Salinity situation statement Tweed River and Gnowergerup Brook

Salinity situation statement: Tweed River & Gnowergerup Brook WRT 41 Water Resource Technical Series
Figure 37 Runoff for response units in 2030 – ‘59% strategic trees’
Scenario 4 — 59% strategic trees and the remainder perennial
pastures
The response units, as in the ‘59% strategic trees’ scenario, are ‘planted’ with trees; with the
rest of the cleared area ‘planted’ with perennial pastures with a rooting depth of 3.5 m.
By 2030, mean salinities in the Tweed River and Gnowergerup Brook are expected to fall to
641 mg/L and 1039 mg/L TDS respectively (Table 4) with further reductions expected by
2060 to means of 543 mg/L and 738 mg/L respectively (Table 4). These are reductions of
2468 mg/L (Tweed River) and 3875 mg/L (Gnowergerup Brook) compared with the ‘base
case’ scenario in 2060.
Scenario 5 — All cleared
All existing vegetation is assumed to be ‘cleared’ in 2008 with both catchments having only
annual pastures. The salinities of the Tweed River and Gnowergerup Brook do not increase
significantly until after 2030 (Fig. 38). The mean projected salinity in 2030 at Jayes Road is
4998 mg/L and continues to increase to 6135 mg/L by 2060. Salinity in the Tweed is
3705 mg/L in 2030 and increases substantially to 5334 mg/L by 2060 (Table 4).
Salt loads are projected to increase significantly: the annual load from the Tweed River is
39.2 kt by 2030, more than twice the ‘base case’ (16.3 kt) and for Gnowergerup Brook,
97.9 kt compared with 66.7 kt for the ‘base case’ (Fig. 40).
The annual salt loads are projected to keep increasing until at least 2060 where averages of
76.4 kt (Tweed) and 138.9 kt (Gnowergerup) are exported annually. These are about five
40 Department of Water