WAMSI 2 - Dredging Node - Theme 2 Project 3.4 Development of a Numerical Dredging Model

Brief description

In Western Australia (WA), the Environmental Impact Assessment process requires dredging proponents to make scientifically sound predictions of the likely extent, severity, and persistence of environmental impacts of the proposed activity under a spatially defined zoning pattern. This is achieved by using coupled hydrodynamic, wave and sediment transport models in conjunction with water quality (ecological) thresholds for sensitive receptors such as corals, filter feeders, or seagrasses/macroalgae. These predictions guide the scale and scope of associated monitoring programs, providing assistance to proponents as to where to establish environmental monitoring and reference sites. Increasingly, modelling is also being used by dredging programs to forecast a few days in advance, so as to understand the potential consequence of various dredging scenarios and optimize the dredging programs to minimize environmental damage.

The overall objective of Project 2/3.4 was to improve the predictive capabilities of sediment dispersion modelling that incorporate dynamic plume and passive plume processes through assessing model sensitivity to key forcing and parameter values, such as met-ocean condition, particle settling velocity distribution, critical shear stress, sediment erosion and deposition, provide frequency and duration of biological stressor fields including suspended sediment concentration, sediment accretion and erosion, and available light; and provide guidance on developing best practice algorithms and parametrizations for dredge plume modelling.

Based on the outcome Project 2/3.1, an appropriate modelling suite that includes hydrodynamics, waves, and sediment transport was chosen (Delft3D) to model the far-field passive plume. The model was set up and validated using the bathymetry and baseline data collected as part of the Chevron Australia Wheatstone Project, located near Onslow, Western Australia.

The model outputs were assessed against monitoring data from Chevron Australia's Wheatstone Dredging program, including, remote sensing and in-situ data collected in Project 2/3.2. A 20 month hindcast of passive plume dispersal from the dredging project to the furthest extent of the passive plume were compared with the field data and MODIS images (where available). Spatial and temporal variability of plume dispersal under different forcing scenarios and sediment release rates were investigated and reported.

This record pertains to the simulation data files.
Lineage: Three models (hydrodynamic, wave and sediment transport models) were set-up for the study site, Chevron Australia's Wheatstone LNG Project, located 12 km west of Onslow (in the Pilbara region of Western Australia). Data from a range of sources were compiled and analysed for use in the study and included electronic and daily dredging logs, current meters, Conductivity Temperature Depth (CTD) measurements, turbidity (NTU) sensors, photosynthetically active radiation (PAR) sensors, sediment traps and multi-beam bathymetric survey data. Data from a field trip completed by CSIRO and Curtain University was also utilised.

A 14-year-long derived TSS dataset for the Pilbara region using Moderate resolution Imaging Spectroradiometer (MODIS) satellite was developed in Dorji et al. (2016).

. A description of the model set-up and results, including details of the sensitivity analysis (and validation of source terms) is included in the Final Report (see online resources link).

Two model output data files are provided in the CSIRO DAP record (see online resources link):

FILE 1 Timeseries output at 14 minute intervals for 256 history points across the model domain (trih-gD1_DSN_Outer.nc)
FILE 2 Map series output at 60 minute intervals for the model domain (trim-gD1_DSN_Outer.nc)

Variable descriptions and units are provided in the file metadata. Example outputs include wave height, peak wave period, suspended solids concentration, water currents, water levels, bed shear stress etc. Simulation data files are in netCDF format with CF-1.6 conventions.