*4.2. Superposition Experiments*

Figure 6 shows the transfer function for the superposition of modelling Experiments 7 and 8 and compares this for both the FEFLOW and PerTy3 model outputs for Experiment 9. While the superposition is higher than either of the outputs for Experiment 9, the shape and time scale of recharge reduction is similar.

**Figure 6.** PerTy3 modelling output for Experiment 10 (1D): 10a new development (new, orange line); 10b water use efficiency (WUE, green line); 10c (whole sequence of new development and water use efficiency (whole, dashed red line); Experiment 10d recharge for superposition of 10a and 10c transfer functions (super, red solid line); Irrigation accession for Experiment 10c (1D) blue line.

Figure 6 shows the results of the superposition Experiment 10. It shows the modelled response to the new development and for the subsequent water use efficiency improvements. The superposition (solid red) resembles the modelled output (red dashed). The resultant pattern is a smoothed and delayed version of the irrigation accession (shown in blue). The irrigation accession is the input to the model and reflects initially the pre-irrigation conditions, then the irrigation history from 1976 to 2010 and then the assumed final irrigation accession of 50 mm/year from 2010 onwards.

Figure 7 shows the results of the superposition experiment 15. Again, the superposition (red dashed) matches the modelled recharge (red solid) and the resultant form is a smoothed and delayed version of the irrigation accession (blue). The irrigation accession reflects the irrigation history from pre-irrigation rate of 10 mm/year, development in 1976 and irrigation improvements from 1981 to 1991 and then the final assumed rate of 50 mm/year.

#### *4.3. Use of Drainage Data to Calibrate the Transfer Function*

Figure 8a shows contours of drainage volumes (mm/year) for the 3a\_1 soil for the Loxton– Bookpurnong District for an irrigation accession rate of 339 mm/year, based on soil hydraulic properties. Negative values mean that there is no drainage. For this value of *IA*, the drainage has been estimated to be 173 mm/year. This implies that the soil properties follow a contour, beginning with *Ks*1*<sup>h</sup>* = 0 and *Ks*2*<sup>v</sup>* = 0.0212 cm/day. The drainage volumes for other values of *IA* in Table 3 leads to the same contour. The relationship between the two conductivities for this contour is shown as a solid line in Figure 8b.

**Figure 7.** PerTy3 model outputs for Experiment 15 (2D): Experiment 15a new development (new, orange line); Experiment 15b water use efficiency (WUE) measures (green line); Experiment 15c sequence of new development and water use efficiency measures (whole, red solid line); Experiment 15d recharge for superposition of transfer functions (super) for 15a and 15b. The Irrigation accession (IA) is shown in blue.

**Figure 8.** (**a**) Contours for drainage for the 3a\_1 soil type for irrigation accession of 300 mm/year. Negative values correspond to no drainage, while positive values correspond to drainage volumes (mm/year). The resultant drainage for Loxton (173 mm/year) corresponds to the contour starting at the vertical conductivity for layer 2 of 0.0212 and horizontal conductivity of layer 1 of zero. (**b**) The blue solid line shows this same contour (3a\_1 soil). Contours (dashed lines) are also shown for 3a\_2 soil for *IA* of 150 (brown, 3a\_2 150) for which there is no drainage and 317 (grey, 3a\_2 317)) for which there is drainage. This means that the soil properties should lie between these contours and is consistent with the blue contour for all but the lowest horizontal conductivity. Further contours (dotted lines) are shown for 3b soils (3b\_1 398; 3b\_2 398; 3b\_3 398; 3b\_4 398). Even for *IA* of 398 mm/year, there is no drainage. Soil properties therefore should lie above these contours. The contour for 3b\_4 forms the strongest constraint.

While the presence or absence of drainage is known for soil 3a\_2, the drainage volumes are not. This knowledge provides some constraints on the soil properties. The absence of drainage for a value of *IA* of 150 mm/year, but drainage at 317 mm/year means that the soil properties lie between the two dashed contours in Figure 8b. If we are seeking one set of soil properties denoted as 3a, the contour found for 3a\_1 would be consistent with this constraint for all but the lowest value of horizontal conductivity.

For 3b soils, there is no drainage, even for a value of *IA* of 398 mm/year. This means that the soil properties must lie above the dotted contours in Figure 8b. If we are seeking a single set of soil properties for all 3b soils, the strongest constraint is given by 3b\_4. This implies that *Ks*2*<sup>v</sup>* > 0.025 cm/day for high values of *Ks*1*<sup>h</sup>* or >0.045 cm/day (low values of *Ks*1*<sup>h</sup>* ). Soil properties can then only be further constrained by fitting to the groundwater response.
