True State of our Basins


 

What is the True State of our Basins?

 

Resource Capacity in 2000 compared with 2015

 

Central to our concerns with the draft WAP are the figures given in the WAP 2000 for the Annual Average Recharge compared with the Resource Capacity given in the draft WAP. Although they have different names in the WAPs we know we are comparing like with like because they are the figures obtained by Recharge Area x Recharge Rate in both cases. In each case the lenses we are comparing are identified as containing ‘potable’ water (ie water below1000mg/l).

 

Lenses                                               2000                                  2015                         %age change

                                          RArea  x  RRate  = AAR                RA  x  RR = RCap.                               

Coffin Bay A                                 11 x 34  = 375                13.8 x 29  = 401                 +6.93      

Uley Wanilla PWS                        37 x 54  = 2000             14.3 x 13  = 186                  – 90.7

Uley South PWS                      129 x 155 = 20,000         65.4 x 129 = 8439                – 57.8       

Lincoln A,B,C                                45 x  56 = 2520             1.2  x  35  =  42                    – 81.12-ABC

Lincoln B                                     3.95 x 35 = 137.25

Lincoln C                                     7.92 x 35 = 277.2

                                                        TOTAL  = 456.45

Uley East                                     19  x  69  = 1310           5.48  x  22  = 120 (A)

                                                                                              2.42  x  22  = 53    (B)

                                                                                                     TOTAL  =  173                 – 86.8 !


 

The first thing of significance between the two sets of figures is the extraordinary difference (given in %age terms) between the 2000 and 2015 in the last column.

 

(1) Uley Wanilla Lens.

 

The volume of potable water calculated to be available for allocation from Uley Wanilla lens is 2000ML/yr in 2000 but only 186ML/yr in 2015. This is an extraordinary difference considering it occurred during water management under a legally binding Water Allocation Plan (WAP). The question now is to determine what caused this huge change. If accurate it reduces considerably the amount of potable water available under the draft WAP being prepared.

 

(i) less rainfall. While an ongoing decline in average rainfall would contribute to such a decrease it cannot possibly account for more than some of it at most. No such significant decline in rainfall is on the records for lower Eyre Peninsula during this period.

 

(ii) change in area. For Uley Wanilla lens, this went from 37 to 14.3 sq. kms. Why? One suggested explanation is that the measurements of the appropriate area have now been more accurately. If this is really correct then one would expect that in at least one or two lenses the area being measured would be larger than the previous measurement. In this case ALL areas are smaller by very large amounts except one (Coffin Bay A lens) where the increase is just a couple of square kilometres. Perhaps the areas measured in 2000 were systematically over-estimated? If so, then it leaves us with another problem (see later). Another possible explanation is that the areas of all these lenses have declined because the underlying lenses have shrunk. Why would they have shrunk? It is unlikely to be because of evaporation so it would have to be over-extraction.

 

(iii) change in recharge rate. There is very little easily understood information about exactly how the recharge rate is calculated for each lens. The recharge rate has been changed and argued about for Uley South over the years. However, let us assume that the recharge rates used in the draft WAP are calculated more accurately now than that used in the first WAP. Assuming that to be the case, once again we are presented with the problem that the ‘new’ (better) method is always giving a decline in the recharge rate for the various lenses.

 

Does this mean that the decline in the availability of potable water in the lenses is explained by:

decrease in area multiplied by decrease in recharge rate = big decrease in resource capacity?

 

The change in potable water available from Uley Wanilla is far too great not to take some action.

 

(2) Uley South Lens

 

Let us assume that the calculations for the resource capacity in the draft WAP (2015) are more correct (ie now) than the calculations done in 2000. The region now finds itself in a dire predicament. The resource capacity for extraction of its most important lens (Uley South) is now only 8439 ML/yr (a far cry from 20,000 ML/yr in 2000). The figure in WAP 2000 gave 8000 ML/yr for alloction.

 

However, not all of the 8439ML/yr for 2015 is available for the reticulated system. There is the need to apply the environment/consumption ratio stated to be 60/40 in the WAP 2000. This was changed dramatically for Uley South lens in the first draft WAP to 30/70, but after dispute, it has since been changed to 48.5/51.5 in the revised draft WAP (so we are told by the NRM Board).

 

Let us look at the implications of applying any of these ratios to the resource capacity of 8439ML/yr:

 

60/40 = 5063/3376 48.5/51.5 = 4093/4346 30/70 = 2532/5907

 

Keeping in mind that the second figure refers to the amount available for consumption which would you want available for the reticulated system? More importantly, which figure is really ecologically sustainable?

 

It is possible that the water managers became aware of this situation if the existing ratio 60/40 was to be left unchanged. They might then have sought to overcome this dramatic decline in potable water by changing the ratio to 30/70. When this was strongly opposed, they settled for the ratio determined by experts at Flinders University of 48.5/51.5. Stakeholders have yet to see exactly what were the parameters identified by the University, from which the ratio of 48.5/51.5 was ultimately selected.

 

Assuming the latest figures (draft WAP 2015) are a much better set from which to work, water managers must now take into account the 15 years of over-extraction that occurred using the earlier much more generous ones. An examination of the extraction graph for Uley South covering the period from 2000 to 2010 (for which we have the figures) shows the magnitude of the deficit resulting from this over-extraction. Each and every year the extraction was 5000ML/yr or more – that is more than 600ML/yr based on the new, best figures. In 8 of those 10 years the extraction was way over 6000ML/yr or 1600ML more than the best figures to be used in the new WAP! Could this “over-extraction” be the cause of the decline in area of the recharge lens?

 

There is another factor to consider. This new set of resource capacity figures should also be modified to ensure that any overdrawn lens is managed from now on so as to start returning it closer to its previous state (or more towards its ecologically sustainable level). This is a quite specific requirement of the National Water Initiative (NWI). The amount by which the storage in the lens should be should be increased each year, over the life of the new WAP has yet to be acknowledged and discussed in relation to the draft WAP.

 

Using the latest compromise ratio of 48.5/51.5 we could make the maximum amount to be extracted in an average rainfall year to be:

 

4346ML/yr minus (say) 350 ML/yr for part restoration leaving 4000ML/yr for

consumption.

This is some 624ML/yr more than if the 60/40 ratio was still being applied. Attempting to increase the storage in Uley South by approx. 350 ML/yr would take more than 30 years to make up the deficit of the period 2000-2010, let alone with the remainder of the time this over extraction has been going on.

 

The figure of 4000ML/yr is an extremely low figure for a reticulated system that uses approximately 5500ML/yr (or more) potable water even when 1400ML/yr is added from the River Murray.

 

The underlying implication is that the Demand exceeding Supply situation may already be less than 5 years away, therefore requiring the Independent Planning Process to be started immediately.

 

The need for additional groundwater (even ‘brackish’) to be added to the reticulated system as indicated in the draft WAP is now understood. However, accessing these additional sources does not solve the problem of past over-extraction.

 

No matter how the “new” sources of water are labeled in the draft WAP (‘brackish’ or whatever) these additional sources of water are already connected to existing lenses. Any new extraction from the Uley South lens might influence the availability of the potable water, as well as increase the possibility of seawater intrusion. Of course, additional water for allocation MUST be a percentage of the recharge, and maintain the volume of the lens.

 

At some time, these issues need much more consideration and explanation before any new WAP is signed into effect.