Rainfall, Extraction and Standing Water Level Part 1


Setting the Scene

 

Prior to 2013 the monitoring of our groundwater basins has revolved around the rainfall, the amount of water extracted and the standing water level. While all three factors can be measured it is extremely difficult to relate them to each other.

Firstly, the rainfall that recharges our basins is not measured where it occurs.

The map is from Figure 3 (page 11) Department of Water Technical Report DFW 2012/04 ‘Impacts of Climate Change on Water Resources Phase 3 Volume 2: Eyre Peninsula Natural Resources Management Region’.

We have placed the red arrows and red names and BOM station numbers on the map to highlight the location of the rainfall stations.

image001


 

 

Secondly, the amount of water extracted from each extraction bore is not available (?) to the community, only the total annual amount from each basin (see table below). The last three dark blue columns are the best approximate estimates from data available at the time.

 image002

 

Thirdly, the standing water level is measured at a range of separate monitoring bores, spread over the whole basin. It is not yet possible (?) to take these numerous pin-point measurements and combine them so as to create an acceptable measure of the change in water level resulting from a combination of rainfall and extraction.

image003                                             

The graph above is from the official Groundwater Data  website showing ULE 101 water levels from 1965. We have highlighted in red on the water graph ULE101 when SA Water commenced extraction, when there were no extractions from  1965 – 1977 and some other years of significance.

 

                   The Ben Bruce Position

Despite the inherit difficulties in bringing these three variables into an acceptable relationship, Ben Bruce attempted to do so at the Parliamentary Inquiry. He presented the argument that “Essentially, if the water levels are going up that means it is above average rainfall, and if it is going down it means it is below average rainfall that is how the tool works”. This is the graph he presented (below) of water levels of ULE101.

 image004

 

In support of his view he offered the graph and the following comment: “As you can see, there is quite a good relationship between the water level and the rainfall level.”

 image005

We have placed in red on Ben’s graph above some years of significance and blue oval shaped lines to highlight some the points we have raised below.    

It is presented to show that the cumulative deviation in rainfall (orange line) (a measure of annual  rainfall and how it has varied over the years) follows closely that of changes in water level (red line). However, a close examination of the graph shows that this is not really the case. Look at the period 1987-94 (in the first blue oval). Here the cumulative deviation (the measure of rainfall) goes up, down, up and down again while the standing water level is virtually the mirror opposite! And again (in the second blue oval) in the period of 1999-2008 the two curves are virtually mirror opposite again!

This performance over a total of 15 years is enough to throw significant doubt over the Ben Bruce Position, if not dismiss it altogether.

So what is a better summary of the relationship between these three variable? Ordens et al (2012), (referring to the same groundwater hydrograph well ULE101 along with the monthly rainfall data

at Big Swamp monitoring station) summarises it this way: “A clear seasonal fluctuation in groundwater level can be recognised together with a steady decline in groundwater levels since the mid-1980’s.  This decline is attributed to the combined effects of pumping and below average rainfall”

 

                   Additional Evidence

                             1. Extraction

The Ben Bruce position is presented without any reference to the rate of extraction from Uley South over the years. This is poor science.                                               

 image006

             

The above graph has the annual extractions of SA Water from Uley South superimposed on top of the Ben Bruce’s graph (the orange line of cumulative rainfall deviation has been removed to just leave the  water levels (in red) compared to SA Water annual extractions).

Taking this piece of information into consideration explains much of the conspicuous lack of correlation between standing water level and cumulative deviation in rainfall. Looking at the second blue oval (from 1999-2008) the lower than expected standing water level (compared with the cumulative deviation) can be directly attributed to the extraordinarily large extractions occurring during that period. Now look at the first blue oval (1987-1994). The rise in standing water level is not so much due to the increase in rainfall, but the decline in extraction during the period 1989-1993. Exactly how much is not obvious but it can’t be ignored

It is the intention of Ben Bruce to attribute no change in water level by pumping and all such change to be attributed to a decline in rainfall. By continuing to downplay any contribution  of extraction to changes in water level, he has only drawn attention to just how important it is.

 

                                    2. Correlation in the Absence of Extraction

 

The graph presented by Ben Bruce starts at 1977, yet there is data available in the 12 years prior to this, and the readings are taken in the absence of any extraction, which only started in late 1976.

 

We have carefully plotted below the same graph that Ben Bruce presented but HAVE extended and included the years from 1965—1977 and highlighted in red when SA Water commenced extraction, some years of significance and the heights of water levels (e.g. 2 metres).  

 image007

This added section of the graph, which was readily available to Ben Bruce to show the Parliamentary Inquiry, on close examination, shows an excellent correlation between the two variables selected by Ben Bruce. Notice that such a close correlation is far from obvious the moment the graph takes in the period in which extraction is occurring. In fact Ben Bruce comments in his presentation: “You will notice that there is quite a good relationship between the water level and the rainfall level [he must be joking]. You will notice that there was a period between 2005 and 2009 where that correlation seems to break down for a bit. There are some theories around why that is but none that has actually been demonstrated yet. That is something we continue to look at, to work out what happened there. Yet you will see that after 2009, when the rainfall returned, the correlation recommenced with rainfall”.

