Turbidity - suspended sediment in stormwater runoff - is a major issue for the metro coastal
waters and has been implicated as the major cause of seagrass loss.
| Turbidity: Silt-laden stormwater being discharged off-shore from the Barcoo Outlet.
Urban development on floodplains has increased flooding risks and reduced the areas available to clean stormwater through wetlands. Opportunities to develop new wetlands are limited. The Pat Creek site is one place that can play a role in alleviating both these issues for the local area.
However, it needs to be used wisely - there is a need to protect the natural heritage values of the site. But there may also be a need to periodically remove build-ups of sediment from the Creek.
This dilemma can best be resolved through proper planning and careful landscape design to ensure that future works are carried out with minimal intrusion, or compromise of volunteer effort.
Andrew Winkler
| Doubling up: The West Beach Road culvert on 22 October 2005,
after works had started
The City of West Torrens has almost completed Stage 1A of the stormwater channel upgrade -
doubling the capacity of the culverts under Tapleys Hill Road and West Beach Road. Recently it held a community information day for the work it is about to commence on Stage 1B, which will increase the
capacity of the channel along Sir Donald Bradman Drive, from Rutland Avenue to West Beach Road.
| Nearing completion: The West Beach Road culvert on 23 March 2006.
This project includes setting back the Airport's perimeter fence and reducing the height of the channel wall on the Airport side. The low bench thus created will be landscaped with a walking/cycle path, and will provide the capacity to accommodate runoff from a 1:100 year storm event. Work is scheduled to be
carried out over the period from April to October.
Stage 2 of the project, for the area south of West Beach Road, hinges on the removal of the silt ponds. This has been delayed due to an unsuccessful tender process; the pond materials are now likely to be used by another government department for use as landfill for the Port Adelaide redevelopment. Site conditions mean that the removal will be delayed until next summer.
A basin will also be constructed in the triangular area west of the Pat Creek site, to accommodate stormwater flows from the residential area of West Beach.
| Exotic grasses: Silt accumulation has built up the creek bed and allowed vegetation to take hold, which in turn will trap more silt ...
| Silting up: View downstream from West Beach Road on 5 March 2006, showing vegetation growth in the creek bed. (Note temporary dam in foreground, to allow rock revetment works on bank to be carried out.)
| Comparison: The same view taken on 20 February 2000, following rain.
Several aspect of these works are of concern to FoPC. Sediment build-up and vegetation growth in the Pat Creek channel has raised its bed considerably in recent years. While much of this material has been derived from gully erosion of the silt ponds, sediment is also washed downstream along the stormwater channel, and a build-up can be seen at present north of the West Beach Road culvert.
| Sediment source: Gully erosion has eaten into the silt ponds. The bund surrounding the ponds was breached in five places on 3 February 1999 because the silt, originally dredged in 1996, was not drying as quickly as predicted. Photo date 23 March 2006.
| Sediment build-up: The northern side of the West Beach Road culvert
on 23 March 2006, with reeds starting to establish.
The Stage 1B works have the potential to generate more sediment, before the landscaped area becomes
effectively stabilised through revegetation. Although the plan does include a reedbed at the Tapleys Hill Road/Sir Donald Bradman Drive corner to capture sediment, this may not be adequate. We would prefer an additional sediment trap north of West Beach Road.
| Silt trap: At the Tapleys Hill Road / Sir Donald Bradman Drive corner, the widened channel will incorporate a reedbed to trap silt. But will it be adequate, and will erosion be prevented from the newly-landscaped flood channel bench (to be excavated on the inside of the bend)?
The increase in potential flows down the Creek has also resulted in the apparent demise of the Taylor-Cullity landscape plan for the site, drawn up five years ago. The bridge across the Creek that the plan envisaged has been found to be hideously expensive, and has been dropped. The silt mounds on the western side of the Creek just south of West Beach Road which have been successfully revegetated according to the plan, through hundreds of hours of volunteer effort, are now to be removed.
| Wasted effort: This 60 metre section of silt mound on the western bank of Pat Creek,
hand-weeded and revegetated over five years, is now scheduled to be removed.
Our Curry Nights have been successful and well-attended. However as many of our regular volunteers are in their seventies, they understandably want to slow down or go on holiday. And in response to our appeals last year for volunteers to help out with food preparation, we had a variable response, ranging from excellent to barely adequate.
We are therefore trying as an experiment to change the event from a Friday night to a Saturday night, in the hope that we might attract a core group of new people who would normally be unable to volunteer due to work commitments during the week.
The next Curry Night is on Saturday 8th April and with Dr Martin Hand speaking on the very relevant
subject of 'Hot Rocks', we are sure to draw a crowd.
If you can spare even an hour or two on the day, please call the Reedbeds office on 8235 1644.
(Office hours 9am - 1pm, Monday, Tuesday, Thursday, Friday.)
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Friends of Gulf St Vincent
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www.chariot.net.au/~littoral/fogsv/index.htm
| Lively: Discussions during the lunch break at the community forum.
FoGStV held a community forum (followed by the AGM) at SARDI, West Beach on 22 October last year. The event was supported by the EPA and featured a number of speakers on the preliminary results of the Adelaide Coastal Waters Study, which is now, after two years, nearing completion.
The largest contributing factor identified by the ACWS as being responsible for the loss of seagrass off the metro coast is turbidity from stormwater runoff, rather than nutrients from wastewater discharge. Turbidity, due to suspended sediments, reduces light penetration and photosynthesis.
| Turbid: Seagrass barely visible in the water in the shallows
of the Breakout Creek channel on 9 January 2006.
Water movements in the Gulf due to tides and currents result in sediments tending to be deposited close inshore. During storms, wave action churns the seafloor, resuspending the sediment, compounding the problems of seagrass loss, littoral drift and beach erosion, and preventing the regrowth of seagrass.
FoGStV, on behalf of its member groups, has recently been lobbying government in relation to turbidity issues.
One example is runoff from the former sand quarry at Maslin Beach, where a poorly-designed rehabilitation plan has seen sediment-laden runoff discharged directly to the Gulf and adjacent reefs rather than through a wetland.
The dredging work on the Outer Harbor shipping channel has also been widely criticised by many, including beach-goers and commercial fishers, for increased turbidity and poor water quality along the metro coast over the summer months.
FoGStV are planning another community forum to be held at Port Vincent in June, and are involved in planning a coastal festival with SALA in August.
Saturday 8 April: Curry & Casserole Night
Fundraiser for FoPC & the Reedbeds Environment Resource Centre.
6:30pm Meal:Cost: $15 ($10 Friends of Reedbeds, S/P/U)
8:00pm Guest speaker: Dr Martin Hand
Associate Professor,
Discipline of Geology & Geophysics,
School of Earth and Environmental Sciences,
University of Adelaide
Topic: Hot Rocks Downunder: future energy for South Australia
(attendance at talk only is welcome Free)
view details
Download the flyer for this event - PDF version (136 Kb)
Thursday, 27 April 2006, 7:30 pm, at:
The Reedbeds Community Centre, cnr. Fitch & Halsey Roads, Fulham (carpark entry off Phelps Court).
The purpose of the meeting is to discuss the work program for the coming workday and other on-going projects
Workdays:
Pat Creek:
Sunday 7 May, from 10 am.
Meet at the busstop (18B) on West Beach Road (west of Tapleys Hill Road,
and adjacent to the Creek and the silt ponds).
Henley & Grange Dunecare have workdays on the second Sunday of each month at the nursery in Atkin Street, Henley Beach, at 10 am.
CREATED BY:
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LINKED TO:
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 Ground Truth:
towards an
environmental history
of South Australia
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