Drain Tech recently undertook a Land Rehabilitation project for Bundaberg Sugar Limited. The 37 hectare block is located near South Kolan on the Bundaberg-Gin Gin Road and although it had a history of cane production, in recent years cropping had been abandoned due to salinity issues.
EM 38 measurements indicated salinity levels of 0.2 to 0.7 dS/m in the top 1.5 metres of soil. The source of this saline intrusion appeared to be from upward seepage through fractures in the underlying mudstone. At some soil pits localised discharge was measured at 7 dS/m which would certainly cause issues for sugar cane with a salinity threshold of 1.7 dS/m.
In order to return this site to cane production two issues needed to be addressed. Firstly the incoming seepage needed to be intercepted and conveyed to the edge of the paddock. Secondly the varying salt concentrations in the soil above the clay/mudstone base needed to be leached and flushed of detrimental soil salts. Traditionally, sub-surface drainage is used to initiate downward percolation of soil salts. The addition of rainfall and or irrigation water commences a flushing effect in the soil profile and remediation can be quite dramatic. Time to cleanse a soil profile is a function of initial salt levels, soil porosity, and the volume and quality of the incoming water.
Drain Tech was asked to design and install a system of sub-surface collector drains which were spaced at 30 metres and approximately 1.5 metres deep. Discharge was to a specially constructed open drain with a dedicated storage and monitoring facility.