2.6.1.6.1 Introduction

Section 2.6.1.6 summarises the prediction results for eight hydrological response variables at 61 surface water model nodes. The eight hydrological response variables for streamflow are:

A ninth hydrological response variable defined in companion submethodology M06 (as listed in Table 1) for surface water modelling (Viney, 2016) – the daily streamflow rate at the 1st percentile (P01) – is excluded from the analysis. The P01 flow is not reported because all of the P01 observations are zero for the Galilee subregion.

For each of these hydrological response variables a time series of annual values is constructed for each model node.

For each model node, 10,000 sets of randomly selected parameter values were used to generate 10,000 replicates of development impact. A filter was applied to remove model runs in which future flow increases were due to overestimated streamflow persistence in the decades following the 2010–2011 floods. This reduced the number of replicates for result analyses to 3463. From these, the best 10% of total model replicates for each hydrological response variable, as assessed by their ability to predict that hydrological response variable at the observation sites, were chosen for further analysis.

Results are presented using a series of bar graphs for each hydrological response variable. Each bar graph was generated from the resulting 347 samples. The bar graphs show the distributions over the 347 replicates of the maximum raw change (amax) in each metric between the baseline and coal resource development pathway (CRDP) predictions, the corresponding maximum percentage change (pmax) and the year of maximum change (tmax). In general, the most meaningful diagnostic for the flux-based metrics (AF, IQR, P99 and FD) will be pmax, while the most meaningful diagnostic for the frequency-based metrics (ZFD, LFD, LFS and LLFS) will be amax. It is important to recognise that the amax and pmax values give the largest annual departure between the baseline and CRDP predictions for the respective hydrological response variables. As such, amax and pmax represent extreme responses. They do not represent the magnitudes of responses that would be expected to occur every year. The bar graphs show the distributions of these predictions of maximum impact from among the 347 replicates.