Water quality sites that don ’ t have stream gauging are traditionally overlooked , for load calculation and water quality analysis , due to inherent difficulties in calculating loads for ungauged sites . However , it was hypothesised that value might be obtained from these sites if a simple load calculation method could be found and verified .
Here , LDC constituent loads for tributaries were calculated via ,
Average annual load = Average concentration of water quality samples * the average annual stream discharge ( 1986-2014 ).
Where long term flow records could not be found , Average annual GBR source modelled flow was substituted using a 28 year period ( 1986-2014 ).
To quickly assess the methdology , we compared the average raw concentrations and average annual load concentrations of GBRCLMP sites ( Table 9 ). It is was found that the average raw concentrations generally fell within + or - 50 % of the average annual load concentrations . Thus , we assumed that useful indicative load could be simply calculated with some confidence . However , caution is obviously still advised , and more work could be done here to better validate protocol around the use of this methodology . Nonetheless users could be confident that large differences between monitoring and modelled estimates , warrant detailed investigation in appropriate areas .
Table 9 . Percentage difference between “ mean annual concentration ’ s ” calculated from annual loads and discharge and the ” average concentration of individual water quality samples ”. Red shading highlights areas above 50 %.
Site
Raw Concentration , years of data
FS PN PP
Burdekin ( EOV ) |
10
-
|
32 |
- |
23 |
- |
11 |
Bowen At Myuna |
7 |
46 |
|
11 |
|
14 |
Haughton |
5
-
|
70 |
- |
45 |
|
49 |
Barratta |
8
-
|
7 |
|
41 |
|
33 |
Upper Burdekin |
10
-
|
18 |
- |
16 |
|
13 |
Normanby |
10
-
|
24 |
|
35 |
- |
4 |
Barron |
10
-
|
28 |
- |
28 |
- |
17 |
Indicative loads and average concentrations for “ Bowen at Myuna ” catchments are shown in Table 10 . Although supplying ~ 70 % of the likely discharge for the “ Bowen Myuna ”, the “ Broken River ” contributes ~ 1 % of the Fine sediment ( FS ) load . In contrast , concentrations of FS are ~ 250 times higher in the “ Little Bowen ”, producing a likely large average annual contribution from this small catchment , despite limited discharge . Although poorly sampled “ Rosella Creek ” appears somewhat similar to the “ Little Bowen ”, indicating a relatively high load of fine sediment .
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