Sustainable Management of the Centennial Parklands Ponds
Total Page：16
File Type：pdf, Size：1020Kb
Sustainable Management of the Centennial Parklands Ponds AUTHORS Mal Brown, Storm Consulting Stephen Nichols, Centennial Parklands George Freeman, Storm Consulting ABSTRACT Centennial Parklands in Sydney’s inner eastern suburbs provide a popular recreational resource with over 3 million visitors per annum. Within the parklands are 12 ornamental ponds providing a range of values. Management of Centennial Parklands ponds is vested with the Centennial Park and Moore Park Trust (the Trust). The Trust maintains and improves Trust lands and ensures environmental protection. Through the early to mid 1990s, the water quality of Centennial Parkland’s ponds deteriorated to the extent that blue-green algal blooms occurred in most ponds perennially over several years. The blooms were attributed to long term pond degradation as a result of ongoing stormwater pollution, and pond design and function which did not cater for the pollution inputs, and the presence of carp in ponds. Any degradation of the ponds’ environment or water quality has far reaching implications for the Park’s amenity and its environmental and heritage values. The pollution of the Park’s waterways is of utmost concern to the Trust. Park visitors rank cleanliness of the ponds as a high priority. In 1997, the Trust prepared the first plan to manage and improve the ponds. The Ponds Restoration Program Strategy Plan 1997 provided a comprehensive discussion of issues facing the ponds, and the resultant management recommendations to remedy them. Initial works on the ponds were completed in five stages from 1998 to about 2003 with works in seven of the 12 ponds. The works included design refinements to facilitate management of stormwater pollution inputs, and others to improve the ecological values of the ponds. In 2010-11 the Trust renewed its focus on the ponds. They amended and revised the previous Plan to create a Ponds Management Plan 2012 which included the identification of new works based on a critical review of the previous works. They invested significant resources to establish the most cost- effective pollution trapping, removal and disposal strategies and they implemented these on two of the ponds. The future value and amenity of the Centennial Park ponds is intrinsically linked to the ongoing management of stormwater pollution inputs from external catchments. This paper describes the extraordinary effort and investment made by the Trust to maintain and improve one of their key assets. 1. INTRODUCTION Located in the inner eastern suburbs of Sydney, Centennial Parklands is an iconic Sydney landmark. First established in 1888 as a commemoration of the centenary of European settlement in Australia, the parklands have a rich and complex cultural history. Extending over approximately 365 hectares, the parklands exist as an invaluable asset within Sydney. The parklands comprise of three separate parks, namely Centennial Park, Moore Park and Queens Park (Figure 1). Together the parks offer a popular recreational resource for upwards of 3 million visitors annually. Situated within the inner metropolitan area of the Sydney, the Centennial Parklands encompass 365 hectares of mixed use public space. They feature open parkland, sports fields, equestrian grounds, formal gardens, ponds and grand avenues amongst a variety of other recreational facilities including walking tracks and a golf course. FIGURE 1 - CENTENNIAL PARKLANDS SHOWING WEST TO EAST MOORE PARK, CENTENNIAL PARK AND QUEENS PARK The parklands perform key environmental functions, most notably providing habitat and a refuge for native flora and fauna while also facilitating urban stormwater treatment in what is an increasingly urbanised catchment. The catchment boundary and flow paths are shown in relation to the ponds in Figure 2. The ponds are predominantly situated at the lower portion of Centennial Park and act as the receiving waters for runoff generated from a 600Ha catchment. FIGURE 2 - CENTENNIAL PARKLANDS PONDS CATCHMENT CONTEXT SHOWING CATCHMENT BOUNDARY AND FLOW PATHS The pond system consists of 12 ornamental ponds in total with a combined surface area of approximately 26 hectares. There are five major stormwater inflows to the pond system and a complex series of flow paths (Figure 3). In addition, the ponds are connected to groundwater in the underlying Botany Aquifer. Pond water is extracted from the lower pond (Kensington Pond east) and is used to intensively irrigate 55Ha of sports fields and golf course. Stormwater flows out of the system in the south, and on to the Botany Wetlands and Botany Bay. FIGURE 3 - CENTENNIAL PARK POND CONFIGURATION AND FUNCTION IN RELATION TO STORMWATER (KIPPAX LAKE NOT SHOWN) Centennial Parklands is managed by the Centennial Park and Moore Park Trust (the Trust), a statutory body which was established under the NSW Centennial Park and Moore Park Trust Act (the Act) of 1983. The Trust has the role of ensuring the maintenance and improvement of Centennial Parklands, including the Centennial Parklands Ponds. The Trust is responsible for