Gawler River, Gawler
2008 Aquatic Ecosystem Condition Report
- Severely disturbed by stormwater inflows.
- Limited aquatic and riparian vegetation invaded by weeds.
- Some bank erosion problems evident.
- Dry at time of inspection in October 2008.
About the location
Gawler River forms at the junction of the North and South Para rivers just to the west of the Gawler township, and flows west before discharging into Gulf St Vincent in the Port Gawler Conservation Park.
Vineyards, livestock grazing and urban development are the major land uses in the catchment, with a number of pipes channelling stormwater into the immediate upstream branches of both Para rivers as they pass through Gawler. The site selected for monitoring was located just downstream from the river junction, off Gosford Street in Gawler.
Adelaide and Mount Lofty Ranges NRM Regional Summary 2008
The river was given a Very Poor rating at this site because the ecosystem was in a severely degraded condition with major changes to both the animal and plant life, and a significant breakdown in the way the ecosystem functions because of human impact. The impacts of urban stormwater, runoff from agricultural areas and drought had contributed to the highly disturbed condition of the stream.
The river was a dry channel, more than 20 metres across, when it was inspected in October 2008. The low banks showed some signs of erosion by floods.
The sediments were mostly sand, gravel and silt, but they also included areas with coarser cobbles and pebbles. There was no evidence they had been anaerobic in the recent times as a result of too much organic material, and there was no sign of dried or decaying filamentous algae.
Scattered sedges (Bolboschoenus caldwellii and Cyperus gymnocaulos) were the only aquatic plants present in the channel.
The riparian vegetation was mostly River Red Gums over a wide range of woody and herbaceous weeds such as Pepper Trees, olives, castor oil plants, various thistles, oats and paspalum grasses.
Weeds also covered the surrounding landscape, which merged into urban development with housing and a railway line.
Special environmental features
Pressures and management responses
|Stormwater runoff causing high water velocities, containing nutrients and sediments (causing habitat disturbance, algal growth and aquatic weeds).||The Adelaide and Mount Lofty Ranges NRM Board has a well developed stormwater quality improvement, harvesting and reuse program which has installed (and maintains) gross pollutant (and silt) traps in several watercourses across the region to catch litter, debris and silt in order to minimise impacts and damage to seagrass in the receiving marine environment. Stormwater captured is also treated through artificial wetlands across the region which act as suspended solid and nutrient filters; these wetlands also provide important habitat for many native species.|
|Extensive weed growth in the riparian zone at the site and upstream (causing habitat disturbance).||The Adelaide and Mount Lofty Ranges NRM Board has several pest plant (weed) mitigation and control programs. They work closely with landholders to control weeds on their property and to help stop the spread to other properties and waterways.|
|Limited riparian zone vegetation at the site and upstream, providing minimal buffer protection from catchment landuses (reducing habitat quality).||The Adelaide and Mount Lofty Ranges NRM Boards land management program encourages and promotes managing land to improve water quality. This includes incentives for revegetation programs around waterways and wetlands and stock exclusion as well as educating landholders about the importance of riparian vegetation in managing soil erosion.|
|Large nutrient inputs from numerous diffuse sources in the catchment (leading to extensive growth of algae and aquatic weeds).||The Adelaide and Mount Lofty Ranges NRM Board’s land management program encourages and promotes managing land to improve water quality. This includes working with industry and landholders to ensure efficient use of fertilisers and discuss ways to reduce runoff of nutrients into waterways.|
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This aquatic ecosystem condition report is based on monitoring data collected by the EPA and prepared in conjunction with the Adelaide and Mount Lofty Ranges NRM Board.