Today, stormwater is resurfacing in our landscapes. Snaking among the rigid geometries of our cities, old riparian lines and links are being rediscovered and retraced. Why? What are these creeks and streams for? Why revive them, protect them, in some instances even invent them? Powered by growing vision by governments, of cities afloat in their original watery networks, riparian corridors are reaching more deeply and numerously into our urban spaces. But at what cost? What are we losing by gaining so much water and associated biota? Four Sydney example of riparian landscape works illustrate the conflicting expectations we are putting upon our riparian corridors.

The Cascades, Mt Annan

A riparian zone is a strip of land along the banks of a drainage feature (Rutherford, 2000), and according to some authorities even includes gullies and dips that only sometimes run with water. In theory, stand watering your front lawn for too long and you might require a permit to develop your waterway. In practice, The Cascades at Mt Annan was created in a drainage line to recall the overflow from several farm dams and to preserve their flora and fauna. Why bother? In the mid 1990s, the Council had designated the space as a collector road, and the developer was ready to install stormwater pipes under that road. At this point, landscape architect, David Martin suggested combining trunk drainage with a recreational/riparian corridor, thus serving the stormwater needs with socially desirable, aesthetic open space. The developer agreed, hoping that buyers might be attracted. They were. David Martin writes, “New residents responded very quickly to the frontage offered onto a high quality and mixed use corridor. The developer’s original sales targets for the neighbourhood were met 2 years ahead of program”.

The NSW Dept of Land and Water Conservation (DLWC, now DIPNR), did not classify the site as a ‘riparian corridor/river or creek’, but merely an ‘intermittent drainage line’. So, authentic riparian restoration was not the prime objective. Bio-filtration and the treatment of stormwater were, however, considered an important environmental objective. A consulting wetland ecologist was involved at the planning stage and recommended a re-circulating aeration pump system and nutrient capture via macrophyte beds to improve water quality. The ecologist also advised the transplanting of the existing biota from the large farm dams into the new ponds and prepared a Wetland Maintenance Manual.

The corridor therefore evolved to combine four functions:

• social (a pleasing open space connection with a strong community focus);
• economic (desirable suburban amenity); and
• eco-infrastructural (stormwater treatment through sediment control and detention basins).

The balance between these functions is still involving. Of significance has been the long-term management of the riparian zone – the ecological function. As living systems, constructed wetlands require ongoing expert management to maintain the kind of water quality people demand of a highly visible social/recreational facility. Water quality depends on an optimum level of macrophyte coverage and a powerful recirculating pumping system. A trust fund was therefore negotiated with Council to pay for the ongoing hydraulic maintenance cost on the pumping system. Nevertheless, the high nutrient levels associated with urban runoff attracts excessive subsurface and floating plants including algae, and open water attracts flocks of aquatic birds, both of which have had some effect on residential amenity. Residents now enjoy easy access to a high quality landscape corridor and the social and recreational benefits of the walking/cycle trail which itself provides a community focus. However, they also expect the clear ponds that drew them to the subdivision, and are still adapting to the changing ecology of their corridor, both of which have had some effect on residential amenity.

Residents now enjoy easy access to a high quality landscape corridor and the social and recreational benefits of the walking/cycle trail which itself provides a community focus. However, they also expect the clear ponds that drew them to the subdivision, and are still adapting to the changing ecology of their corridor, both through an education program and by observation. A resident education program has been established, with brochures encouraging residents not to feed the ducks to reduce faecal contamination/algal blooms, reducing nutrient loads by avoiding car washing in streets, minimizing fertilizer use, etc.

Strangers Creek, Baulkham Hills

One of two heavily scoured and denuded creeklines, Strangers Creek marks the boundary between commercial and residential development in Sydney’s Norwest Business Park. By the late 1990s, the DLWC, beginning to flex its muscles under the Rivers and Foreshore Improvement Act, initially wanted to restore the creekline to “catchment health” , and promote the riparian corridor as a habitat for flora and fauna and as a place to educate the public about ecology, whilst accommodating its function to carry stormwater. The Department was also progressing towards a policy of restricting human access to corridors. By contrast, the developer (Norwest) wanted a visual focus for the subdivision and a place of recreational amenity and quality for residents. The landscape architects, PSB negotiated a compromise, planting a dense corridor of riparian woodland along just one edge – the commercial, high security edge – with no human access for most of its length.

