Blue Lake water levels
AHD stands for Australian Height Datum, and basically means above sea level. Water levels need to be measured against a datum to take out any topographic differences so that the height of the groundwater can be compared across a region, and all Australian states now have a common datum. All the Blue Lake levels charted are shown in metres above AHD.
How is the lake measured? Both the Blue and Valley lakes have AHD level points located close to the water surface. Additionally the Blue Lake has a gauge board located at the water’s edge. This gauge board reads the lake level in metres above AHD. The data you are viewing at this site has been collected by data logger, which is an instrument that measures the pressure of water above a sensor point. This value is then interpreted as a value above AHD. The beauty of a data logger is that it can be programmed to read at any frequency required and in the case of the two lakes the data is collected every four hours. The data logger averages the water level over this period of time and then once a week all the information is downloaded using telemetry.
Blue Lake water quality
SA Water test the water quality weekly and you can request a copy of their annual drinking water quality report, where you can access more detailed water quality information from the last year.
The City's water-use for the last month of 2008 was a huge 120ML under the December average. I assume that this is directly related to the mild and relatively wet summer season we have been experiencing. By contrast, our water use for November – 328.5ML for the month, was 45ML above average! Although it appears from the graph that Mount Gambier residents used a lot less water than average over the past winter, we were actually using water from another source – the confined aquifer (as well as Blue Lake water) which is why our Blue Lake consumption looks down in this chart. We were also just above average* in September, but under in (just) in October and August. *The average figure for comparison in these notes includes ALL the water used by residents – including Blue Lake and confined aquifer water, as opposed to the graph which only displays water pumped from the Blue Lake.
This shows trends in Mount Gambier's total water use over time. The total water use depicted for 2007/08 includes water from the Blue Lake and the confined aquifer, as this emergency water supply was accessed while SA Water lowered the pump at the Blue Lake during 2008. It is clear that above "average" amounts of water were consumed by the City in the years 2000/01, 2006/07 and 2007/08. While 2006/07 was a very dry year, the rainfall in 2000 and 2001 was above average so the amount pumped is not always directly related to the amount of water the City uses.
This chart shows the longer term trends of the Blue Lake water level alongside the pattern of Mount Gambier's water consumption.
This chart is up to date as of the 19/12/2008. The level of the Blue Lake on the 19/12/2008 was 11.152m AHD – up from the month before. There is a little jump evident in the water level in mid December responding to the heavy rain we had that month. The overall trend in the level of the Blue Lake is clear, and climate is the main driver of this, however Mount Gambier should be serious about water conservation because the level of the water in the Blue Lake provides an insight into the falling level of our groundwater. This water supports not only the city with all our homes and businesses, but the surrounding industry, agriculture and our environment.
This chart is up to date as of the 19/12/2008. You can clearly see that the water level responding to that heavy rain in the middle of December. Over the last century the water level of the Blue Lake has fallen and so has the average rainfall, but the relationship is not as simple as that. The level of the Blue Lake is a reflection of the surrounding watertable (top of the aquifer or groundwater level) which is affected by many factors including faulting, irrigation, industry use and recharge.
This chart is up to date as of the 19/12/08 when the level of the Lake was 11.269m AHD. You can see the level of the Lake responding to the rain of December 2008. This charts shows how the level of the Valley Lake is related to the season. The Valley Lake is attached to the groundwater system, however because of the volcanic eruption much of the debris blown sky-high dropped back into the crater. The Lake bottom, instead of being a clean limestone, is clay-like. This slows the groundwater flow into and out of the Lake and so it tends to be always a little out of step with the surrounding groundwater - i.e. some water mounding at the end of winter and conversely a little lower at the end of summer from evaporation.
This chart is up to date as of the 19/12/08. If you look closely, you can see the level of the Lake responding to different rainfall events - including the rain in the middle of December 2008.
This chart is up to date as of the 19/12/08. Note the little peak in the middle of December 2008 in response to that heavy rain and back in early in November 2007, when it rained all weekend. This chart is interesting because it shows that although the Blue Lake and Valley Lakes are very different Lakes they are both showing a similar overall trend.
In the South East are subject to permanent water conservation measures from SA Water. You can be fined for not following these guide.