Kamarooka Project Update October 2016

The following is a summary of the results from the NUFG Kamarooka Saltland Reclamation project from October 2016. It includes a photo-map of the site showing the contrast in watertable before and after the ‘big wet’ experienced over the past 6 months. 

The climate over last two decades has been erratic and this is reflected in the Kamarooka groundwater records. Extreme climate variability became evident from 1996 onwards. First there was the protracted dry conditions that prevailed from the mid 1990s through to 2009. This was coined the 'millennium drought'. Then there were floods in 2010 reflecting the coincidence of warm water conditions in the Indian Ocean and La Nina conditions in the Western Pacific. These conditions produced the highest annual rainfall on record across many parts of eastern Australia, including Bendigo. Wet conditions in the spring of 2009 had folded into the early months of 2010 and storms generated extreme flooding in already saturated catchments. 

In strong contrast most of the years post-2010 were very arid causing the Kamarooka watertable to decline to levels not seen since the end of the millennium drought in 2009. By May this year the watertable across Kamarooka had fallen to between 4 and 6 metres from the land surface. Then, the extreme dry of early 2016 gave way to persistent heavy rainfall over autumn, winter and early spring and flood conditions returned once again. 

 

As in 2010 the Kamarooka watertable has returned to levels less than 1.0 to 1.5 metres from the land surface.  Interestingly, however, there are a couple of notable exceptions. The rapid rise of groundwater experienced across the non-treed lands (see the attached hydrographs) did not occur below the Eucalypt plantations. Looking closely at the attached hydrograph reveals that groundwater at the centre of the 2004 plantation (bore 8) remains more than 6 metres below the land surface. Note the circled October measurement. This is highlighted in this way because readings because several previous records are absent because the bore had been dry for most of the previous 12 months reflecting the combined impact of drought and transpiration. 

 

Clearly the land within the 2004 plantation is now buffered against a shallow watertable by the trees. Recharge is avoided by tree water use preventing soil saturation and deep percolation, and through modest transpiration of high salinity groundwater. It is equally interesting to note the groundwater hydrograph from the biodiversity plantation. This, to a large extent, is also controlling the watertable. Following the wet conditions groundwater only reaches within about 2.5 metres of the land surface under the shrubby vegetation. 

These latest results consolidate the knowledge we have accumulated regarding rainfall-vegetation-salinity at Kamarooka over the past 13 years. In these old deeply weathered landscapes that are in part overlain by the shallow alluvial sediments along the upland-plains interface native vegetation has the opportunity to interact with shallow saline groundwater. There is opportunity to mitigate a shallow watertable, in part, in the immediate region of Eucalypt plantations/forests. 

Recharge at Kamarooka is now predictable. Eucalypt plantations either prevent it through transpiration that avoids soil saturation, and in part uses some of the groundwater, shrubby native vegetation achieves the same but is less effective in controlling watertables, and cleared agricultural land with a shallow watertable is simply not in the race irrespective of species. 

Salt is not an for the trees. They have worked out how to deal with it. The bigger issue is waterlogging combined with salinity.