Received a call from the Head Engineer Steve Mc Veigh today to clarify the concern over the conflicting information in the salt water data.
He advised that the data displayed was a limited graphical representation of the changes in salt hence the confusion over the timing of tides. Steven confirmed that underlying data that Griffith analysed confirmed groundwater tidal influence from the canal.
In relation to improved monitoring of salt inputs, the difficulty of monitoring was confirmed but given the trend of increasing salt and the negative effects, a clearer understanding is required.
In the recent meeting in regard to fitting a one-way valve, Griffith responded in the meeting minutes by stating;
- The data from the vertical profiler indicated there is a direct link to tidal patterns in both the deeper sections and the upper sections of the lake and the blocking of the exchange pipe would not reduce saltwater inflow due to this direct link.
The diagram below shows the profiler data and the variations in salt levels – Griffith are stating these changes relate to tide levels showing significant groundwater input pushed in by the tides.
Unfortunately these assumptions ARE INCORRECT!
If you break down the data into days you can see that the peaks occur at THE SAME TIME EVERY DAY. See daily lines on diagram.
Tidal patterns advance by approximately 1 hour every day so if these variations were related to tidal variations they would occur at different times of the day but they do not!
The conclusion is that THESE VARIATIONS DO NOT RELATE TO ANY TIDAL PUMPING OR GROUND WATER INTRUSION AND THAT ANY ASSUMPTIONS BASED ON THIS ARE ALSO INCORRECT!
The result is that Griffith have not progressed further and investigated the influence of the canal and ran modelling on the effects.
The result is that the review of the one-way valve by Alluvium has been compromised by not just misleading but incorrect data and assumptions.
The fact that Alluvium highlighted only medium confidence in their review due to no modelling if a further indication of a compromised assessment.
So where is the evidence of significant groundwater?
The Care Group have requested clarification over these important findings and will advise if these observations are correct.
Please see link to minutes of Meeting – Minutes
On the back of favourable weather conditions as a result of La Niña, Algae levels have continued to remain relatively low through winter into spring. Typically a spike in Algae has occurred during this time. It is too early to see any positive effects from the Phoslock Treatment in August but water clarity has definitely improved.
Only time will tell if the success of treatment is compromised by high inputs of nutrients from the canal and the catchment as we head towards Summer.
Griffith University have indicated groundwater as a significant source of saline inflow. Although impossible to measure the extent or even the concentration of any groundwater, ongoing in-lake measurements clearly indicate substantial inflows of salt from the canal having an impact. See diagram.
At the recent meeting with Council, the Care Group requested investigation into all inputs into the lake and to clarify the readings that indicate this salt input. Regardless of where the salt is coming from, the increasing trend in salt means more salt is entering the lake than exiting. Reducing a major input of salt from the canal has the potential to reduce the overall salt content of the lake and reduce stratification and lake decline.
The Griffith report 3 years ago highlighted the need for further information stating;
“More information on inflows is needed, both in terms of nutrient concentrations and volumes of water input from the storm water drains, as well as exchange of groundwater and/or the adjacent canal. An understanding of the source of the higher salinity water accumulating in the lake bottom is needed.”
Unfortunately 3 years on, Council has not taken steps to investigate and provide the necessary information/monitoring to determine the detrimental effects from the canal.
The key questions are;
- How can Griffith make a determination of significant groundwater without even assessing input from the canal in both tidal and rain events?
- Are Council planning to effectively monitor salt, flow and nutrients from the canal to assist in this determination?
The Care Group will advise on the reply once received.
The Alluvium report unfortunately did not include the option that provides mixing of bottom waters near the lake exit pipe that was discussed at initial meeting with Consultants.
This option has the potential to reduce both salt and high nutrient levels in lake so well worth consideration and assessment by Alluvium. Both are major issues.
As highlighted, there is no perfect option but to not take steps on these issues will only result in the continual decline in water quality. Below is the link to the proposal.
Option For Consideration – Mixing Near Lake Exit
The options report is now available on the Council Website. Link included below.
The key to any report is the follow-up with action to address the key issues affecting the long term health of the lake. The Care Group will be looking forward to the plan to implement the best options to address the ongoing trend of increasing stratification and increasing salt that is has been a major contributor to the decline in water quality.
The one way valve did not score as well as expected – Alluvium only had medium confidence in their assessment given the minimal evidence and no modelling. Despite the significant influence the canal input has on both the salt and nutrient levels, there has been no assessment, investigation or modelling to determine how this input effects the lake.
Given the importance, the Care Group request that proper investigation including modelling be carried out on canal input.
Alluvium Lake Options Report