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The effect of salt composition of groundwaters on the rate of salinisation of soils from a water table

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Jayawardane, NS (1977) The effect of salt composition of groundwaters on the rate of salinisation of soils from a water table. PhD thesis, University of Tasmania.

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Abstract

The rate of salinisation of soils from a water table has been
shown to be related to the concentration of salts in groundwaters
and the rate of upward flow of saline groundwater. The maximum
rate at which soil can transmit soil solution from a water table
to the surface is governed by hydraulic conductivity characteristics
and depth to water table. In the present study the effects of
chemical composition of groundwaters on the rate of salinisation
of three different soils by upward flow were evaluated in soil
columns. These effects were related to changes in pore geometry
and hydraulic conductivity characteristics of the soils in salt
solutions.
The pore geometry, saturated and unsaturated conductivity,
and the capacity of the soil to transmit soil solution from a
water table to the surface varied little in krasnozem soil
exposed to different salt solutions, but marked changes of
different magnitudes occurred in the case of alluvial and red
brown soils.
With a reduction in cation concentration of salt solution
at a given SAR, the inter-aggregate pores of alluvial and red
brown soils decreased in size, apparently due to swelling of
soil aggregates. The extent of this decrease in pore sizes was
greater for solutions of higher SAR. A pore size index was
proposed to evaluate quantitatively these changes in pore geometry.
Patterns in the volume changes of different sized pores with
changes in salt composition were discerned and used to predict
the moisture release curves of these soils for other salt solutions
and also for soils at slightly different bulk densities in the same
Salt solutions.
The saturated and unsaturated conductivity at high pressure
heads of alluvial and red brown soils decreased markedly with
reduction in cation concentration at a given SAR, while unsaturated
conductivity at low pressure heads showed only small decreases.
Existing methods for computing hydraulic conductivities from
moisture release curves could not accurately predict the
conductivities at saturation and high pressure heads in different
salt solutions. It was suggested that the discrepancy was partly
due to changes in internal pore geometry during desaturation as a
result of aggregate shrinkage. These changes were described
qualitatively in terms of a theoretical model.
A concept of equivalent salt solutions was also developed and
used to predict, fairly closely, the hydraulic conductivities of the
soils in different salt solutions. It is proposed that this method
could be used to correlate directly flow of different salt solutions
in soils under specific boundary conditions.
The computed maximum depths to water table for specific rates of
upward flow in alluvial and red brown soils decreased as the cation
concentration was reduced at a given SAR. However, marked decreases
in maximum depths to water table for specific rates of flow occurred
only with solutions of low cation concentration, in the presence of
which the values of unsaturated conductivity within a critical range
showed marked decreases. This critical range was defined using the
•data from a flux/unsaturated conductivity ratio method of computing
upward flow. The changes in measured rates of upward flow, AS the
•cation concentration was reduced at a given SAR, were generally
similar in nature to the changes in computed rates. The application of
these results and concepts to field problems and areas for future
research have been discussed.

Item Type: Thesis (PhD)
Keywords: Soils, Salts in, Groundwater
Copyright Information:

Copyright 1977 the author - The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s).

Additional Information:

Sections of Appendix A were published as a paper in the Australian journal of soil research, Vol. 15, 17-25, 1977.

Date Deposited: 19 Dec 2014 02:23
Last Modified: 21 Sep 2016 01:27
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