Point Fraser Monitoring and Evaluation Program

 

Summary

 

2014

 

Mark Lund, Michelle Newport, Jay Gonzalez-Pinto, Eddie van Etten, Pascal Scherrer, Rob Davis

History of Point Fraser

Point Fraser is named after the colonial botanist Sir Charles Fraser who explored the Swan River in 1827 when he accompanied Captain Stirling’s expedition. The site was originally named ‘Boodjargabbeelup’ by Noongar peoples, when it was still a peninsula. Prior to 2004, the site was a lawn area containing a car park, a helipad and a shipping container used for bike hire. A stormwater drain (Point Fraser Main Drain) discharged into the river at this point.

After 2000, the City of Perth sort to improve the quality of stormwater discharge to the Swan River and improve aesthetic, recreational and environmental values of the area. This culminated in the Point Fraser redevelopment; the first stage was the creation of a constructed wetland which was completed in 2004. The second stage saw the redevelopment of the remaining area which was completed in 2007.

The constructed wetland

The constructed wetland at Point Fraser is designed to treat stormwater prior to it entering the Swan River (Figure 1). Water enters the wetland from the catchment via a splitter box where low flows are directed into a bubble-up grate (BUG) in W1. High flows which might damage the wetland bypass the wetland and are directed to the River. These high flows typically contain relatively low contaminant levels. Water flows from W1 to W2 (Zone 1), and then when levels exceed those of the weir, water flows into W3 and then W4 (Zone 2) before exiting via a small pipe into the foreshore vegetation (Zone 3) and then into the River. W1 to W4 are lined to prevent interaction with underlying acid sulphate soils. W1 and W2 are covered with a thin layer (approx. 20 mm) of Supersorb activated zeolite clay, while W3 and W4 have an additional layer of soil to grow plants in. To prevent the wetland from drying in summer, water is pumped from Lake Vasto.

Figure 1.    Aerial photograph showing the movement of water (red arrows) through the Point Fraser constructed wetland. Yellow circles mark the fixed inlet and outlet monitoring structures. Sampling sites are indicated as W1 to W4. Imagery adapted from Google Earth, 2010.

The Monitoring Project

The City of Perth commissioned the authors to undertake a 5 year monitoring program to evaluate how the redevelopment was meeting its original objectives. Specifically to monitor, evaluate and report on the following:

  1. The effectiveness of the constructed wetland for treating stormwater;
  2. The quality of wetland habitat (vegetation) for biodiversity (aquatic macroinvertebrates and birds);
  3. Public usage of the reserve
  4. The success of foreshore revegetation.

This is the final annual report summary of the monitoring program and covers the period January to December 2014.

Main findings

  1. In 2014, backflow continued, however it could be estimated more accurately than in previous years and appears less significant than previously thought (Table 1).
  2. Approximately 5 – 10 kg of N and 0.2 – 0.5 kg of P were estimated to enter Point Fraser with approximately 9 kg of N and 0.8 kg of P exported to Zone 3. This represents a removal efficiency of -45 – 11% for N and 20 – 34% for P. Although inputs of N have not substantially altered from 2013, removal efficiency is poor with potential net export. Plants releasing N as a consequence of the high salinities back in 2012 are believed to be cause. It is likely that removal efficiency for N will improve in 2015 as the plants recover. This illustrates the limitations with using plants as the main uptake pathway for nutrients – under some conditions nutrients can be released. Phosphorus removal remains very high. Overall the wetland is working well at nutrient removal. Flows were only a small fraction of that which the wetland was designed for and this is likely enhancing nutrient removal.
  3. Wetland vegetation is growing well, however Juncus kraussii is now out-competing all other species and Baumea articulata and Typha domingensis are almost extinct within the wetland and Eleocharis acuta has a very limited distribution (Figure 2). The plants are now so thick that they are interfering with water flow through the wetland and action is needed to improve the water flow path.

Figure 2.    Map of vegetation types and other cover as of October 2014.

  1. Total N on a number of occasions (78% of samples) exceeded the target concentrations for discharge. Removal of P appeared successful in preventing exceedances of the target values for discharge (ANZECC/ARMCANZ, 2000; Swan River Trust, 2009a, b).
  2. As salinities within the wetland dropped, there is evidence that aquatic macroinvertebrate diversity returned to 2010 levels.
  3. Point Fraser does not appear to be a destination of choice for people but is used extensively by people exercising or parking to access the city. Most respondents viewed Point Fraser positively with 91% stating they would visit again. There was concern about the lack of facilities, although it was accepted that the commercial development may address these. A few respondents were not supportive of commercial developments at Point Fraser fearing their impact on the environment. The time taken for the commercial development to be completed was also identified as an issue by the majority of users. About a Bike Hire is a key driver for current recreational activities within the parkland.

