Annual monitoring in Rapid Creek
Annual monitoring of stream health is currently undertaken in Rapid Creek during the transition from wet to dry season. The creek is monitored for water quality and the health of the water bug community. Underwater video techniques to monitor fish are also being trialled.
Three sites have been monitored since 2001:
- Yankee Pool in the upper part of the creek
- Middle Site in the central section and
- the V-notch weir in the lower reaches.
Environmental water quality indicators monitored by the Department of Environment and Natural Resources (DENR) include:
- dissolved oxygen
- water clarity and
The early dry season water quality of Rapid Creek for these indicators was within the expected range for a creek in the Top End. Water quality has been stable over time.
Water bug community
Water bugs are small invertebrate animals living in streams and rivers. Common ones, which are visible to the naked eye and known as macroinvertebrates, are:
- caddis fly larvae and
The types of water bugs in a stream can tell us about its condition or “health”. In general, the more different types of bugs occur the healthier the stream. Caddisfly larvae similar to this one are commonly found in Top End creeks.
How does it work?
Water bugs are monitored using the Australian River Assessment System (AusRivAS).
The method compares water bugs found in a stream, with those expected to be found in reference streams of a similar type. A score is calculated (“OE50”) which is then grouped into bands A to D.
Band A means a site is equivalent to high quality reference streams. Bands B to D show that the stream is below reference condition and is degraded to varying degrees.
In 2018, the three sites received scores of 0.5 to 0.6 (Band B to C). This is typical of a stream with an urbanised catchment that has a slightly impoverished water bug community.
There is no evidence of a decline in health over time.
Fish monitoring using underwater video is being used to document fish assemblages in Rapid Creek.
The following video shows some of the common fish found in the freshwater section of Rapid Creek (2016).
Per- and poly-fluoroalkyl substances (PFAS)
Fire fighting foam that contained PFAS chemicals was used at the Defence training facilities at Darwin Airport. These chemicals have polluted soil and ground water on the site.
Rapid Creek is affected by the pollution from these chemicals. Information about PFAS can be found on the Northern Territory Environment Protection Authority (NTEPA) website.
In 2018, PFAS was included in the monitoring program. Concentrations exceeded the recreational and environmental guideline values for PFOS+PFHxS. These results were similar to results published by the Department of Defence.