facilitating environmental protection and continued public amenity of the parklands, developing and upholding strategies to increase the recreational, historical, scientific, educational, cultural and environmental value of the lands. The Trust first prepared a plan to manage and improve the Centennial Parklands Ponds in 1997 with the development of the Ponds Restoration Program Strategy Plan 1997. Since that point management plans and strategies have been adapted to allow for the continued refinement of pond designs and associated works in order to facilitate the management of stormwater pollution inputs and the enhancement of the ecological values of the ponds. The preparation of the Ponds Management Plan 2012 represents the most recent strategy for the sustainable ongoing management of the Centennial Parklands pond system. The plan provides a holistic and comprehensive planning document with aims of guiding future pond restoration works and maintenance activities over the period 2012-2020. The plan has focused on achieving a physically and ecologically robust pond system through contemporary management measures that reflect best practice and are considerate of life-cycle costs of implementation. This paper presents the current stormwater-related problems facing the Centennial Parkland Ponds and how these are proposed to be managed using the Ponds Management Plan 2012. 2. PROBLEMS WITH THE PONDS Between the period 1837-59, the ponds were used as Sydney’s second water supply because the Tank Stream in the CBD became too polluted. Then in turn development and inappropriate land use in the pond’s catchment caused water pollution and this supply also had to be abandoned. Therefore, water quality and degradation of the ponds are not new issues in the history of Centennial Parklands. On 1 January 1901, the Parklands became the focus of the nation as the site of the inauguration of the Australian Federation. At this time, the ponds had been converted into a series of flood mitigation and storage dams and later, to the ornamental pond system that stands today. In a period between the early to mid 1990s, it became evident that the capacity of the ponds to function in light of increasing catchment development pressures was becoming severely impeded. Extensive and prolonged drought caused pond water quality to deteriorate to the extent that perennial blue-green algal blooms occurred in the majority of the 12 ponds causing them to turn a vivid green colour. Signs were erected at ponds warning people not to make contact with the water due to the toxins released by the algae. As the algal blooms died off they floated and rafted then decayed causing serious odours. The situation was dire. The algal blooms were symptomatic of a pond system that had become physically, chemically and biologically degraded over time and it was apparent that management practices would need to be altered to restore the health and ecological functions of the pond system, to support amenity to park users. At this time, the ponds became the focus of an inter-governmental committee to investigate water quality and to make recommendations on how to improve it. All of this early work has lead to an understanding among Parklands managers that the values and amenity provided by the ponds is reliant on them being healthy, attractive and stable. None of these outcomes can be achieved without effective water quality management across the pond system. The following issues were identified as being the most significant to manage in relation water quality in the ponds, and this is still relevant today: the pond system has a long hydraulic retention time meaning water can stagnate, especially in dry times pond stormwater inflows allow pollutants to spread, making retrieval impractical some ponds short circuit creating stagnant zones pond outflows do not allow for water level control pond sediments are nutrient-enriched and unstable making them susceptible to re-suspension the ponds have extensive weed macrophytes as opposed to desirable reeds. These weeds die off seasonally and contribute vast quantities of decaying organic matter into ponds. As this decomposes, it strips the water of oxygen which affects the biota present European carp feeding behaviour constantly churns up sediments which re-releases nutrients, and they cycle nutrients within the ponds. They also prey on other aquatic biota. As a response to the pond water quality problems in the mid 1990s, the Trust commissioned and implemented the Ponds Restoration Program Strategy Plan 1997. In the subsequent period 1998- 2003 capital works were undertaken in several of the ponds to improve their water quality function and aesthetics. The works provided considerable improvement in pond condition as evidenced by the fact that in a subsequent extended drought in the mid 2000s, no blue-green algal blooms persisted. However, the lack of effective gross pollutant trapping at inflows was causing the accumulation of significant quantities of pollution near pond inflow zones. It was clear this pollution was in a position to again spread through the pond system causing widespread problems.