Gosford City Council Historical Water Quality Review & Analysis

RESULTS OF WATER QUALITY DATA ANALYSIS 3-6
3.1.1.5 Salinity
Median annual salinity for the Gosford waterways is presented in Table 3.8, while mean quarterly
salinity is presented in Table 3.9.
Salinity responds to freshwater catchment inflows, and is dependent on the ability of the tides to
restore oceanic waters following fresh events. The influence of catchment runoff on salinity is
particularly highlighted in the quarterly results. Low salinity levels (< 15ppt) at the sites near creek
outlets occur following catchment runoff. Tidal flushing then restores oceanic salt levels (~35ppt)
over the following months. Salinity was generally lowest in the period Apr – Jun 2002, following
extensive rainfall in February, March and April 2002.
Of particular interest in the data is the evidence of Cockle Creek behaving as a backwater area (with
sustained higher salinity levels during general catchment runoff events). Also, the behaviour of
salinity in the coastal lagoons is further complicated by the lagoon entrance conditions. When closed,
water levels in the lagoons increase (reducing salinity) until the entrance berm is breached, the lagoon
is drained, and oceanic waters are flushed into the lagoon (before the entrance closes once again).
Table 3.8
Annual Medians for Salinity
Salinity (ppt)
Site No. and Location 2001/ 2002 2000/ 2001 1999/ 2000
n=11 n=12 n=9 Trend
Site : 77 - Booker Bay 34.4 30.4 28.7
Site : 78 - Narara Creek Entrance 27.0 26.0 25.7
Site : 79 - Erina Creek Entrance 24.2 26.8 25.4
Site : 80 - Kincumber Creek Entrance 18.7 24.2 27.1
Site : 81 - Cockle Creek 33.2 30.5 27.2
Site : 82 - Woy Woy Creek 30.2 27.1 24.4
Site : 83 - Wamberal Lagoon 15.9 6.1 15.7
Site : 84 - Terrigal Lagoon 16.3 9.3 9.4
Site : 85 - Avoca Lagoon 13.2 16.8 18.6
Site : 86 - Cockrone Lagoon 15.7 7.2 14.7
Average Rainfall at Gosford 1248mm 1038mm 1228mm
Table 3.9
Quarterly Means for Salinity
Salinity (ppt)
Site No. and Location
Apr - Jun Jan - Mar Oct - Dec Jul - Sep Apr - Jun
2002 2002 2001 2001 2001
n=4 n=1 n=3 n=3 n=3 Trend
Site : 77 - Booker Bay 31.9 34.4 36.1 35.2 32.8 Rain dep.
Site : 78 - Narara Creek Entrance 8.8 27.0 34.5 26.6 16.5 Rain dep
Site : 79 - Erina Creek Entrance 6.0 25.7 34.1 24.5 13.4 Rain dep
Site : 80 - Kincumber Creek Entrance 12.6 26.9 32.8 2.1 17.0 Rain dep
Site : 81 - Cockle Creek 30.7 32.3 36.1 34.5 30.5 Rain dep
Site : 82 - Woy Woy Creek 16.2 26.8 35.1 31.4 24.3 Rain dep
Site : 83 - Wamberal Lagoon 11.8 34.3 18.2 14.2 15.5 Rain dep
Site : 84 - Terrigal Lagoon 17.9 23.1 16.4 13.4 12.7 Rain dep
Site : 85 - Avoca Lagoon 14.0 23.0 12.5 13.3 19.4 Rain dep
Site : 86 - Cockrone Lagoon 16.2 24.4 14.8 16.5 14.5 Rain dep
Average Rainfall at Gosford 150mm 735mm 189mm 174mm 445mm
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