Drain M, near western edge of Bool Lagoon
2009 Aquatic Ecosystem Condition Report
- Dry in autumn and spring 2009.
- Likely to show signs of obvious nutrient enrichment when wet due to the surrounding land uses.
- Riparian vegetation limited to weeds and introduced grasses.
About the location
Drain M is a large drain in the South East with a catchment area of almost 4,000 km2. It rises near Edenhope in Victoria as Mosquito Creek and flows west into Bool Lagoon Game Reserve. Drain M flows out from Bool Lagoon, flows in a southwesterly direction and receives drainage from Sutherland Drain, Mount Hope Drain, Reedy Creek M Drain, Bellinger Swamp Drain, Baker Range Drain and Drain C, and eventually discharges into Lake George, near Beachport.
Drain M 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 uses are grazing and cropping with some areas of vineyards and native vegetation. The monitoring site was located on Crooked Lane, just downstream of Bool Lagoon, about 18 km west of Struan.
The drain was given a Poor rating because the site sampled showed evidence of major changes in ecosystem structure and moderate changes to the way the ecosystem functions. There was evidence of human disturbance, including a lack of vegetative cover in the riparian zone and surrounding landscape.
The drain was dry in autumn and spring 2009 so macroinvertebrate and water quality data were not available for the site.
The sediments were dominated by sand, clay and detritus, with smaller amounts of boulder, cobble and gravel also present; samples taken from below the surface were well aerated.
No aquatic plants were growing in the channel or on the water’s edge, emphasising the very ephemeral nature of this section of the drain in recent years. The narrow riparian zone consisted of only weeds and introduced grasses. The surrounding vegetation at the site was grazing land and included only a few scattered gum trees.
Special environmental features
None detected at the site sampled, however, other locations further downstream on Drain M provide significant refuge habitats for threatened species of fish (Yarra Pygmy Perch and Southern Pygmy Perch) and the Southern Bell-frog.
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.|