Development of Computer Code to Optimise the Production of Hydrographs in Sydney, Australia

Long term groundwater level monitoring has been conducted in support of the environmental impact statement (EIS) prepared for the WestConnex M4-M5 Link project (RMS, 2017). The M4-M5 Link will connect two predominately underground twin drained motorway tunnels and multiple interchanges which will be excavated from the Hawkesbury Sandstone and Ashfield Shale. In order to assess the impacts of the tunnels and associated infrastructure on the local groundwater systems, a groundwater level baseline data set is being developed to characterise natural seasonal and tidal variations in the existing hydrogeological regimes.

A network of data loggers have been installed in groundwater wells screened in alluvium, Ashfield Shale and Hawkesbury Sandstone and are programmed to monitor groundwater levels through hydrostatic pressure fluctuations at an hourly interval. Barometric monitoring was also undertaken to correct for atmospheric pressure variations. Due to the large amount of data generated by the project and the shortcomings of Microsoft Excel as a streamlined graphing tool, innovation was required on the traditional method of using Excel for data analysis. As such, a custom R code was created to automate the process of hydrograph generation. The code imports folders of raw data logger files, barometrically corrects the data, identifies the groundwater well location of each raw data logger file, matches each file to the manually recorded standing water levels, and converts the groundwater level to m AHD from the raw pressure files. The code then produces hydrographs, plotting the reduced standing water levels against rainfall, exporting a fully formatted combined PDF of each hydrograph. This process significantly reduces the time spent on data manipulation and graphing and the potential for human error during the data manipulation phase.

This visualisation of the data has allowed groundwater trends within the measured time to be observed, including the tidal and rainfall dependant nature of recharge. In the Hawkesbury Sandstone, groundwater fluctuations shown in the hydrographs display a high correlation with rainfall patterns observed over the monitoring period. The alluvium is primarily controlled by local recharge and discharge conditions within the measured time. Several hydrographs also show tidal oscillations, suggesting hydraulic connections with nearby canals, creeks and Sydney Harbour. The creation of this data processing code has greatly reduced the time required for data manipulation in assessing groundwater patterns in the area of the M4-M5 Link WestConnex project. For other large groundwater monitoring projects, investing time early in the development of data processing codes could add similar benefits.