Specifications

A Remote Automated Water Quality Stream Gauging System Design 17
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If a pump is installed at the site, the pump is turned on for a preset period of time prior to
sample collection to purge the sample hose. This ensures that fresh water will be collected
by the auto sampler.
When a sample is required to be collected, the program, pulses the auto sampler, the sample
number and bottle number counters are incremented, the bottles remaining counter is
decremented and data is logged. The position of the current sampling window is tested and
adjusted as required.
4.4.1. Sample windows
Sample windows are created by dividing the distance between the river bed and full bank
height into equal intervals. A sample is collected when a trigger value falls outside of the
range of the current window and the window is adjusted to the next range up or down.
For example, if the rising stage sample window is set to 200 mm, then a sample is collected
at 200 mm water depth, then the upper limit of the window is moved to 400 mm, then 600
mm etc. The previous upper limit will become the falling stage sample limit if both window
sizes are the same. It is possible to set different windows for rising and falling stage
sampling.
The number of bottles remaining in the auto sampler is used to optimise sampling along the
tail of the event hydrograph. If the number of bottles remaining is insufficient to sample the
entire falling stage, the program will alter the sample window size accordingly.
4.4.2. Sample window buffers
If the water level fluctuates slightly above and below a sample window or event threshold the
program would collect a number of samples over a short period of time. If a time constraint is
added to the sampling code, a sharp rise in water level would not initiate sampling. To
address this, a buffer is added to each window (usually 50% of window size). The water level
must cross either above or below this buffer before a new sample window can be initiated.
4.4.3. Sample identification
When a sample is collected, the logger will record a timestamp, the sample bottle position,
the sample number and the event number. The sample identification number (SampleID) is
unique for any given season. It is assigned by combining the site identification number and
the sample number at each site. For example, if site 4001 has collected 35 samples, the next
SampleID will be 41036. This system allows up to 1000 samples to be collected from any site
in one season. The SampleID counter is reset at the end of the financial year.