Managing root zone water quality

This GWRDC/CSIRO project was commissioned to obtain a better understanding of the
leaching of contaminants through the root-zone and to suggest management options to
improve drainage water quality. In this project the quality of the drainage waters was
assessed in several regions (Sunraysia, Riverland, Murrumbidgee Irrigation Area,
McLaren Vale and Southeast of South Australia) during the period of 2007-09. Water
samples were collected from the few tile drains that were still flowing, from suction cups
deployed at different depths in vineyards and from the deep drainage from lysimeters. The
data showed that little drainage past the root-zone was occurring, and as a result the load
(but not concentrations) of agrochemicals in drainage water has declined dramatically in
recent years. The project highlighted new challenges on root-zone salinity build-up and
potential accumulation of other chemicals in the lower layers of soil profile. The
accumulation is anticipated to affect both quantity and quality of grape harvest as well as
presenting a threat to drainage water quality when a flushing event does occur. The
occasional natural flushing can cause elevated concentrations of agrochemicals in the
drainage water. A balance between adequate drainage and efficient water usage is
therefore essential.