Wetland Science
Modelling the effect of restored tidal regime on estuarine wetland water quality: Little Broadwater, Clarence River Floodplain
Contributor: Nicole White and Richard Faulkner
University of New England
National Marine Science Centre
PO Box J321
Coffs Harbour NSW 2450
Australia
Ph: +61 2 6648 3919/3924
Fax: +61 2 6651 6580
Research is being conducted on the restoration of tidal regime to remediate acid sulphate soils and improve wetland health. It is hoped that the Little Broadwater restoration project will eventually be used as a model for remediation and management of other drained wetlands in the region. Current research by Nicole White is focused on modelling the impact of tidal restoration on the
water quality in Little Broadwater1.
Research Aim
To evaluate the effect of tidal restoration, through floodgate management, on water quality in Little Broadwater. In order to achieve this aim, the specific objectives of the thesis are:
- Examine the geomorphic history and soils present in the Little Broadwater catchment;
- Assess spatial and temporal variation in surface water quality, including an investigation of rainfall/runoff patterns and interaction between groundwater and surface water;
- Apply a hydrodynamic model to predict water movement around the wetland;
- Apply a hydrodynamic model to predict changes in water quality in the wetland.
Wetland Description
Little Broadwater is a brackish water wetland, with salinity ranging from very saline over spring, to fresh in the late summer after heavy rains. The most common vegetation species found in little broadwater include Swamp Oak (Casuarina Glauca), Spikerush (Eleocharis Spp.), Phragmites (Phragmites Australis) and Water Couch (p\Paspalum Distichum). There is also a large range of birds, reptiles and fish found in the area.
Water Quality
Initial analysis of surface water chemistry suggests that Little Broadwater can be divided into five areas of different water quality. The pilot study involved mass sampling of the wetland over three months, and chemical analysis by ICP and IC for a range of cations and ions. Ordinance plots were used to determine the primary chemical characteristics of the water. These chemical characteristics were then used in cluster analysis and MDS plots to determine areas of differing water quality. A Greenspan datalogger was installed in the drain on the wetland side of the floodgates in March 2002 to compare discharge water quality before and after the installation of tidal gates.
Groundwater
To assess the importance of groundwater in the system, six piezometer wells were placed around the wetland, and water level loggers were installed to record every hour, timed with the surface water datalogger at the floodgates.
ACIDITY
Current results indicate that the groundwater at the major acid scald area has an average pH of 6.65 and salinity of 16.4 ppt. The groundwater at the north end of the wetland and furthest from the creek has an average pH of 4.18 and salinity of 9.4 ppt.
Further Research
The next stage of the project is to begin modelling and predicting water movement throughout the wetland and predicting changes in water quality under different tidal gate management regimes.
h4. Further Information
The quality of water discharged from Little Broadwater, Everlasting Swamp Complex can be viewed through the Acid Sulphate Soil Hotspot Monitoring System, at http://www.data.greenspan.com.au/dlwchotspots/
1 Little Broadwater is on Sportsmans Creek at Mantons Rd, Lawrence, in the
Clarence Valley, North Coast of NSW, Australia
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