Rapid Creek monitoring

Introduction

Rapid Creek is a small, relatively natural drainage system located in Darwin’s Northern suburbs. The creek extends for a distance of 9.8 kilometres and drains a catchment of approximately 28km2. Unlike many such drainage lines elsewhere in urban areas, Rapid Creek supports a number of important remnant vegetation communities and the creek channel is virtually undeveloped for its entire length.

The reestablishment of the Rapid Creek Water Advisory Committee is to ensure a consultative approach to water management and planning. The Committee will provide advice to the Controller of Water Resources on water quality and water resource management issues affecting Rapid Creek and its catchment. They will also contribute to the development of a Water Management Plan and contribute to monitoring and annual assessment against the plan.

Reports and publications

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.

Rapid Creek catchment and monitoring sites

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Water quality

Environmental water quality indicators monitored by the Department of Environment and Natural Resources (DENR) include:

  • dissolved oxygen
  • water clarity and
  • nutrients.

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:

  • shrimps
  • caddis fly larvae and
  • snails.

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.

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.

Monitoring results

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

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.

Other monitoring

The Darwin International Airport also conducts extensive water quality monitoring in Rapid Creek. This includes a wide range of toxicants as well as bacteriological sampling.

The Department of Defence conducts ongoing monitoring of PFAS in Rapid Creek.

Last updated: 22 July 2019

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