George, P.R. and Lenane, L. 1982. Saltland drainage?can it pay? Western Australian Journal of Agriculture. Vol. 23, No. 4, p. 136-138.

This study investigates the feasibility of deep drainage (large open drains and buried drains) to control elevated soil salinity and waterlogging, with reference to four trial sites in Western Australia, namely, Gunyidi (large open drains), Watheroo (large open drains and buried drains) and Esperance (buried drains).

The project notes that there are large areas in Western Australai which are being taken out of production by excess soil salinity. Control of water entering the system can have impacts on the reclamation of the salinised land. A significant issue is evaluating the treatment of waterlogging and salinity on plant growth. The importance of controlling water logging may have effects which do not necessarily assist in reclamation of salinsed areas which require removal of salt from soils. The economic benefits of the respective treatments needs to be determined in the management process.

The detailed site geology and hydrogeology vary for the different sites,. However the sites are typically areas of shallow watertable in areas of relatively shallow bedrock.

At Gunyidi, a farming company installed 15 km of deep open drains on soils overlying sedimentary deposits west of the granite country of the Darling scarp. The aim was to reclaim up to 500ha of land and in doing so to halt further spread of salinisation.
At Watheroo, deep open drains were installed at 2 metres in depth on the property of M. Sutherland. A second trial site was initiated on the property of R. Crombie and buried drains, 1.5 metres in depth were installed at 15 metres and 30 metres spacings .

At Esperance Downs Research Station, where the water table was 1m below the ground surface, 5 parallel buried drains were installed 1.6 to 1.7 metres deep and 40 metres apart to drain 5 ha of saline and waterlogged soil which had developed on a sloping area underlain by shallow rock. Drainage water was discharged through a 500 metre length underground pipe to a surface drain downslope.

At Gunyidi, only farmer comments suggested that only around 10% of the newly drained land failed to germinate. This was mainly in the heavier wetter soils. Annual field measurements of soil salinity in winter indicate there was little improvement to salinity following the installation of the deep open drains. The monitored areas ability to carry a crop in the two years of observation showed no improvement, however the owner of the property considered that waterlogging had reduced and the bare 'scalded' area was smaller. The improvements over the short term are likely to be due to reduced waterlogging in non-saline and mildly saline land.

At M. Sutherland's property at Watheroo, the water level decreased by 0.8 metres immediately following the installation of the deep open drain. Saline water was discharged continuously. The drawdown effect was observed in a bore at least as far out as 75m from the drain. The area was cropped to wheat in 1982 and reasonable growth was achieved in parts considering the severity of the salt impact.
At R. Crombie's property at Watheroo, the water level decreased by up to 0.5 metres. It was reported that the area was cropped to barley in 1982 for the first time since the sub-surface drains were installed. There was greater lowering at closer drain spacing, but even at the wider spacing there was an improvement in growth, suggesting that with more time for leaching to occur, longer term improvements may be possible.

At the EsperanceDowns site, following 7 months of monitoring, the water level had lowered by 0.6 to 0.7 metres to the level of the subsurface drains. The water table rose during the opening seasonal rains, but the drains collected the additional discharge, and the water table reduced to the drain level by late in 1981. During the 1981 winter, approximately 2,000 m3 of water containing 40 tonnes of salt were drained from the area. Field salinity measurements demonstrated that in 1982, the area of saline soils at the discharge site had decreased and the salinity of the saltiest areas was only half that of the previous year. In 1982, the area was cropped to barley with excellent results, although the areas identified as the saltiest before drainage still produced poor crop. It is anticipated that more time is required for the salt to leach from the soil profile.

Drainage trials at three sites in Western Australia has demonstrated that the overall technical success of both deep open drains up to 1-2m deep, and subsurface drains. Each of the trial sites investigated responded differently to drainage and have required different drainage intensity. The scheme has shown to decrease water levels and in some cases increased pasture productivity, however their economic viability requires evaluation prior to considering implementation. However the installation costs are high and the engineering option is largely site specific.

The following are key determining factors for the successful implementation of deep drains and subsurface to control shallow water levels and elevated soil salinities in dryland areas:

• drain spacing adequate to maintain the water table at a particular depth below the ground surface;
• a ?perceptive value? derived from the visual decline of waterlogging and saline scalds;
• a level of economic return from the land subject to the drains;
• a level of economic value of the re-used water;
• ability to re-use the drained water; and
• a suitable drainage disposal or storage strategy.