Designed to appear as a single flowing waterway, the water actually circulates in two distinct systems: along the upper part of the creek is a naturalistic water feature, for both water quality treatment and aesthetic and landscaping purposes, from which a very low flow of water is simply re-circulated to the head of the stream, and a more ‘natural’ riparian corridor further ‘downstream’, whose water is also, as at The Cascades, recirculated. A series of interventions along the upper part of the creek – bridges, cascading weirs, fountain, ornamental blade walls, drop structures – and a wide pool fringed with wetland plants act as a visual focus and entry statement to the development. Bridges and paths weave along the Creek. In effect, the government’s aim of ‘catchment health’ is tempered by the socio-economic imperative.

PSB’s Management Plan for the lower part of the Creek balances the social and economic functions with habitat creation. Riparian planting, native fish, and bed habitats such as logs and boulders provide for invertebrate and vertebrate life in a creek functioning to treat stormwater. Once again, ecological methods achieve engineering outcome. As landscape architect James Rosenwax of PSB explains, “Stormwater is treated by a matrix of boulders, graded gravels, sand, and ponds for macrophyte bioremediation. A buffer zone of endemic riparian plants and surrounding canopy and under story were chosen from the Cumberland Plain Woodland and the River Flat Forest communities endemic to Western Sydney. These cool the water and discourage algal blooms. Steep earth batters, boulders and hard pool-edges reduce mosquito habitat yet allow fauna ingress and egress. Gravel shoals, islands, logs and stumps placed in the main pond provide natural habitats for birds, indigenous fish and crustaceans. Cascades fed by gently recirculated water further discourage mosquitoes and oxygenate the water. Low maintenance pumps not only re-circulate the water to maintain ‘environmental flows’ but also provide irrigation for the parkland. The cost of maintenance and pumping is built into resident rates.” As with The Cascades, open water has attracted birds and associated faeces. And like The Cascades, design features essential to an artificial system have resulted in algal bloom in some of the shallow pools.

Restoring the Waters, Fairfield

Another desire to replace an engineered structure with a biotic system, but with a different emphasis, has generated the multi-funded Restoring the Waters project. Its stated aim was, “to improve the water quality and biodiversity of urban waterways”. There was also some economic motivation in the search for replacement options for conventional drainage infrastructure. The Stormwater Trust of NSW was inspired by a paper written by landscape architect, Barbara Schaffer, and presented by Sue Salmon of the Australian Conservation Foundation. Thus, in collaboration between government and a public organization (ACF), the Trust began looking in the mid-1990s for a model site to return one of Sydney’s many concrete channels to creekline. Along with the ACF, Fairfield City Council, and the Environmental Protection Agency, they chose a lifeless 2.7km of open channel along Clear Paddock Creek in the Georges River sub-catchment of Sydney’s west.

Habitat restoration has had to be simplified. Revegetation is via an “abstracted representation” of the original Grey Box plant community. Plants were chosen to suit the hydrological dictates of water flows and levels of inundation (the original reason for channeling the Creek), the community need for simple and safe open spaces, and the need for structurally diverse habitats. Attempts for provenance from local seedstock have not always been possible. Alternatives have come from a broader range of similar but more successful communities. Cultivars are used where they outperform local species. And, due partly to extremes of dry and wet especially in the startup phase, and partly to the inability of riffles to provide a variety of rock sizes, aquatic habitats for macro invertebrates, fish and water birds cannot be sustained.

In consultation with the community, the Landscape Architects, Barbara Schaffer, and Sue Barnsley, tried to connect these eco-infrastructural functions with the need for recreational and educational spaces. They have replaced a boringly homogenous landscape with a sinuous collection of riffles, chokes and runs, amplifying and adapting the “Memory Line” of the original creekline, where adjacent development permits.

The objective was always to integrate the new creek with overbank park plantings and recreational infrastructure. However the grants system supported narrow, water quality improvement projects rather than multidimensional or ‘holistic’ restoration projects. Funding only for creekbank elements was granted in the initial construction program. And as often occurs, the landscape architect was demoted to sub-consultant during construction, with the usual compromising of design standards.