Table 1.    Water and nutrient budget for the Point Fraser wetland, including removal efficiency for nutrients. Numbers in brackets are total inputs without losses due to backflow. Removal efficiency determined from total input (excluding backflow) and total output.

 

Water (m3)

N (g)

P (g)

TSS (kg)

Inflow

5,884-11,315

4,269 – 8208

249-479

297 – 571

Rainfall

3,606

967

76

0

Top-up from Vasto

7,215

2,768

812

0

Backflow

-2,107

-1,833

-105

-90

TOTAL INPUTS

14,598-20,029

6,198 – 10,110

1,032-1,262

207 – 481

Outflow

7,525

9,029

828

128

Evaporation

8,246

NA

NA

NA

TOTAL OUTPUTS

15,771

9,029

828

128

Removal Efficiency

 

-45 – 11%

20 – 34%

38 – 73%

 

Conclusions

Point Fraser was developed in 2004 to convert former lawn area to a recreation space, with environmental values. In addition, a wetland was constructed to intercept and treat a stormwater drain from East Perth (catchment 18.3 ha) that had previously discharged untreated into the Swan River.

  1. The quality of urban stormwater discharging to the Swan River long term, as a result of the redevelopment of Point Fraser by determining the amount of pollutant removal via the constructed wetland;
  1. The on-going ecological health of the constructed wetland via its conformance with relevant water quality guidelines and legislation requirements.

Results suggest that water quality is generally within the normal ranges that might be expected in stormwater wetland on the Swan Coastal Plain. A major issue over the 5 years of the project has been salt intrusion into the wetland from influx of saline Swan River water during high tides. It appears that the 2013 installation of a valve on the outflow from W4 has substantially reduced salt levels within the system.

The team has identified in previous years issues associated with the inlet structure that means that much of the water (46% of the total water inputs in 2012, 13% in 2014) that enters the wetland later drains back (backflow) into the drainage network, and as such it is effectively lost from the wetland. Backflow is not desirable simply as it would be more useful for the water to move through the wetland, adding to storage and dilution.

In 2014, the wetland was likely a net exporter of nitrogen with a removal efficiency of -24 to 26% but was effective at removing phosphorus (63-70%) and total suspended materials (41-76%). Total N on a number of occasions exceeded the target concentrations for discharge. Removal of P appeared successful in preventing exceedances of the target values for discharge.

Wetland vegetation has survived a series of low rainfall years and high salinities in the wetlands over the project; however Juncus kraussii is out-competing the other species, with all the others on the decline. Although Eleocharis acuta appeared healthy, the degree of coverage has declined substantially. Baumea articulata and Typha domingensis are almost extinct likely due to high salinities in 2012. The impact of the high salinities are only now being felt in low productivity in the plants, with excessive release of nitrogen. This illustrates the role that plants play in nutrient uptake – they are a nutrient pool rather than store. The sediment in W3 was substantially more effective at removing nutrients than the Supersorb clay in W2.

  1. The quality of wetland habitat and the quantity and quality of breeding places for native avifauna presence, behaviours and habitat use;

Biodiversity measured through bird and macroinvertebrate communities showed communities rich in cosmopolitan common taxa. A total of 37 bird species from 23 families have been recorded which is very encouraging given the scale of the wetland. Macroinvertebrate communities have largely recovered from the high salinities of 2012/13.

  1. The quality, quantity and type of recreational and educational use of Point Fraser by determining the diversity of visitor presence, behaviour, use, expectations and satisfaction and awareness of reports/information specific to Point Fraser performance;

Social monitoring was undertaken to see how people use the site. Point Fraser does not appear to be a destination of choice but is used extensively as people pass through it primarily for exercise or park in the car parks to access the city.

  1. The long term integrity and quality of the restoration of the foreshore edge, as a result of the redevelopment of Point Fraser by determining vegetation health and structural reliability.

Foreshore monitoring has revealed erosion and plant loss (including trees) along the foreshore particularly in area 1. Area 2 was largely inaccessible due to construction of the commercial development.

  1. References

ANZECC/ARMCANZ (2000). Australian and New Zealand guidelines for fresh and marine water quality, Volume 2. Aquatic ecosystems – rationale and background Information. Australian and New Zealand Environment and Conservation Council and Agriculture and Resource Management Council of Australia and New Zealand, Canberra.

Swan River Trust (2009a). Local Water Quality Improvement Plan: Mounts Bay Catchment. In: Swan River Trust, (Swan River Trust.Swan River Trusts Swan River Trust). Perth: WA Government.

Swan River Trust (2009b). Swan Canning Water Quality Improvement Plan. In: Swan River Trust, (Swan River Trust.Swan River Trusts Swan River Trust). Perth: WA Government.

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