Correction to trigger values and units for visual water clarity in New Zealand rivers (ANZECC 2000 water quality guidelines)
Background
ANZECC guideline users in New Zealand have identified an issue with default trigger values for visual water clarity in New Zealand rivers. The issue was subsequently queried with Dr Rob Davies-Colley (NIWA-Hamilton) on whose work this section was based. He confirmed that there are errors in the ANZECC guidelines for visual water clarity units. These are inconsistent with the original text submitted to the Australian and New Zealand Environment and Conservation Council (ANZECC).
The following text identifies the errors and provides a correction.
Table 3.3.11 on page 3.3-18 of the ANZECC 2000 guidelines specifies default trigger values for visual water clarity in New Zealand rivers. The table below shows Table 3.3.11 as it appears in the guidelines (excluding footnotes):
| Ecosystem types | Upland Rivers | Lowland Rivers | ||
|---|---|---|---|---|
Visual Clarity (m-1) |
Turbidity (NTU) |
Visual Clarity (m-1) |
Turbidity (NTU) |
|
| 0.6 | 4.1 | 0.8 | 5.6 | |
The errors
It has been confirmed that Table 3.3.11 contains two errors on visual water clarity in New Zealand rivers. The errors are as follows:
- Visual water clarity units. The units used for visual clarity in the table are m-1. This is an error. The units should be m, not m-1 because visual clarity is measured as the maximum visual range (a distance in metres) of a standard target.
- Visual water clarity values for upland and lowland rivers. The visual clarity values for upland and lowland rivers have been mistakenly reversed during guideline drafting.
The correction
Table 3.3.11 with the visual water clarity units and values corrected should read:
| Ecosystem types | Upland Rivers | Lowland Rivers | ||
|---|---|---|---|---|
|
Visual Clarity (m) |
Turbidity (NTU) |
Visual Clarity (m) |
Turbidity (NTU) |
|
0.8 |
4.1 |
0.6 |
5.6 |
Note:
The existing footnotes to the original text are unchanged.
Please note that there is no change to the turbidity numbers and units, or to the table notes.