Slightly freed of the economic imperative, and involving a different arm of government, the project represents a change of focus. It combines the ecological functions of water purification and biodiversity, the hydrological functions of bank stability and flood control, and the social functions of recreation and strong aesthetic improvement. Without developer funding, the project has relied on the slow process of attracting funds from local, State, and Federal governments. Such incremental funding has produced a series of staged developments, overseen by steering committees. The Council, fortunately, is committed to maintenance of the Corridor.

Elizabeth MacArthur Creek, Baulkham Hills

By the time the Elizabeth MacArthur Creek project began in 2001, DLWC/DIPNR’s new policy on permit requirements had become more resolute and exacting. That policy aims at re-establishing these restoration zones as biodiversity corridors and virtually prohibits recreational access. As with previous creeks, the primary function was the collection and treatment of run-off water, but here it became an even more rigorous ecological exercise to characterise the environment that would have existed here pre-settlement and rebuild it as a dynamic bio-diversity corridor. The DIPNR required a 40-metres exclusion zone and all water treatment to be off-line. The landscape architects, PSB again, argued for using the fully-restored ecosystem as the stormwater treatment system in itself. The compromise was to create a 40 metre wide bush corridor where run-off water in the revitalised creek line is treated by both mechanical and natural means. From a sediment pond at the top end of the main water feature, the water flows over a weir and slowly down through a large macrophyte zone into a rocky creek setting.

One key innovation developed for the site is a series of bio-remediation filters that work as an initial phase nutrient removal system. Instead of run-off water from both the subdivision and the commercial development passing straight into the Creek, it is directed into planted rock basins and channels, which dissipate flow energy and detain the water for up to three days (just long enough to prevent mosquitoes from breeding). Gross pollutants are also collected here. As the water percolates through a sandy substrate on its way to the Creek, suspended pollutants and sediments are removed before reaching the main channel and water feature.

Groundwork, based on studies of water flow, soil remediation and engineering, raised the level of the bed between two and three metres. Habitat niches were incorporated at different flood levels – pools and meanders for fish and frogs, tumbles of rocks where lizards can sun or hide, swathes of native grasses and groves of eucalypts. As with Strangers Creek, native fish stocks are planned to characterise the original biodiversity of the environment as closely as possible. To ensure species are able to migrate along the whole one kilometre corridor length of the Creek, both wet and dry ‘critter’ paths will follow the corridor.

Mark Blanche, landscape architect and environmental scientist at PSB, investigated indigenous plant communities. “The planting establishes two types of natural communities characteristic of endangered ecological communities indigenous to the area – the Sydney Coastal River-Flat Forest and the Cumberland Plain Woodland. We varied the structure of the Woodland – some parts are heavily wooded with a dense understorey of shrubs, while others are planted with sporadic trees and a dense carpet of native grasses. This created a visually diverse landscape with views of the water provided through the tress”. Ecological integrity is reinforced by using locally provenanced seedstock and 38 different species.

For the developer, the loss of the Creek as a recreational open space has come at a cost. And public perception of the Creek as a less ‘hospitable’ space than the type designed for The Cascades and Strangers Creek is likely to impact on sale prices. From a practical point of view, the need to clear and replant the entire site at once has allowed greater weed invasions than the traditional method of gradual plant revegetation. And locally provenanced seeds are not as easy to find, especially quickly and in as wide a range of species, as nursery stock.

Elizabeth MacArthur Creek attempts to represent an endangered ecological community. Yet only one bridge crossing was permitted. Better than none, but by attempting to cocoon to the adjacent community are lost.

Conclusion

The pendulum is swinging back. We have always needed our waters – for transport, nourishment, cleaning, recreation – the list is long. Now, after 40 years starved, choked and often locked underground, our waters are reemerging. Aided by a growing political will, based on a deeper understanding of the ecologies of survival, and the natural human desire to live beside water, we are rediscovering our waterways. But these four projects demonstrate that no one approach must be tempered by the economic need to turn a profit; the engineering approach must lie down with the desire of community for pleasant amenity. The bottom line is not the bottom line.

Acknowledgements

My thanks to Sue Barnsley (Sue Barnsley Design), Mark Blanche (PSB), Kathryn Duchatel (PSB), Steven Frost (Fairfield Council), Stephen Lloyd (Camden Council), David Martin (EDAW Gillespies), James Rosenwax (PSB) and Barbara Schaffer (SOPA).

Reference
Rutherford, I. et al, 2000 A Rehabilitation Manual for Australian Streams, Vol. 1 Land and Water Australia, Canberra.