2.5.2.2 Surface water balances for the Namoi subregion


Surface water balances are provided at model node 13 (Figure 4) in the Namoi River at Mollee. The model node is immediately downstream from major coal resource development activities in the Namoi subregion.

Rainfall was identical for baseline and CRDP, therefore only a single rainfall volume is provided for the water balance for each 30-year period. The decreasing mean annual rainfall input over the three 30-year periods reflects the global warming changes assumed in the modelling (see companion submethodology M06 (as listed in Table 1) for surface water modelling (Viney, 2016)).

The streamflow term in the surface water balances includes the surface water – groundwater flux component from the groundwater model. As stated in Section 2.5.1, water balances are reported separately for surface water and groundwater modelling, as they apply to different areas.

These water balances account for water that recharges groundwater but is not discharged to the stream as a residual. The residual is a balancing term that comprises evapotranspiration, change in storage and leakage from the river.

Surface water balances at model node 13 on the Namoi River are provided in Table 7 for 2013 to 2042, Table 8 for 2043 to 2072 and Table 9 for 2073 to 2102. The contributing area to model node 13 is about 26,534 km2 and includes all coal resource development areas in the subregion.

The median and the 10th and 90th percentile values for each variable of the baseline and CRDP set of simulations are reported. The difference reflects the change attributable to additional coal resource development, obtained from subtracting the baseline value from the CRDP value.

Table 7 Surface water balance for 2013 to 2042 at model node 13 (Namoi River)


Water balance term

Under the baseline

(GL/y)

Under the coal resource development pathway

(GL/y)

Difference

(GL/y)

Rainfall

18,871

18,871

0.0

Streamflow

761.6 (663; 832)

760.3 (662; 831)

1

Mine discharge

NM

NM

NM

Diversion

149.5 (136.0; 164.8)

149.5 (136.0; 164.7)

0.0

Residuals

17,960 (17,874; 18,072)

17,961 (17,876; 18,073)

–1

NM = not modelled. There is no plan to discharge mine water to the river.

For some (but not all) terms, three numbers are provided. The first number is the median, and the 10th and 90th percentile numbers follow in brackets. Some numbers are rounded to whole numbers.

Data: Bioregional Assessment Programme (Dataset 2, Dataset 3)

Table 8 Surface water balance for 2043 to 2072 at model node 13 (Namoi River)


Water balance term

Under the baseline

(GL/y)

Under the coal resource development pathway

(GL/y)

Difference

(GL/y)

Rainfall

18,710

18,710

0.0

Streamflow

736 (637; 806)

735 (636; 805)

1

Mine discharge

NM

NM

NM

Diversion

148.1 (134.2; 163.9)

148.1 (134.1; 163.8)

0.0

Residuals

17,826 (17,740; 17,939)

17,827 (17,742; 17,940)

–1

NM = not modelled. There is no plan to discharge mine water to the river.

For some (but not all) terms, three numbers are provided. The first number is the median, and the 10th and 90th percentile numbers follow in brackets. Some numbers are rounded to whole numbers.

Data: Bioregional Assessment Programme (Dataset 2, Dataset 3)

Table 9 Surface water balance for 2073 to 2102 at model node 13 (Namoi River)


Water balance term

Under the baseline

(GL/y)

Under the coal resource development pathway

(GL/y)

Difference

(GL/y)

Rainfall

18,554

18,554

0.0

Streamflow

704 (611; 774)

703 (611; 774)

1

Mine discharge

NM

NM

NM

Diversion

145.7 (131.7; 162.0)

145.6 (131.7; 161.9)

0.1

Residuals

17,704 (17,618; 17,811)

17,705 (17,619; 17,812)

–1

NM = not modelled. There is no plan to discharge mine water to the river.

For some (but not all) terms, three numbers are provided. The first number is the median, and the 10th and 90th percentile numbers follow in brackets. Some numbers are rounded to whole numbers.

Data: Bioregional Assessment Programme (Dataset 2, Dataset 3)

Diversions from the river for irrigation use were modelled in the Namoi Regulated River. Regulated rivers are the main source of water to meet the needs of irrigators and town water supply along these reaches. Diversion from the river does not vary between the baseline and CRDP, but the model may predict a decrease in extractions over the 90 years in response to a drying climate.

The additional coal resource developments are predicted to cause negligible reductions in streamflow at model node 13 in all three periods relative to the baseline streamflow. The difference between CRDP and baseline is 1 GL/year for all periods (less than 0.1% reduction relative to the baseline). The discharges from Narrabri Gas Project are not modelled because they are negligible at the regional scale (Santos, no date).

Last updated:
6 December 2018