Anyone who cares to take a look at the water extraction graph of water from Uley South will notice, that during the period 2008-10 there is a dramatic reduction in extraction! Might that not go some way towards explaining the better correlation, and not just rainfall on its own? If not, why not??

 

                                    3. Standing Water Level Above Cumulative Rainfall

The relative positions between standing water level and the cumulative deviation in rainfall is determined by the units used in constructing the graphs. However, it is interesting to note that the extended graph (below), ranging from 1910 to the present has the standing water level above the cumulative deviation right up until water extraction from the basin begins in 1977. While not conclusive it does draw attention to the average lower level of the standing water in the later period of the graph compared with the first period.

image008

If the cumulative deviation from about 1930 to 1960 indicates lower than average rainfall, then one could expect the standing water level for the same period to be lower as well. Judging (and it is a judgement) by the standing water level from 1966-1977 and extrapoling backwards towards 1950 and earlier, it would be reasonable to conclude on the meagre evidence that the standing water level was still above the cumulative deviation during that time (using the same units)

 

                                    4. USING ULE101 TO REPRESENT ULEY SOUTH

One can’t help but be suspicious of the information presented by Ben Bruce and to examine it thoroughly. In his presentation he makes much use of ULE101 as representing Uley South.

This graph below is from the Groundwater Data (old Obswell) website of water levels at ULE101.

image009

The question must be asked: is in fact ULE101 a good representive of Uley South? The problem we now face is determining exactly which monitoring bores can be used to assess this. This is because over the years some monitoring bores have been monitored and then monitoring has stopped (even after 30 or more years), others have been monitored for extremely short periods and not monitored again, others have been monitored right up to the last few years and then classified as “historic”, others have only started to be monitored in very recent years, with few bores still being monitored from the early years right up to the present and classified as “current”.

 

The map below illustrates locations of some monitoring bores in Uley South Basin.

image010

It is true to say that there are a number of monitoring bores that resemble ULE101, but that is the result of picking and choosing which bores to keep monitoring, which ones to ignore and where new bores are needed to support the view that Uley South is not under any threat from the extensive extraction of water in the last 20 years or so.

 

The Monitoring Bore Map (dated 2006) shows 52 bores marked on it of which only 26 remained “current” in the Southern Basins PWA Status Report of 2009. The remaining 26 bores on the map were reported as being “historic” in 2009 (ie no longer monitored) of which 24 were historic before 2006 when the map was made!

 

Appendix 1 (below) lists the monitoring bores from the map along with the dates they were first monitored and when they were last monitored. Also given is their status as being historic or current (information taken from the Appendix A: Groundwater Level Hydrographs of the Southern Basins PWA Status Report of 2009). Note: the information in this section of our presentation may contain the odd error, based on trying to read the Bore Map and interpreting the start and finishing dates contained in the Status Report.

 

Before accepting Ben Bruce’s Monitoring Bore of ULE101 without question, the following bores and their standing water levels over the years should be looked at too.

 

ULE094          monitoring ceased in 1991 – water level going up.

ULE105          monitoring ceased in 1997 – water level up

ULE126          monitoring current – water level going down

ULE146          monitoring ceased in 2009 – water level up (extreme)

ULE162          monitoring ceased in 2003 – water level down (extreme)

ULE169          monitoring current – water level down (extreme)

ULE175          monitoring current – water level down (located between US and UW basin)

 

What is happening in these monitoring bores need to be explained just as much as accepting ULE101 and others like it.

ON A FINAL NOTE

 

The other possible influencing factor (among others) of the relationship between rainfall, extraction and standing water level that is conveniently omitted from the Ben Bruce Position is that of interconnectivity. The position of the water authorities on this matter for years has been an unequivocal rejection of any interconnection between the aquifers in the Southern Basins.

 

Landholders here have never accepted that position. It has been weakened if not completely overturned by the recent discovery of this comment in a document which states “The previous conclusion supports the assumption that an increase in extraction of ~10% or 1000 ML/y [in Uley South] should not be of great concern and it should not have a detrimental impact on the groundwater resource in Uley South. However, it would cause a 2-3 m drawdown in Uley East, which in turn might affect current users and limit future development in this lens” in which one of the authors is Scott Evans.

 

All this leads us to the conclusion that:

(1) Much of the testimony by Ben Bruce cannot be trusted.

 

            (2) The storage component of the water in Uley South (even since 2001 when the WAP started) has been compromised despite the injunction in the WAP for that not to happen.

 

            (3) Uley South no longer has any significant input (ie support) from Uley Wanilla and Uley East now that both of them have been reduced in terms of storage volume. Without this, any future over-extraction within Uley South will have the effect of reducing its long-term ecological sustainability.

Leave a comment

Your email address will not be published. Required fields are marked *