A detailed study has been carried out on the sedimentation in Lower Whitby Lake, to identify issues and come up with options to improve water quality.
The Whitby Lakes are two man-made lakes, initially built in the 1970s to hold stormwater and sediment run-off from the surrounding urban areas. In recent times they’ve become a refuge for wildlife and a valued asset for the people of Porirua.
Last year the lower lake had a considerable amount of sediment enter its ecosystem, discolouring the water and raising concerns about the lake’s health, says Porirua City Council Parks Manager Olivia Dovey.
“We engaged scientists from the Cawthron Institute’s coastal and freshwater team to investigate the impact of the increased sediment in the lake – both now and in the future,” she says.
During the six month study high levels of sediment made their way to the lower lake.
“In total, about 163 tonnes of sediment entered the lower lake – approximately 20 times the annual sediment load expected for a lake like ours,” Ms Dovey says.
“This could lead to increased nutrients due to deoxygenation, poor water quality and higher chances of algal blooms in warmer months.
“The lake bed now also has higher levels of phosphorus and the control of this will be vital to improving the lake.”
The report identified a number of options for Council to consider as part of an ongoing management plan. These, and the report’s findings, were discussed at a meeting with the Whitby Residents Association last month.
“After that helpful discussion the options are now being considered,” Ms Dovey says.
“The aerator and fountain will continue to operate to reduce the likelihood of algal bloom and an ongoing monitoring plan will be developed and implemented.
“Any large scale or high cost projects requiring funding will be considered as part of the Long-term Plan.”
6 Aug 2019