Lakes Beach Desalination Plant Groundwater Investigations
Client: NSW Department of Commerce
Year: 2004-2007
Project Reference: 04137
WRL Technical Reports: Site Investigations - Lakes Beach (2004/32); Three-Dimensional Modelling of Groundwater Extraction via Lateral Wells at Lakes Beach NSW (2005/01); Detailed concept design for beach bore intakes and brine discharge to ocean, Temporary Desalination Plants, Wyong Area (2006/19)
Drought and population growth in the 21st century has seen unprecedented pressures on the water supply of the Central Coast of NSW. To supplement existing water supply, emergency construction of temporary desalination plants (1-8 ML/day) was investigated, sourcing saline groundwater from subsurface seawater intakes. WRL was engaged to complete a number of complimentary projects surrounding these investigations, including initial hydrogeological site investigations, complex groundwater modelling of the site and proposed pumping regime, and further detailed concept design of beach bore intakes and brine discharge to the ocean.
To conceptualise the Lakes Beach dune aquifer system, detailed site investigations were completed. WRL designed and supervised the installation of a network of piezometers (including several multi-level piezometers), and production bores, during which stratigraphic data was collected. Hydraulic conductivity was calculated using slug tests of the piezometers, and aquifer properties were determined using a 24-hour pump test of the production bore, whilst monitoring drawdown and recovery in the monitoring piezometers. The freshwater-saline interface was determined using conductivity measurements of the multi-level piezometers and water quality samples were collected for analysis. High-frequency water level measurements were recorded using pressure transducers over several months.
Data collected during the site investigations was subsequently used by WRL to develop and parameterise firstly a 2D, then 3D model of Lakes Beach using the FEFLOW groundwater modelling code. Detailed topographic data was also collected by walking transects across the site using high resolution Trimble GPS-RTK equipment. The boundaries of the model were the lake to the west and the dynamic ocean boundary to the east. The model was calibrated to the water level measurements recorded during the site investigations phase and local tidal measurements. Model predictions demonstrated that at the desired pumping rate from traditional high flow production bores, drawdowns in the lake would be unacceptable. As a result, the alternative of innovative lateral wells was investigated and WRL found that more water could be pumped with less drawdown. Multiple options in terms of numbers of wells and pumping regimes were compared.
With WRL’s experience in the area of beach dynamics and brine discharge, WRL was also able to provide a detailed concept design for the beach bore intakes and brine discharge to the ocean. Design of the temporary structures was based on optimising a combination of 1 ML/day units to prevent screen dewatering, minimise drawdown and maximise dispersion and dilution of brine discharged to the ocean.
Using the previously established groundwater model of the site, WRL optimised the screen length, number of bores, distance between adjacent bores, distance between bores and discharge point and location relative to the high tide mark. WRL analysed five brine discharge options, recommending an offshore diffuser pipe, or alternatively discharge into swash zone.
For further information about UNSW’s research on coastal zone connectivity, please visit the Connected Waters Initiative
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