Figure 1 - uploaded by Thusitha Gunawardena
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Schematic illustration of the system of any one lysimeter: collection trap, vacuum line and vacuum tower layout. One vacuum tower operates all three lysimeters in any one field.
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![Figure 2: Calculated and observed drawdown [m] with discharge and...](profile/Thomas-Nuber/publication/336383616/figure/fig2/AS:812437003575298@1570711484753/Calculated-and-observed-drawdown-m-with-discharge-and-without-discharge-at-the_Q320.jpg)
Citations
... Water not used for plant growth or lost to evaporation, drains below the root zone (deep drainage). Deep drainage of 100-200 mm/yr has typically been measured under furrow irrigation in a large number of sites on Vertosols and Sodosols in Australia (Silburn and Montgomery, 2004;Smith et al. 2005;Gunawardena et al. 2008). There is some evidence, from bore monitoring, of rises in groundwater level in shallower aquifers in the alluvium (DERM groundwater database), likely due to recharge from deep drainage, but many shallower bores have been dry for many years. ...
... Overall, these results indicate changes in conductivity in the upper profile are predominately due to differences in soil water. The depth of the highly conductive zone is shallower at the tail drain (near the native vegetation) than towards the head ditch, consistent with less drainage occurring along furrow irrigated fields (Gunawardena et al. 2008). ...
Over use of one of Queensland's most productive groundwater systems, the Condamine River alluvium, has led to substantial depletion in groundwater levels. Most use is for irrigation (mainly furrow), which is known to increase deep drainage below the root zone. Thus irrigation should create greater groundwater recharge, but this is not generally detected in groundwater levels. The enhanced deep drainage may be filling a moisture deficit in the unsaturated zone and is therefore not yet causing greater recharge. Geophysical 2D resistivity imaging and soil coring was used to look at changes in stored regolith water in the alluvium. Transects were imaged across naturally vegetated landscapes (as a reference) into irrigated paddocks. All soils under native vegetation were found to be very dry (low conductivity) even when only sparsely populated by trees. In contrast, significant long-term migration of water has occurred to deep within the regolith (up to 15 m) in most irrigated paddocks. A wet (close to saturated) zone was found in the upper 6 m of soil in the irrigated paddocks. Deeper regolith (20-60 m) was resistive, both above and below the water Table, due to low salinities in the groundwater and coarser textures. Introduction The Condamine River Alluvium and its tributaries is one of the most productive and utilized groundwater resources in Queensland. The main system is over 150 km long, up to 30 km wide, and over 120 m deep in places, with multiple sand and gravel aquifers in a matrix of clayey sediments. An estimated 95 000 ML/yr are used for agriculture (90%) on Vertosols, and some urban purposes. Groundwater levels have fallen substantially because of over use, particularly in the Central Condamine where ~70% of all usage occurs (Murphy, 2008). This decline has been particularly evident over the last decade as the system has been in a virtual 'recharge drought'. There is also increasing evidence of water quality deterioration, both in shallow groundwater as a result of increased salt leaching, and in deep systems as a result of the migration of poor quality groundwater from adjacent areas and from bedrocks (Murphy, 2008). Irrigation alters the surface water balance. Water not used for plant growth or lost to evaporation, drains below the root zone (deep drainage). Deep drainage of 100-200 mm/yr has typically been measured under furrow irrigation in a large number of sites on Vertosols and Sodosols in Australia (Silburn and Montgomery, 2004; Smith et al. 2005; Gunawardena et al. 2008). There is some evidence, from bore monitoring, of rises in groundwater level in shallower aquifers in the alluvium (DERM groundwater database), likely due to recharge from deep drainage, but many shallower bores have been dry for many years. Diffuse recharge (i.e. through the soil) in the alluvium is considered to be small, with the aquifers mainly recharged by river leakage (Lane, 1979). Thus there is a disparity—deep drainage below the root zone is seen to be high but recharge from this source is thought to be low. This would be explained, in part, if deep drainage was being stored in an unsaturated zone left dry by the previous native vegetation, creating a time lag between deep drainage and recharge.
Deep drainage (DD) - water that passes beyond the root zone – is an important
process in irrigated cropping soils to ensure leaching of salts through the soil
profile to deeper soil layers, the vadose zone (the zone between the rootzone and the watertable) or to groundwater. Salt can either be naturally present within some soils or be added through low quality irrigation water. Furthermore, excessive DD may cause water table rise to the rootzone with associated salts, so precluding the growth of salt sensitive species.
DD is also an economic negative, as costs of pumping and storage are not realised in increased yields or possible increased area under production. The loss of irrigation waters to DD is particularly important in drought years where the rare water resource must be carefully utilised to ensure crops attain maximum yield per unit volume of applied water.
The study reported here focused on DD water losses and the quality of those lost waters (in terms of salinity) on 7 irrigated cotton farms (all but one under
traditional furrow irrigation management) in the upper Murray Darling basin
(UMDB) near the towns of Boggabilla (2 sites), Dalby, Goondiwindi, Macalister,
Pampas and St George.
