraulic conductivity and hence increase groundwater recharge rates. This research focuses on the impacts of gypsum treatments and increased irrigation water salinity on soil chemistry, soil hydraulic conductivity and deep drainage rates. To determine the current properties of local sodic soils, previous soil surveys were reviewed and field work was conducted to collect soil samples. From the analysis of these soils, it was determined that sodicity levels remain high at some locations even under irrigation and that the high sodicity levels extend below the typically sampled “root zone” Using the samples of the collected sodic soils, experiments were conducted to measure changes in hydraulic conductivity in response to selected treatments. The results of these column experiments showed that gypsum applications can lead to increases in hydraulic conductivity of an order of magnitude when compared with the maximum hydraulic conductivity of a surrogate for good quality irrigation water. Hydraulic conductivity increases occurred when sodic soils were leached continuously with a saturated gypsum solution for at least three weeks. These increases in hydraulic conductivity were positively correlated with decreases in exchangeable sodium and magnesium concentrations. The salt concentration of the applied solution was found to have a significant influence on the maximum hydraulic conductivity; however continued leaching with mixed cation saline waters caused a rapid increase in hydraulic conductivity followed by a gradual decrease. vi Numerical modelling was used to study the expected depth and timing of the impacts of amelioration, compare the impacts of different treatments on deep drainage and to determine the influence of large amounts of rain during the relatively short wet season on soil properties and deep drainage. When the amelioration of ten metre profiles of sodic clays was simulated using HYDRUS-1D, decreases in soil sodicity only occurred close to the soil surface but deep drainage rates still increased. When gypsum applications occurred during the irrigation season, deep drainage rates during the following wet season were at least three times greater than when no gypsum was applied. Gypsum applications and increased irrigation salinity have the potential to increase soil hydraulic conductivity and deep drainage rates. The overall impact of sodic soil amelioration on rising groundwater tables in the Lower Burdekin depends on the initial soil sodicity and soil hydraulic properties of the active crop root zone, the frequency and duration of treatments, the rates of irrigation and rainfall, and the hydraulic conductivity of the materials in the deeper unsaturated zone below the crop root zone.
Keyword gypsum
sodic soils
Hydraulic Conductivity
Deep Drainage
groundwater recharge
Additional Notes Colour pages: 36,37,38,45,46,48,51,63,80,88,103,109,110,111, 161,187,225,226,227,229,230,232,234, (based on page numbers for document e.g. the cover page = page 1)

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Created: Wed, 29 Sep 2010, 13:05:27 EST by Mrs Lucy Reading on behalf of Library - Information Access Service