Salinity situation statement Tweed River and Gnowergerup Brook

Salinity situation statement: Tweed River & Gnowergerup Brook WRT 41 Water Resource Technical Series
Salinity (mg/L)
18000
16000
14000
12000
10000
8000
6000
4000
2000
0
Average monthly flow weighted salinity (1999 – 2006)
Average monthly flow (1999 – 2006)
Jan Feb Mar Apr May Jun Jul Aug Sept Oct Nov Dec
Month
Figure 15 Average monthly flow and salinity at the Jayes Road gauging station
The mean annual streamflow of Gnowergerup Brook was 16 GL with the highest annual flow
recorded in 2005 when 30 GL flowed through the Jayes Road gauging station (Fig. 16).
Streamflow volumes are seasonal and so vary considerably across the year: lowest during
March, with a monthly average of 0.024 GL, and highest during August at an average of
4.021 GL (Fig. 15).
Although salinities during winter are lower as a result of higher streamflows, the
Gnowergerup Brook still carries significant salt loads. July had the highest monthly average
salt load (18 kt) and February the lowest (average 0.29 kt). Total annual salt loads through
Jayes Road were related to streamflows (Fig. 17); however, in low-flow years salt loads
tended to be proportionately higher.
The Rylington gauging station (Tweed River) has 6.09 km 2 catchment area and the average
salinity (2004–07) was 3616 mg/L, with the annual salinity range 2090 mg/L in 2005 to
5656 mg/L in 2006. Annual streamflows ranged from 122 in 2006 to 428 ML in 2005 (a high
rainfall year in the catchment).
Although streamflows and salinities varied markedly between years, salt loads discharged
and measured at the Rylington gauging station were relatively stable over the four years of
monitoring: the highest was 923 t in 2004. In 2007, which had a significantly lower
streamflow of 155.5 ML compared to 428 ML in 2005, the salt load was 860 t.
20 Department of Water
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
Flow (GL)