Seymour–Robertson Drain, Bool Lagoon
2009 Aquatic Ecosystem Condition Report
- Dry in autumn and spring 2009.
- Expected to be nutrient enriched when wet due to the surrounding land uses.
- Riparian vegetation limited to weeds and introduced grasses.
- Banks largely bare, steep-sided and vulnerable to erosion.
About the location
Seymour–Robertson Drain consists of a small series of drains in the lower South East with a catchment area of just over 20 km2. Robertson and Seymour drains each extend northwards for several kilometres before they join into the one drain that eventually flows into the south-eastern end of Bool Lagoon. The major land use is grazing.
Seymour–Robertson Drain 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 monitoring site was located on a track that runs along the southern boundary of Bool Lagoon Conservation Park, about 20 kilometres south from Naracoorte.
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. There was considerable evidence of human disturbance, including the very degraded in-stream and riparian habitats and the extent of vegetation clearance in the surrounding terrestrial environment.
The drain was dry in autumn and spring 2009, so macroinvertebrate and water quality data were not available for the site inspected.
The sediments were dominated by silt and clay; samples taken from below the surface were dry and well aerated but would be expected to become blackened and anaerobic when wet, due to the presence of a large amount of organic matter in the sediments. The banks were steep-sided and largely un-vegetated and appear to be vulnerable to significant erosion when the drain flows.
No aquatic vegetation was growing in the channel that only had a few patches of introduced terrestrial grasses present, highlighting the limited time that the drain has been wet in recent years.
The narrow riparian zone consisted of large areas of bare soil with weeds and introduced grasses growing in patches along the banks. The surrounding vegetation at the site was cropping land that extended up to the edge of the banks in places.
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 doesn’t impede access for management and maintenance.|