A journey up the Hawkesbury Nepean

Natalie Noakes - Sydney Water Corporation , 22 August, 2012


Sydney Water is developing a new modelling capability for the Hawkesbury-Nepean River system and South Creek to inform the wastewater servicing of Sydney’s new growth centres. The model will be a powerful tool to predict and compare different options for urban development, environmental flows and other water resource management options in the Hawkesbury-Nepean system. The new model will inform infrastructure investment decisions of up to $2 billion.

This paper encompasses my journey as a Science graduate and a new Hydrographer working in the team delivering a challenging field work and data delivery program to support the development of the model, often during difficult conditions.

The program started in January 2011 and is expected be completed by September 2012 and comprises of four components:

  • bathymetric (hydrographic) surveys
  • macrophyte (submerged aquatic vegetation) surveys
  • tidal estuary profile Acoustic Doppler Current Profiler (ADCP) surveys
  • event and dry weather water quality sampling

The main focus of this paper is on the bathymetric survey including the technologies and methodology used and the challenges encountered along the way. It required the collection and processing of reliable position and bed level elevation data (x, y, z) at appropriate spatial density, along 220km of the Hawkesbury-Nepean River and South and Eastern Creek. The three supporting campaign monitoring programs required a combination of hydrographic and related hydrometric skills and knowledge, similar to those used in the bathymetric surveys. This also included the development and adoption of new technologies and methodologies specific to each campaign program.

The aim of the macrophyte survey is to generate information on the spatial distribution of aquatic weeds and native ‘macrophytes’ in freshwater reaches, with a particular focus on post flood and seasonal changes. The methods and technologies used in the bathymetric survey were adopted and modified for use in developing a new methodology for carrying out macrophyte surveys.

The tidal estuary profiling of the Hawkesbury River required teams concurrently gauging using ADCP’s and water quality profilers over full (semi diurnal) Spring and Neap tidal cycles at six key locations. The actual transects were selected using the recently collected bathymetry data and hydrometric principles. The key river locations, where tidal volume data was required, were spaced over a river reach of approximately 100km from Bar Point (near Brooklyn) in the lower reaches of the Hawkesbury River to upstream Pitt Town (near Windsor). This gauging exercise required the safe and effective management of six boat crews including contractors, working in rotational shifts day and night and often in adverse weather conditions to cover the end to end cycles and full velocity reversals.

The event and dry weather water quality sampling program required the installation and operation of refrigerated, auto samplers at existing hydrometric gauging stations located in catchments with a range of land uses including rural, forested, and urban areas. Supplementary miniature data loggers (Divers) were deployed in-stream order to obtain time series water temperature data as well as back up conductivity and water level data