Drain C2, near Coonawarra
2009 Aquatic Ecosystem Condition Report
- Dry in autumn and spring 2009.
- Likely to be enriched with nutrients when wet due to surrounding land uses in the catchment.
- Riparian vegetation limited to a low cover of introduced grasses.
- Fine sediments dominate the channel.
About the location
Drain C2 is a small drain in the South East with a catchment area of about 32 km2. It rises at an elevation about 60 metres above sea level near Coonawarra, and flows in a northerly direction into Drain C, then Drain M, and ultimately discharges into Lake George at Beachport.
Drain C2 is an artificially constructed drain where the primary function is to remove surface water and draining saline groundwater to improve agricultural productivity in the region (Department for Water 2010). Given its artificial character, the drain is not expected to be in a highly rated aquatic ecosystem condition, although it does provide significant habitat for many aquatic species in the region.
The major land use is sheep grazing. The monitoring site was located on the Tricia Reschke Road, about 3.5 km east of Coonawarra.
The drain was given a Very Poor rating because the site sampled showed evidence of major changes in ecosystem structure and a significant breakdown to the way the ecosystem functions. The ephemeral nature and extent of poor habitat features supported rating this drain in a severely degraded state. It is likely that only a few highly tolerant aquatic species would be present in this drain when water is present.
The drain was dry in autumn and spring 2009, so macroinvertebrate and water chemistry data were not available for the site inspected.
The sediments were dominated by detritus, fine sediments and a small amount of boulder; samples taken from below the surface were aerobic but would be expected to become anaerobic when wet due to the decomposition of the organically enriched sediments.
No aquatic plants were growing in the channel or on the water’s edge. Terrestrial grasses had invaded the channel, which indicates that the drain had been dry for at least a few years.
The narrow riparian zone consisted of a sparse cover of introduced grasses among the bare soil on the banks of the drain. The surrounding vegetation at the site was grazed grassland with a few scattered gum trees.
Special environmental features
Pressures and management responses
|Drought||The Drainage Network in the region supports nearly 200 regulators for water conservation and adaptive flows management practices. The freshwater weir pools of some regulators in the Lower South East are now known to support colonies of threatened aquatic species. The South Eastern Water Conservation and Drainage Board has undertaken preliminary investigations to identify additional biological hot spots in the Lower South East, and further investigations may be undertaken. This may lead to the installation of additional regulators to retain water as drought refuge at these key drain locations.|
|Livestock having direct access (causing sediment erosion and adding excessive nutrients).||Drains have been constructed since the 1860s as an engineering solution to support agricultural development and it is South Eastern Water Conservation and Drainage Board practice to lease drain reserves for grazing in certain circumstances. Not all drains are subject to grazing and leases for grazing are only approved following an engineering and environmental assessment. Lease conditions require the lessee to fulfil pest plant, pest animal and CFS management requirements, thereby relieving the Board of these responsibilities.|
|Limited riparian zone vegetation (reducing habitat quality, increasing sediment erosion).||The South Eastern Water Conservation and Drainage Board has undertaken a limited revegetation program at key locations, and has the ability to undertake further revegetation works when resources allow. Revegetation at biological hotspots is recognised as a mechanism to reduce nutrient input and soil erosion, and can be undertaken if it does not impede access for management and maintenance.|