At the recent community info session, Alluvium consultants highlighted the importance of submerged aquatic vegetation not only in removing nutrients from the water but a necessity in overall lake health. This vegetation typically grows below the 2ft water depth.
In 2013 substantial loss of vegetation occurred as a result of a significant rise in lake salt levels and has struggled to return with the trend in salt increasing. Council have indicated that existing salt tolerant plants will eventually make up for the loss. 8 years on, there is very little evidence of this along the shoreline.
The recent improvement in water clarity has confirmed that since 2013, very little vegetation has returned to the key transition zone between the shallow and deep water.
As this area receives the most light, vegetation has the best chance of survival during algal blooms and reductions in water visibility during rain events. In relation to the west side of the lake, where the majority of the lake is too deep to support vegetation, ONLY the shallow areas are suitable for growth. With the west side having high nutrient load and practically zero vegetation, planting is a necessity.
The option to replant areas of the lake with species effective in nutrient removal rated highly in the options report.
In formulating the LHM Management Plan, Council need to include widespread planting of salt tolerant plants to assist the current limited vegetation along with salt water management to ensure substantial plant losses do not occur in the future.
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.
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 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.
With Spring just around the corner, now is a great time to get in a do some overdue maintenance to your garden to reduce green waste from entering the lake.
Council have a FREE service called Flexiskip where they will supply a skip to remove household rubbish including green waste.
This is a great opportunity for waterfront residents to dispose of any waste lakeside and for residents in the catchment to remove any leaf litter, weeds, excess lawn clippings etc that can find their way into the lake.
Please follow the link below for full info and to order your skip!
Just a brief update on the meeting held on the 12th of August.
Poor attendance from user groups with only one other representative from tri clubs present.
No commitment to Phoslock top up until assessment of initial treatment.
Reedbed removal shortly due to age /structural issues. Care Group recommend replacement habitat established BEFORE removal to reduce impact to wildlife.
Planting of foreshore plants adjacent to parklands with existing species planned by Council. This will provide habitat but delays to supply/grow mature plants, then establishment.
Presentation of Options report. Options are scored on various criteria. Phoslock and submerged aquatic plants rated highly with one-way value down the list due to no modelling done and the indication by Griffith of significant saline groundwater intrusion. The Care Group are still waiting for clarification on the assessment of salt and nutrient inputs from the canal vs groundwater.
Option of mixing waters near lake exit during rain events missing from assessment. Option can assist in removal of both nutrient and salt water from the lake. Request that consideration and analysis be included.
Only one option to resolve stratification that scored highly on both environmental and social criteria. The option involves shallowing of the west side of the lake to induce natural cycling of the water column as is the case with the eastern side of the lake. See image for clarification – Image courtesy of Princeton Hydro.
Options report used to develop a lake management plan but no timeframe.
Digital copy of options report to be available on Councils website shortly.
On further analysis of the option report, the Care Group will be following up with numerous questions to clarify the assessment of options and Councils current/future plan to stop the decline.
The Phoslock application has now been completed. This treatment along with sand capping was recommended by Griffith Uni as the best option to reduce the occurrence of algal blooms.
It does not however, resolve the serious lake health issues that resulted in an ongoing decline in lake health for over 20 years.
A meeting with Council scheduled in 3 weeks, COVID permitting will discuss the options to best address the long term health issues including increasing stratification and increasing salt that has resulted in a significant decline in aquatic vegetation.