Subject: Control bore at Kamarooka


Further to the e-mail below I downloaded the control bore yesterday and updated the plot.  

The results are attached.  
 
Regards Phil 


Dear all,  

I had a recent e-mail from Western Australia this week advising the lack of recharge under the ridge at Kamarooka is echoed in the northern areas of the wheat belt in Western Australia. They asked me about control bores in the lower landscape that would allow for a comparison with the drawdown we are seeing in response to the plantation. The question was can we remove the general decline in watertable from the decline we are seeing in response to the plantation?    

We do indeed have a control bore, and, again, it is one of the deep bores I drilled in the very early 1980s. It is on the Elmore-Tandara Road immediately northeast of the project site. The bore is located on the western side of the main area of saltland. It penetrates through the alluvial sediments of the Riverine Plain and is screened in the fractured bedrock below. In this sense it is a very good indicator of pressure levels in the main artery (so to speak).  

I have included in this e-mail both the long term hydrograph from monitoring performed by myself and DPI over many years, as well as the more recent numbers I have captured with an electronic logger. I only have the logger data up until March of this year as that is all I have downloaded thus far. Time for another download......maybe this weekend.  

What do the numbers tell us?  Well, once again the interesting thing is the response to climate. Groundwater in the bedrock was artesian in this bore on a seasonal basis until the climate changed in 1996 (numbers shown are measured from the top of the casing which is about 0.5 metres above the land surface). Prior to 1996 recharge (in the catchment) each winter produced elevated groundwater pressures in the region of the saltland. Increased pressure head in the ridge produced an increase in pressure and saline groundwater discharge at the break of slope.    

The lack of recharge post 1996 saw pressure levels beneath the saline land fall. As per previous e-mails, whilst groundwater levels in the lower land have fallen they still remain relatively close to the land surface. The bore shows that groundwater levels have only fallen about 2 metres on the plains post 1996 compared with 7 metres in the upper catchment.  

Depth to watertable in this bore is consistent with the depth we see both on and immediately adjacent the saline land within the project site, and is in strong contrast with the deeper levels now attained under the plantations. The drawdown under the plantation relative to the control bore is currently about 2 to 3 metres.

Thanks to the WA guys for motivating me to fix this errant file. As with CO72 I had to re-build the date log and chop out every second record before I could do all the normal number crunching that allows the numbers to be plotted. As with CO72 I have not removed the barometric pressure influence so the graph is quite noisy.

The other thing to note from the electronic data is the amazing response to that one day of intense rainfall in December 2007 and the length of time taken to recover. This speaks volumes about episodic recharge. 

Enjoy..... 

Regards Phil