NUTRIENT REMOVAL INFRASTRUCTURE
Lake Yanyebup, Cockburn
The aim of this project was to reduce excess nutrients in Lake Yangebup by using solar power to pump nutrient rich water from the lake through a treatment train, then allowing the treated water to flow back into the lake.
Lake Yangebup required nutrient treatment of the lake water to reduce the level of contaminants, as previous land use had severely contaminated the lake water. Various water treatment options were reviewed and costs assessed to determine the most cost-beneficial approach.
A total of 10,000 cubic metres of soil was brought to site, logs and riffles installed, and 19,000 sedges, trees and shrubs planted. A solar array was installed on a pole and submersible pump constructed on a float in the lake powered by this solar array.
A meandering swale drain was designed which allowed water to be pumped from the lake using the solar powered pump to flow through an array of fringing vegetation to reduce the contaminant quantity. Water sampling was undertaken at the drain inflow and outflow points to monitor the effectiveness of the system.
Following the success of the Stage 1 works, the City of Cockburn requested Stage 2 works be undertaken.
A study undertaken by Murdoch University reviewed the effectiveness of the nutrient removal of the Stage 1 treatment system. This study recommended that slow sand filtration be constructed to better treat the nutrient rich water.
This involved review of the area surrounding Lake Yangebup to find an area with suitable space, soil type, and distance to ground water. The chosen area was to the north west of the Stage 1 works.
Soil borehole samples were taken to determine the soil type and to check the distance to the groundwater. Basin locations were optimised using the results.
Two infiltration basins were designed based on recommendations in the Murdoch University study. It was proposed to pump lake water into a central pumping pit, which was designed to balance the water level in each infiltration basin. This allowed two basins to function at one time, to promote vegetation growth for treatment. It also permitted one basin to be shut down for short durations to allow vegetation trimming and basin scraping, which removes the build up nutrients across the basin surface.
February 2014 (Stage 1)
November 2017 (Stage 2)
September 2015 (Stage 1)
May 2018 (Stage 2)
Design of nutrient stripping swale