Specifications

A Remote Automated Water Quality Stream Gauging System Design 16
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4.1. Initialisation
On initialisation, the program loads the variables used to control operation at that site. This
state occurs if the system has lost power or when a new program is uploaded to the logger.
Each site is assigned a unique site number based by region/project. For example all
identification numbers for stations located in the Mingela region begin from 3000, those on
Hervey’s Range from 5000. The four sites at Mingela therefore are assigned 3001, 3002,
3003 and 3004. This not only provides an easy way to recognise related sites but forms the
basis for the assignment of water sample identification numbers discussed later in section
4.4.3.
4.2. Non-event mode
In this mode, the program tests the event threshold every cycle. Data is logged hourly for
diagnostic purposes and to provide a rainfall record. If the program has transitioned from
event mode to this mode, the sampling window is also reset.
4.3. Event modes
If the water depth (or any other variable) crosses a predefined threshold, the event state is
initiated, an event counter is incremented, stream data is logged with a higher temporal
resolution and samples are collected (Figure 9).
Figure 9 An example hydrograph showing the operation of the sample collection procedure
during a flow event in the Bowen River near Collinsville, Australia. Note the increased temporal
resolution of data logging after depth rises above the 300mm event threshold.
4.4. Sample collection
In event mode, there are three conditions that will trigger a sample to be collected:
 State 3: Event (Rising). This condition is met when the water depth is rising. If the
current depth exceeds the top of the current sample window interval, a sample is
collected and the sample window is moved upwards.
 State 4: Event (Timed sample). This condition is met if there has been no change in
the sample window for the specified period of time. A sample is collected but the
windows remains in its current position.
 State 5: Event (Falling). This condition is met when the water depth is falling. If the
current depth is lower than the bottom of the current sample window, a sample is
collected and the window is moved downwards.
Before a sample is collected, the program checks if there are any bottles left in the auto
sampler via means of a counter. If the number of bottles remaining is greater than zero, the
program will commence the sampling routine.