The perennial reaches of the Richmond River network were explicitly simulated using the MODFLOW River package . Long-term average river stages for the steady-state model were interpolated from measurements obtained at 12 gauge sites located within the model domain (Figure 14). Transient river stages at the 12 gauges were derived from rating curves based on historical records and the component of the AWRA-L outputs. Figure 15 demonstrates an example of the derived river stage time series at gauge 203004 for the period between 1983 and 2102.
where Kn and Mn represent the hydraulic conductivity and thickness of the riverbed, respectively, and Ln and Wn represent the length and width of the river reach, respectively . Due to a lack of data in the , the initial hydraulic conductivity of the riverbed was assigned values that range from 1e-6 to 1e-3 m/day, which were sourced from a previous study conducted in the Murray-Darling Basin . It is widely accepted that the riverbed hydraulic conductivity is primarily a function of reach geometry, streamflow velocity, composition and erodibility of catchment, and bed disturbance frequency . The riverbed hydraulic conductivity generally increases with riverbed slope when other factors are similar . In the current study, we assume that the hydraulic conductivity varies directly with the riverbed slope due to the lack of other data. Riverbed thicknesses that had initial values ranging from 0.5 to 4 m, were assumed to vary inversely with the riverbed slope.
The initial values of the riverbed conductance were adjusted through 22 pilot points during the and analysis (Figure 16). Twelve pilot points were placed at locations where gauges exist (Figure 14). Cross-sections of the stream at these locations were used to obtain reach-width information. Another 10 pilot points were placed where gauges are not available to provide an even coverage of the stream network in the model. Reach-width data for these locations were sourced from the hydrographic survey data by NSW Office of Environment and Heritage (2012).
Apart from the perennial streams that were explicitly simulated in the groundwater model, there were other features such as local intermittent streams and swamps, which were considered to function as local features ; such features were lumped together and implicitly simulated using the MODFLOW Drain package. A drain boundary condition is assigned to each model grid cell in layer 1 with a drainage elevation equal to topography. The drainage conductance is set to 1 m2/day and allowed to vary through a multiplier (DRN_C2) in the uncertainty analysis.
PAE = preliminary assessment extent
Coal resource development pathway = baseline + additional coal resource development (ACRD)
The river stage is referred to the local gauge reference elevation.
Product Finalisation date
- 188.8.131.52 Methods
- 184.108.40.206 Review of existing models
- 220.127.116.11 Model development
- 18.104.22.168 Boundary and initial conditions
- 22.214.171.124 Implementation of the coal resource development pathway
- 126.96.36.199 Parameterisation
- 188.8.131.52 Observations and predictions
- 184.108.40.206 Uncertainty analysis
- 220.127.116.11 Limitations and conclusions
- Contributors to the Technical Programme
- About this technical product